Emissions of particles from gas engine powered CHP

Transcription

Index - Final Report
1.
Final report
1.1
Project details
1.2
Executive summary
1.3
Project results
1.4
Utilization of project results
1.5
Project conclusion and perspective
1.6
Updating Financial Appendix and submitting the final report
2
2
2
5
166
166
168
1
1.
1.1
Final report
Project details
Project title
Emissions of particles from gas engine powered CHP
plants
Project identification
Energinet.dk project no. 10612
Name of the programme
ForskEL
which has funded the project
Name and address of the
FORCE Technology
enterprises/institution
responsible for the project
CVR (central business register)
55 11 73 14
Date for submission
1.2
Executive summary
In Denmark, more than 200 CHP plants utilize gas engines for district heating supply. The
majority of the CHP plants are located in smaller communities and their main function is to
provide district heating for residential areas using boilers and/or power and heat using gas
engines, depending in the immediate price of electricity.
In the development, design, and manufacturing of gas engines for CHP plants, emission reduction is an important issue with regards to NOx, UHC, and CO2. Emissions of particulate
mass from gas engines has so far been considered of minor importance, and the reduction of
particulate emissions has so far not been addressed specifically by the manufacturers of gas
engines. Recent studies have shown that the emissions of fine and ultrafine particles from
combined heat and power plants may be surprisingly high. However, the available data material from these studies was limited, and factors that may control the emission level were
not investigated and therefore no conclusions as to the origin of these emissions were drawn.
In 2010, Energinet.dk initiated the present study. The study was undertaken by FORCE
Technology, DGC (Danish Gas Technology Centre),Bergen Engines Denmark A/S, Wärtsilä
Denmark A/S, Statoil Fuel & Retail Sweden AB and Dansk Fjernvarme. The primary objective
of this study was to identify the primary causes of fine and ultrafine particles emitted from
CHP plants using gas fired engines.
The study has included a literature survey. The information on particle emissions from gas
engines was sparse, but based on indications on the potential factors determining the particle emissions, the literature survey concluded that a field test program should include monitoring of particle emissions and corresponding NOx concentration under varying ignition timing and fuel/air ratios.
Through an extensive field measurement program, the most important factors influencing
particle emissions from five selected gas engine powered CHP plants in Denmark was assessed. The gas engine plants were selected with respect to engine type and size as being
representative for Danish CHP plants. To identify which operational parameters have the
greatest influence on the particulate emissions from gas engines, the measurement program
included logging and collection of relevant engine operating parameters as well as measure-
2
ment of relevant gaseous and particulate emissions. This study also included an assessment
of options for future mitigation of particle emissions from gas fired CHP plants.
The results obtained showed that:

No significant differences could be found between the particle emissions from the two
involved engine types (Bergen Engines and Wärtsilä).

When an engine is well maintained and service checks are performed regularly,
overall particle mass and number emissions do not vary strongly before and after the
performance of an engine service. This study also indicates that for a given engine
type and design there is a lower limit to the level of particle mass and number emissions attainable, beyond which no further reduction of particle emission can be
achieved by engine tuning. This minimum “base level” is assumed to depend highly
on the efficiency of parts that ensure a minimum loss of lubrication oil to the combustion chamber or through crankcase ventilation (such as gaskets, and piston
rings).

For the four different lubrication oils that were used at the five different plants, no
significant correlation could be found between the particle emissions and the type or
age of lubrication oil.

Due to the lack of information on additives in the lubrication oil, it was not possible
to correlate the measured particle emissions to specific additives in the lubrication
oil. However, results from analyses of metals in lubrication oil samples could be well
correlated with metals analyzed in the particles emitted from the engine. This confirms that e.g. Ca, Mg and Si in lubrication oil additives will occur in particles emitted
from the engine. A weak correlation was found between the density and viscosity of
the lubrication oils and the measured emission of uncombusted hydrocarbons (UHC)
– the higher the density (and the higher the viscosity) of the lubrication oil, the lower
the emitted concentration of UHC. It is concluded that for engines that are properly
maintained, and for lubrication oils that are controlled within the required specifications, lubrication oil type and composition seem to have a minor effect on particle
emissions.

Measurements showed that 50% - 80% of the number of particles emitted consisted
of volatile material, most likely deriving from uncombusted lubrication oil components. This share is equivalent to 30% - 60% of PM1.

From oil mist measurement at the five plants, it is concluded that during normal operation, the majority of the oil consumed by the engine is combusted in the engine
(or trapped in the exhaust system), and that only a minor fraction of the oil consumed will appear in the exhaust gas as vapor or liquid oil particles. The measured
emissions of oil mist was significantly lower than that found in studies from Danish
CHP gas engines in 2001 /ELTRA rapport/. The reason for this may partly be a reduced oil consumption in the engines, and partly due differences in measurement
procedures for determination of oil mist.

A silicon carbide (SiC) filter would probably be highly efficient for removal of ultrafine
particles, but due to the financial implications, SiC filters are not seen as an immediate solution for gas engines on CHP plants. Silicon carbide filters have been developed for use in diesel engines, and particles from CNG engines have a lower PM level
and a higher ash level as compared to diesel engines. Therefore, back pressure effects, and type and frequency of regeneration of the filter should be investigated before a SiC filter can be installed at a gas engine fired CHP plant.
3

The effect of the adjustment of lambda (surplus air ratio) on particle emissions is
limited. No significant effect on was found on neither PN nor PM during an extensive
4 day measurement program at plant E.

It is possible to reduce particle emissions from gas engines by adjusting the ignition
timing. By adjusting BTDC, particle emissions can be reduced by up to a factor of 5.
In this study, it is concluded that through a change in BTDC, a reduction in the NOx
concentration by about 50% (from e.g. 600 mg NOx/m³ to 300 mg NOx/m³), a simultaneous reduction in both PN and PM emissions by ~50% will be obtained. This was
obtained by reducing BTDC from about 13.5 to 11.5 on the plant E engine. The required adjustment in BTDC for this reduction in NOX and particle emissions will cost
about 1% loss in the engine efficiency. For a CHP plant gas engine, the loss in electricity production may to a certain extent be counterbalanced by a gain in heat production. However, this has not been investigated in this study.
Due to the recently introduced levy on NOX emissions introduced by the Danish government,
a number of the CHP plants are currently adjusting their gas engines in order to reduce lower
NOX emissions. This NOX reduction is typically obtained through an adjustment of ignition
timing and the surplus air ratio (lambda). The extent to which the ignition timing is adjusted
is dependent on the economy, i.e. the engine operation will be adjusted in order to minimize
the loss in efficiency. It may be concluded that CHP plants that are presently reducing their
NOX emissions will most probably also obtain a significant reduction in particle number and
mass emissions. From the results in this study, it is expected that the reduction in particle
emissions will depend on the extent to which NOX reduction is obtained through the adjustment of ignition timing.
4
1.3
Project results
5
Energinet.dk
ForskEL project No. 10612
Particle emissions from natural gas engines
Emissions of particles from gas engine powered CHP plants
Final report
31-10-2013
1 of 32
ForskEL projekt 10612 - PM emission from natural gas engines
Contents
Introduction ............................................................................................................................................ 3
Objective ................................................................................................................................................ 4
PM and ultrafine particles ........................................................................................................................ 5
Experimental........................................................................................................................................... 5
Measurement program ......................................................................................................................... 5
Sampling and analysis .......................................................................................................................... 6
Results ................................................................................................................................................... 8
Particle emission measurements from 5 Danish CHP plants .................................................................... 8
Engine type. ..................................................................................................................................... 9
Lubrication oil .................................................................................................................................. 9
Lubrication oil consumption and oil mist emissions ........................................................................ 10
Physicochemical lubricant oil properties and emissions .................................................................. 11
Assessment of additives and physical properties ........................................................................... 12
Effect of engine service on particle emissions ................................................................................... 16
Engine operation conditions (ignition timing and lambda) ................................................................. 17
Changing lambda () ................................................................................................................... 19
Changing engine ignition timing ................................................................................................... 21
Volatile particle fraction .................................................................................................................. 24
Calculation of total Emissions from CHP plants ........................................................................................ 26
Benefits to the environment ................................................................................................................... 28
References ........................................................................................................................................... 30
Appendices ........................................................................................................................................... 32
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Introduction
Atmospheric particles in the fine and ultra fine (defined as smaller than 1 µm and 100 nm respectively in this
work) are of growing concern, both from a public health perspective as well as from an climate and air
quality management perspective. There is mounting evidence showing a strong correlation between adverse
health effect and particles smaller than 2.5 µm 1 and mounting evidence of fine and ultrafine particulate
matter being responsible for a significant fraction of these effects 2-5 due to the fact that they penetrate deep
into the lungs when respired. Since they easily enter the indoor environment and remain suspended in the
air for extended periods of time, enabling them to be transported over long distances, the exposure to these
particles is relatively ubiquitous. However, current knowledge of which components of particulate matter by
size, composition, and source show the greatest impact on public health is still weak and inconclusive.1 As
increasing evidence of the effects of fine and ultrafine particles on human health and climate is mounting,
greater focus has been directed to potential sources. Among these, stationary sources with low stack heights
that are situated in or near urban areas are identified as potentially problematic. On a larger scale, it has
long been recognized that particles influence local, regional and global climate, both directly, by interactions
with electromagnetic waves resulting in changes in the radiation balance, and indirectly by interactions with
atmospheric water resulting in changes of cloud formation and properties resulting in e.g. changes in
increased cloudiness and changes rainfall patterns. The magnitude of the influence of the particles on the
environment is dependent on a number of physic-chemical factors like size, composition, and physical state.6
A number of studies have shown that in urban environments, vehicular sources can comprise up to 80% of
the mass emissions measured and as much as 90% of the number concentrations measured.7-11 In areas not
dominated by road vehicular emissions, the main sources are more mixed, but it is still found that particles
below 100 nm and 300 nm contribute more than 80% and 99% respectively, of the total particle number
concentration measured.12 In Denmark approximately 4% of the particulate mass emission (particles smaller
than 10 µm, PM10) is from power plants, refineries and CHP plants. 13
Several hundred combined heat and power (CHP) plants have been commissioned and are widely used in
Denmark due to their high efficiency and their ability to utilize the heat generated during power production.
The CHP plants all have an electricity production of less than 25 MW and are fired by either by waste, coal,
biomass, gasoil, or by gas (natural- or biogas). The magnitude and kind of emissions emitted from the
specific CHP plant is strongly dependant on the energy source and abatement technology installed.14
Numerous studies have shown that the installation of technologies like wet electrostatic precipitators (W-ESP)
and bag filters remove up to 99 of the emitted particle mass15-19 with an efficiency that is to some degree
dependant on the size distribution of the particles as well as the physico-chemical properties of the
emissions. Due to the very different nature of the fuels used in CHP plants, the characteristics of the
emissions are also expected to be very different. The waste, coal, or other solid fuels used to fire some CHP
plants is expected to produce emissions containing relatively large amounts of pollutants like metal oxides,
sulfur, and soot, and consequently these plants are all fitted with sophisticated abatement technologies.
However, CHPs fired by natural- or biogas is not expected to produce the same kind or amount of solid
phase pollutants. The main constituent of the gas fuels is CH4 with small amounts of heavier gaseous
hydrocarbons and the main reaction products expected from their combustion is CO2 and H2O along with
very low concentrations of other gas phase species. For this reason, the abatement devices utilized at these
CHP plants are normally limited to an oxidation catalyst for carbon monoxide. In terms of green house
gasses (GHGs) CHP plants are considered a cleaner energy source compared to e.g. coal fired power plants
due to the fact that natural and bio-gas inherently have low carbon/hydrogen (C/H) ratios which in turn lead
to less CO2 per energy unit production. However, recent measurements performed on gas fired CHP plants20
as well as on road and non-road vehicles running on natural- or biogas21-24, have shown evidence of large
particle number concentrations from these sources. Given that gas combustion in CHP plants emit a
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significant amount of particles combusting mainly methane and other low molecular weight hydrocarbons,
which are not expected to produce significant particle emissions, it is expected that the particulate emissions
originate from evaporation and partial combustion of engine lubrication oil and from engine wear.
In total, more than 200 CHP plants utilize gas engines for district heating supply in Denmark. Besides from
the CHP plants, a number of private enterprises utilize gas engines for e.g. production in greenhouses. The
majority of the CHP plants are located in smaller communities in less densely populated areas and their main
function is to provide district heating for residential areas using boilers and/or power and heat using gas
engines, depending in the immediate price of electricity. As about 28 % of the electricity production in
Denmark is supplied from wind energy in 2011 (as of 2011, 29% of the total capacity is wind energy)25, the
gas engine powered CHP plants offer flexible and fast supply of electricity in peak consumption periods and
in periods where the supply of wind energy is low. The gas engines used in the Danish CHP market are, for
the main part, turbo charged, 4-stroke, lean-burn type operating at typical oxygen levels of 8 – 12 % per
volume in the exhaust gas.
This study was undertaken by FORCE Technology, DGC (Danish Gas Technology Centre),Bergen Engines
Denmark A/S, Wärtsilä Denmark A/S, Statoil Fuel & Retail Sweden AB and Dansk Fjernvarme. Planning and
evaluation of the project activities was undertaken by a steering committee consisting of:
Per G. Kristensen, DGC
Lars Jørgensen, DGC
Bent Iversen, Wärtsilä Danmark A/S
Kim Larsen, Bergen Engines Denmark A/S
Thomas Norrby, Statoil Fuel & Retail Sweden
John Tang, Dansk Fjernvarme
Thomas Rosenørn, FORCE Technology
Karsten Fuglsang, FORCE Technology
Objective
Previous projects investigating fine and ultrafine particle emissions from combined heat and power plants
showed that natural and bio gas fired plants have surprisingly high particle emissions. It was speculated that
a correlation could exists between lubrication oil use/consumption and particle mass and number emissions.
The available data material from these projects was limited and factors that may control the emission level
were not investigated and therefore no conclusions as to the origin of these emissions were drawn.
The primary objective of this study was to identify the primary causes of fine and ultrafine particles emitted
from CHP plants using gas fired engines. Through an extensive field measurement program, the most
important factors influencing particle emissions from five selected gas engine powered CHP plants in
Denmark was assessed. The gas engine plants were selected with respect to engine type and size as being
representative for Danish CHP plants. To identify which operational parameters has the greatest influence on
the particulate emission from gas engines, the measurement program included collection of relevant engine
operating parameters as well as measurement of relevant gas and particulate phase components. The
influence from lubrication oil formulation on particle emissions has also been assessed in this study.
Furthermore, this study has included an assessment of options for future mitigation of particle emissions
from gas fires CHP plants.
4 of 32
PM and ultrafine particles
The ambient atmosphere contains large numbers of particles from both natural (e.g. volcanic eruptions,
sand storms, sea spray), biogenic (e.g. secondary particles from plant emissions) and anthropogenic sources
(e.g. stack emissions, tail pipe emissions, wood burning). The size of particles in the atmosphere span from
less than a few nanometers to several micrometers. Particles smaller in than 100 nm are usually referred to
as ultrafine particles (PN0.1 for number or PM0.1 for mass) and particles smaller in than 1 µm are usually
referred to as fine particles (PN1 for number or PM1 for mass). A few other size categories are in common
use for regulatory use; among these are PM2.5 and PM10.
Fine and ultrafine particles in exhaust from combustion are formed from gaseous precursors condensed as
temperature decreases in the exhaust system and/or after mixing with cold air in the atmosphere. Species
with low vapor pressures tend to condense first (e.g. metals), often with carbonaceous material following in
a layered structure as the aerosol cools down. Along with metals from engine wear and lubrication oil, even
trace amounts of sulfur in the combustion gas will influence the initial particle formation process and
resulting size distribution. The carbonaceous material mainly consists of incompletely combusted fuel and/or
lubrication oil.
Aerosol measurements have traditionally been performed on a per mass basis, but with an increased focus
on fine and ultrafine particle that carry very little mass, particle numbers have gained increased attention in
particle measurements. It is very important to realize that large particles have very little influence on particle
number measurements but heavily influence particle mass measurements, and that small particle have great
influence on particle number, but almost no influence on particle mass.
A more thorough introduction to the system layout at Danish CHP gas engine plants, and relation to particle
number, mass, properties and formation can be found in section 3 of the WP1 sub-report found in Appendix
1 along with an introduction to the use of natural gas engines in Danish CHP applications (Section 5).
Experimental
Measurement program
The measurement program comprised a total of seven field measurements conducted over a time span of 13
month at five Combined Heat and Power (CHP) plants at various locations in Denmark. A list of the five
selected sites, engines and lubricant types investigated is presented in Table 1.
Table 1: List of the 5 selected CHP plants.
Site
Plant A
Plant B
Plant C
Plant D
Plant E
Engine type
(Brand)
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
E-power output Engine lubricant
(kW)
(Brand)
6074
3118
2066
4794
3271
Shell Mycella
Geotex PX40
Geotex PX40
Mobil 805
Q8 Mahler
One measurement campaign was conducted at each location in order to investigate the variability between
the plants during normal operation. A number of engine and emission parameters were tracked and logged
to test for correlations. This was done to determine the most important parameters controlling the level of
particulate phase emissions as well as the emission of semi-volatile oil components measured as oil mist.
Based on the first five measurement campaigns and a number of challenges experienced with the selected
5 of 32
measurement method, it was decided to perform a second measurement campaign at Plants A and E in
order to ascertain the correct method to measure oil mist emissions in the flue gas. This was performed at
both plants as parallel measurements conducted by Danish Gas Technology Centre (DGC) and FORCE
Technology (FT) simultaneously over the span of two days. The second measurement campaign at Plant E
was also conducted in order to test the effects of a comprehensive engine overhaul on the emission levels.
The timing of the campaigns at plant E was selected in a manner that allowed the two measurements to be
conducted shortly before and shortly after a previously scheduled engine service.
During most of the campaigns a broad suite of instrumentation for gas and aerosol measurements was
employed to characterize the emissions. Table 2 summarizes the parameters measured during the individual
campaigns along with the entity responsible for the measurement during the campaign.
Table 2: Summary of the methods applied during the seven measurement campaigns and the entity
responsible for the measurement. ELPI: Electrical Low Pressure Impactor, TD: Thermodenuder, Filter/XAD:
Combination of heated filter cassette and absorption tube packed with XAD® polymeric adsorbent, FID:
Flame Ionization Detector, NDIR: Non-dispersive Infrared detector, CLD: Chemiluminescence Detector,
ZrO2: Zirconium Oxide sensor, SEM-EDX: Scanning Electron Microscope - Energy-dispersive X-ray
spectroscopy, AAS/ICP-MS: Atomic Absorption Spectroscopy/Ion Coupled Plasma – Mass Spectroscopy.
Field test #
1
2
3
4
5
6
7
Site
Plant A
Plant A
Plant B
Plant C
Plant D
Plant E
Plant E
Particle number and
Particulate
size distribution volatile fraction
Oil mist
UHC
CO
NOX
O2
Size resolved
Oil analysis
elemental analysis
ELPI
TD-ELPI
Filter/XAD
FID
NDIR
CLD
ZrO2
SEM-EDX
FT
FT
FT
FT
FT
FT
FT
FT
FT
FT
FT
FT
DGC
FT/DGC
DGC
DGC
DGC
DGC
FT/DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
FT
FT
-
Stack gas
temperature
AAS/ICP-MS Thermocouple
Statoil
Statoil
Statoil
Statoil
Statoil
-
DGC
DGC
DGC
DGC
DGC
DGC
DGC
The second campaign at plant A focused solely on the oil mist measurement, and during the second
campaign at plant E (after service), no lubrication oil sample was extracted due to the fact that the engine
oil had not been changed during the service. Furthermore, the oil mist samples at the second campaign at
plant E were performed a day before the rest of the sampling was done meaning that no other parameters
were determined simultaneously but were measured during normal operation the following day. The reason
for this was that only two sampling ports are available at both locations and no other sampling was possible
when they were being used for oil mist sampling.
Sampling and analysis
Both samples for particulate phase and gas phase analysis were extracted using specialized sample probes
(M&C heated probe SP34-H). From the gas phase sampling probe, the exhaust gas was transferred to a
mobile gas phase analyses rack consisting of an M&A model Thermo FID Flame Ionization Detector (FID) to
measure unburned hydrocarbons (UHC), a SICK model S710 Non-Dispersive InfraRed (NDIR) detector to
determine the level of CO/CO2, a Thermo Electron model 42 CHL ChemiLuminescence Detector (CLD) and a
SICK model S710 paramagnetic detector for NO/NOX and O2 level detection, respectively. Particulate phase
sample were transferred through a temperature controlled stainless steel tube (Hillesheim stainless steel) to
a custom designed dilution and conditioning system. The system is designed according to the particle
measurement protocol (PMP) and is a two step partial flow dilution system (PFDS). Total dilution in the PFDS
is approximately 1:100 achieved using two Dekati model DI-1000 ejector diluters, each providing a dilution
factor of 1:10. The goal of the PMP protocol is to ensure that only the solid part of the particulate phase is
measured. This is achieved by heating the first ejector diluter and the dilution air feeding it (up to 350 °C)
and consequently repartitioning the compounds in the aerosol resulting in a complete evaporation of volatile
and semi-volatile compounds whereupon the diluted sample is fed into the second ejector in which it is
6 of 32
diluted and cooled to a temperature compatible with the sampling equipment (close to room temperature).
For these experiments, the first dilution step of the dilution and conditioning system was run at a
temperature that was approximately 20 K higher than the temperature of the stack gas at the sampling
point. This setup was chosen to enable analysis of the volatile fraction of the particulate phase. From the
dilution system the aerosol was fed to an electrical low pressure impactor (Dekati ELPI classic) where the
particles were classified, counted, and collected on aluminum foils according to size. Analysis of the solid
particulate phase was conducted by running the sample through a thermodenuder (Dekati Thermodenuder,
set at 300 °C) before ELPI analysis. Measurement of solid particles was performed at all measurement sites
along with the measurement of total-PN. A validation test of the thermodenuder for evaporation of
lubrication oil particles was performed during this study in a laboratory test. The result of validation test is
shown in appendix 3: The thermodenuder was fully able to evaporate and remove lubrication oil particles in
the concentration range expected for gas engine exhaust. The exposed ELPI collection foils were analyzed
from selected campaigns using scanning electron microscopy with energy-dispersive X-ray spectroscopy
(SEM-EDX) to produce images of the collected particles along with the elemental composition (elements
from Carbon, Atomic Number 6, and up) of the particles.
The volatile fraction of the particles was measured by subtracting the solid PN (particle number measured by
placing the thermodenuder before the ELPI) from the total PN (total particle number measured by means of
the ELPI without the thermodenuder). In this report, all results given for PN will – unless otherwise stated be identical to total-PN, i.e. the sum of volatile and solid particles. Results giving the volatile fraction will be
clearly stated.
Using the measured number concentration by means of ELPI, conversion was done from number to mass
concentration using a particle density of unity. It should be noted that the ELPI mass and number
determination for particle in the upper size categories are subjected to an increased uncertainty, when
measurements are performed on a mixture between a very large number of ultrafine particles, and a very
small number of coarse particles (such as in exhaust gas from a gas engine). In this study, particle mass
calculations from ELPI measurement data has therefore been based on number measurements in the size
classes either < 1 µm or < 2.5 µm.
Lubricant oil samples were extracted by pouring the engine lubricant directly from the engine oil reservoir
(sump) into glass sample containers. The samples were subsequently analyzed at Statoil Lubricants’
Laboratoryi for metals and oxidation state using Atomic Absorption Spectroscopy (AAS) and Ion Coupled
Plasma – Mass Spectroscopy (ICP-MS).
Oil mist sampling was based on a Danish standard sampling protocol (MEL-14)26 which is a modification of
US-EPA Method 10. The 4 main differences between the two methods are that the Danish method allow 1)
an option to use a temperature controlled out-stack filter configuration, 2) an option to not heat the probe
and filter cassette if the flue gas non condensable, 3) an option to only analyze and report the particulate
fraction (i.e. filter) of the sample, and 4) an option to substitute the solvent used for rinsing with toluene for
work-environment and health reasons. The expanded method utilized in these experiments used sample
extraction through a heated out-stack particle filter followed by a condenser to extract semi-volatile
hydrocarbons and an XAD column to capture the gas phase hydrocarbons. After each sample had been
extracted, the equipment was rinsed using toluene which was also collected for analysis. All four sample
fractions (filter, condensate, XAD, and rinse) were analyzed by the Danish Technological Institute using a
gas chromatograph with a flame ionization detector. Using this method, hydrocarbons with vapor pressures
in the range of alkanes with between 14 and 40 carbon atoms (boiling points from 250°C to 525°C) are
quantified using n-hexadecane as a reference compound.
7 of 32
Results
Particle emission measurements from 5 Danish CHP plants
Particle number concentrations and supporting parameters were measured during campaigns at five selected
CHP plants in Denmark. Table 3 shows the average results from the seven individual campaigns which
comprised a total of 20 separate oil mist samples along with ELPI measurements of particle number and size
distributions. In accordance with MEL-14, the fraction collected on the filter is used primarily for data
analysis in this work. However, in some instances, the fraction collected on the XAD column has also been
considered in order to provide a more thorough analysis. The results shown in light shaded boxes indicate
that the supporting values were not measured simultaneously with the oil mist samples, but during the
following day of the same campaign. This was necessary due to the limited number of sampling ports
available during the campaign being used to perform parallel oil mist measurements to test the rigorousness
of the method. The result show in the dark grey shading is considered to be an outlier and is most likely due
to a sampling or analysis error on the XAD fraction.
Table 3: Average measurement results from the seven individual field campaigns which comprised a total
of 20 separate oil mist samples shown along with a number of key parameters measured during the
campaigns. The light shaded boxes indicate that the values were not measured simultaneously, but during
the following day of the same campaign. The results shown in the dark grey boxes are considered to be
outliers. Field tests 1 and 2 were performed on the same engine at Plant A and field tests 6 and 7 were
performed on the same engine at Plant E. Field test 6 was performed before service and field test 7 was
performed after service
Number based
Site
Oil consumption NOx mg/m³ UHC mgC/m³ PN1 #/cm³
Field test #
(g/kWh)
(n, ref)
(n, ref)
(n,ref O2)
Oil fraction
(PN1)
Mass based
Oil mist
PM1 mg/m³ Oil fraction Oil fraction Oil mist on filter Oil mist on XAD Oil mist on filter+XAD
(n, ref O2)
(PM1)
(PM10) mg/m³ (n, ref O2) mg/m³ (n, ref O2) mg/m³ (n, ref O2)
Plant A
1
0.160
327
1016
1.66E+06
61%
0.36
3%
42%
0.35
0.29
0.64
Plant A
2
-
-
-
-
-
-
-
-
0.11
0.07
0.18
Plant B
3
0.107
503
1511
1.99E+06
75%
0.72
57%
74%
0.26
0.22
0.48
Plant C
4
0.409
524
1812
1.49E+06
84%
0.19
37%
42%
0.76
0.98
1.74
Plant D
5
0.146
606
1135
1.96E+07
54%
2.08
32%
48%
0.43
3.85
4.28
Plant E
6
0.080
438
1589
1.31E+06
52%
0.17
39%
60%
0.14
0.29
0.43
Plant E
7
-
332
1593
8.81E+06
49%
0.26
39%
46%
0.12
0.05
0.17
A number of factors and correlations were investigated and analyzed in order to understand the particle
emissions from CHP plants. Among these engine type, lubrication oil type, time since service, and engine
operating conditions received special attention as these were the factors deemed most likely to influence the
particle emissions during these campaigns. A second field campaign was conducted at Plant E, both to
investigate the consequences of an engine overhaul, but also to further investigate how engine operating
conditions affected the emission levels. It was during the first five field campaigns found that there is a
correlation between the concentration of particles and the level of NOX in the flue gas (see Figure 1).
8 of 32
Figure 1: Particle mass and number concentration as a function of NOX level.
To probe the effects of NOX level on particle mass and number concentrations in the flue gas emissions, a
number of experiments were designed. These experiments and the results from them are discussed in the
section “Engine operation conditions (ignition timing and lambda)”
Engine type.
Two specific engine types and models are in use in the five plants selected for field testing. Plant A and plant
D both utilize a Wärtsilä model 18V34SG and Plants B, C, and E all use a Rolls Royce (Bergen) type K engine.
Table 4 shows the engine type in use at the investigated plants along with the measured particle number
and calculated particle mass (PM1) emissions, oil consumption, and the oil content inferred from the size and
number distribution measurements using a thermodenuder (see Appendix 3 for a thorough discussion on the
design, methodology, and validity of thermodenuder measurements on engine oil).
Table 4: The engine type in use at the investigated CHP plants along with particle number and mass
emissions. The oil consumption given is based on data on the individual engine as reported by the Plants.
Site
Plant A
Plant B
Plant C
Plant D
Plant E
Engine type
(Brand)
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
Engine load
(kW)
PN1
( #/cm³)
6074
3118
2066
4794
3271
1.66E+06
1.99E+06
1.49E+06
1.96E+07
1.31E+06
PM1
Oil consumption
(g/kWh)
(mg/m³)
0.365
0.716
0.186
2.082
0.166
0.160
0.107
0.409
0.146
0.080
As shown in Table 4 there is no apparent correlation between engine type and oil consumption. Neither does
there appear to be any correlation between engine type and particle mass emissions, particle number
emissions, or oil content measured using a thermodenuder setup.
Lubrication oil
At the five selected plants, four different engine lubrication oils were in use. Of these four, three were based
on group 3 base oils (Geotex PX40, Mobil 805, and Q8 Mahler) and one was based on a group 2 base oil
(Shell Mycella). A more thorough discussion of base oil groups definitions and the influence on oil properties
can be found in section 5 of Appendix 1 Interim report WP1_Literature Survey as well as a thorough walk
through of equilibrium considerations on oil emission from gas engines (Appendix 2 (DGC WP1 note on oil
emission). Table 5 shows a summary of the engine lubricant and base oil group in use at the CHP plants.
9 of 32
Table 5: Engine lubricant and base oil group (API definition) used at the selected CHP plants.
Site
Plant A
Plant B
Plant C
Plant D
Plant E
Engine type
(Brand)
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
Engine load
(kW)
6074
3118
2066
4794
3271
Engine lubricant
(Brand)
Shell Mycella
Geotex PX40
Geotex PX40
Mobil 805
Q8 Mahler
Base oil group
(API definition)
Oil consumption
(g/kWh)
2
3
3
3
3
0.160
0.107
0.409
0.146
0.080
Due to the limited number of data points in the present study, it is not possible to draw any conclusions on
the correlations between oil brand, type, or base oil group and particle emissions or oil consumption.
However, a strong correlation is seen between the engine oil consumption and the amount of oil mist in the
flue gas. This is described in greater detail in the section “Lubrication oil consumption and oil mist emissions.”
In order to examine how the choice of engine oil influence composition of the particle emissions, impactor
foils (aluminum foil covering the impactor stages) from the ELPI were analyzed using electron microscopy
with x-ray diffraction spectroscopy. The results from this work are described below in the section
“Assessment of additives and physical properties.”
Lubrication oil consumption and oil mist emissions
In appendix 2, theoretical calculations on the oil mist concentrations in the exhaust from gas engines are
shown. According to the engine suppliers, typical gas engines in Danish CHP plants consume 0.2 to 0.4 g oil
for each kWe power produced. In the case of lean burn engine with 110 % excess air (approximately 11.5 %
O2 in dry exhaust) this corresponds to an oil consumption of 38-76 mg/m3 exhaust. The actual concentration
of oil mist in the exhaust system will depend on the degree to which the oil components are combusted in
engine’s combustion chamber. Furthermore, oil particles passing the engine’s combustion chamber may be
caught in the exhaust system. Sporadic data obtained in an earlier project have indicated that emissions of
oil mist from gas engines may be quite high. 20-30 mg/m³ was measured for some gas engines in 2001,
indicating that a high fraction of the consumed oil passes the engine without combustion.27 In the following,
results will be shown for oil mist measurements on the five plants listed in Table 1.
Table 3 shows the average of the results from the seven individual campaigns which comprised a total of 20
separate oil mist samples. The samples were collected on heated (120 °C) glass fiber filter followed by a
condenser and an absorption column packed with Amberlite XAD-2 resin beads. The collected samples are
subsequently extracted and the collected amount of oil is determined using GC-FID analysis and the data
analysis in this work is primarily based on the fraction collected on the filter as in accordance with MEL-1426.
However, the fraction collected on the XAD column has also been considered in order to provide a more
thorough analysis. Shown in the table are also measured values for oil consumption.
Figure 2 shows the correlation between measured oil mist in the stack gas and the lubricant consumption.
The open circles indicate results where only the filter samples are included; the crosses also include the
fraction collected on the XAD column.
10 of 32
Oil mist on Filter
Oil mist on Filter and XAD
Linear (Oil mist on Filter)
Linear (Oil mist on Filter and XAD)
1.00
2.00
y = 4.0916x + 0.0488
R² = 0.9936
0.75
1.50
y = 1.71x + 0.0792
R² = 0.926
0.50
0.25
1.00
0.50
0.00
0.00
0.0
0.1
0.2
0.3
0.4
0.5
Oil mist on filter+XAD mg/m³ (n, ref O2)
Oil mist on filter mg/m³ (n, ref O2)
Oil mist vs. lubricant consumption
Oil consumption (g/kWh)
Figure 2: Correlation between measured oil mist and lubricant consumption. The open circles indicate
results where only the filter samples are included; the crosses also include the fraction collected on the
XAD column.
As can be seen in the graph in Figure 2, a very strong correlation is found between the oil consumption
reported by the CHP plants and the oil mist measured in the flue gas. The open circles indicate results where
only the filter samples are included; the crosses also include the fraction collected on the XAD column. A
strong correlation between oil mist measured and engine lubricant consumption was found (R2=0.93), and
an even stronger correlation was found when the gas phase was included in the analysis (R2=0.99). No
other significant correlations were found between the oil mist results and other measured parameters in this
work (see Table 2 for a list of measured parameters).
The measured concentrations of oil mist found in this study are significantly lower than expected from the
measurement results performed in 2001, as listed in appendix 2. It can be concluded that the overall share
of the oil consumed by the engine is combusted in the engine (or trapped in the exhaust system), and that
only a minor share of the oil consumed will appear in the exhaust gas as vapor or liquid oil particles.
Potential reasons for the discrepancy between the measurement results reported in 2001 and in this study
are (1) a lower oil consumption in the engines in this study (4 out of five engines had an oil consumption
that was < 0.2 g/kWh); (2) differences in the measurement method, and/or (3) differences in engine
operation conditions (4) some of the engines in the 2001 study had an oil consumption that had been
identified as too high, and they may therefore not represent normal operation.
Physicochemical lubricant oil properties and emissions
Weak correlations were found between a few of the physicochemical properties and the measured emissions.
As shown in the left plot in Figure 3, there is a weak correlation between the lubricant density and the
emitted amount of unburned hydrocarbons. The left plot in the figure illustrates a weak correlation between
the analyzed viscosity and the emitted amount of unburned hydrocarbons. The correlations are too weak
and the dataset too limited to be used as evidence and hence these correlations do not serve as evidence of
a connection between these parameters. No other correlations were found between the emissions and the
physicochemical properties of the lubrication oil (see Table 6 for a list of investigated parameters)
11 of 32
Figure 3: Weak correlations between physical properties and emissions.
A much more rigorous study is needed in order to establish significant correlations and possibly causations
between physicochemical properties of the lubrication oil and emissions.
Assessment of additives and physical properties
The lubrication oil used in gas engines must possess several properties like controlling oxidation and
nitration, limit ash levels, extend oil drain/turnover intervals, prevent corrosion, reduce wear, and maintain
internal engine cleanliness, as well as be compatible with flue gas treatment systems where present. The
main challenges for gas engine lubrication oil are nitration, oxidation, acid formation and deposits control. If
deposits are allowed to develop in the combustion chambers, natural gas engines are prone to ring sticking,
spark plug fouling, pre-ignition and detonation.
Like all lubrication oils used in combustion engines, the oils utilized by the plants in this study are based on a
base stock (base oil) and an additive package. The compositions of these additive packages are not
disclosed by the manufacturers, and unfortunately information on the type and amount of additives was not
available for this work. However, in most packages for gas engine lubrication oil, the main constituents
arethe detergent (responsible for deposit control) and the antioxidant (AO), (responsible for acid
neutralization, and oxidant control), these together account for around 80% of the total additive content.
Apart from the detergent and AO, a number of organic and organometallic compounds and salts(mainly
containing calcium (Ca), zinc (Zn), barium (Ba), magnesium (Mg), phosphorus (P), and sulfur (S)) are added
to the package, but the exact mixing ratios and compounds are unknown.
Figure 4 shows SEM-EDX analysis of the size segregated ELPI impactor foils collected from two of the five
plants investigated. EDX is capable of qualitative and quantitative analysis of elements with Atomic Numbers
higher than 5 (Boron).
12 of 32
Figure 4: Size segregated elemental analysis of particles sampled using the ELPI and analysed using SEMEDX. The left two panels show results from Plant A, the right hand panes show results from Plant E. The
bottom two graphs shown a zoom of the top two figures to allow for better resolution of the low mass
stages.
Figure 5 shows the normalized size segregated elemental compositions of the samples collected at Plants A
and E. This is the same data presented in Figure 4, but normalized to the total mass collected on each of the
10 analyzed stages. The top left side shows a graphical representation of the elemental composition
obtained from Plant A. The top two tables below shows the amount of each element collected on each stage
of the ELPI impactor as depicted in Figure 4, the bottom two tables show the numerical format of
normalized elemental distributions depicted in the top part of Figure 5. The right side of the figure shows the
same data obtained from Plant E. The numbers in the table shown in bold are the elements that were also
detected in significat concentrations in the oil analysis.
During the field campaigns, oil was sampled from the sump of each of the five CHP plants directly into 500
ml Pyrex sample flasks. The samples were sent to Statoil Lubricants Laboratory where the oil samples were
analyzed for elemental composition along with a number of physical and chemical properties. A summary of
the results is presented in Table 6. The numbers in the table for Plants A and E shown in bold are the
elements that were also detected in significat concentrations in the SEM-EDX analysis of the samples
collected using the ELPI.
The size segregated particle composition data holds some evidence of the origin of the different size classes
of collected particles. For both Plants A and E it is apparent from Figure 5 that the main component of
particles small than ~400 nm (the first five bins in the SEM-EDX analysis) is carbon along with smaller
amounts of oxygen and silicon. This indicated that they probably originate from products formed from
incomplete combustion of the fuel and subsequent reaction and/or condensation to the condensed phase.
Combustion particles are often seen as fractal agglomerates of small particles created from the combustion
products during cooling of the gasses. The left SEM image shown in Figure 6 show a typical example of this
kind of particles collected on the third stage (mean diameter = 120 nm) at Plant A during the field campaign.
13 of 32
Geo. Mean (µm)
0.04
0.07
0.12
0.20
0.31
0.48
0.76
1.23
1.95
3.08
C
0.0036 0.0216 0.0748 0.0709 0.1343 0.0692 0.0130 0.0879 0.1400 0.0112
O
Na
Mg
Si
P
S
0.0005 0.0014 0.0038 0.0045 0.0127 0.0062
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0001 0.0006 0.0009 0.0016 0.0035 0.0017
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0 0.0014
Cl
Ca
Zn
SUM
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0 0.0012 0.0110 0.1338 0.0755
0.0
0.0
0.0
0.0
0.0
0.0
0.0 0.0013 0.0 0.0240
0.0042 0.0236 0.0796 0.0770 0.1506 0.0785 0.0170 0.1188 0.3899 0.2278
0.0018
0.0001
0.0
0.0003
0.0002
0.0003
0.0135
0.0
0.0
0.0004
0.0005
0.0042
0.0569
0.0
0.0
0.0021
0.0287
0.0285
0.0710
0.0
0.0
0.0000
0.0105
0.0357
Geo. Mean (µm)
0.04
0.07
0.12
0.20
0.31
0.48
0.76
1.23
1.95
3.08
C
84.7
91.7
94.0
92.1
89.2
88.1
76.7
74.0
35.9
4.9
O
Na
Mg
Si
P
S
12.6
0.0
0.0
2.7
0.0
0.0
5.8
0.0
0.0
2.6
0.0
0.0
4.8
0.0
0.0
1.2
0.0
0.0
5.9
0.0
0.0
2.0
0.0
0.0
8.5
0.0
0.0
2.3
0.0
0.0
7.9
0.0
0.0
2.1
0.0
1.8
10.8
0.6
0.0
1.8
1.1
2.0
11.4
0.0
0.0
0.4
0.4
3.5
14.6
0.0
0.0
0.5
7.4
7.3
31.1
0.0
0.0
0.0
4.6
15.7
Cl
Ca
Zn
SUM
0.0
0.0
0.0
100.0
0.0
0.0
0.0
100.0
0.0
0.0
0.0
100.0
0.0
0.0
0.0
100.0
0.0
0.0
0.0
100.0
0.0
0.0
0.0
100.0
0.0
7.0
0.0
100.0
0.0
9.3
1.1
100.0
0.0
34.3
0.0
100.0
0.0
33.1
10.5
100.0
Geo. Mean (µm)
C
O
Na
Mg
Si
P
S
Cl
Ca
Zn
SUM
0.04
0.0046
0.0009
0.0
0.0
0.0003
0.0
0.0
0.0
0.0
0.0
0.0058
0.07
0.0187
0.0015
0.0
0.0
0.0009
0.0
0.0
0.0
0.0
0.0
0.0212
0.12
0.0227
0.0021
0.0
0.0
0.0013
0.0
0.0
0.0
0.0
0.0
0.0261
0.20
0.0134
0.0014
0.0
0.0
0.0006
0.0
0.0
0.0
0.0
0.0
0.0154
0.31
0.0032
0.0003
0.0
0.0
0.0001
0.0
0.0
0.0
0.0
0.0
0.0036
0.48
0.0023
0.0009
0.0
0.0
3E-05
0.0001
0.0005
0.0
0.0009
0.0002
0.0049
0.76
0.0249
0.0044
0.0
0.0
0.0003
0.0003
0.0018
0.0
0.0053
0.0004
0.0374
1.23
0.041
0.0528
0.0006
0.0
0.0297
0.0
0.0007
0.0024
0.0216
0.0
0.1489
1.95
0.0173
0.0138
0.0288
0.0083
0.0
0.0
0.0
0.0187
0.0
0.0
0.0869
3.08
0.0761
0.058
0.0838
0.0362
0.0
0.0
0.0
0.0651
0.0
0.0
0.3192
Geo. Mean (µm)
C
O
Na
Mg
Si
P
S
Cl
Ca
Zn
SUM
0.04 0.07 0.12 0.20 0.31 0.48 0.76 1.23 1.95 3.08
79.6 88.3 87.0 86.9 89.4 47.4 66.6 27.6 19.9 23.8
14.9
7.2
8.0
9.3
7.4
19.3 11.6 35.5 15.9 18.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.4
33.1 26.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
9.6
11.3
5.5
4.5
5.0
3.8
3.1
0.6
0.8
20.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
2.1
0.8
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
9.3
4.8
0.5
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.6
21.5 20.4
0.0
0.0
0.0
0.0
0.0
17.9 14.2 14.5
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.5
1.1
0.0
0.0
0.0
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
Figure 5: Normalized size segregated particle compositions from Plants A (left) and E (right) along with
tables showing the fractional elemental composition. The top tables are the amount of each element
collected on each stage of the ELPI impactor, the bottom tables are the normalized distribution. The
numbers in bold are the elements that were also detected in significat concentrations in the oil analysis.
Particles in the range between ~400 nm and 1.5 µm still contain a large fraction of carbon, but also
significant amounts of the additives and wear elements detected in the lubrication oil samples. The origin of
these particles is most likely the combustion of the engine lubrication oil. Two processes are important to
take into consideration when investigating oil transport from the engine into the particle phase, namely
evaporation from the cylinder walls, and droplets formed from the shearing forces of the piston movement.
The latter process gives rise to a larger amount of additive and wear elements than the first process, as the
first process shows fractionation based on vapor pressure of the elements during evaporation from the
cylinder walls. In support of this, previous studies of combustion particles have shown that spherical
particles larger than 400 nm are often present in relatively large numbers. Using a focused ion beam (FIB)
microscopy (FIB used along with the SEM-EDX setup enables analysis of the internal topography of the
collected samples by slicing the samples while imaging) has shown that these particles are in fact hollow
spheres consisting of ash and carbonaceous material.20 A SEM images of a spherical particle from sample
collected on the eighth stage (mean size = 1.23 µm) at Plant A is shown in the middle pane of Figure 6
14 of 32
Table 6: Engine lubricant oil analysis for the five selected CHP plants
Oil condition
Unit
Plant A
Plant B
Plant C
Plant D
Plant E
Density at 15 °C
kg/m3
882.8
861.9
859.7
892.8
863.6
Viscosity at 40 °C
mm2/s
140.9
95.0
92.1
152.2
90.2
Viscosity at 100 °C
Corrosive acid content
Base number / alkali reserves
Pour point
Flash point
Water content
mm2/s
KOH/g
KOH/g
°C
°C
ppm
14.4
1.8
3.6
-37
268
160
13.4
2.7
3.1
-29
266
164
13.2
2.1
4.8
-29
264
171
15.1
1.8
3.7
-20
252
260
12.6
2.2
3.7
-19
270
152
-log[H+]
scale (0-40)
Weight %
G-M-P
A/0.1mm
A/0.1mm
ppm
5.6
9
0.0
G
11
30
<100
4.5
9
0.0
G
12
29
<100
5.7
9
0.0
G
12
23
<100
6.0
9
0.0
G
14
40
100
4.5
9
0.0
G
13
27
<100
ppm
ppm
ppm
ppm
ppm
<1
1543
9
290
382
<1
1458
3
316
387
<1
1484
3
322
390
<1
1309
6
287
358
<1
1687
3
294
361
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
2
34
14
<1
<1
2
1
7
12
2
3
<1
<1
<1
<1
<1
<1
3
1
4
<1
<1
<1
<1
1
4
6
3
3
<1
<1
<1
<1
<1
6
1
2
<1
<1
<1
<1
<1
2
2
2
3
<1
<1
<1
<1
<1
<1
98
3
1
<1
1
<1
19
9
3
1
<1
<1
<1
<1
<1
<1
1
2
2
<1
<1
<1
<1
1
4
9
2
1
<1
<1
<1
<1
<1
Initial pH
Oil condition index
Soot
Dispersancy
Nitration
Oxidation
Chlorine
Additive elements
Barium
Calcium
Magnesium
Phosphorus
Zinc
Contamination and wear elements
Boron
Sodium
Silicon
Potassium
Lithium
Aluminum
Chromium
Copper
Iron
Lead
Tin
Molybdenum
Nickel
Titanium
Silver
manganese
Vanadium
In the largest particle fractions (i.e. on impactor stages that collect particles larger than ~1.5 µm), large
amounts of Na, Mg and Cl was found. When sodium is detected in the lubrication oil samples, it is usually an
indicator of contamination or engine wear. Chlorine is used as a lubricant condition marker along with a
number of chemical and physical characteristics, and magnesium is added to the lubricants as a detergent as
part of the additive package. The large Na content detected in the largest particles, was not seen in the oil
analysis from Plant E, but traces of Cl and Mg were detected in the oil from plant E. However, the trace
amounts detected in the oil sample from plant E does not explain the large amounts found in the particle
samples. As the compounds are also not found in significant amounts in the fuel, the origin of these
elements in the particle samples, is most likely from the intake air drawn into the engine. A possible
explanation might be that Plant E is located near the western coast of Denmark. Plant E therefore
experiences strong impact from western winds (the predominant wind direction in Denmark) containing high
loadings of sea spray aerosol particles which are know to by relatively large and contain large amounts of Cl
and Na.
15 of 32
Figure 6: SEM images of particles collected during the field campaigns. The left image is from the third
stage (mean diameter = 120 nm) collected at plant A, the middle image is from the eighth stage (mean
diameter = 1.23 µm) collected at Plant A, and the right image is from the tenth stage (mean diameter =
3.08 µm) collected at Plant E.
Plant A does not show the same influence of sea spray aerosols since Plant A is not in a coast-near
environment. The largest particles from Plant A therefore show increasing amounts of the additives and
wear elements detected in the particle fraction between ~400 nm and 1.5 µm, and this correlates well with
the results of the lubrication oil analysis. The SEM-image shown to the right in Figure 6 depicts a particle
collected on the impactor stage collecting particles of a mean aerodynamic diameter of 3.08 µm at Plant E.
The particle in the image show some of the characteristics expected from a mineral particle like clearly
defined layers, sharp corners, and clearly defined edges. Such a particle could be formed from mechanical
wear in the engine, consisting of a core of oxidized metals.
Effect of engine service on particle emissions
Another hypothesis tested was that particle mass emissions would be lower after service than before service
due to lower oil consumption after changing piston rings and cylinder linings. This was tested by conducting
a measurement campaign on the same engine at the same plant before and after a large engine service that
included a complete overhaul of the cylinders and pistons. The measurement campaign after the engine
service was performed after an initial run-in period of the new parts of approximately 500 engine hours.
However, as can be seen in Table 3, that from field test 6 (before service) to field test 7 (after service),
particle number concentrations went up from 1.31106 particles/cm3 to 8.81106 particles/cm3 and mass
concentrations (PM1) went up from 0.17 mg/m3 to 0.26 mg/m3. While these numbers are significantly
different, they are both within the observed range of particle emissions observed during normal operating of
gas engines investigated in this work.
Representative mass and number size distributions from the measurement campaigns are shown in Figure 7.
As can be seen from the plots, there is a difference in the particle populations before and after service with
a larger fraction of smaller particles (< 0.75 µm) during the after service measurements. It was not possible
to quantify the mass of particles larger than 1 µm with a sufficiently low uncertainty from the ELPI data, and
it is therefore not possible to provide results for PM10 in this study. However, close inspection of the data
shown in Figure 7, reveals that there appears to be fewer particles > 0.75 µm during the after service
measurements than during the before service measurements. The lowering in particle number concentration
< 0.75 µm and apparent increase in particle number concentration > 0.75 µm indicates that the service of
the engine, in this case, has shifted the particle population towards smaller particles. It should be noted that
these changes are not statistically significant.
16 of 32
1.00E+06
1.00E+05
Particle mass concentration
Before service
After service
After service
Before service
10.00
1.00
1.00E+04
0.10
1.00E+03
1.00E+02
0.01
1.00E+01
1.00E+00
0.01
0.10
1.00
10.00
0.01
Particle size (µm)
0.10
1.00
Mass concentration (mg/m³)
Number concentration (#/cm³)
Particle number concentration
1.00E+07
0.00
10.00
Particle size (µm)
Figure 7: Particle number and mass size distributions measured before and after service check.
However, in general, this result clearly shows that when an engine is well maintained and service checks are
performed regularly, overall particle mass and number emissions are not dependent on when the service is
performed or when it was last performed. It also indicates that for a given engine type and design there is
an absolute lower limit to the particle mass and number emissions attainable, beyond which further
reduction of particle emission is not possible by engine tuning.
Engine operation conditions (ignition timing and lambda)
Figure 1 shows the relationship between particle mass and number concentrations and the level of NO X in
the exhaust gas. In the graph a weak correlation is seen, but the number of data points is limited and the
variables changing between CHP plants is too large to draw meaningful conclusions. A series of experiments
was designed to be conducted during the second field campaign at Plant E where the level of NO X was
changed in a stepping manner while emission parameters were monitored. The resulting particle number
and mass concentrations measured as a function of NOX in the flue gas are shown in Figure 8. Note that due
to the relatively large number of particles smaller than 100 nm, the number concentration markers of
particle concentrations containing larger sizes (PN1, PN2.5, and PN10) are masked by the PN0.1 markers.
Figure 8: Particle number (left) and mass (right) concentrations measured as a function of NOX in the flue
gas at Plant E. Note that due to the relatively large number of particles smaller than 100 nm, the number
concentration markers of fractions containing larger sizes are masked by the PN 0.1 markers.
Two different ways to control the level of NOX were selected for the experiments, namely the air to fuel ratio
(lambda, ) and the ignition timing (measured as the crank angle before top dead center at which the spark
fires, in short BTDC (Before Top Deck Center)). Figure 9 shows the dependency of NOX on changing  or
BTDC. It is important to note that in the dataset on the right (NOX as a function of changing BTDC), small
changes in  are automatically performed by the engine management software as BTDC is changed.
17 of 32
Figure 9: NOX as a function of changing  (left) and BTDC (right). Note that in the dataset on the right,
small changes in  are performed by the engine manegement software as BTDC is changed.
The experiments were designed in such a way that during the experiments, all parameters were kept
constant, except the chosen one (λ or BTDC), which was changed until the desired NOX level in the exhaust
gas was attained. However, during the experiments where BTDC was changed, a minor auto correction of 
was automatically performed by the engine management software to prevent engine knocking and/or
damage. This in turn led to a more complicated and convoluted data processing and analysis.
Figure 10: Particle number and mass concentrations measured as a function of NOX in the flue gas at Plant
E. The plots on the left show number concentrations as a function of NOX measured, the figures on the
right hand side show mass concentrations as a function of NOX measured.
Figure 10 shows particle number and mass concentrations measured as a function of NO X in the flue gas at
Plant E separated such that the data is differentiated based on NO X control mechanism. The plots on the left
show the number concentrations as a function of NOX measured, the figures on the right hand side show
18 of 32
mass concentrations as a function of NOX measured. The plots each show four size fractions, namely PX0.1
(particles smaller than 100 nm), PX1 (particles smaller than 1 µm), PX2.5 (particles smaller than 2.5 µm), and
PX10 (particles smaller than 10 µm). The markers with lines represent the averaged result for the fraction in
question, and the markers with no lines represent the individual results. During the campaign, a total of four
measurement series were conducted, two identical series where NOX was adjusted by changing  and two
identical series where NOX was regulated by controlling BTDC. As shown in Figure 10, the repeatability of the
BTDC experiments was excellent. However, the two datasets for the lambda experiments differ significantly.
During one of the experiment days, both the mass and the number concentration are much higher than
during the other experiment days. The reason for these discrepancies could not be explained and
consequently, we have no basis for ruling out one of the two datasets.
As explained previously in this work, the ELPI mass and number determination for particle in the upper size
categories are subjected to an increased uncertainty, and for the majority of the work presented herein,
particle mass calculation based on number measurements in the size classes > 2.5 µm were omitted during
analysis. Figure 11 shows PM0.1, PM1, and PM2.5 data recorded during this campaign using the ELPI.
Figure 11: PM0.1, PM1, and PM2.5 data recorded during this campaign using the ELPI. The plot on the left
shows the data recorded during the experiments with varying lambda, and the plot on the right shows the
dataset from the BTDC experiments.
In the following two sections, reflections on the effects of changing lambda and ignition timing will be given,
and the results obtained will be assessed in detail.
Changing lambda ()
The air-fuel ratio needed to stoichiometrically combust methane is calculated from the reaction of methane
with pure oxygen as shown in Equation 1.
2O2 + CH4  CO2 + 2H2O
Equation 1
The stoichiometric ratio for this reaction on a per mole basis is 2:1 oxygen to methane. If this number
calculated on a per mass basis from the mass of fuel (mfuel), using the mass of air (mair) taking the average
mass fraction of oxygen in the atmosphere into account, the air to fuel ratio (AFR) is 17.2:1 (see Equation
2).
Equation 2
19 of 32
The AFR is dependent on the fuel used and varies from very low numbers for oxygenated species (e.g.
AFRmethanol = 6.4) to very high numbers for reduced species of low molecular mass (e.g. AFRhydrogen = 34).
Table 7 shows a small selection of AFRs for fuels commonly used in internal combustion engines.
Table 7: Examples of calculated mass based air-to-fuel ratios for a small range of typical fuels used in
internal combustion engines.
Compound
Methane
Gasoline/octane
Propane
Ethanol
Methanol
Hydrogen
Diesel
Stoichiometric AFR
17.2
14.7
15.5
9
6.4
34
14.6
Natural gas and biogas consist of a mixture of hydrocarbons along with impurities of inert compounds and
consequently the AFR depend on the composition of the gas. In order to deal with this challenge, internal
combustion engines are often equipped with an oxygen sensor in the exhaust system (-probes) that allow
real-time control of the AFR to attain a specified stoichiometric ratio. λ is defined as the ratio of the actual
AFR (AFRactual) to the stoichiometric AFR (AFRstoichiometric) as shown in Equation 3.
Equation 3
If  > 1, the combustion is said to be lean (in fuel), and if  < 1, the combustion is said to be rich (in fuel).
The gas engines investigated in these experiments are lean-burn engines and were set to run at
approximately  = 2. The two main reasons for running at lean conditions is 1) that the excess air reduces
the temperature of the combustion process and this in turn reduces the amount of nitrogen oxides (NO X)
produced, and 2) that since there is excess oxygen available, the combustion process is more efficient and
more power is produced from the same amount of fuel. The downside to lean running conditions is that the
accelerating power (torque) of the engine is reduced when compared to rich running conditions. However,
this is not an issue under steady state power production in power plant applications.
Figure 12: Particle number (PN0.1) and mass (PM1) concentrations as a function of . The markers show
the measured data points from the two days and the dashed line shows the average of the two
measurement series.
Figure 12 shows particle number and mass concentrations as a function of . The markers show the
measured data points from the two data series recorded while changing  during the field campaign, the
dashed line shows the average of the two measurement series. No clear trend is seen in the data collected
on February 7th, but the data from February 5th suggest that there is a decrease in particle number
20 of 32
concentration (~64%) with higher . The data for PM1 shows similar trend (~58% reduction), but again, this
is also only present in the data from February 5th. The data is summarized in Table 8.
Table 8: Summary of the particle mass and number concentrations collected during the experiments with
varying  on February fifth and seventh. Efficiency is defined as the amount of energy produced divided by
the energy content of the fuel combusted.
BTDC angle (°)

11.5
11.5
11.5
11.5
11.5
1.94
1.96
2.01
2.08
2.18
2012-02-05
PM1 (mg/m3) PN1 (#/cm3) Efficiency
0.231
0.228
0.199
0.172
0.098
1.80E+06
1.64E+06
1.45E+06
1.27E+06
6.45E+05
41.8%
41.7%
41.4%
40.9%
41.3%
BTDC angle (°)

11.5
11.5
11.5
11.5
11.5
1.94
1.96
2.01
2.08
2.21
2012-02-07
0.368
0.328
0.261
0.345
0.317
2.03E+07
1.55E+07
1.04E+07
1.64E+07
1.83E+07
41.7%
41.6%
41.5%
41.4%
40.9%
As can be seen from Figure 12, the particle concentration measurements show quite different results during
the two days, with the concentrations recorded on February 7th showing significantly higher values than the
measurements on February fifth. Figure 13 illustrates that the gas phase engine exhaust parameters show
no significant difference between the two days, indicating that the discrepancy in particle concentrations is
not caused by the engine operation.
Figure 13: Left: NOX, UHC, and CO concentrations measured in the flue gas as a function of Right:
Energy efficiency (defined as the amount of energy produced divided by the energy content of the fuel
combusted) plotted versus .
Changing engine ignition timing
The ignition timing of a spark ignition internal combustion engine is measured as the angle of the crankshaft
relative to top dead center, at which a spark will occur in the combustion chamber. Figure 14 (A) illustrates
the principle of ignition at 10° angle BTDC (Before Top Dead Centre).
21 of 32
Figure 14: Illustration of ignition at 10° BTDC. Illustration is a reproduction from reference 28.
It is necessary to advance the timing of the ignition to occur before the piston reaches top dead center
(TDC), due to the time it takes the flame front to propagate from the spark plug to the rest of the fuel in the
cylinder. The timing advance, measured as BTDC, is among other factors dependent on the angular velocity
of the crankshaft (rotations per minute, RPM) which lengthens or shortens the time available before TDC is
reached. Advancing the spark timing (higher BTDC) means that the spark is energized earlier relative to the
point where the combustion chamber reaches its minimum size (at TDC, maximum mechanical compression).
The purpose of the power stroke is to use the energy converted during combustion of the fuel, to use the
increased cylinder chamber pressure to push the piston down to rotate the crankshaft and produce
mechanical energy. While the flame front is propagating through the air/fuel mixture, the pressure in the
cylinder increases, due to (1) the increase in temperature, and (2) the compression performed by the piston
(the energy needed for compressing the gasses is derived from the energy released during previous
combustion cycles and from the same of other cylinders). Optimal ignition timing is determined by adjusting
a number of factors like timing of the intake valves or fuel injectors (determining the mixing state of the air
and fuel in the cylinder), the type of ignition system used (e.g. a pre-chamber or open chamber), the type
and condition of the spark plugs, the fuel composition, temperature, and pressure, the engine speed and
load, the air and engine temperature, and intake air pressure. Incorrect ignition timing often leads to
excessive vibration (BTDC too high), engine knocking (BTDC too low), and consequently may lead to engine
damage and failure.
Changing the ignition timing also alters the flame propagation velocity and consequently the heat release
rate due to the altered physicochemical properties of the air/fuel mixture as a function of crank angle caused
by altered temperatures and pressures. This alters the peak pressure in the cylinder which in turn alters the
peak temperature, the combustion chemistry, and consequently the amount of NO X produced from the
process. Since higher peak temperatures and pressures equals higher output from the engine for the same
amount of fuel but also higher output of NOX, this type of mechanical NOX control comes at a cost in the
form of higher fuel consumption and higher CO 2 emissions.
Figure 15 shows particle number and mass concentrations as a function of BTDC. The markers show the
measured data points from the two data series recorded while changing BTDC during the field campaign, the
dashed line shows the average of the two measurement series. A clear trend is seen in the data collected on
both February 6th and 8th showing a strong increase in particle number concentration (by a factor of ~3)
with an increase in BTDC from 10 to 13.8 degrees.
22 of 32
Figure 15: Particle number (left) and mass (right) concentration as a function of BTDC. The dashed line
shows the average of the two separate measurement series.
The data for particulate mass concentration (PM1) shows similar trend with a ~3-fold increase in February 6th
and a ~5-fold increase on February 8th . If taking the behavior of particle loading as a function of λ into
account, the increase in particle loading as a function of BTDC would have been even stronger, assuming
the two effects are in some way additive. Figure 16 shows the change in λ done by the engine management
software to protect the engine when BTDC was adjusted.
Figure 16:  as a function of BTDC.  is adjusted by the engine management software when BTDC is
changed to prevent engine damage.
From Table 8 we know that a change in  from ~2 to ~2.15 yields a decrease in PN/PM concentration of
approximately 40-50% (based on the data from February 5th ). This works in the same direction as the
increase in BTDC angle reflected by the measurements performed on 5 Feb 2012 (increasing BTDC 
decreasing  increasing PN/PM from ), but is strongly overpowered by the contribution from BTDC. Table
9 shows a summary of the particle mass and number concentrations collected during the experiments with
varying BTDC on February 6th and 8th .
Table 9: Summary of the particle mass and number concentrations collected during the experiments with
varying BTDC on February 6th and 8th . Efficiency is defined as the amount of energy produced divided by
the energy content of the fuel combusted.
BTDC angle (°)

13.8
13.3
12.5
11.5
10
2.01
2.03
2.05
2.1
2.16
2012-02-06
0.542
0.410
0.337
0.293
0.169
2.85E+06
1.93E+06
1.89E+06
1.53E+06
9.97E+05
41.8%
42.1%
42.0%
41.6%
40.6%
BTDC angle (°)

13.8
13.3
12.5
11.5
10
2
2.01
2.03
2.08
2.14
2012-02-08
0.396
0.266
0.184
0.133
0.082
3.65E+06
1.90E+06
1.36E+06
1.28E+06
1.19E+06
42.2%
41.8%
41.7%
41.5%
40.7%
23 of 32
Figure 17 illustrates that, as during the  experiments, the gas phase engine exhaust parameters show no
significant difference between the two days.
Figure 17: Left: NOX, UHC, and CO concentrations measured in the flue gas as a function of BTDCRight:
Energy efficiency (defined as the amount of energy produced divided by the energy content of the fuel
combusted) plotted versus BTDC.
The results shown in Table 8 and Table 9 clearly show that there is a correlation between emissions and
engine control parameters. It also shows that when tuning an engine, it is very important to consider the
magnitude in the changes this will lead to in emissions. It is also important to realize that changes in engine
parameters will lead to changes in engine efficiency as a result of the changes in combustion conditions and
kinetics. This aspect will be discussed further in the section Calculation of total Emissions from CHP plants
Volatile particle fraction
As briefly described in the section “Sampling and analysis”, a thermodenuder was used to quantify the
volatile fraction of the condensed phase. The volatile fraction is defined as the fraction of the particles
removed by inserting a thermodenuder upstream of the ELPI when performing a measurement. In practice
this is done by performing consecutive measurements with and without the thermodenuder in place while
the engines are run under steady state conditions. During these experiments the evaporation zone of the
thermodenuder was set to 300 °C in order to ensure evaporation and removal of all engine oil and volatile
combustion products. The thermodenuder setup was tested to ensure the applicability to engine oils and
was found to perform as expected. This sub-study is described in appendix 3.
Table 10 Volatile fractions from five CHP Plants. The Volatile fractions are shown as number based
fractions as well as mass based fractions.
Site
Plant A
Plant B
Plant C
Plant D
Plant E
PN1
Volatile fraction PN1
PM1
Volatile fraction PM1
( #/cm³) (fraction removed by TD) (mg/m³) (fraction removed by TD)
1.66E+06
1.99E+06
1.49E+06
1.96E+07
1.31E+06
61%
75%
84%
54%
52%
0.365
0.716
0.186
2.082
0.166
26%
57%
37%
32%
39%
Table 10 shows the inferred volatile fractions from the five investigated plants. The number fraction of
particles removed by the thermodenuder was at least 50% in all cases and in one case up to 85%. In terms
of mass removal for particles smaller than 1 µm, the thermodenuder removed between 25% and 60% of the
particulate mass.
The interpretation of these data is complicated by the fact that the measured volatile fraction is strongly
dependant on the shape of the particle size distribution, as particles may move in and out of the detection
range when exposed to the thermodenuder. The particles investigated in this study are not single
24 of 32
component particles, but may comprise multiple phases and compounds like elemental carbon, metals,
sulfates, hydrocarbons, and particle bound water. This means that in some cases, when the particles are
exposed to thermodenuder treatment, only part of the particle evaporates resulting in a change in size and
in other cases, the entire particle evaporates and it is no longer counted. If particles larger than 1 µm are
present, they may partially evaporate and move from a part of the size spectrum that is not included in the
study, to a part of the spectrum that is counted. In a similar manner particles may be removed from the
lower end of the spectrum. For this reason numbers concerning volatile fractions should be interpreted and
used with caution and the shape of the size distribution has to be considered when doing so.
Figure 18 shows the number and mass based volatile fractions as functions of  and BTDC and illustrates
that as λ increases, the fraction of volatile material also increases. There does not appear to be any change
in volatile fraction as BTDC is changed. However, it is important to remember that, as described in
“Changing engine ignition timing”, lambda changes along with BTDC, which means that the change in BTDC
counteracts the change in volatile fraction introduced by the change in i.e. increasing BTDC decreases
the volatile fraction.
Figure 18: Number (left) and mass (right) based volatile fractions plotted against  (top) and BTDC
(bottom).
Taking the volatile fraction into account during the data analysis from the second campaign at Plant E
further strengthens the trends and conclusions presented in the previous section.
The change in lambda from 1.94 to ~2.2 leads to an approximately 30% reduction in particulate material,
both on per-mass and on per-number basis. This reduction is about half the reduction shown in Table 8 for
particles that were not exposed to thermodenuder treatment, indicating that a relatively larger fraction of
the particles are volatile at higher . Table 11 shows particle number and mass concentrations measured by
the ELPI after thermodenuder treatment along with the relative reduction in concentrations resulting from
engine parameters.
25 of 32
Table 11: Particle number and mass concentrations measured by the ELPI after thermodenuder treatment.
The table shows the relative reduction in particle number (Red. PN) and mass (Red. PM) concentrations,
resulting from the set change in BTDC and  which are also shown in the sub-tables.
BTDC angle (°) 
11.5
11.5
11.5
11.5
11.5
1.94
1.96
2.01
2.08
2.18
BTDC angle (°) 
13.8
13.3
12.5
11.5
10
2.01
2.03
2.05
2.1
2.16
2012-02-05
PM1 (mg/m3) PN1 (#/cm3) Red. PN Red. PM
0.159
0.139
0.139
0.113
0.162
1.12E+06
9.30E+05
8.10E+05
7.80E+05
1.38E+06
0.0%
17.1%
27.8%
30.5%
-23.2%
BTDC angle (°) 
0.0%
12.5%
12.4%
28.6%
-2.0%
11.5
11.5
11.5
11.5
11.5
2012-02-06
0.317
0.258
0.202
0.164
0.112
1.39E+06
1.14E+06
7.48E+05
7.57E+05
5.76E+05
0.0%
18.1%
46.2%
45.6%
58.6%
1.94
1.96
2.01
2.08
2.21
BTDC angle (°) 
0.0%
18.6%
36.3%
48.1%
64.8%
13.8
13.3
12.5
11.5
10
2
2.01
2.03
2.08
2.14
2012-02-07
0.234
0.206
0.164
0.190
0.162
7.86E+06
6.55E+06
4.37E+06
6.46E+06
5.09E+06
0.0%
16.7%
44.4%
17.8%
35.3%
0.0%
11.8%
29.8%
18.5%
30.9%
2012-02-08
0.232
0.158
0.110
0.092
0.045
1.28E+06
8.49E+05
6.88E+05
5.95E+05
4.03E+05
0.0%
33.6%
46.2%
53.4%
68.5%
0.0%
31.9%
52.5%
60.3%
80.4%
Figure 18 shows no dependency between volatile fraction and BTDC, which is also evident when comparing
Table 11 to Table 9, which also shows a ~3-5 fold reduction in concentration.
Calculation of total Emissions from CHP plants
In order to facilitate comparison and applicability of the measured values, particle emission factors have
been calculated on an energy basis (GJ electricity produced and GJ consumed). Table 12 shows the
calculated emission factors for NOX, UHC, and particle mass and number concentrations.
Table 12: Emission factors based on an energy basis (GJ electricity produced and GJ consumed) for NOX,
UHC, and particle mass and number concentrations. Results from Plant D are excluded from the average,
as they are considered outliers in the dataset due to flow restrictions on the engine air intake.
Site
PN1 (#/GJ)
PM1 (mg/GJ)
NOX (g/GJ)
UHC (gC/GJ)
e-Produced Consumed e-Produced Consumed e-Produced Consumed e-Produced Consumed
Plant A
1.33E+15
Plant B
1.68E+15
Plant C
1.28E+15
Plant D
1.67E+16
Plant E
1.13E+15
Average (Excl. D) 1.35E+15
5.78E+14
6.97E+14
5.20E+14
6.84E+15
4.57E+14
5.63E+14
292
605
160
1770
143
300
127
252
65
726
58
125
237
383
407
465
341
342
103
160
165
191
138
141
737
1153
1408
871
1238
1134
319
480
572
357
501
468
E-energy efficiency
(GJ e-produced/GJ consumed)
43%
42%
41%
41%
40%
42%
The conversion from particle concentration to emission factors is dependent on the amount of exhaust gas
produced per GJ. This is not a constant number, but depends on how efficient the engine converts fuel to
energy at a given setting, which in turn is highly dependent on engine settings. Figure 19 shows particle
number (left side) and mass (right side) emission factors for Plant E as a function of  (top two plots) and
BTDC (bottom two plots).
26 of 32
Figure 19: Particle number (left side) and mass (right side) emission factors as a function of lambda (top
two plots) and BTDC (bottom two plots).
The plots in Figure 19 show that neither the emitted mass of particles nor the emitted number of particles
exhibits any significant dependence on , but that – as described in section “Engine operation conditions” –
both particle number and mass is strongly dependent on the ignition timing. By comparison of the results
shown in Figure 9 (right side graph) with Figure 19 (lower graphs), it may be concluded that through a
change in BTDC, a reduction in the NOx concentration by about 50% (from e.g. 600 mg NOx/m³ to 300 mg
NOx/m³), a simultaneous reduction in both PN and PM emissions by 50% can be obtained. This was
obtained by reducing BTDC from about 13.5 to 11.5 on the plant E engine. From Figure 17 (right side graph),
it can be seen that a reduction in BTDC from 13.5 to 11.5 will cost about 1% loss in the engine efficiency.
This loss in energy efficiency is measured as loss in kWe (electricity production). It may be possible that the
loss in electricity production at a CHP plant to a certain extent is counterbalanced by a gain in heat
production. However, this has not been investigated in this study. Table 13 compares the PN1 and PM1
emission factors determined in this study with an earlier study performed by NERI, DGC and FORCE 29 in
2010. Results from plant D have been omitted from the average in this study, as the engine operation at this
plant turned out to be unstable and therefore not representative. The relative standard deviation (RSD) is
shown along with the results from this work, illustrating the consistency of the measured emission factors.
27 of 32
Table 13: Average number (PN1) and mass (PM1) emission factors determined as part of this work,
compared to previously determined emission factors from a number of other CHP plants. Number of plants
is the number of plants that constitute the basis for the shown factor, RSD is the Relative Standard
Deviations.
Average this study (Excl. D)
Gas fired plant (natural gas)
Gas fired plant during start up (natural gas)
Gas fired plant (landfill gas)
Gas oil plant (diesel)
Bio mass plant with bag filter
Bio mass plant with electrostatic precipitator
Waste to energy plant with bag filter
Waste to energy plant with electrostatic precipitator
Number of Particle number
Particle mass
RSD
RSD
Reference
plants (#/GJ consumed)
(g/GJ consumed)
4
5.6E+14
18.00%
0.125
72.00% This study
1
1.6E+16
NA
2.618
NA (DMU REPORT)
1
4.1E+17
NA
13.694
NA (DMU REPORT)
1
1.6E+13
NA
0.012
NA (DMU REPORT)
1
2.4E+14
NA
0.173
NA (DMU REPORT)
1
5.4E+13
NA
0.119
NA (DMU REPORT)
1
3.2E+14
NA
0.811
NA (DMU REPORT)
1
3.6E+12
NA
0.251
NA (DMU REPORT)
1
2.3E+13
NA
0.053
NA (DMU REPORT)
Table 11 shows that the average emission factor determined for particle number emissions from the gas
fired CHP plants in this study are comparable to, albeit somewhat lower, results from earlier measurements
of particle emissions from gas fired CHP plants. Particle mass emissions are also lower than the previously
measured values, but this can also be ascribed to the natural variability of emissions factors between gas
engine fired plants.
Benefits to the environment
In the development and production of gas engines for CHP plants, emission reduction is an important issue
with regards to NOx, UHC and CO2. Emissions of particle mass from gas engines has so far been considered
of minor importance, and the reduction of particulate emissions has so far not been addressed specifically by
the manufacturers of gas engines.
In the following, options for mitigation of particle emissions from gas engines are listed.



Engine type. The potential for development of gas engines with lower particle emissions should be
investigated. Currently, a large number of gas turbines are being installed in the US. The emission
profiles for gas turbines are very different from the emission profile of gas engines and due to their
size are often connected to flue gas treatment systems. However, gas turbines are more costly and
less flexible for fast start-up in supply networks that operate on renewable energy sources like wind
power. The development of gas engines with reduced particle emissions from lubrication oils should
be supported. In this study, particle emissions from gas engine produced by two different
manufacturers (Bergen Engines and Wärtsilä) were studied and no significant differences between
the two involved engine types could be found.
Engine maintenance and service. It seems clear from the results of this study that when an
engine is well maintained and service checks are performed regularly, overall particle mass and
number emissions do not vary strongly before and after the performance of an engine service. This
study also indicates that for a given engine type and design there is a lower limit to the level of
particle mass and number emissions attainable, beyond which no further reduction of particle
emission can be achieved. This minimum “base level” is assumed to depend highly on the efficiency
of parts that ensure a minimum loss of lubrication oil to the combustion chamber or through
crankcase ventilation (such as gaskets, and piston rings).
Lubricant oil. No significant correlation between the measured particle emissions and the
properties of the different types of lubrication oil could be found in this study. For the four different
lubrication oils that were used at the five different plants, no significant correlation could be found
between the particle emissions and the type or age of lubrication oil. Furthermore, due to the lack
28 of 32



of information on additives, it was not possible to correlate the measured particle emissions to
specific additives in the lubrication oil. Results from analysis of metals in lubrication oil samples
could however be well correlated with metals analysed in the particles emitted from the engine. This
confirms that e.g. Ca, Mg and Si in lubrication oil additives will occur in particles emitted from the
engine. A weak correlation was found between the density and viscosity of the lubrication oils and
the measured emission of uncombusted hydrocarbons (UHC) – the higher the density (and the
higher the viscosity) of the lubrication oil, the lower the emitted concentration of UHC. It may be
concluded that for engines that are properly maintained, and for lubrication oils that are controlled
within the required specifications, lubrication oil type and composition seem to have a minor effect
on particle emissions. From the findings of this study, the occurrence of e.g. metals in additives
should be carefully assessed in relation to their occurrence in the engine exhaust.
Adjustment of engine operation. This study shows that it is possible to reduce particle emissions
from gas engines by adjusting the ignition timing. By adjusting BTDC, particle emissions can be
reduced by up to a factor of 5. In this study, it is concluded that through a change in BTDC, a
reduction in the NOx concentration by about 50% (from e.g. 600 mg NOx/m³ to 300 mg NOx/m³), a
simultaneous reduction in both PN and PM emissions by 50% can be obtained. This was obtained by
reducing BTDC from about 13.5 to 11.5 on the plant E engine. The required adjustment in BTDC for
this reduction in NOx and particle emissions will cost about 1% loss in the engine efficiency. It may
be possible that the loss in electricity production at a CHP plant to a certain extent is
counterbalanced by a gain in heat production. However, this has not been investigated in this study.
Due to the recently introduced levy on NOx emissions introduced by the Danish government, a
number of the CHP plants are currently adjusting their gas engines in order to reduce lower NOx
emissions. This NOx reduction is typically obtained through an adjustment of ignition timing and the
air to fuel ratio (lambda). The extent to which the ignition timing is adjusted is dependent on the
economy, i.e. the engine operation will be adjusted in order to minimize the loss in efficiency. It may
be concluded that CHP plants that are presently reducing their NOx emissions will most probably
also obtain a significant reduction in particle number and mass emissions. From the results in this
study, it is expected that the reduction in particle emissions will depend on the extent to which NOx
reduction is obtained through the adjustment of ignition timing.
Installation of particle filters for emission reduction. A silicon carbide (SiC) filter would be
highly efficient for removal of ultrafine particles. However, reported installations of particle filters on
CNG engines are few. Installation of a particle filter has been tested on a CNG driven bus in
California and found applicable.30
Silicon carbide filters have been developed for use in diesel engines, and particles from CNG engines
have a lower PM level and a higher ash level as compared to diesel engines. Therefore, some issues
must be dealt with before a SiC filter can be installed at a gas engine fired CHP plant. This involves
e.g. investigation of back pressure effects, and type and frequency of regeneration of the filter.
29 of 32
References
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Air & Waste Manage. Assoc. 2006 56:709–742
2. Brunekreef, B.; Forsberg, B. Epidemiological Evidence of Effects of Coarse Airborne Particles on
Health. Eur. Respir. J. 2005, 26, 309-318.
3. Ostro, B.D.; Broadwin, R.; Lipsett, M.J. Coarse and Fine Particles and Daily Mortality in the Coachella
Valley, California: A Follow-Up Study; J. Expo. Anal. Environ. Epidemiol. 2000, 10, 412-419.
4. Laden, F.; Neas, L.M.; Dockery, D.W.; Schwarts, J. Association of Fine Particulate Matter from
Different Sources with Daily Mortality in Six U.S. Cities; Environ. Health Perspect. 2000, 108, 941947.
5. Delfino, R.J.; Sioutas, C.; Malik, S. Potential Role of Ultrafine Particles in Associations between
Airborne Particle Mass and Cardiovascular Health; Environ. Health Perspect. 2005, 113, 934-946.
6. Seinfeld, J. H.; Pandis, S. N. Atmospheric Chemistry and Physics : From Air Pollution to Climate
Change; John Wiley & Sons, Inc.: United States of America, 2006
7. Harrison, R.M.; Beddows, D.C.S.; Dall’Osto, M. PMF analysis of wide-range particle size spectra
collected on a major highway. Envir. Sci. & Tech. 2011 45, 5522-5528.
8. Johansson, C.; Norman, M.; Gidhagen, L. Spatial & temporal variations of PM 10 and particle number
concentrations in urban air Environ. Monit. Assess. 2007 127, 477e487.
9. Kumar, P.; Robins, A.; Vardoulakis, S.; Britter, R. A review of the characteristics of nanoparticles in
the urban atmosphere and the prospects for developing regulatory controls. Atmos. Environ. 2010
44, 5035-5052.
10. Kumar, P.; Robins, A.; Vardoulakis, S.; Quincey, P. Technical challenges in tackling regulatory
concerns for urban atmospheric nanoparticles. Particuology 2011 9, 566e571.
11. Pey, J.; Querol, X.; Alastuey, A.; Rodríguez, S.; Putaud, J.P.; Van Dingenen, R. Source
apportionment of urban fine and ultra fine particle number concentration in a Western
Mediterranean city. Atmos. Environ. 2009 43, 4407-4415.
12. Heal, M.R.; Kumar, P.; Harrison, R.M. Particles, air quality, policy and health. Chem. Soc. Rev. 2012
41, 6606-6630.
13. Danish Environmental Protection Agency report: Luftforurening med Partikler I Danmark;
Miljøprojekt Nr. 1021; Danish Ministry of the Environment: Copenhagen, 2005;
http://www2.mst.dk/udgiv/publikationer/2005/87-7614-720-7/pdf/87-7614-721-5.pdf
14. Fuglsang K.; Markussen J. B.; Frederiksen T. G.; Hummer K. B. Measurement and Characterization
of Fine and Ultrefine Particles in Emissions From CHP Plants in Denmark. Conference abstract
presented at 9th International conference on Emissions Monitoring. 2009.
15. Buonanno, G., Ficco, G., Stabile, L., 2009a. Size distribution and number concentration of particles
at the stack of a municipal waste incinerator. Waste Management 29, 749e755.
16. Buonanno, G., Stabile, L., Avino, P., Belluso, E., 2011. Chemical, dimensional and morphological
ultrafine particle characterization from a waste-to-energy plant. Waste Management 31, 2253e2262.
17. Hinds, W.C., 1999. Aerosol Technology: Properties, Behaviour and Measurement of Airborne
Particles. John Wiley & Sons, UK, 483 pp.
18. Kumar, P., Fennell, P., Symonds, J., Britter, R., 2008. Treatment of losses of ultrafine aerosol
particles in long sampling tubes during ambient measurements. Atmospheric Environment 42,
8819e8826.
19. Maghun, J., Karg, E., Kettrup, A., Zimmermann, R., 2003. On-line analysis of the size distribution of
fine and ultrafine aerosol particles in flue and stack gas of a municipal waste incineration plant:
effect of dynamic process control measures and emission reduction devices. Environmental Science
& Technology 37, 4761e4770.
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20. ForskEl report: Characterization of Ultrafine and fine Particles from CHP Plants; ForskEl project no.
2008-1-0071; Energinet.dk: Copenhagen 2009
21. Kumar P.; Pirjola L.; Ketzel M.; Harrison R. M. Nanoparticle emissions from 11 non-vehicle exhaust
sources – A review. Atmos Environ. 2013 67, 252-277
22. Jayaratne, E. R.; He, C.; Ristovski, Z. D.; Morawska, L.; Johnson, G. R. A Comparative Investigation
of Ultrafine Particle Number and Mass Emissions from a Fleet of On-Road Diesel and CNG Busses.
Environ. Sci. Technol. 2008, 42, 6736-6742
23. Jayaratne, E. R.; Meyer, N. K.; Ristovski, Z. D.; Morawska, L.; Miljevic, B. Critical Analysis of High
Particle Number Emissions from Accelerating Compressed Natural Gas Buses. Environ. Sci. Technol.
2010, 44, 3724–3731
24. Hallquist Å.M.; Jerksjo M.; Fallgren H.; Westerlund J.; Sjödin Å. Particle and gaseous emissions from
individual diesel and CNG buses. Atmos. Chem. Phys. 2013, 13, 5337–5350
25. Danish Energy Agency report: Energistatistik 2011; Danish Energy Agency: Copenhagen 2011;
http://www.ens.dk/sites/ens.dk/files/info/tal-kort/statistik-noegletal/aarligenergistatistik/Energistatistik%202011.pdf
26. Danish Environmental Protection Agency, MEL 14 (rev 2)(2008) http://www.ref-lab.dk/reflab_docs/showdoc.asp?id=080506074434&type=doc&pdf=true
27. National Environmental Research Institute report: Emissionsfaktorer og emissionsopgørelse for
decentral kraftvarme; Copenhagen 2003 ;
http://www2.dmu.dk/1_viden/2_Publikationer/3_fagrapporter/rapporter/FR442.pdf
28. http://www.waybuilder.net/sweethaven/MechTech/Automotive01/default.asp?unNum=1&lesNum=3
&modNum=4
29. National Environmental Research Institute report: Emissionskortlægning for decentral kraftv arme
2007 – Energinet.dk miljøprojekt nr. 07/1882 Delrapport 5. Emissionsfaktorer og emissionsopgørelse
for decentral kraftvarme: Copenhagen 2006;
http://www.energinet.dk/SiteCollectionDocuments/Danske%20dokumenter/Klimaogmiljo/Emissionsp
rojektet%20-%20Emissionsfaktorer%20og%20opg%C3%B8relse%20for%20decentral%20%20kraftvarme%202006.pdf
30. http://www.aqmd.gov/tao/ultrafine_presentations/Session5_4_JonathanHarris.pdf
31 of 32
Appendices
Appendix 1
Particle emissions from natural gas engines - Emissions of particles from gas engine powered
CHP plants - WP1 Literature survey. Interim report, ForskEL project No. 10612. 23 September
2011.
Appendix 2
Oil emissions from gas engines. DGC-note 2011. Interim report, ForskEL project No. 10612.
Appendix 3
Fordampning af oliedråber. Rapport over resultater til validering af målemetode til måling af
olieholdige partikler fra gasmotorer (in Danish), 2011. Interim report, ForskEL project No.
10612.
Appendix 4
Rosenoern, T. et al. Factors controlling condensed phase emissions from gas engine fired
combined heat and power plant (CHP) – a field study. (draft submitted for peer reviewed to
the journal Environmental Science and Technology).
Appendix 5
Fuglsang, K. mfl. (in press). Ultrafine partikler fra gasmotorer på danske kraftvarmeværker.
Article accepted for publication in Dansk Kemi (12), 2013 (in Danish).
Appendix 6
combined heat and power plant (CHP) – a field study. Poster presented at 17th ETHConference on Combustion Generated Nanoparticles, June 23th – 26th 2013, Zürich.
Appendix 7
combined heat and power plant (CHP) – a field study. Paper presented at EPRI (Electric
Power Research Institute) Workshop on Air Quality Impacts of Natural Gas Combustion for
Electricity Generation, August 26 - 27, 2013, Palo Alto, CA
Appendix 8
Fuglsang, K. mfl. (in press). Ultrafine partikler fra gasmotorer på danske kraftvarmeværker.
Article accepted for publication in “Dansk Fjernvarme”, 2013 (in Danish).
i
Statoil Fuel & Retail Sweden AB, BASP Lubricants Analytical Laboratory, P.O. Box 194, SE-14922
Nynäshamn, Sweden
32 of 32
Appendix 1
Energinet.dk
ForskEL project No. 10612
Emissions of particles from gas engine powered CHP plants
WP1 Literature survey
Interim report
23 September 2011
Dokumentrevision
Rev.
Reference for
ændring
Rev. dato
Bemærkninger
Init.
WP1: Literature survey
Contents
1
Paige
1 Summary ...................................................................................................................................... 3
2 Introduction .................................................................................................................................. 5
3 Short introduction to PM and ultrafine particles .......................................................................... 6
4 Results from the project ”Characterization of ultrafine and fine particles from CHP Plants” .... 9
4.1 Particle number ...................................................................................................................... 9
4.2 Particle composition ............................................................................................................ 12
5 The lean-burn natural gas engine ............................................................................................... 13
5.1 General description .............................................................................................................. 13
5.2 Natural gas engines in Danish CHP applications ................................................................ 16
5.2.1 System layout ........................................................................................................ 16
5.2.2 Temperature profile in the exhaust system ........................................................... 17
5.2.3 Gas engine makes and models in the Danish CHP production ............................. 19
5.3 Emissions from lean-burn gas engines ................................................................................ 20
5.3.1 General .................................................................................................................. 20
5.3.2 Operating conditions and emissions of the lean burn gas engine ......................... 22
5.4 Lubrication ........................................................................................................................... 26
5.4.1 Engine lubrication system ..................................................................................... 26
5.4.2 Lubrication oil temperature ................................................................................... 27
5.4.3 Crankcase ventilation ............................................................................................ 28
5.4.4 Lubrication oil and its requirements...................................................................... 31
5.4.5 Oil and oil consumption in gas engines at Danish CHP plants ............................. 32
6 Particulate matter from natural gas engines ............................................................................... 35
6.1 Lubrication oil consumption ................................................................................................ 36
6.1.1 Engine design ........................................................................................................ 36
6.1.2 Lubricant design and composition ........................................................................ 40
6.1.3 Operating conditions ............................................................................................. 42
7 References .................................................................................................................................. 45
8 Appendices ................................................................................................................................. 47
Appendix 1 .................................................................................................................................... 48
Appendices
Appendix 1 Base oil groups (from wikipedia)
2
1
Summary
A literature survey has been performed in order to serve as basis for establishing a measurement
program with the purpose of investigate particulate emissions from gas engine powered CHP
plants. The objective was to determine the most important factors for PM emissions. Furthermore,
data regarding oil consumption has been collected from Danish District Heating Association.
The study has showed that the most important factors related to engine PM emissions are:
-
Engine design
o Piston-ring-liner system
o Exhaust system
-
Lubrication oil consumption
o Strongly dependent on piston-ring-liner system and oil “design” in terms of base oil
type, viscosity, volatility, additive formulation etc.
-
Lubrication oil formulation and operating condition
o Additive package
o Base stock (mineral/synthetic)
o Physical characteristics (volatility, viscosity)
o Oil age
-
Operating conditions
o Load
o Ignition timing
o Combustion temperature
o NOx emission (related to combustion temperature)
o Engine coolant temperature (liner temperature)
o Temperature profile in the exhaust system
o Misfiring
During the test programme to be performed in WP2 in this project, it is not likely that it will be
possible to change the engine design and the scope of the project is to consider gas engines on the
Danish CHP market.
Besides from the high cost of changing the oil formulation or oil type, there is an issues regarding
the requirement for approval of the lubrication oil gas engines. Engine suppliers prescribe specific
Draft 27-09-2011/LJO
approved engine oils and any deviation should be examined and approved by the engine supplier
and plant owner.
If an oil drain is planned during the project, measurements may be performed on an engine running on old engine oil and afterwards on operation with fresh oil of the same type. This way, the
effect of oil aging on particle emissions may be investigated during WP2.
One other opportunity is (if possible) to identify two engines of same make and model but with
different (high and low) oil consumption.
It is also recommended to perform measurements on similar engines operating on an ordinary
Group I mineral base stock oil and on new high performance Group III oil, respectively. The
Group III oil may perform better with respect to cooling, evaporation etc.
In order to examine the effect on PM emissions, it seems most feasible in this project to change
the operating conditions of the engines.
Due to the strong correlation between on one side oil consumption and NOx/combustion temperature and on the other side cylinder liner temperature it is recommended to set up a test programme
with (monitoring of?) NOx concentration, ignition timing, fuel/air ratio and coolant temperature
(during different operating conditions?).
The effect of misfiring on particulate emission should also be examined. Some gas engines operate as close as possible to the limit of engine knock in order to maintain a high efficiency. These
conditions may be obtained at the expense of a higher emission of PM and in particularly higher
emissions of ultrafine particles.
2
Introduction
As part of the data collection under work package 1 during the Energinet.dk project “Emissions of
particles from gas engine powered CHP plants”, a literature survey has has been performed. The
study relates on information and experiences regarding emission of particulate matter (PM) from
stationary natural gas fired gas engines in combined heat and power (CHP) plants collected from
the literature, and from communication with manufacturers and end users of gas engines.
This interim report has been elaborated under WP1 “Data collection on engine types in relation to
particle emissions” in ForskEL project no. 10612 “Emission of particles from gas engine powered
CHP plants”.
The background for this project is a recently performed PSO project which has shown that gas
engine powered CHP plants can emit very high numbers of ultrafine particles /ref: ForskEL Report No. 2008-1-0071 (2009). Characterization of ultrafine and fine particles from CHP Plants /7/.
The primary focus of this study has been on providing sources and references describing the relationship between PM emission and the engine technology, operating conditions of the gas engine
itself and the influence from lubrication oil on PM emissions.
The primary sources of information have been:
- Abstracts, papers and articles obtained and found using search machines on the internet or
DTV library
- relevant books
- contact to gas engine manufacturers
During progress of the work it was clear that very little information could be found covering the
exact description of the task. Therefore, more general sources and references of a broader nature
have been involved in the study.
3
Short introduction to PM and ultrafine particles
Particles from natural gas fired CHP plants belong to the unintentional anthropogenic sources of
PM emission to the atmosphere. Airborne particles may be described according to their size in the
following modes 1 /4/:
-
-
Ultrafine mode:
< 100 nm
The ultrafine mode may be subdivided into
o Nucleation mode:
< 10 nm
o Aitken mode:
10 nm – 100 nm
Accumulation mode:
100 nm to 1 – 3 µm
Coarse mode:
> 1 – 3 µm
Nucleation mode
Newly formed particles formed by fusion of gas phase molecules followed by condensation. The
particles grow to Aitken mode by condensation and/or coagulation.
Aitken mode
Named after the scientist John Aitken, who was the first to describe the mechanisms of cloud condensation. Newly formed nucleation mode particles may grow through condensation or coagulation and exist in the Aitken mode (10 nm – 100 nm) before they grow to larger particles (accumulation mode).
Accumulation mode
(Also known as secondary particles) These are particles that are formed in the atmosphere due to
both the chemical and physical processes that take place with the interactions of primary gaseous
emissions (condensation and coagulation). The primary gaseous emissions (e.g. NOx, SO2, VOCs)
typically originate from combustion processes like vehicles and power plants.
Coarse mode
Particles that is larger than 1 – 3 µm in diameter. They come from sea sprays, volcanoes, crushing
or grinding of rocks, windblown soil, fly ash and soot. They have short residence time in the atmosphere and account for about 95% of the aerosol particles in ambient air.
Figure 1 and Figure 2 show some characteristics of particulate matter in the atmosphere. Kittelson
/22/ shows in Figure 3 the “history” of particle formation in an engine. This figure shows the size
distribution of atmospheric particles as typically found at roadside locations.
1
Some sources defines nucleation and Aitken mode particles as one group
Figure 1 Idealized sized distribution of particles in ambient air (Source: EPA)
Figure 2 Formation processes and particle size (atmospheric aerosols)
Figure 3 History of Particle Formation in an Engine from the Combustion Chamber to the Nose
/22/
Particulate emissions from engines are primarily dominated by the nuclei mode and accumulation
mode mechanisms.
Nuclei mode particles in combustion gases are formed from gaseous precursors condensed as
temperature decreases in the exhaust system and/or after mixing with cold air in the atmosphere.
Nuclei particles consist mainly of soot particles (elemental carbon) and condensed compounds
such as organic carbon. Nuclei particles in the exhaust gas may also consist of sulphates or oil
droplets, forming if vapour concentrations of e.g. SO3 (and water vapor) or lubrication oil are high
enough (super saturated) to condense in the exhaust gas – in this case, sulphuric acid or oil droplets may be formed as nuclei particles.
Accumulation mode particulates are formed during combustion by agglomeration of primary carbonaceous particles and other solid materials. In diesel engines the majority of the accumulation
mode particulates form in the core of the burning fuel spray. They are known as ‘black carbon’ or
‘soot’. Furthermore, gases and condensed hydrocarbon vapours are absorbed into the surface of
the particles. The formation of accumulation mode soot often occurs in the diesel combustion
process and is only partially dependent on fuel quality.
Units of measurement applied
Airborne particles may be measured according to their mass or their number. Traditionally, particles emissions from combustion processes is regulated according to their mass (either in g/m3(n),
in g/h or in g/kWh). However, as ultrafine particles have an insignificant mass as compared to
larger particles, the unit of mass is not an appropriate measure for the concentration of ultrafine
particles in neither ambient air nor exhaust gases from combustion. To quantify ultrafine particle,
the number of particles must be measured. During the last decade, new methodologies has been
introduced for the measuring the number of particles in exhaust gases.
A limit value for the emission of the number of ultrafine and fine particles from heavy duty vehicles will be introduced from 2015 in the EU. It is to be expected that particle number emissions
from stationary sources will also be discussed in the future.
4 Results from the project ”Characterization of ultrafine and fine particles from CHP Plants”
In the following, results for emissions factors, calculated from results obtained in the project entitled ”Characterization of ultrafine and fine particles from CHP Plants” will be shown. This project
was performed in 2009-2010 /ref: ForskEL Report No. 2008-1-0071 (2009). Characterization of
ultrafine and fine particles from CHP Plants /7/. The project is closely linked to another
Energinet.dk project entitled “Emissionskortlægning for decentral kraftvarme 2007 – Energinet.dk
miljøprojekt nr. 07/1882. “/8/.
4.1
Particle number
Table 1 and Figure 4 show a summary of the calculated emission factors (in particle number per
GJ) based on measured emissions of particle number from gas engine fired CHP plants
compared to other types of CHP plants commonly used in Denmark. The results originate from the ForskEl project No. 2008-1-0071 “Characterisation of ultrafine and fine
particles from CHP plants” /7/.
Table 1 and Figure 4 show that natural gas fired CHP plants emit large numbers of ultrafine particles comparable to the levels of biomass plants.
The characterization project concluded among other things:
“The measurements at the gas fired CHP plants showed that the overall number of particles emitted from the gas fired engines consisted of ultrafine particles (PM0.1). The relatively high emissions of particles from the gas fired engine at plant GF1 (natural gas fired) are likely to be caused
by the use of lubrication oil”.
Table 1
Particle number emission factors according to CHP plant type/ emission reduction type
PN < 0.1 µm average
PN < 1 µm average
particles per GJ
particles per GJ
WTE plant/ ESP
7,16 E+12
1,18 E+13
WTE plant/ bag filter
1,97 E+11
3,85 E+12
BM plant/ bag filter
4,35 E+14
4,79 E+14
BM plant ESP
5,58 E+14
7,41 E+14
GF plant (nat. gas)
6,54 E+14
6,84 E+14
GF plant (nat. gas start-up)
1,71 E+16
1,72 E+16
GF plant (landfill gas)
2,11 E+13
2,25 E+13
GO plant (diesel)
3,44 E+14
4,46 E+14
Plant and emission reduction type
Figure 4 Particle number emission factors according to CHP plant type/ emission reduction type
4.2
Particle composition
Samples of a number of particle sizes were analysed through elemental analysis in the project /7/.
The conclusion based on the composition of elements found is shown below (“GF” represents
CHP plants with gas fired engines):
The EDX analysis showed that all particle size fractions from GF1 and GF2 were primarily dominated by carbon and oxygen, indicating that most of the particles were soot particles consisting of
EC (Elemental Carbon) and OC (Organic Carbon). Besides from carbon and oxygen, Ca, Fe, Cr,
Zn and P were found to be the most abundant compounds in the particles from the gas fired
plants. Calcium is known to be a detergent additive in the lubrication oil added to the gas engines
and has previously been found as one of the most abundant elements in submicron particles from
natural gas engines. The particles from GF2 contained higher levels of sulphur and silicium than
the particles from GF1. This may be explained by the content of H2S and siloxanes typically present in landfill gas.
The SEM analysis showed that the particles from GF1 and GF2 were primarily spherical soot
particles. A 3D analysis was made by means of FIB-SEM of selected particles from GF1 and GF2.
The FIB-SEM analysis showed that several of the spherical particles in the range 1000 nm 2000
nm from plant GF1 were hollow. As described in section 5.4.3, these large hollow soot particles in
gas fired engines could hypothetically be formed from combustion of small droplets of lubrication
oil entering the combustion chamber from the piston cylinder walls. Further research should be
made in order to investigate the mechanism of formation of the observed hollow soot particles.
The 3D images from GF2 showed that the selected particles from GF2 consisted of a solid core
covered by a thin layer of a different structured material. This may be explained by the formation
of soot particles by heterogeneous condensation, where organic compounds such as PAH condenses at the surface of a core of EC. Similar solid particles were found in the 3D images from
GF1.
5
The lean-burn natural gas engine
5.1
General description
Natural gas engines used in the Danish CHP market are turbo charged, 4-stroke, lean-burn type
operating at oxygen levels of typical 8 – 12 % volume in the exhaust gas. Two sub types of engines are predominantly used:
-
The open chamber engine
The pre-chamber engine
Both the open chamber and pre-chamber engine are characterized by premix combustion i.e. the
fuel (natural gas) and air is mixed prior to intrusion in the combustion chamber. Open chamber
engines operate at oxygen levels of 8,5 – 10 % volume and the pre-chamber engines slightly
higher with 10,5 – 12 % volume in the exhaust gas.
In the open chamber engine the fuel/air mix is ignited in the combustion chamber by a spark plug.
In the pre-chamber engine a fraction of rich fuel/air mixture is ignited in a small pre-chamber. Hot
combustion products and flames are then forced into the main combustion chamber igniting the
main, but leaner fuel/air mixture.
Figure 5 and Figure 6 gives examples of pre chamber combustion lay out.
Figure 5 Scematic layout of a pre chamber combustion chamber (http://www.td.mw.tum.de/tumtd/de/forschung/themen/knocking_in_gasengines/layout)
Figure 6 The Rolls-Royce/Bergen lean-burn (pre chamber) combustion system (Rolls-Royce)
Input from Rolls-Royce and Wärtsilä would be appreciated here, ie. drawings and perhaps some
more detailed explanatory text.
Lean-burn natural gas engines are designed to operate with lower peak combustion temperatures
than stoichiometric engines due to the diluting effects of the additional air. The average exhaust
temperature upstream of the turbo charger is in open chamber engines approx. 540 – 600 °C while
somewhat lower for the pre-chamber engine (approx. 430 – 575 °C).
Natural gas engines in the Danish CHP system operate mostly at steady state nominal power and
the control management system of the engine seeks to maintain constant power delivery. In order
to obtain a high electricity production and efficiency the engines often operate close to the knocking limit. Adjusting the ignition timing is used to avoid engine knock (pre-ignition). However,
detuning by ignition retarding affects performance and fuel efficiency.
5.2
Natural gas engines in Danish CHP applications
5.2.1
System layout
The CHP installation consists of several units:
-
The gas engine
Engine cooling system
Lube oil tank
Lube oil cooling system
The electrical generator
Silencer
Oxidation catalyst for carbon monoxide
High temperature heat exchanger (flue gas)
Medium temperature heat exchanger (flue gas)
Low temperature heat exchanger (flue gas)
Stack
The exact configuration of a CHP installation differs from plant to plant. For example the number
of heat exchangers can vary. Below are examples of typical CHP installations.
Figure 7 CHP gas engine layout (Energy Solutions Center)
Figure 8 CHP gas engine layout (GE Jenbacher)
5.2.2
Temperature profile in the exhaust system
Cooling conditions (i.e. absolute temperature and magnitude of temperature gradient) are likely to
have an impact on the particle number measured at the different locations in the exhaust gas system. Key hardware parameters that may influence the temperature profile of the exhaust gas are:
- Open chamber/pre-chamber engine
- Wet/dry exhaust manifold2
- Number of heat exchangers
- Catalyst
- Length of exhaust gas system
The specific temperature profile of the exhaust gas from leaving the engine until it reaches the
stack depends of the configuration at the individual CHP plant. Figure 9 shows typical gas engine
full load exhaust gas temperature levels through a CHP plant /2/.
2
A watercooled exhaust manifold is usually referred to as a ”wet manifold”.
Gas engine
Open Chamber engines:
540 – 600 °C
Pre-chamber engines:
430 – 575 °C
Open Chamber engines:
450 – 500 °C
Pre-chamber engines:
350 – 440 °C
Turbo Charger
Silencer
CO catalyst
HT exchanger
150 °C
MT exchanger
75 °C
LT exchanger
40 - 60 °C
Stack
Figure 9 Typical exhaust gas temperatures in natural gas fired gas engine CHP plants
5.2.3
Gas engine makes and models in the Danish CHP production
The natural gas fired engines at the Danish CHP market are dominated by 4 large suppliers/manufacturers. In Table 2 , the consumption of natural gas in Denmark (2006) by gas engine
can be seen according to the make and model of the engine. Eight engine models consume 88 % of
the total natural gas consumption.
Table 2
Natural gas powered engines divided by make and model, 2006 /17/
Engine make
Model
Rolls-Royce
K
Open chamber or precombustion chamber engine
Pre-combustion chamber
Natural gas consumption, 2006
23
Jenbacher
300
Open chamber
15
Caterpillar
3500
Open chamber
14
Caterpillar
3600
10
Jenbacher
600
8
Wärtsilä
34SG
8
Wärtsilä
25SG
5
Wärtsilä
Other
5
Open chamber
3
2
Deutz
604/620
Caterpillar
GM34
Jenbacher
400
Open chamber
2
Rollo
Open chamber
2
MAN
Rolls-Royce
B
Waukesha
All
Cummins
All
Niigata
All
Other
Pre-combustion chamber /
Open chamber
Pre-combustion chamber/
Open chamber
-
1,30
0,90
0,20
0,10
3
5.3
Emissions from lean-burn gas engines
5.3.1
General
Table 3 includes emission factors for natural gas fired gas engines in Denmark. The values are the
result of a large survey /8/ based on emission data from 2007-2008. From the many emission
components only NOx, CO and UHC emissions are directly regulated by Danish law.
Table 3
Emission factor from natural gas fired gas engines in Denmark /8/
Parameter
SO2
NOx
UHC
NMVOC
CH4
CO
N2O
NH3
TSP
As
Cd
Co
Cr
Cu
Hg
Mn
Ni
Pb
Sb
Se
Sn
Tl
V
Zn
PCDD/-F
PBDD/-F
PAH (BaP)
ΣPAH
Naphthalene
HCB
PCBs
Formaldehyde
Acetaldehyde
Acrolein
Propanal
Acetone
Butanal
Pentanal
Hexanal
Benzaldehyde
Odour
Efficiency
Unit
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
μg per Nm3
pg per Nm3
pg per Nm3
ng per Nm3
ng per Nm3
ng per Nm3
ng per Nm3
pg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
mg per Nm3
OU per m3
%
Emission factor
NE
429
1381
291
1529
185
1.8
NE
NE
0,143
0,009
0,65
0,15
0,047
0,31
0,15
0,14
0,14
0,16
0,03
NE
0,62
0,15
9,3
1,8
NE
41
3256
7791
NE
NE
45
3,2
0,050
0,25
1,4
0,23
0,038
0,020
0,006
3904
39,6
Table 4 gives the results of measurements of fine and ultrafine particles on a natural gas fired gas
engine at normal full load operation.
Table 4
Fine and ultrafine particle emission from a natural gas fired CHP gas engine at normal
operation /7/
PM0,1
PM1
PM2,5
1,31
1,37
1,37
Concentration [mg per Nm ]
0,04
0,22
N/A
Emission [g per hour]
0,62
3,8
N/A
6
-3
Concentration [10 ·cm ]
3
Until recently, particle emissions from natural gas engines have not been a major issue compared
to diesel engines where extensive work has been performed. This is due to the fact that particle
emissions have traditionally been measured by mass (filter collection and gravimetrical analysis of
the mass collected), and thus ultrafine particles have not yet been described through the standard
emission measurements performed on gas engines.
Due to the low peak combustion temperature the lean-burn engines NOx formation is kept on a
relatively low level. However, NOx is exponentially related to combustion temperature and is because of that sensitive to fuel/air equivalence ratio which affects combustion temperature.
CO is a result of incomplete combustion where UHC mostly originates from the natural gas fuel
passing unburned through the engine. However, a part of the unburned hydrocarbons emitted by
the exhaust gas originates from incomplete combustion, a fraction which increase if the engine
runs poorly with misfires and knock.
Particulate matter emissions (including ultrafine particles) from gas engines are caused by several
factors but consumption of engine lubrication oil seems to play a significant role.
5.3.2
Operating conditions and emissions of the lean burn gas engine
Changing operating conditions may very likely have an impact on the emission of particulate matter from a natural gas fired gas engine.
Thermal conditions in the combustion chamber are among other affected by changes of ignition
timing and excess air ratio which again influences the emissions, especially NOx. Some sources
indicate a correlation between NOx emissions and emission of particulate matter, see chapter
6.1.3. Knowing about the correlation of operational parameters and emissions is therefore important in deciding a test programme.
In the project “Environmental optimisation of natural gas fired engines” /16/ DGC have investigated correlations between selected emission constituents by changing ignition timing and/or
lambda. Furthermore the influence on the electrical and overall efficiency of the CHP plant was
studied. Figure 10 to Figure 13 indicates selected results from the project covering a pre-chamber
gas engine.
120
120
100
100
NOx / ppm (dry)
NOx / ppm (dry)
Figure 14 to Figure 16 shows various correlations for an open chamber gas engine covering one of
the well represented engine models on the Danish CHP market.
80
60
40
20
IT=14 CAD BTDC
60
40
20
0
11,6
80
11,8
12
12,2
12,4
12,6
O2 = 12,1 % (dry)
0
12,8
10
11
O2 / % (dry)
12
13
14
15
16
IT / CAD BTDC
1700
1700
1600
UHC / ppm (dry)
UHC / ppm (dry)
IT=14 CAD BTDC
1500
1400
1600
1500
1400
O2 = 12,1 % (dry)
1300
11,6 11,8
1300
12
12,2 12,4 12,6 12,8
O2 / % (dry)
10
11
12
13
14
IT / CAD BTDC
15
16
Figure 10
The effect of variation of excess of air and ignition timing. IT: Ignition Timing; CAD
BTDC: Crank Angle Degree Before Top Dead Centre /16/
200
45
95
1600
160
44
93
1200
120
43
91
800
80
42
89
400
0
60
80 100 120
NOx / ppm.
140
htot / %
hel / %
40
UHC
CO
40
CO / ppm.
UHC / ppm. C
1,eq.
2000
41
0
160
87
Electrical efficiency
Overall efficiency
40
40
60
80
100 120
NOx / ppm.
140
85
160
Figure 11 Emissions and efficiencies for a pre-chamber gas engine /16/
220
NOx, CO [ppm]; O2 [vol % x 10]
1700
1636
1600
1470
200
1405
1500
1379
180
1400
160
1300
140
1200
120
1100
100
1000
TI=14 CAD BTDC
80
60
700
691
900
800
692
689
40
700
20
Gasforbrug [m3/h] ; UHC [ppm]
240
600
460
470
480
490
500
510
Tudst °C
NOx
CO
O2 (x10)
Gasforbrug
UHC
Figure 12 Emission correlations for a pre-chamber gas engine at fixed ignition timing (DGC)
1700
1582
220
1600
1483
200
1500
1405
1383
180
1400
160
1300
140
1200
O2 = 12,1 % (tør)
120
1100
100
1000
80
900
60
696
689
40
800
707
700
686
20
480
Gasforbrug [m3/h] ; UHC [ppm]
NOx, CO [ppm]; O2 [vol % x 10]
240
600
485
490
495
500
505
Tudst °C
NOx
CO
IT BTDC x 10
Gasforbrug
UHC
Figure 13 Emission correlations for a pre-chamber gas engine at fixed lambda (DGC)
Figure 14 Operational and emission correlations for a open chamber gas engine as a function of
excess air ratio (DGC)
ignition timing (DGC)
engine load (DGC)
5.4
Lubrication
5.4.1
Engine lubrication system
The lubrication system has several functions:
-
Reduce friction to ensure maximum mechanical efficiency
Protect the engine against wear
Contribute to cooling the piston and other regions
Absorb and remove impurities from lubricated regions
Ensure minimum level of gas and oil leakage
The main moving parts of the engine (piston, rings, liner, bearings) are lubricated by oil from a
pressurized system. Oil is distributed from the engine oil sump via a lube oil pump through channels in crank shaft, con rods, pistons etc. Unlike the lubrication systems in some smaller engines
(cars etc.) no parts in the larger gas engines are splash lubricated.
Figure 17 Example of engine lubrication system (for principle use) (Rolls-Royce)
5.4.2
Lubrication oil temperature
The lubrication oil temperature of the gas engines on the Danish CHP market seems to vary over a
wide range from below 60 °C to 100 °C. However the most common temperature range is approx.
60 – 85 °C.
One of the 4 large suppliers of gas engines in Denmark states that typical oil temperatures in their
engines are 70 – 85 °C. Engines running at biogas tend to operate at slightly higher oil temperatures. Depending on the age of the engines the control valve for oil temperature can be located
internally or externally on the engine. Oil temperatures of engines with external valve do have a
larger span due to the influence of the surroundings a different location on the engine installation.
Another large supplier indicates common oil temperatures from 58 – 61 °C and an alarm limit of
62 °C is set in the engines control management system. However there are few examples of
slightly higher levels.
The above mentioned temperatures all refer to upstream measurements i.e. before the oil is entering the gas engine. In the gas engine the oil temperature will rise due as the oil absorb heat induced by the moving parts of the engine (piston, liner, valves etc.).
A minor survey of lubrication oil temperatures monitored at emission measurements is shown in
Table 5.
Table 5
Observed lubrication oil temperature of selected gas engines
Engine manufacturer
Rolls-Royce
Wärtsilä
Jenbacher
Caterpillar
Engine model
Engine speed
[rpm]
Oil temperature
[°C]
KVGS 18G4
1000
57
KVGS 12
1000
59
KRGS 9G4
1000
58
18V34 SG
750
68 – 74
20V34 SG
750
66
16V25 SG
1000
68 – 73
JMS 316
1500
84 – 86; 96
JMS 320
1500
90 – 100
JMS 420
1500
83
JMS 612
1500
72
JMS 616
1500
65
JMS 620
1500
68 – 77
Type 3500
1500
83 – 88
Type 3600
1000
77 – 81
Type CM34
750
64
3
4
5
The above indicated oil temperatures are based on limited amount of observations during emission
measurements on gas engines.
Question for Thomas Norrby: Do we expect higher particle emissons at higher lube oil temperatures? We discussed this point briefly at our first meeting. It is relevant in relation to the selection
of engines and test conditions for WP2.
5.4.3
Crankcase ventilation
The pressure variations (due to the movement of the piston?) in the crankcase housing must be
taken into account. This is done by a vent pipe leading the vent fumes to the atmosphere or redirects the fumes to the engines intake.
Due to environmental, and in some countries legislative, requirements new CHP gas engines are
often equipped with filters or separators, see Figure 18, to reduce or eliminate oil mist emissions
coming out from the crank case ventilation. Crankcase ventilation gas cleaning is also a necessity
3
Natural gas – Emissionskortlægning 2007
Landfill gas – Emissionskortlægning 2007
5
Biogas
4
when redirecting the ventilation gas to the turbo inlet in order to protect this part from fouling or
oil accumulation in the intercooler.
Rolls-Royce /10/ informs that crank case oil mist and fumes mostly is vented to the atmosphere
outside the building and often through a filter. In general Wärsilä machines are equipped with
crank case ventilation filters /12/ and filtered crank case gas/air are led to the atmosphere or redirected to the engine inlet. All new engines are fitted with Alfa Laval PureVent system, see Figure
18.
Figure 18 Alfa Laval PureVent crankcase ventilation gas cleaning, here in a Wärtsilä configuration (Wärtsilä)
The efficiency compared to particle size of the PureVent separator is shown in Figure 19. The efficiency of the separator decreases at smaller particle sizes indicating approx. 60% at 0,1µm which
is the upper size limit in the definition of ultrafine particles. This means that most of the ultrafine
particles from the crank case oil (present as solid or liquid particles at the temperature in question)
mist will probably pass the filter.
Figure 19 PureVent efficiency at 90 m3per hour (Wärtsilä)
5.4.4
Lubrication oil and its requirements
The gas engine (lubrication) oil (GEO) must possess several properties:
-
Control oxidation
Control nitration
Limited ash level
Compatible with catalyst
Extended oil drain interval
Prevent corrosive and adhesive wear
Maintain engine cleanliness
The major oil challenges for gas engines are nitration, oxidation, acid and deposits control. Natural gas engines are prone to ring sticking, spark plug fouling, pre-ignition and detonation if deposits develop in the combustion chamber.
A GEO is like any oil made up by a base oil system and an additive system. GEO formulations
have mainly been blended using conventional (Group I) mineral base oils and recently also Group
II and Group III oils (hydro-processed mineral oil and high viscosity index base oil). The latter
types excel in their improved resistance to nitration and oxidation. Synthetic (Group IV) base oils
are not widely used as gas engine oils. See Appendix 1for detailed information of the different
base oil groups.
The detergent is the key constituent in the additive system as it accounts for approx. 80 % of the
additive concentration. The detergent technology i.e. type of surfactant is responsible for deposit
control, oxidation control and acid neutralisation.
Oil additive packages contain several substances which can cause or act as precursors for the formation of particulate matter in the exhaust gas. The formulation of the GEO is therefore an important factor in lube oil consumption and as a consequence, lube oil derived PM emission.
More information regarding lubrication oil and additives can be found in /13/, /14/ and /15/.
Måske et afsnit ”Effect of lubrication oil aging”? Hent noget af teksten fra afsn. 6.2.2 ind her.
5.4.5
Oil and oil consumption in gas engines at Danish CHP plants
Until the end of 2010 Danish District Heating Association (DDHA) collected operating data regarding oil consumption, oil type, power production, operating time etc. from the members of
their organisation. The most dominating engine manufactures and engine models on the Danish
CPH market are well represented in the data material.
Referring to the data from DDHA, the most widely used lubrication oils are:
-
SHELL
o Mysella LA 40 (Gr. I oil)
o Mysella XL 40 (Gr. II oil)
-
MOBIL
o Pegasus 705 (Gr. I oil)
-
Hydro Texaco
o Geotex HD 40 (Gr. I oil)
o Geotex LA 40 (Gr. I oil)
o Geotex PX 40 (Gr. III oil)
-
Caterpillar (ExxonMobil)
o NGEO 40 (Gr. I oil)
o NGEO EL 350 (Gr. I oil)
-
Q86
o Mahler R 40 (Gr. III oil)
(LJO kontakter olieselskaberne vedr. verificering af ovenstående gruppering af olierne)
Oil consumption varies from approx. 0,1 g to 0,5 g per kWh however most values are below 0,4 g
per kWh. Correlation between oil consumption and different variables has been investigated. Fig-
6
Recently several plants have changed from other oil brands to Q8 Mahler R oil
ure 20 indicates the specific oil consumption as a function of engine power. The plot shows quite
scattered data with no strong correlation.
Figure 21 shows oil consumption versus engine make/model. Caterpillar 3600 and Jenbacher 300
models seem to operate with lower oil consumption than the other engine types although the difference is not large.
The make and type of the lubrication oil represented in the data doesn’t seem to have a significant
influence on oil consumption as indicated in Figure 22.
Figure 20
Specific oil consumption as a function of electrical power per engine (DDHA January 2010)
Figure 21
Specific oil consumption as a function of engine make/model (DDHA; average January, February and December 2010)
Figure 22
Specific oil consumption as a function of lubrication oil make/type (DDHA; average
January, February and December 2010)
Question (for discussion): Some engine manufacturers recommends that lube oil is added continuously to the engine, in stead of making a full oil replacement during service. One example is Rolls
Royce’s engines. Can this explain why (some) RR engines seem to have a slightly higher oil consumption, as shown in figure 21? (KFU)
6
Particulate matter from natural gas engines
Ultrafine and fine particles emitted from natural gas fired gas engines include:

trace amounts of metals, from engine wear and lube oil

non-combustible inorganic material

condensable, semi-volatile organics which result from volatized lubricating oil, engine
wear, or from products of incomplete combustion.

Soot
Several sources indicate that minimising lube oil consumption is an effective way to reduce PM
emissions.
According to /19 /, the literature concerning the impact on engine oil consumption on particulate
emissions can be divided in two “classes”:
-
The impact of engine design on oil consumption
-
The impact of lubricant “design” on particulate
These two parts impacts the engine-out emissions.
6.1
6.1.1
Lubrication oil consumption
Engine design
Figure 23 schematically illustrates the oil consumption sources /19 /. There is a general agreement
among the found references regarding these sources as main contributors to lubrication oil consumption.
Figure 23
Oil consumption sources /19/
One of the latest sources to updated references of engine oil consumption is the Phd. Thesis of
Petter Tornehed /21/. Figure 24 shows the in-cylinder mechanisms of oil consumption. In his thesis, Tornehed points out that if best-known, common available technology is used, the cylinder
system (piston-ring-liner system) normally is the largest contributor to oil-related particles in the
exhaust.
Froelund and Yilmaz /19 / shows in Figure 25 a more detailed picture of the oil transport in the
piston-ring-liner system.
Experiences from “the real world” support the findings in these references. Rolls-Royce informs
that increased oil consumption typically can be addressed to worn liner surface and rings.
Figure 24
In-cylinder oil consumption /21/
Figure 25
Oil transport in the clearances of the piston-ring-liner system /19/
Froelund and Yilmaz /19 / further state the influence of engine speed and load on oil consumption,
illustrated by Figure 26. In the figure below “Oil transport” is equal to “Throw off” as depicted in
Figure 24. Oil transport or Throw-off” is the mechanical transport of liquid oil into the combustion
chamber due to inertia forces caused by acceleration and deceleration of the piston assembly.
Figure 26
Influence of engine speed and load on oil consumption type /19/
Another source describes how measurement of nanoparticles where used to detect an engine oil
control ring failure /24/. When fixing the problem, particle number emissions went down.
Figure 27
Magnified photographs (magnification, 610) showing the oil control ring fracture
looking at the outer diameter (a) from the side and (b) from the top /24/
Although several references indicate the significance of the piston-ring-liner system regarding
engine oil consumption, Jyrki Ristimaki from Wärtsilä OY /11/ informs that at 100 % load and a
well maintained engine changes of the piston-ring-liner system only have smaller influence on oil
consumption. However oil consumption is typically measured by mass (oil stick in sump) and
Wärtsilä have no experience in oil consumption related to ultrafine particles from natural gas fired
gas engines. Focus is primarily on developing fuel efficient engines with low operating costs.
Wärtsilä informs that load level and a well maintained engine are key factors that influence oil
consumption. Cracks in piston rings, defect oil seals etc. increase oil consumption.
A comment from Wärtsilä may be appropriate here
6.1.2
Lubricant design and composition
The characteristics of the engine oil like volatility, viscosity and formulation of the additive package are major factors that impact the oil consumption and particle emission from a gas engine.
During the lifespan of the engine oil properties and composition of the oil change as the oil absorbs combustion bi-products and wear products from abrasion between cylinder and piston-ring
and bearings. Typical wear metals are Fe, Ni and Cu. Metals originating from the oil additive
package are Zn and Ca /26/.
Froelund and Yilmaz /19/ lists the following points concerning the impact of lubricant design on
particulate emissions:
-
Higher oil viscosity reduces most likely the oil consumption and the oil-derived particulate
emissions.
Lower oil volatility reduces the oil consumption and the oil-derived particulate emissions.
Oil evaporation increases strongly with engine load.
Viscosity and volatility are connected properties through a trade-off curve for a given base
stock.
Constraints on either the viscosity or the volatility may necessitate a substitution to a more
refined base stock.
The impact of auxiliary lubricant additives on oil consumption is poorly documented in the
literature.
Oil friction characteristics have shown a strong effect on nitrogen oxide emissions.
Mayer /26/ suggests diminishing the metal content in the lubrication oil to reduce the problem of
metal oxide particles in the engine exhaust.
For diesel vehicles, it is known that an increase in oil consumption leeds to an increase in the
emission of lube oil based particles /se: http://papers.sae.org/900587 og
http://papers.sae.org/900591/. Thomas Norrby from Svenska Statoil /28/ informs that the formulation of the lubrication oil have a significant impact on oil consumption and thereby the particle
emission. The problem is that the most used conventional oils (Group I and to some extent Group
II and III oils) is designed to a broader spectrum of gas engines, fuels and operating conditions.
Using synthetic oils designed to a very narrow scope of use will probably reduce oil related PM
emissions. This includes the use of specific additive formulation to for example lower the TBN.
Changing lubrication oil on the CHP plants is most likely out of the question in this project due to
the high costs and risks involved with operating a gas engine on an unproved lubrication oil.
Usually a gas engine manufacturer demand 7000 – 10000 trouble free hours of operation before
they blue print a lubrication oil to their engines.
However Norrby suggests performing certain risk assessments/analysis. This may be a tool to ensure trouble free operation with an alternative oil.
6.1.3
Operating conditions
Changing the operation conditions of the gas engines is one corner stone in the reduction of lube
oil consumption and particle emissions.
As an example, Quillen /20/ and Miller /29/ reports a strong correlation between NOx and particle
concentration on diesel fired ship engines. Quillen also reports that the geometric mean diameter
(GMD) of the particles was approximately 30 nm and did not change with air to fuel ratio. Particulate concentrations were found to decrease at leaner engine operating conditions.
The above stated correlation between NOx and particle concentration should indicate a correlation
between NOx and oil consumption also for gas engines (??). Combining oil consumption data
from DDHA, see Appendix 1, with NOx emission factor from the emission mapping project /9/ is
shown in Figure 28.The NOx emission factors of the different engine models are plotted as a function of the oil consumption. There seems not to be a strong correlation but a slight tendency of
increasing NOx emissions when oil consumption increase.
Figure 28
NOx emission as a function of specific oil consumption
From /16/ it is shown how NOx emission can be changed by varying air to fuel ratio (lambda) and
ignition timing on typical Danish CHP gas engines.
Yilmaz have investigated the sources and characteristics of oil consumption in a spark ignition
engine /27/. Yilmaz found a linear relationship between the coolant and liner temperature. The oil
consumption as a function of liner temperature was then investigated showing a linear relationship
and decreasing oil consumption with decreasing liner temperature. The use of synthetic oil seems
to lower oil consumption as well.
Figure 29
Relation between coolant and liner temperature (75 % load)/27/
Figure 30
Relation between coolant temperature and oil consumption /27/
From an emission evaluation of New York City buses Lanni et al /30/ reports increased particulate
emissions from CNG driven engines that misfired during the measurements. Although it might not
have a strong relevance due to the differences of CNG driven buses and CHP gas engines it is
known that misfiring CHP gas engines exhibit larger UHC emissions and therefore the potential of
increasing PM emissions are present.
7
References
1. Impact of engine oil consumption on particulate emissions
2. Methane Oxidation Catalyst for Gas Engines
3. Emissions from decentralised CHP plants 2007 - Energinet.dk, Environmental project no.
07/1882
4. Schmidt, Lone M., Ultrafine partikler, DGC, September 2003
5. Telephone conversation, Prof. Thomas Norrby, Svenska Staoil AB
6. Garner, Terry (2010). Effective lubrication of gas engines. Infineum.
7. Fuglsang et al. ForskEl project No. 2008-1-0071 “Characterisation of ultrafine and fine
particles from CHP plants”, 2009
8. Nielsen, Malene et al. Emissionskortlægning for decentral kraftvarme 2007 – Energinet.dk
miljøprojekt nr. 07/1882. 2010
9. Jørgensen, L., Andersen, M., Andersen, S.D., Kristensen, P.G. & Lovett, D.M. 2010b:
Emissionskortlægning for decentral kraftvarme 2007, Energinet. dk miljøprojekt nr.
07/1882, Delrapport 4, Maaleprogram og analyse af emissioner fra gas- og oliefyrede anlæg mindre end 25 MWel, 2010. (Project report 4 – In Danish).
10. Telephone conversation, Kim Larsen, Rolls-Royce DK.
11. Telephone conversation, Jyrki Ristimaki, Wärtsilä OY
12. Mail correspondence, Bent Iversen, Wärtsilä.
13. Effective lubrication of gas engines, Infineum, 2010
14. Additives for future lubricants, Infineum, 2006
15. Gas engine lubricants, June 2011 Insight, Infineum.
16. Kvist, T. Environmental optimisation of natural gas fired engines, 2010
17. Jørgensen, L. et al: Emissionskortlægning for decentral kraftvarme 2007, Anlægskarakterisering og emissionsdata for gas- og oliefyrede decentrale kraftvarme anlæg < 25 MWe,
2010.
18. Rose, Malcom. Infineum. Gas engine oils – a question of balance. Machinery Lubrication
(3/2004)
19. Froelund, K., Yilmaz, E. Impact of of engine oil consumption on particulate emissions.
20. Quillen, Kris et al. Characterization of Particulate Matter Emissions From a 4-Stroke,
Lean-Burn, Natural Gas Engine. ASME 2007.
21. Tornehed, Petter. Particulate Emissions Associated with Diesel Engine Oil Consumption.
Phd. Thesis 2010.
22. Kittelson, D.B., Recent measurements of nanoparticle emissions from engines. Center for
Diesel Research, Mechanical Engineering Department, University of Minnesota. 2001.
23. Miller, A., L. et al. Role of Lubrication Oil in Particulate Emissions from a HydrogenPowered Internal Combustion Engine.
24. Swanson, J. et al. Nanoparticle measurements used to detect an engine oil control ring failure. Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA. 2009.
25. Eaves, M., Ultrafine control in natural gas engines. Ultrafine particle conference 2006.
26. Mayer, Andreas C. et al. Metal-oxide particles in engine exhaust. SAE paper 2010-010792.
27. Yilmaz, E. Sources and characteristics of oil consumption in a spark ignition engine. 2003.
28. Telephone conversation, Thomas Norrby, Svenska Statoil AB.
29. Miller, Thomas C. et al. Prevention of Air Pollution from Ships: Diesel Engine Particulate
Emission Reduction via Lube-Oil-Consumption Control.
30. Lanni, T. et al. Performance and Emissions Evaluation of Compressed Natural Gas and
Clean Diesel Buses at New York City's Metropol itan Transit Authority. SAE paper 200301-0300.
8
Appendices
Appendix 1
Base oil groups (from wikipedia)
Mineral oil term is used to encompass lubricating base oil derived from
crude oil. The American Petroleum Institute (API) designates several types
of lubricant base oil:
-
Group I – Saturates <90% and/or sulfur >0.03%, and Society of Automotive Engineers (SAE) viscosity index (VI) of 80 to 120
Manufactured by solvent extraction, solvent or catalytic dewaxing,
and hydro-finishing processes. Common Group I base oil are 150SN
(solvent neutral), 500SN, and 150BS (brightstock)
-
Group II – Saturates over 90% and sulfur under 0.03%, and SAE
viscosity index of 80 to 120
Manufactured by hydrocracking and solvent or catalytic dewaxing
processes. Group II base oil has superior anti-oxidation properties
since virtually all hydrocarbon molecules are saturated. It has waterwhite color.
-
Group III – Saturates > 90%, sulfur <0.03%, and SAE viscosity index over 120
Manufactured by special processes such as isohydromerization. Can
be manufactured from base oil or slax wax from dewaxing process.
-
Group IV – Poly-Alpha-Olefins (PAO)
-
Group V – All others not included above such as naphthenics, PAG,
esters.
In North America, Groups III, IV and V are now described as synthetic
lubricants, with group III frequently described as synthesized hydrocarbons, or SHCs. In Europe, only Groups IV and V may be classed as synthetics.
Appendix 2
DGC-note
Oil emissions from gas engines
1/8
Equilibrium considerations on oil emission from gas
engines
Resume
Equilibrium calculations have been performed in order to clarify the behavior of oil emission from gas engines. The outset has been known vapour
pressures for lubrication oil and consumption data for oil on full-scale engines combined with the knowledge on oil emission measurements performed in previous projects by DGC.
The main conclusion is that the observed emission data and the observed oil
consumption data are comparable in size and fit an emitted fraction of the
oil consumption around 30 %.
Due to the temperatures of the exhaust after the heat exchangers the oil
emission is shown to be present as liquid phase while only a small fraction
is in gas phase.
The conclusions of this work will have implications on the sampling procedures which can be used to measure the emission of ultrafine particles. In
order to quantify which part of the currently known emissions that can be
attributed to oil mist and which part can be attributed to other particles condensation must be avoided.
Engine oil consumption and emission
The gas engines in Denmark are normally operated on 100 % load, part load
is not commonly used. According to the engine suppliers (Rolls Royce and
Wärtsilä) the engines consume 0.2 to 0.4 g oil for each kWe power produced. In the case of lean burn engine with 110 % excess air (approximately
11.5 % O2 in dry exhaust) this corresponds to an oil consumption of 38-76
mg/m3 exhaust. A fraction of the oil is expected to be consumed by combustion processes or caught in the exhaust system, but there are no data available for this fraction on Danish gas engines.
DGC has performed a limited number of oil emission measurements. The
results have been reported in the PSO 3141 emission mapping project (part
736-30
August 2011
DGC-notat
2/8
report 4) where the average emission was 28 mg/m3 at 5 % O2 dry exhaust.
The measurements are representative of the exhaust gas content of vapor
and fine droplets just before the chimney on the plants. The individual emission results in this study are shown in Table 1.
Table 1 Emission of oil from natural gas engines
Make
3
Bergen
Emission mg/m
@ 5 %O2, dry exhaust
19.5
Bergen
26.5
Bergen
28.9
Caterpillar 3616
66.0
Jenbacher JW320
5.0
Wärtsilä
23.2
The emissions observed correspond to an average emission of 28.2 mg/m3
@ 5 % O2, dry exhaust. At an excess air ratio of 110% this corresponds to
15.1 mg/m3 actual exhaust O2 and moist exhaust conditions.
Combining the vapour pressure information on the known oils shown in
Figure 1 and with the actual amount of oil consumed, a dew point and phase
split calculation can be performed for the oil behaviour in the exhaust system. The main results are shown in Figure 2 and 3.
Figure 1 Vapour pressure for three different lubrication oils
Energinet.dk - ForskEL project No. 10612
DGC-notat
3/8
Figure 2 Oil dew point temperature as fraction of the oil emitted from the
engine based on the low consumption case of 0.2 g/kWh power produced
Figure 3 Oil dew point temperature as fraction of the oil emitted from the
engine based on the low consumption case of 0.4 g/kWh power produced
Figure 2 and 3 reveal that from an equilibrium point of view it is expected
that the oil vapour exiting the cylinder into the exhaust system will at a certain point in the exhaust system start to form a condensed oil phase.
DGC-notat
4/8
From the available data it is not possible to quantify the different mechanisms for oil consumption, but it might be reasonable to expect four major
ways for the oil to disappear from the oil lubrication cycle:

Oil might be combusted during the combustion cycle of the engine

Loss of oil from the oil sump venting/crankcase venting

Condensation in the exhaust system

Emission through the chimney
Data are only available on the latter of these routes of oil consumption. Figure 4 compares the emissions observed during measurements with the consumed oil range of 0.2-0.4 g/kWh.
Figure 4 Comparing oil emissions (dashed lines for range, solid line for
average emissions observed) with the amount of oil consumed (red and blue
line)
As it can be seen from Figure 4, an average of around 30 % of the oil consumed seems to be emitted through the chimney. The dashed lines representing the largest and the lowest measured emissions also reveal that there
are very large variations on the relative amount emitted.
It is important to note that the data do not include any information on the
amount of oil caught and drained from the exhaust system, but this additional amount will be present as vapour when the exhaust gas leaves the cylin-
DGC-notat
5/8
der and enters the exhaust system. This additional amount of oil will influence the oil dew point in the exhaust.
If this above mentioned but unknown amount of oil is ignored, it is possible
to estimate the fractions of oil that are present as vapour and liquid phase in
the exhaust system. Figure 5 shows such a calculation, assuming that 30 %
of the oil consumed is present in the exhaust system.
Figure 5: Calculated phase split of lubrication oil in the exhaust system as
function of temperature. It is assumed that 30 % of the oil consumed (0.20.4 g/kWh) is present in the exhaust system
It is again important to mention that the dew point and the condensed phase
fraction in Figure 5 will be higher if the oil loss due to condensation from
cylinder to chimney is taken into account. Based on the fraction of condensed phase it is possible to calculate a particle number which can be attributed to the liquid phase oil emission. This is shown in Figure 6 for an
assumed droplet size of 10 nanometers and in Figure 7 for the actual size
distribution measured in the exhaust from a natural gas engine.
DGC-notat
6/8
Figure 6 Calculated particle number due to condensed lubrication oil in the
exhaust system as function of temperature. Assumptions are as in Figure 5
and 10 nanometer particles
Figure 7 Calculated particle number due to condensed lubrication oil in the
exhaust system at 30 degrees C using the size distribution from field measurements performed in a previous project (reference xxx)
As can be realized from Figure 7, the liquid phase is capable of producing
approximately ten times the particle number observed in the field. In principle, all particles seen in the field could be condensed phase lubrication oil
particles.
DGC-notat
7/8
Implications on sampling strategy in this project
The results outlined above need to be taken into consideration when new
field measurements are performed. It is an objective for this project to investigate the possible origin of the observed ultrafine particles from gas engines. It is one of the major hypotheses that a significant part of the observed ultrafine particles arise from condensed lubrication oil. The above
performed evaluation confirms that the needed amount of oil is present. In
order to confirm or reject the hypotheses, field measurements must be performed without introducing condensation of oil.
Since the sampling device needs a temperature of maximum 30 degree C
there are, in principle, two ways of achieving this. One can choose to dilute
with ambient temperature air or to remove oil vapour before condensation
followed by minor dilution and/or cooling of the exhaust sample.
Figure 8 shows the needed dilution which in case of oil 2 or 3 is in the range
of 100.000. In addition, the figure shows the risk for entering the condensation range if dilution air of 30 degree C is used for the initial dilution steps.
Figure 8 Oil dew points and exhaust temperature in exhaust sample as function of air dilution rate. Start exhaust temperature is assumed to be 150 C
and air is 20 C. Conditions otherwise as in Figure 5
DGC-notat
8/8
Figure 9 Oil dew points and exhaust temperature in exhaust sample as function of oil removal factor. Conditions otherwise as in Figure 5
Figure 9 shows the needed efficiency in removal of oil vapour in order to
lower the dew point of the oil in the exhaust.
It is seen from both Figure 8 and 9 that it is an extremely difficult task to
ensure that the exhaust sample is not influenced by oil condensation in the
sampling system, and probably a combination of oil vapour removal with
dilution needs to be performed.
Per G. Kristensen
DGC, Hørsholm
September 2011
Appendix 3
Fordampning af oliedråber
En opsummering af resultaterne
Thomas Rosenørn & Karsten Fuglsang
Formål
Ved måling på udstødning på motorer der bruger naturgas som brændstof har man målt høje
koncentrationer af fine og ultrafine partikler. Da forbrændingen af naturgas (der hovedsageligt
består af methan) kun forventes at danne CO2 og H2O var dette en overraskelse. For at forklare
dette er man begyndt at undersøge andre mulige kilder til partikel dannelse i disse motorer og
man har fundet ud af at smøreolien er en mulig kilde. For at opnå en indsigt i hvor disse partikler
kommer og hvordan de er blevet dannet, ønskes det undersøgt hvor stor en dal af det
kondenserede materiale der består af uforbrændt smøreolie. For at undersøge dette bruger man
en thermodenuder der først bringer olierne på gas-form og herefter fjerner dem fra gas-fasen ved
adsorption på aktivt kul.
Formålet med denne forsøgsrække var at validere thermodenuderen til brug for fjernelse af
smøreolie i aerosoler. Dette er gjort ved at udføre en række forsøg i Afdeling 202s værksted (U8)
hos FORCE Technology i Brøndby.
Olierne
En bil-motorolie (IQ-X, fuldsyntetisk olie fra T-hansen) og fire smøreolier til gasmotorer (SL 11-346,
SL 11-347, SL 11-348 og SL 11-349) er blever undersøgt i denne forsøgsrække. Tidligere er én
parafinolie (GLAD ISO 15) blevet undersøgt i filterlaboratoriet hos FORCE Technology i Brøndby
som et indledende testforsøg.
SL 11-346 er en gruppe I mineralsk base olie med 10 % additiver.
SL 11-347 er en gruppe II mineralsk base olie med 10 % additiver.
SL 11-348 er en gruppe IV polyalfaolefin (PAO) syntetisk base olie med 10 % additiver.
SL 11-349 er en blanding af gruppe III olie (65 %) og PAO (25 %) med 10 % additiver.
Forklaring af hvordan olier kategoriseres og inddeles i oliegrupper foreligger i separate dokumenter.
Yderligere detaljer om olierne kan findes i Appendix A
GLAD ISO 15 er en paraffinolie, produktblad findes i Appendix B
IQ-X er en fuldsyntetisk olie fra T-Hansen, produktblad findes i Appendix C
Forsøgsopstilling
Forsøgsopstillingen bestod af en oliedråbegenerator, en Dekati Thermodenuder og en Dekati
Electrical Low Pressure Impactor(ELPI). Beskrivelser af Thermodenuderen og ELPI kan findes i de
tilhørende manualer. Der blev til forsøgene brugt to forskellige metoder til at generere oliedråber.
I de indledende forsøg på GLAD ISO 15 olien blev dråberne genereret i en Dräger
parafinoliedråbe generator beregnet til test af åndedrætsværn. Figur 1 nedenfor viser
opbygningen af dråbegeneratorcellen.
Figur 1: Dräger oliedråbegenerator. 9: oliebeholder, 15: luftinjektionsdysse/bobler, 14: temperatursensor.
Ved normal brug bobles luft igennem olien i oliebeholderen, men i disse forsøg var oliestanden
med vilje sænket til mellem luftinjektionsdyssen og temperatursensoren. Luften blev dermed ledt
gennem oliebeholderen uden at boble gennem olien og på denne måde blev partiklerne dannet
ved at den varme olie fordampede og blev ført med luftstrømmen ud af beholderen, hvor den
efterfølgende kondenserede til små dråber ved rumtemperatur.
Til de resterende forsøg blev dråberne genereret med en anden opsætning (se Figur 2 nedenfor).
Opstillingen bestod af en rundbundet kolbe med smøreolien placeret i en termostateret
varmekappe (temperatur: ~130 ℃).
Figur 2: Forsøgsopstiling til fordampning af smøreolier med efterfølgende partikelgeneration og
kondensation.
Luft til forsøget bliver suget gennem et HEPA-filter henover olien hvor den bliver dampmættet ved
varmekappens temperatur. Efter kolben passerer luften gennem svaleren (reservoir fyldt med vand
og is) for det bliver suget gennem ELPIen.
Resultater
I det følgende sammenfattes resultaterne for GLAD ISO 15 og smøreolierne. Fælles for dem alle,
er at der ikke var problemer med at fjerne oliedråberne fra de dannede testerosoler.
GLAD ISO 15
Der var ingen problemer med at fordampe partikler bestående af GLAD ISO 15 parafin olie. Som
det ses i Figur 3 fordampede partiklerne i varierende grad i temperaturområdet fra 80 ℃ til 200 ℃.
på Som det ses af den stiplede linie fordampede det meste af massen inden 100 ℃ og resten
inden 200 ℃. Prikkerne indikerer partikler på det nederste trin i ELPI’en og en del af dem skyldes
en baggrundskoncentration som skyldes at partikelgenereringssystemet ikke slutter helt tæt.
Figur 3: Fordampning af GLAD ISO 15 ved brug af Dekati Thermodenuder. Partikelantal som funktion af
temperaturen.
Figur 4 viser størrelsesfordelingen som funktion af temperaturen og viser tydeligt at alle partikler
bliver mindre når temperaturen bliver højere og størrelsesfordelingen flyttes derfor med mindre
partikler med højere temperatur. Grunden til at ikke alt fordamper ved samme temperatur er, at
olien består af en lang række paraffin-molekyler med forskellige egenskaber der tilsammen giver
olien de ønskede karakteristika.
50 ℃
150 ℃
200 ℃
300 ℃
Figur 4: Størrelsesfordelinger af GLAD ISO 15 dråber målt med ELPI efter thermodenuderen. Bemærk
skiftende skala på y-aksen. De tilbageværende partikler ved 300 ℃ skyldes utætheder i
partikelgenerationssystemet.
Smøreolier
Smøreolierne fordampede over et mindre temperaturinterval end paraffin-olien. Som det ses af
Figur 5 fordamper alle smøreolierne i intervallet inden 100 ℃.
Figur 5: Partikelantal som funktion af temperatur.
Det ses af Figur 6 at en gruppe I olie (SL 11-346) fordamper over et bredere temperaturinterval
end en gruppe II olie (SL 11-347).
Figur 6: Normaliseret plot af partikelantal som funktion af temperaturen.
Gruppe IV olien (SL 11-348) har også et lidt bredere interval end gruppe II olien. SL 11-349, som
er en blanding mellem en gruppe III og en gruppe IV, har en temperaturprofil der ligner gruppe II
olien. IQ-X motorolien er den olie der udviser det snævreste interval for fordampningstemperatur.
Figur 7: Partikelantal som funktion af temperaturen for to målinger udført på SL 11-346 på to forskellige
dage.
For at teste reproducerbarheden af forsøgsopstillingen og metoden, blev samme olie analyseret to
gange på to forskellige dage. Som det ses af Figur 7 ovenfor er der ingen nævneværdig forskel i
resultaterne for de to målinger.
Figur 8: Partikelantal som funktion af temperaturen. Y-aksen er logaritmisk for bedre at illustrere
måleområdet.
Figur 8 viser partikelantallet som funktion af temperaturen på logaritmisk skala. Figuren viser
tydeligt hvordan partikelantallet bringes ned fra mellem 10.000.000 og 40.000.000 partikler pr.
cm3 til mellem 20.000 og 20 partikler pr. cm3.
Figur 9: Normaliseret partikelantal som funktion af temperaturen.
Hvis dataene normaliseres til partikelkoncentrationen ved 30 grader, fremgår det tydeligt at
mellem 0.2 % og 0.0001 % af partiklerne er tilbage efter end fordampning (se Figur 9). Det er
ikke muligt at afklare om dette skyldes, at der er utætheder i partikelgenereringssystemet, eller
om dette skyldes noget helt andet.
Figur 10: Massefraktion tilbage som funktion af temperaturen.
Figur 10 viser massefraktionen tilbage efter thermodenuderen som funktion af temperaturen. I
intervallet fra 30 ℃ til 75 ℃ ser man, som forventet en aftagende tendens, men i intervallet fra
75 ℃ til 100 ℃ ser man en stigende tendens i den tilbageværende massefraktion. Når
temperaturen passerer de 100 ℃ aftager den tilbageværende massefraktion igen som forventet.
En nærmere beskrivelse af dette dataforløb, som ligger udenfor denne rapports områdeda det
baserer sig på masse målinger af partikler over 1 m, findes i Appendixerne D og E.
Figur 11: Tilbageværende massefraktion af partikler mindre end 380 nm som funktion af temperaturen.
Figur 11 ovenfor viser den tilbageværende massefraktion af partikler mindre end 380 nm som
funktion af temperaturen. Det ses at massen af partikler, hvis man kun kigger på partikler mindre
end 380 nm, aftager monotont som funktion af temperaturen. Forklaringen på dette er at der i
temperaturintervallet mellem 75 ℃og 100 ℃
partikler dannet før de viser sig som en betydelig tilvækst i massen.
APPENDIKS A
Email fra Thomas Norrbytil Thomas Rosenørn af d. 22. December 2011
Hi again,
they are all based on the same commecial gas engine additive + a PPD (pour point
depressant) at a treat rate of about 10%
SL 11-346 is a Group I mineral base oil + 10 % additive
SL 11-347 is a Group II mineral base oil + 10 % additive
SL 11-348 is a Group IV Polyalfaolefin ( PAO) syntetic base fluid + 10 % additive
SL 11-349 ia a blend of Group III (VHVI) base fluid (65%) and PAO (25%), with 10% additive
346 corresponds to "any commercial" traditional mineral oil
347 corresponds to "any" OEM-approved commercial Gr II fluid
SL 11-348 is a Group IV Polyalfaolefin ( PAO) syntetic , and does not have any commercial
"siblings"
Basic data
KV 40 = 17.5 cSt
KV 100 14.48 cSt
VI = 138
SL 11-349 (Mainly Gr III based) corresponds in general to the data below, but is a modification of
the underlying product:
These are some characterisctic that I could find right now.
We can always make more detailed analyses or comments depending on what your need is.
Merry Christmas!
Best regards,
Prof. Thomas Norrby
R&D Manager
LUB MD R&D
Svenska Statoil AB
PO Box 194, SE -49 22 Nynähamn, Sweden
m: +46704296803
t: +4684296803
f: +4684296860
e: [email protected]
Visitor address: Raffinaderivägen 4, SE-14941 Nynäshamn
Incorporation number: 556000-6834
www.statoillubricants.com
Please consider the environment before printing this email.
------------------------------------------------------------------The information contained in this message may be CONFIDENTIAL and is
intended for the addressee only. Any unauthorised use, dissemination of the
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addressee, please notify the sender immediately by return e-mail and delete
this message.
Thank you
APPENDIKS B
APPENDIKS C
APPENDIX D
Figur 12 nedenfor viser massen som funktion af partikelstørrelse ved 3 forskellige temperaturer.
Det ses tydeligt at der ingen masse findes over 200 nm ved 75 °C, mens næsten al masse findes
mpet.
75 °C
95 °C
120 °C
Figur 12: Partikelstørrelsesfordeling målt i masse ved tre forskellige temperaturer. Bemærk at skalaen
ikke er konstant.
Figur 13 på næste side viser de samme forsøg afbilledet som antalsstørrelsesfordelinger hvor yaksen er holdt konstant. Det ses tydeligt at der ingen partikler findes over 200 nm ved 75 °C. Ved
95 °C findes et signifikant antal partikler i de højere kanaler og det ses at der er partikler i det
75 °C
95 °C
120 °C
Figur 13: Partikelstørrelsesfordeling målt som antal som funktion af partikelstørrelse. Skalaen er konstant.
Hvor disse partikler stammer fra og hvordan de dannes er ikke klarlagt i denne undersøgelse og
bør nærmere undersøges i efterfølgende studier. Det vil være interessant at undersøge om de har
samme komposition som den undersøgte olie eller om partiklerne er dannet som
pyrolyseprodukter etc. Det er værd at bemærke at den tilbageværende massefraktion i langt de
fleste tilfælde falder til 0.1 (10 % tilbage), og stiger til 1 igen før den endeligt aftager – hvorvidt
er ikke afklaret. Appendix E viser alle størrelsesfordelinger som funktion af temperaturen for 2
olieprøveforsøg (SL11-346 exp-1 og SL11-349).
APPENDIX E
SL11-346 experiment 1
start
end
Olie temp
Number
(#/cm3)
Mass
(mg/m3)
Temp
Masss
bin 1-6
10:42:30 AM 10:43:10 AM
132.2
7925249.1 0.531091
30
0.531091
10:52:45 AM 10:54:00 AM
132.5
8111837.9
0.39426
40
0.392496
11:15:20 AM 11:16:00 AM
133.2
7505081.5 0.204994
50
0.204994
Number size distribution (dN/dlogDp)
Mass size distribution
start
end
Olie temp
Number
(#/cm3)
Mass
(mg/m3)
Temp
Masss
bin 1-6
12:25:30 PM 12:25:55 PM
133
5230864.3 0.043665
60
0.043665
12:38:30 PM 12:38:50 PM
132.8
3197448.7 0.095138
80
0.020044
12:51:30 PM 12:51:45 PM
133.2
2489046.6 0.305935
85
0.014567
Olie temp
Number
(#/cm3)
Mass
(mg/m3)
Temp
Masss
bin 1-6
1:02:00 PM 1:04:32 PM
133.2
1639583
0.409127
90
0.009693
1:14:45 PM 1:15:05 PM
133.3
952333.86 0.407317
95
0.006417
1:25:25 PM 1:25:45 PM
133.7
475552.05 0.366083
100
0.003939
start
end
start
end
Olie temp
Number
(#/cm3)
Mass
(mg/m3)
Temp
Masss
bin 1-6
1:40:30 PM 1:43:35 PM
133.2
128565.98 0.089646
105
0.000876
1:48:30 PM 1:56:30 PM
133.2
48084.32
0.000831
110
0.000227
2:02:45 PM 2:10:30 PM
133.3
33048.758 0.000156
115
0.000156
start
end
2:19:10 PM 2:20:00 PM
Olie temp
135
Number
(#/cm3)
Mass
(mg/m3)
23398.106 0.016245
Temp
Masss
bin 1-6
130
0.00023
SL11-349
start
end
9:34:00 AM 9:50:00 AM
Olie temp Number (#/cm3)
Mass
(mg/m3)
Temp
Masss
bin 1-6
130.9
24498257.02
2.341363365
30
2.341363
9:50:00 AM
10:05:00
AM
130.7
18557413.23
1.413891596
40
1.413892
10:05:00 AM
10:20:00
AM
130.1
17963443.36
0.948427468
50
0.948427
Mass
(mg/m3)
Temp
Masss
bin 1-6
17705623.62
0.330241808
60
0.330242
131
15792877.55
0.172264068
70
0.172264
131
12559800.03
0.093435125
75
0.093435
start
end
10:20:00 AM
10:35:00
AM
130.6
10:35:00 AM
10:50:00
AM
10:50:00
11:05:00
AM
Mass
(mg/m3)
Temp
Masss
bin 1-6
9826064.974
0.061350561
80
0.059889
131
5866146.699
0.033522077
85
0.576123
131.6
4711068.818
0.029113875
90
0.925785
start
end
11:05:00 AM
11:20:00
AM
131
11:23:00 AM
12:10:00
PM
12:10:00 PM
12:25:00
PM
start
end
12:25:00 PM
12:40:00
PM
Mass
(mg/m3)
Temp
Masss
bin 1-6
131.6
1976273.755
0.017098016
95
1.240364
12:41:00 PM 1:06:00 PM
130.6
876074.3352
0.009319623
100
0.868513
1:06:00 PM 1:21:00 PM
131.1
111273.2395
0.002225617
105
0.221691
start
end
Mass
(mg/m3)
Temp
Masss
bin 1-6
1:25:37 PM 1:45:00 PM
130.4
4999.830925
0.000594322
110
0.0404
1:45:00 PM 1:55:00 PM
131.3
424.0482042
0.000540005
120
0.023959
1:55:00 PM 2:05:00 PM
131.2
456.8129241
0.00059867
150
0.031058
start
end
Mass
(mg/m3)
Temp
Masss
bin 1-6
2:05:00 PM 2:16:00 PM
131.2
514.3964622
0.000666262
200
0.03615
2:16:00 PM 2:42:00 PM
131
244.4248889
0.000429438
300
0.014633
Appendix 4
Factors controlling condensed phase emissions from gas engine fired combined
heat and power plant (CHP) – a field study
Thomas Rosenoern1*, Karsten Fuglsang1, Lars Jørgensen2, Per G. Kristensen2, Kim Larsen3. Bent Iversen4, Thomas
Norrby5, John Tang6
1
FORCE Technology, Brøndby, Denmark, 2Danish Gas Technology Centre, Hørsholm, Denmark, 3Bergen Engines Denmark A/S, Aalborg,
Denmark, 4Wärtsilä Danmark A/S, Hirtshals, Denmark, 5Statoil Fuel & Retail Sweden AB, Nynäshamn, Sweden, 6Danish District Heating
Association, Kolding, Denmark
*Corresponding author, e-mail: [email protected]
Abstract
Gas fired, reciprocating, 4-stroke, engines are commonly used for energy production and are in general
considered a relatively clean energy form. This study aims at investigating and quantifying the particle
number and mass emissions from this type of energy producing plant. It was found that when an engine is
well maintained and service checks are performed regularly, there is a lower limit to the level of particle
mass and number emissions attainable, beyond which no further reduction of particle emission can be
achieved by engine tuning. Measurements showed that 50% - 80% of the particle number concentration
emitted, equivalent to 30% - 60% of particle mass, consisted of volatile material, which most likely derives
from uncombusted lubrication oil. It is possible to reduce particle emissions from gas engines by adjusting
the ignition timing. Through a change in timing, reducing the NOx concentration by ~50%, a similar
reduction in particle emissions can be obtained.
It was found that gas fired reciprocating engines are a relatively clean way of producing energy in terms of
particle mass emissions, but because the particle emissions primarily consist of ultra fine particles (which
have very little mass contribution), the particle number emission factors are relatively high.
TOC/abstract art
Introduction
Fine and ultra fine atmospheric particles are of growing concern, from a public health perspective as well as
from a climate and air quality management perspective. There is mounting evidence correlating particles
smaller than 2.5 µm and adverse health effect 1 and growing evidence that fine and ultrafine particulate
matter is responsible for a significant fraction of these effects 2-5 due to the fact that they penetrate deeper
into the lungs when respired. Since they easily enter the indoor environment, remain suspended for
extended periods of time, and are transported over long distances, the exposure to these particles is
relatively ubiquitous. However, current knowledge of which components of particulate matter, that being
segregated by size, composition, or source, show the greatest impact on public health, is still weak and
inconclusive.1 As evidence of the effects of fine and ultrafine particles on human health and climate is
mounting, greater focus has been directed to potential sources. Among these, stationary sources with low
stack heights that are situated in or near urban areas are identified as potentially problematic. On a larger
scale, it has long been recognized that particles influence local, regional and global climate, both directly, by
interactions with electromagnetic waves resulting in changes in the radiation balance, and indirectly by
interactions with atmospheric water resulting in changes of cloud formation and cloud properties resulting in
e.g. changes in increased cloudiness and changes rainfall patterns. The magnitude of the influence of the
particles on the environment is dependent on a number of physic-chemical factors like size, composition,
and physical state.6
A number of studies have shown that in urban environments, vehicular sources can comprise up to 80% of
the mass emissions quantified and as much as 90% of the particles counted.7-11 In areas not dominated by
vehicular emissions from road traffic, the main sources are more mixed, but it is still found that particles
below 100 nm and 300 nm contribute more than 80% and 99% respectively, of the total particle number
concentration measured.12
Several hundred combined heat and power (CHP) plants have been commissioned and are seeing increased
use in Denmark due to their high efficiency and their ability to utilize the heat generated during power
production. On a per mass basis, power plants, refineries and CHP plants are responsible for approximately
4% of the particulate emission (particles smaller than 10 µm, PM10) in Denmark.13 The CHP plants in
Denmark all have an electricity production of less than 25 MW and are either fired by waste, coal, biomass,
gasoil, or by gas (natural- or biogas). The magnitude and kind of emissions emitted from CHP plants is
strongly dependant on the energy source and the abatement technology installed.14 Numerous studies have
shown that the installation of technologies like wet electrostatic precipitators (W-ESP) and bag filters can
remove up to 99% of the emitted particle mass15-19 with an efficiency that is dependent on the particle size
distribution as well as the physico-chemical properties of the emissions. Due to the different fuels used in
CHP plants, the characteristics of the emissions are also expected to be very different. CHP plants fired using
waste, coal, or other solid fuels are expected to produce emissions containing relatively large amounts of
pollutants like metal oxides, sulfur, and soot, and consequently these plants are all fitted with sophisticated
abatement technologies. However, CHPs fired by natural- or biogas are not expected to produce the same
kind or amount of solid phase pollutants. The main constituent of the gas fuels is CH 4 with small amounts of
heavier gaseous carbohydrates and the main reaction products expected from their combustion is CO 2 and
H2O along with very low concentrations of other gas phase species. For this reason, the abatement devices
utilized at these CHP plants are normally limited to an oxidation catalyst for carbon monoxide. In terms of
green house gasses (GHGs), gas fired CHP plants are considered a cleaner energy source, compared to e.g.
coal fired power plants, due to the fact that natural and bio-gas inherently have low carbon/hydrogen (C/H)
ratios which in turn lead to less CO2 per energy unit produced. However, recent measurements performed
on gas fired CHP plants20, as well as on road and non-road vehicles running on natural- or biogas21-24, have
shown evidence of large particle number concentrations being emitted from these sources.
A total of more than 200 CHP plants utilize gas engines for heat and power production in Denmark. The
majority of these plants are located in smaller communities and their main function is to provide district
heating for residential areas using boilers and/or power and heat using gas engines, depending on the
immediate price of electricity. As about 28 % of the electricity production in Denmark was supplied by wind
energy in 2011 (as of 2011, 29% of the total capacity is wind energy)25, the gas engine powered CHP plants
offer flexible and fast supply of electricity in peak consumption periods and in periods where the supply of
wind energy is low. The gas engines used in the Danish CHP market are, for the main part, turbo charged,
4-stroke, lean-burn engine types operating at typical oxygen levels of 8 – 12 % per volume in the exhaust
gas.
Previous projects investigating fine and ultrafine particle emissions from combined heat and power plants
showed that natural and bio gas fired plants have surprisingly high particle emissions. It was speculated that
a correlation could exists between lubrication oil use/consumption and particle mass and number emissions.
Given that gas combustion in CHP plants emit a significant amount of particles, while combusting mainly
methane and other low molecular weight hydrocarbons, it is expected that a significant fraction of the
particulate emissions originate from evaporation and partial combustion of engine lubrication oil and from
engine wear. However, data from previous projects is limited and factors that may control the emission level
were not investigated in detail and therefore no conclusions as to the origin of these emissions were drawn.
The primary objective of this study was to quantify the emissions of fine and ultrafine particles emitted from
CHP plants using gas fired engines and to identify some of the primary parameters determining the
magnitude of the emissions. Through an extensive field measurement program, particle emissions from 5
selected gas engine powered CHP plants in Denmark were assessed. The gas engine CHP plants were
selected with respect to engine type and size as being representative for Danish CHP plants. To identify how
operational parameters influenced on the particulate emission from gas engines, the measurement program
included collection of relevant engine operating parameters as well as measurement of a number gas and
particulate phase species.
Methods
The work presented herein covers four connected studies that comprise a total of seven separate field
measurements campaigns conducted at five Danish gas fired Combined Heat and Power (CHP) plants over a
time span of 13 month.
Study 1: Particle emissions from different plants
The first study comprises results from a measurement campaign at each one of the five locations (Field tests
no. 1, 3, 4, 5, and 6). The purpose of this study was to investigate the levels and variability between
selected emission parameters during normal operation. A number of engine and emission parameters were
tracked and logged to determine the most important parameters controlling the level of particulate phase
emissions as well as the emission of semi-volatile oil components measured as oil mist.
During all measurements campaigns the sample extraction was performed using specialized sample probes
(M&C heated probe SP34-H). The flue gas was split between a mobile gas phase analyses rack and a
condensed phase analysis system. The gas phase was analyzed using a M&A model Thermo FID Flame
Ionization Detector (FID) to measure unburned hydrocarbons (UHC), a SICK model S710 Non-Dispersive
InfraRed (NDIR) detector to determine the level of CO/CO 2, a Thermo Electron model 42 CHL
ChemiLuminescence Detector (CLD), and a SICK model S710 paramagnetic detector for NO/NOX and O2 level
detection. Samples for condensed phase measurements were transferred through a temperature controlled
stainless steel tube (Hillesheim) to a custom designed dilution and conditioning system designed according
to the particle measurement protocol (PMP) which is a two step partial flow dilution system (PFDS). A total
dilution of 1:100 is achieved in the PFDS using two Dekati model DI-1000 ejector diluters sequentially (each
providing a dilution factor of 1:10). The PMP protocol is designed to ensure repeatability of particle
measurements by removing the volatile fraction of the aerosol by heated dilution in first stage (up to 350 °C)
and subsequent room temperature dilution in the second stage. In this work the dilution was performed
according to an altered PMP protocol in order to minimize removal of the volatile fraction, while still attaining
the same dilution rate. This was done by running the first stage at approximately 20 K higher than the
temperature of the stack gas at the sampling point. From the dilution system the aerosol was fed to an
electrical low pressure impactor (Dekati ELPI classic) where the particles were classified, counted, and
collected on aluminum foils according to size. Analysis of the particulate volatility was conducted by running
the sample through a thermodenuder (Dekati Thermodenuder) before ELPI analysis. The volatile fraction is
defined as the fraction of the particles removed by inserting a thermodenuder upstream of the ELPI when
performing a measurement. In practice this is done by performing consecutive measurements with and
without the thermodenuder in place while the engines are run under steady state conditions. During these
experiments the evaporation zone of the thermodenuder was set to 300 °C in order to ensure evaporation
and removal of all engine oil and volatile combustion products. The exposed ELPI collection foils were
analyzed from selected campaigns using scanning electron microscopy with energy-dispersive X-ray
spectroscopy (SEM-EDX) to produce images of the collected particles along with the elemental composition
(elements from Carbon (6 protons) and up) of the particles.
Conversion of number concentrations measured using ELPI was done from assuming a particle density of
unity. In general, the ELPI data has been truncated at 1 µm in this work, since ELPI mass and number
concentration for larger particles are subjected to an increased uncertainty, when measurements are
performed on an aerosol with a large number concentration of fine (particles smaller than 1 µm) and
ultrafine particles (particles smaller than 100 nm), and a low number concentration of coarse particles.
Lubricant oil samples were extracted directly from the oil reservoir (sump) of the engine into glass sample
containers that were subsequently analyzed at Statoil Lubricants Laboratory for metals and oxidation state
using Atomic Absorption Spectroscopy (AAS) and Ion Coupled Plasma – Mass Spectroscopy (ICP-MS).
Study 2: Oil mist measurements
Oil mist was measured at all five CHP plants during all seven measurement campaigns (Field tests no. 1
through 7). This was in part done to ascertain the best way to determine oil mist concentrations in the flue
gas and in part to test for correlations to e.g. engine operating parameters
The samples were collected on heated (120 °C) glass fiber filter followed by a condenser and an absorption
column packed with Amberlite XAD-2 resin beads. The collected samples are subsequently extracted and the
collected amount of oil is determined using GC-FID analysis. Oil mist sampling was performed according to
an extended Danish Standard sampling protocol for oil mist26 (MEL-14) which is a modification of US-EPA
Method 10. The 4 main differences are that the Danish method allow 1) an option to use a temperature
controlled out-stack filter configuration, 2) an option to not heat the probe and filter cassette if the flue gas
is non-condensable, 3) an option to only analyze and report the particulate fraction (i.e. filter) of the sample,
and 4) an option to substitute the solvent used for rinsing with toluene for work-environment and health
reasons. The expanded method utilized in these experiments used sample extraction through a heated outstack particle filter followed by a condenser to extract semi-volatile hydrocarbons and an XAD column to
capture the gas phase hydrocarbons. After each sample had been extracted, the equipment was rinsed using
toluene which was also collected for analysis. All four sample fractions (filter, condensate, XAD, and rinse)
were analyzed using gas chromatography with flame ionization detection. Using this method, hydrocarbons
with vapor pressures in the range of alkanes with between 14 and 40 carbon atoms (boiling points from
250°C to 525°C) are quantified using n-hexadecane as the reference compound. The data analysis in this
work is primarily based on the fraction collected on the filter as in accordance with MEL-14. However, the
fraction collected on the XAD column has also been considered in order to provide a more thorough analysis.
Study 3: Effect of engine service
The third study investigated the effect of a comprehensive engine overhaul on emission levels (Field tests no.
6 and 7). The overhaul included full service of cylinder liners, piston rings, bearings, etc., but does not
include a change of the engine lubrication oil. Engine oil is generally not changed according to a fixed
schedule on this type of engines, but is changed on the basis of an oil analysis. Engine oil is replenished as
part of regular engine service, according to consumption and need. The two measurement campaigns at
plant E were planned to ensure that the two measurements would be conducted shortly before and shortly
after scheduled engine service, but still with time to allow break-in of new engine parts. During the second
campaign at plant E (after service), no lubrication oil sample was extracted due to the fact that the engine
oil had not been changed during the service.
Study 4: Dependency on engine control parameters
During the first six field campaigns, a correlation between particle number and mass concentration and NO X
was observed, but the number of data points is limited, the span investigated was to narrow, and the
number of variables changing between CHP plants was too large to draw meaningful conclusions. To further
investigate this, a series of experiments was designed where the level of NO X was changed in a stepping
manner while emission parameters were monitored. The campaign (Field test no. 7) was conducted at Plant
E where the concentration of NOX in the exhaust gas was changed in a stepping manner by changing engine
control parameters. Two different ways to control the level of NOX were selected for this series of
experiments, namely the air surplus ratio (lambda, ) and the ignition timing (measured as the crank angle
before top dead center at which the spark fires, in short BTDC (Before Top Deck Center)). The experiments
were designed in such a way that during the experiments, all parameters were kept constant, except one (λ
or BTDC), which was changed until the desired NOX level in the exhaust gas was attained. It is important to
note that small changes in  are automatically performed by the engine management software as BTDC is
changed. This in turn led to a more complicated and convoluted data processing and analysis. This is done
to protect the engine from knocking and/or damage. A further discussion of  and BTDC can be found in
supplementary note 1.
Results
Study 1
Particle number concentrations and supporting parameters were measured at five selected CHP plants in
Denmark during field campaigns no. 1, 3, 4, 5, and 6. Table 1 shows a summary of the results from the five
campaigns
Table 1: Average results from 5 field campaigns. E-power output is the electrical power output. Emission factors are
given both based on electrical output (E-output) and based on energy consumed (fired). E-energy efficiency is the
electrical energy efficiency (energy unit produced per energy unit consumed).
Site
Plant A
Plant B
Plant C
Plant D
Plant E
Average (Excl. D)
E-power output
(kW)
6074
3118
2066
4794
3271
-
PN1 (#/GJ)
PN1
( #/cm³)
E-output
6
15
1.66x10
1.99x106
1.49x106
1.96x107
1.31x106
1.61x106
1.33x10
1.68x1015
1.28x1015
1.67x1016
1.13x1015
1.35x1015
PM1 (mg/GJ)
Volatile fraction PM1
PN1/PM1
(mg/m³) E-output Fired
Fired
14
5.78x10
6.97x1014
5.20x1014
6.84x1015
4.57x1014
5.63x1014
61%/26%
75%/57%
84%/37%
54%/32%
52%/39%
68%/40%
0.365
0.716
0.186
2.082
0.166
0.358
292
605
160
1770
143
300
127
252
65
726
58
125
NOX (g/GJ)
NOX
Oil consumption
(g/kWh)
(mg/m3) E-output Fired
0.160
0.107
0.409
0.146
0.080
-
327
503
524
606
438
448
237
383
407
465
341
342
103
160
165
191
138
141
UHC
UHC (gC/GJ)
(mgC/m3) E-output
1016
1511
1812
1135
1589
1482
737
1153
1408
871
1238
1134
Fired
319
480
572
357
501
468
E-energy efficiency
Field
(GJ e-output/GJ fired) campaign #
43%
42%
41%
41%
40%
42%
1
3
4
5
6
-
A number of factors and correlations were investigated and analyzed in order to understand the particle
emissions from CHP plants. Among these engine type, lubrication oil type, time since service, and engine
operating conditions received special attention as these were the factors deemed most likely to influence the
particle emissions during these campaigns. Two specific engine types and models are in use in the five
plants selected for field testing. Plant A and plant D both utilize a Wärtsilä model 18V34SG and Plants B, C,
and E all use a Rolls Royce (Bergen) type K engine. No apparent correlation between engine type and oil
consumption is found. Neither does there appear to be any correlation between engine type and particle
mass emissions, particle number emissions, or oil content measured using a thermodenuder setup.
The lubrication oil used in gas engines must possess several properties like controlling oxidation and
nitration, limit ash levels, extend oil drain/turnover intervals, prevent corrosion, reduce wear, and maintain
internal engine cleanliness, as well as be compatible with flue gas treatment systems where present. Due to
the inherent nature of the gas fueling the engine at the CHP plants investigated, the main challenges for gas
engine lubrication oil are nitration, oxidation, acidity and deposits control. If deposits are allowed to develop
in the combustion chambers, natural gas engines are prone to ring sticking, spark plug fouling, pre-ignition
and detonation. Like all lubrication oils used in combustion engines, the oils utilized by the plants in this
study are based on a stock oil (base oil) and an additive package. The compositions of these additive
packages are not disclosed by the manufacturers, and unfortunately information on the type and amount of
additives was unfortunately not available for this work. However, in most packages for gas engine lubrication
oil, the main constituent is the detergent (responsible for deposit control, acid neutralization, and oxidant
control) which accounts for around 80% of the total additive content. Apart from the detergent, a number of
organic compounds and metals (mainly calcium, zinc, barium, magnesium, phosphorus, and sulfur) are
added to the package, but the exact mixing ratios and compounds are unknown. At the five selected plants,
four different engine lubrication oils were in use. At plant A, a Shell Mycella was used, at plants B and C, a
Geotex PX 40 was used, Plant D used a Mobil 805, and at Plant E used a Q8 Mahler lubrication oil. Of these
four, three were based on group 3 base oils (American Petroleum Institute, API, definition) (Geotex PX40,
Mobil 805, and Q8 Mahler) and one was based on a group 2 (API definition) base oil (Shell Mycella). A weak
correlation (R2=0.8025) was found between the lubricant density and the emitted amount of unburned
hydrocarbons (UHC) in the flue gas and between the viscosity at 40°C and UHC (R2=0.835). However, the
correlations are too weak and the dataset too limited to show significant evidence beyond the measurement
uncertainties in the dataset. Furthermore, due to the spread of the data and the limited number of data
points in the present study, it was not possible to draw any conclusions on correlations between oil brand,
type, or base oil group and oil consumption or emissions of particles or gasses. A much more rigorous study
is needed in order to establish significant correlations and possibly causations between physicochemical
properties of the lubrication oil and emissions.
Using a scanning electron microscope with an energy dispersive x-ray spectrometer (SEM-EDX), ELPI
impactor foils from two plants (plants A and E) were analyzed for morphology and elemental composition.
The EDX analysis is capable of qualitative and quantitative analysis of elements with atomic numbers higher
than five (Boron).
Table 2: Normalized size segregated elemental analysis of particles sampled using the ELPI and analysed using SEMEDX. The numbers in bold are the elements that were also detected in significat concentrations in the analysis of the
engine lubrication oil.
Geo. Mean (µm)
Element
C
O
Na
Mg
Si
P
S
Cl
Ca
Zn
SUM
0.04
Plant A Plant E
84.7% 79.6%
12.6% 14.9%
2.7%
5.5%
100% 100%
0.07
Plant A Plant E
91.7% 88.3%
5.8%
7.2%
2.6%
4.5%
100% 100%
0.12
Plant A Plant E
94.0% 87.0%
4.8%
8.0%
1.2%
5.0%
100% 100%
0.20
Plant A Plant E
92.1% 86.9%
5.9%
9.3%
2.0%
3.8%
100% 100%
-
0.31
Plant A Plant E
89.2% 89.4%
8.5%
7.4%
2.3%
3.1%
100% 100%
0.48
Plant A Plant E
88.1% 47.4%
7.9% 19.3%
2.1%
0.6%
2.1%
1.8%
9.3%
17.9%
3.5%
100% 100%
0.76
Plant A Plant E
76.7% 66.6%
10.8% 11.6%
0.6%
1.8%
0.8%
1.1%
0.8%
2.0%
4.8%
7.0% 14.2%
1.1%
100% 100%
1.23
Plant A Plant E
74.0% 27.6%
11.4% 35.5%
0.4%
0.4% 20.0%
0.4%
3.5%
0.5%
1.6%
9.3% 14.5%
1.1%
100% 100%
1.95
Plant A Plant E
35.9% 19.9%
14.6% 15.9%
33.1%
9.6%
0.5%
7.4%
7.3%
21.5%
34.3%
100% 100%
3.08
Plant A Plant E
4.9% 23.8%
31.1% 18.2%
26.3%
11.3%
4.6%
15.7%
20.4%
33.1%
10.5%
100% 100%
Table 2 presents the normalized mass concentrations of the detected elements found on the impactor stages
collected at plants A and E. The EDX-data is also presented in Figure S1 which shows the total collected
mass and normalized collected mass of samples collected at Plants A and E, in a plot of size segregated
elemental compositions. The numbers shown in bold in Table 2 are the elements that were also detected in
significant fractions in the analyzed lubrication oil samples extracted from the engine lubrication sump at
Plants A and E during the field campaigns. The same elements are highlighted in Table S1 that shows a
summary of the results from the lubrication oil analysis for all five CHP plants. The analysis was performed
by Statoil Lubricants Laboratory and investigated the elemental composition and a number of physical and
chemical properties.
The size segregated particle composition data holds some evidence of the origin of the different size classes
of collected particles. For both Plants A and E the main component of particles small than ~400 nm (the first
five bins in the SEM-EDX analysis) is carbon along with smaller amounts of oxygen and silicon. This indicated
that they primarily originate from products formed from incomplete combustion of hydrocarbons in the fuel
and lubrication oil and subsequent reaction and condensation to the condensed phase. Combustion particles
are often seen as fractal agglomerates of small particles created from the combustion products during
cooling of the gasses. The SEM image shown in Figure 1a show a typical example of this kind of particles
collected on the third stage (mean diameter = 120 nm) at Plant A during the field campaign no. 1. Particles
in the ~400 nm to 1.5 µm range also contain a large fraction of carbon, but, in addition, significant amounts
of the lubrication oil additives and wear elements detected in the lubrication oil analysis are found. The
origin of these particles is most likely from combustion of the part of the engine lubrication oil present in the
cylinder. Two processes are important to take into consideration when investigating oil transport from the
engine into the particle phase, namely evaporation from the cylinder walls and droplets formed from the
shearing forces of the piston movement. The latter process gives rise to a larger amount of additive and
wear elements than the first process, as the first process shows fractionation based on vapor pressure of the
elements during evaporation from the cylinder walls. In support of this, previous studies of combustion
particles have shown that spherical particles, larger than 400 nm, often are present in relatively large
numbers. Using a focused ion beam (FIB) it is possible to “slice” the samples while imaging using the SEMEDX. This kind of analysis has shown that these particles are in fact hollow spheres consisting of ash and
carbonaceous material.27 Figure 1b shows a SEM images of a spherical particle from sample collected on the
eighth stage (mean size = 1.23 µm) at Plant A.
In the fractions with particles larger than ~1.5 µm, large amounts of Na, Mg and Cl was found. When
sodium is detected in the lubrication oil samples, it is usually an indicator of contamination or engine wear.
Chlorine is used as a lubricant condition marker along with a number of chemical and physical characteristics,
and magnesium is added to the lubricants as a detergent as part of the additive package. The large Na
content detected in the largest particles, was not seen in the oil analysis from Plant E, but traces of Cl and
Mg were detected in the oil from plant E. However, the trace amounts detected in the oil sample from plant
E does not explain the large amounts found in the particle samples. As the compounds are also not found in
significant amounts in the fuel, the origin of these elements in the particle samples, is most likely from the
intake air drawn into the engine. Plant E is located near the western coast of Denmark and therefore
experiences large amounts sea salt aerosol (the predominant wind direction in Denmark is from the west)
which are know to by relatively large and contain large amounts of Cl and Mg.
Figure 1: SEM images of particles collected during the field campaigns. The left image is from the third stage (mean
diameter = 120 nm) collected at plant A, the middle image is from the eighth stage (mean diameter = 1.23 µm)
collected at Plant A, and the right image is from the tenth stage (mean diameter = 3.08 µm) collected at Plant E.
Plant A does not show the same influence of sea spray aerosols since it is not positioned in a coast-near
environment. The largest particles from Plant A therefore show increasing amounts of the additives and
wear elements detected in the particle fraction between ~400 nm and 1.5 µm, and this correlates well with
the results of the lubrication oil analysis. The SEM-image shown in Figure 1c depicts a particle collected on
the impactor stage collecting particles of a mean aerodynamic diameter of 3.08 µm at Plant E. The particle
in the image show some of the characteristics expected from a mineral particle like clearly defined layers,
sharp corners, and clearly defined edges.
Table 1 shows the inferred volatile fractions from the five investigated plants. The number fraction of
particles removed by the thermodenuder was at least 50% in all cases and in one case up to 85%. In terms
of mass removal for particles smaller than 1 µm, the thermodenuder removed between 25% and 60% of the
particulate mass. The interpretation of these data is complicated by the fact that the measured volatile
fraction is strongly dependant on the shape of the particle size distribution, as particles may move in and out
of the detection range when exposed to the thermodenuder. The particles investigated in this study are not
single component particles, but may comprise multiple phases and compounds like elemental carbon, metals,
sulfates, hydrocarbons, and particle bound water. This means that in some cases, when the particles are
exposed to thermodenuder treatment, only part of the particle evaporates resulting in a change in size and
in other cases, the entire particle evaporates and it is no longer counted. If particles larger than 1 µm are
present, they may partially evaporate and move from a part of the size spectrum that is not included in the
study, to a part of the spectrum that is counted. In a similar manner particles may be removed from the
lower end of the spectrum. For this reason numbers concerning volatile fractions should be interpreted and
used with caution and the shape of the size distribution has to be taken into account.
Study 2
A total of 20 separate oil mist samples were collected at the 5 campaign locations. The results are presented
in Figure 1 and can also be found as a summary of the measured oil mist concentration in the flue gas in
Table S2. The Figure shows the correlation between measured oil mist concentrations gas and lubricant
consumption. The open circles indicate the results from the filter samples only; the crosses indicate the total
amount of oil mist collected i.e. both the fractions collected on the filters and the fractions collected on the
XAD column.
Figure 2: Correlation between measured oil mist and lubricant consumption. The open circles indicate results where
only the filter samples are included; the crosses also include the fraction collected on the XAD column.
Figure 2 shows very strong correlations between the oil consumption reported by the CHP plants and the oil
mist measured in the flue gas. A strong correlation between oil mist measure d and engine lubricant
consumption was found (R2=0.93), and an even stronger correlation was found when the gas phase was
included in the analysis (R2=0.99). It was tested if other parameters showed significant correlations to the
measured oil mist concentrations and no other significant correlations were found.
Study 3
The hypothesis tested in this study, was that particle mass emissions would be lower after engine service
than before, as it was speculated the less oil would be carried over into the combustion cylinders after
changing piston rings and cylinder linings. This was tested by conducting two measurement campaigns on
the same engine at plant E before and after the engine was serviced by, among other things, a complete
overhaul of the cylinders and pistons. The measurement campaign performed after the engine service was
done after an initial run-in period of approximately 500 engine hours to insure that the part were worn in.
However, from field test 6 (before service) to field test 7 (after service), particle number concentrations
went up from 1.31106 particles/cm3 to 8.81106 particles/cm3 and mass concentrations (PM1) went up from
0.17 mg/m3 to 0.26 mg/m3. While these numbers are significantly different, they are both within the
observed range of particle emissions observed during normal operating of gas engines investigated in this
work. As can be seen from the plots in Figure 3, showing representative mass and number size distributions
from the measurement campaigns, there is a clear difference in the particle size distributions before and
after service. As it was not possible to quantify the mass of particles larger than 1 µm with a sufficiently low
uncertainty from the ELPI data, and it is therefore not possible to provide results for PM 10 in this study.
However, close inspection of the data shown in Figure 3, reveals that there appears to be fewer particles >
0.75 µm during the after service measurements than during the before service measurements and a clear
shift is found towards smaller particles (< 0.75 µm) in the size distributions measurements performed after
engine service. The lowering in particle number concentration for particles smaller than 0.75 µm and
apparent increase in number concentration for larger particles indicates that the service of the engine shifted
the particle population towards smaller particles. The observed shift in particle distribution shape may be
explained by a thinner and more uniform oil film layer in the cylinder creating a smaller number of large
sheer droplets and an increased amount of evaporation from the cylinder walls (less oil to absorb the same
amount of energy leads to higher temperatures) which is followed by an increase in smaller particles from
partial combustion and condensation of lubrication oil.
Figure 3: Particle number and mass size distributions measured before and after engine service.
However, in spite of the are subtle changes observed, generally, the results illustrate that when an engine is
well maintained and service checks are performed regularly, the overall particle mass and number emissions
are not dependant on when the service is performed or when it was last performed. It also indicates that for
a given engine type, design and build, there is an absolute lower limit to the particle mass and number
emissions attainable, beyond which further reduction of particle emission is not possible by engine tuning.
Study 4
Four measurement series of each five set measurement points were performed over the span of four days.
The measurements were performed by adjusting one of the selected 2 engine control parameters ( or
BTDC) on alternating days. The dependence of NOX on  and BTDC is shown in Figure S2 and the resulting
particle number and mass concentrations measured as a function of NO X in the flue gas are shown in Table
3.
Table 3: Particle number and mass concentrations measured before and after thermodenuder treatment.
2012-02-05
BTDC (°)
Before thermodenuder treatment
(solid and volatile fraction)
PN1 (#/cm3) PM1 (mg/m3) Reduction (PN 1/PM1)
After thermodenuder treatment
(solid fraction)
Thermodenuder
removal efficiency
Reduction (PN 1/PM1)

NOX (mg/m³)
11.5
1.94
782
1.80x106
0.231
0%/0%
1.12x106
0.159
0%/0%
38%/31%
11.5
1.96
639
1.64x106
0.228
9%/1%
9.30x105
0.139
17%/13%
43%/39%
11.5
2.01
481
1.45x106
0.199
20%/14%
8.10x105
0.139
28%/12%
44%/30%
11.5
2.08
332
1.27x106
0.172
29%/25%
7.80x105
0.113
31%/29%
38%/34%
11.5
2.18
191
6.45x105
0.098
64%/58%
1.38x106
0.162
-23%/-2%
-114%/-66%
2012-02-07
BTDC (°)

NOX (mg/m³)
11.5
1.94
782
2.03x107
0.368
0%/0%
7.86x106
0.234
0%/0%
61%/36%
11.5
1.96
629
1.55x107
0.328
24%/11%
6.55x106
0.206
17%/12%
58%/37%
11.5
2.01
470
1.04x107
0.261
48%/29%
4.37x106
0.164
44%/30%
58%/37%
11.5
2.08
321
1.64x107
0.345
19%/6%
6.46x106
0.190
18%/19%
60%/45%
2.21
185
7
6
0.162
35%/31%
72%/49%
11.5
2012-02-06
BTDC (°)
1.83x10
0.317
10%/14%
5.09x10

NOX (mg/m³)
13.8
2.01
777
2.85x106
0.542
0%/0%
1.39x106
0.317
0%/0%
51%/41%
13.3
2.03
628
1.93x106
0.410
32%/24%
1.14x106
0.258
18%/19%
41%/37%
6
5
12.5
2.05
469
1.89x10
0.337
34%/38%
7.48x10
0.202
46%/36%
60%/40%
11.5
2.1
325
1.53x106
0.293
46%/46%
7.57x105
0.164
46%/48%
51%/44%
10
2.16
192
9.97x105
0.169
65%/69%
5.76x105
0.112
59%/65%
42%/34%
2012-02-08
BTDC (°)

NOX (mg/m³)
13.8
2
755
3.65x106
0.396
0%/0%
1.28x106
0.232
0%/0%
65%/41%
13.3
2.01
625
1.90x106
0.266
48%/33%
8.49x105
0.158
34%/32%
55%/41%
12.5
2.03
465
1.36x106
0.184
63%/54%
6.88x105
0.110
46%/52%
49%/40%
11.5
2.08
311
0.133
65%/66%
53%/60%
53%/31%
2.14
197
0.082
67%/79%
5.95x105
4.03x106
0.092
10
1.28x106
1.19x106
0.045
68%/80%
66%/45%
Table 3 shows particle number and mass concentrations measured as a function of NOX in the flue gas at
Plant E differentiated by day and NOX control mechanism. As seen in the table, the repeatability of the BTDC
experiments was excellent, but the datasets for the  experiments differ significantly. On February 7, it was
observed that the particle number concentrations were an order of magnitude higher than on the other
experiments days. In addition, it was also noted that neither particle number nor mass concentrations
followed the trends observed during the other experiments. Gas phase engine exhaust parameters show no
significant difference between the two days, indicating that the discrepancy in particle concentrations is not
caused by the engine operation (cf. Figure S3). The reason for the discrepancy in particle loading could not
be explained and consequently, we have no basis for ruling out any of the datasets. However, it is the belief
of the authors that the root cause of the discrepancy is in the sampling system (e.g. a change in compressed
air pressure utilized in the dilution system) and that the true particle loading level is therefore best
represented by the numbers measured during February 5, 6 and 8 (though the data on February 7 may still
show valid trends internally in the dataset). Table 3 shows that there is a correlation between the measured
NOX level and the particle loading in the flue gas where an increase in  leads to a either a decrease or no
apparent trend in particle loading (  NOX  PN and PM or no PN/PM trend) whereas an increase in
BTDC leads to an increase (BTDC  NOX  PN and PM).
The data presented in the table can also be seen in Figure S4, which shows the particle mass (PM2.5, PM1,
and PM0.1 are presented in panes a and b) and number (PN2.5, PN1, and PN0.1 in panes c and d)
concentrations as a function of NOX for the experiments varying  (panes a and c) or BTDC (panes b and d).
In the number concentration data collected on February 5 varying , a decrease in particle number (~64%)
and mass (~58%) concentration is observed with higher No significant trends are observed in the data for
February 7. A clear trend is also seen in the data collected while varying BTDC on both February 6 and 8
with a strong increase in particle number concentration (by a factor of ~3) with an increase in BTDC from 10
to 13.8 degrees. The corresponding particulate mass concentrations (PM1) show similar trends with a ~3fold increase on February 6 and a ~5-fold increase on February 8. If it assumed that the two effects are
additive, the increase in particle loading as a function of BTDC would have been even stronger when the
behavior of particle loading as a function of λ is taken into account. From Table 3 we know that the change
in  imposed by the engine management software (from ~2 to ~2.15) yields a decrease in PN/PM
concentration of approximately 40-50% (based on the data from February 5). This works in the same
direction as the increase in BTDC angle (increasing BTDC  decreasing  increasing PN/PM from ), but is
strongly overpowered by the contribution from the change in BTDC.
The average volatile mass and number fractions measured as a function of  and BTDC measured in study 1
(PN and PM reduction of ~70% and ~40% respectively), agrees reasonably well with the number presented
in Table 3. The decrease in particle number is somewhat smaller, but considering the variability between the
different engines, this is within uncertainty. It is also evident from the Table 3 that the volatile fraction is not
dependent on the setting or neither  nor BTDC.
In general, the results shown in Table 3, clearly illustrate that there is a strong correlation between particle
mass and number concentrations emitted and engine control parameters. It further demonstrates that when
tuning an engine, it is very important to consider the magnitude in the changes this will lead to in emissions.
It is also important to realize that changes in engine parameters will lead to changes in engine efficiency as
a result of the changes in combustion conditions and kinetics.
Emissions and efficiency
In order to facilitate comparison and applicability of the measured values, particle emission factors have
been calculated on an energy basis (GJ produced and GJ consumed). The average emission factors found in
Study 1 was 1.351015 particles or 300 mg per GJ electricity produced and 5.631014 particles or 125 mg per
GJ of gas consumed by the engines. Table 1 shows the calculated emission factors for NOX, UHC, and
particle mass and number concentrations determined for the 5 CHP plants.
The conversion from particle concentration to emission factors is dependent on the amount of exhaust gas
produced per GJ. As this is not a constant number, this depends on how efficient the engine converts fuel to
energy at a given setting, which in turn is highly dependent on engine settings. Depending on engine
efficiency, exhaust gas volume, and particle concentration, the number emission factors for particles smaller
than 1 µm range from 6.871014 particles/GJ consumed (BTDC: 11.5°, : 2.18) to 3.241015 particles/GJ
consumed (BTDC: 13.8°, : 2.00) before the thermo denuder (including volatile material) and 4.111014
particles/GJ consumed (BTDC: 10.0°, : 2.14) to 1.261015 particles/GJ consumed (BTDC: 13.8°, : 2.01)
after thermo denuder treatment (solid matter only). Mass emission factors for particles smaller than µm
range from 84 mg/GJ consumed (BTDC: 10.0°, : 2.14) to 491 mg/GJ consumed (BTDC: 13.8°, : 2.01)
before the thermo denuder (including volatile material) and 46 mg/GJ consumed (BTDC: 10.0°, : 2.14) to
287 mg/GJ consumed (BTDC: 13.8°, : 2.01) after thermo denuder treatment (solid matter only). This
corresponds to a factor of 4.6 and 3.1 before and after the thermo denuder, respectively, for number
concentrations and factors of 5.8 and 6.2 for mass emission factors. The reasons that the changes are not
equal are that the evaporation is not uniform over the particle size distribution and that only particles smaller
than 1 µm are taken into account for this estimate (cf. Table S3 and Figure S5 for a full list and graphical
representation of calculated particle emission factors from study 4)
Particle mass and number emissions factors shows no significant dependence on , but both particle number
and mass emissions factors show strong dependence on BTDC e.g. through a change in BTDC to achive a
reduction in the NOx concentration by about 50% (e.g. from 600 mg NOx/m³ to 300 mg NOx/m³), a
simultaneous reduction in both PN and PM emissions by 50% can be obtained. This was obtained by
reducing BTDC from about 13.5 to 11.5 on the plant E engine. From Table S3, it can be seen that a
reduction in BTDC from 13.5 to 11.5 will cost about 1% loss in the engine efficiency. This loss in energy
efficiency is measured as loss in kWe (electricity production) and it may be possible that the loss in
electricity production at a CHP plant to a certain extent is counterbalanced by a gain in heat production.
However, this is beyond the scope of this work and has not been investigated further.
The average particle emission factors found in study 1 in the work are lower than the emission factors
previously determined in a study performed in 2010 comparing different types of energy producing
installations.27 Results from plant D have been omitted from the average in this study, as the engine
operation at this plant turned out to be unstable and therefore not representative for the plant type. As can
be seen from Table 4, gas fired reciprocating engines are a relatively clean way of producing energy in terms
of particle mass emissions. However, due to the lack of legislation on particle number emissions, no
abatement technology is currently in use on gas fired engines. This means that, because the particle
emissions primarily consist of ultra fine particles (which have very little mass contribution), the particle
number emission factors are relatively high.
Table 4: Average number and mass emission factors determined as part of this work, compared to previously
determined emission factors from a number of other CHP plants. Number of plants is the number of plants that
constitute the basis for the shown factor, RSD, Relative standard deviations, is not reported for the measurements from
reference 27 as these were single point measurements.
Average this study (Excl. D)
Number of Particle number
Particle mass
RSD
RSD
plants (#/GJ consumed)
(g/GJ consumed)
4
5.6E+14
18.00%
0.125
72.00%
Gas fired plant (natural gas) 27
1
1.6E+16
NA
2.618
NA
Gas fired plant during start up (natural gas) 27
1
4.1E+17
NA
13.694
NA
Gas fired plant (landfill gas) 27
1
1.6E+13
NA
0.012
NA
Gas oil plant (diesel) 27
1
2.4E+14
NA
0.173
NA
Bio mass plant with bag filter27
1
5.4E+13
NA
0.119
NA
Bio mass plant with electrostatic precipitator 27
1
3.2E+14
NA
0.811
NA
Waste to energy plant with bag filter27
Waste to energy plant with electrostatic precipitator 27
1
3.6E+12
NA
0.251
NA
1
2.3E+13
NA
0.053
NA
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Supplementary Table 1
Table S1: Results of the engine lubrication oil analysis performed on samples collected at the five selected CHP plants.
The numbers in the table shown in bold are the elements that were also detected in significat concentrations in the
SEM-EDX analysis of the samples collected using the ELPI at Plants A and E.
Oil condition
Unit
Plant A
Plant B
Plant C
Plant D
Plant E
Density at 15 °C
kg/m3
882.8
861.9
859.7
892.8
863.6
Viscosity at 40 °C
mm2/s
140.9
95.0
92.1
152.2
90.2
Viscosity at 100 °C
Corrosive acid content
Base number / alkali reserves
Pour point
Flash point
Water content
mm2/s
KOH/g
KOH/g
°C
°C
ppm
14.4
1.8
3.6
-37
268
160
13.4
2.7
3.1
-29
266
164
13.2
2.1
4.8
-29
264
171
15.1
1.8
3.7
-20
252
260
12.6
2.2
3.7
-19
270
152
-log[H+]
scale (0-40)
Weight %
G-M-P
A/0.1mm
A/0.1mm
ppm
5.6
9
0.0
G
11
30
<100
4.5
9
0.0
G
12
29
<100
5.7
9
0.0
G
12
23
<100
6.0
9
0.0
G
14
40
100
4.5
9
0.0
G
13
27
<100
ppm
ppm
ppm
ppm
ppm
<1
1543
9
290
382
<1
1458
3
316
387
<1
1484
3
322
390
<1
1309
6
287
358
<1
1687
3
294
361
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
2
34
14
<1
<1
2
1
7
12
2
3
<1
<1
<1
<1
<1
<1
3
1
4
<1
<1
<1
<1
1
4
6
3
3
<1
<1
<1
<1
<1
6
1
2
<1
<1
<1
<1
<1
2
2
2
3
<1
<1
<1
<1
<1
<1
98
3
1
<1
1
<1
19
9
3
1
<1
<1
<1
<1
<1
<1
1
2
2
<1
<1
<1
<1
1
4
9
2
1
<1
<1
<1
<1
<1
Initial pH
Oil condition index
Soot
Dispersancy
Nitration
Oxidation
Chlorine
Additive elements
Barium
Calcium
Magnesium
Phosphorus
Zinc
Contamination and wear elements
Boron
Sodium
Silicon
Potassium
Lithium
Aluminum
Chromium
Copper
Iron
Lead
Tin
Molybdenum
Nickel
Titanium
Silver
manganese
Vanadium
Table S2: Average measurement results from the seven individual field campaigns which comprised a total of 20
separate oil mist samples. The light shaded boxes indicate that the values were not measured simultaneously, but
during the following day of the same campaign. The results shown in the dark grey boxes are considered to be outliers.
Field tests 1 and 2 were performed on the same engine at Plant A and field tests 6 and 7 were performed on the same
engine at Plant E. Field test 6 was performed before service and field test 7 was performed after service
Site
Field test #
Oil consumption
(g/kWh)
NOx
(mg/m³)
UHC
(mgC/m³)
Oil mist on filter
(mg/m³)
Oil mist on XAD Oil mist on filter+XAD
(mg/m³)
(mg/m³)
Plant A
1
0.160
327
1016
0.35
0.29
0.64
Plant A
2
-
-
-
0.11
0.07
0.18
Plant B
3
0.107
503
1511
0.26
0.22
0.48
Plant C
4
0.409
524
1812
0.76
0.98
1.74
Plant D
5
0.146
606
1135
0.43
3.85
4.28
Plant E
6
0.080
438
1589
0.14
0.29
0.43
Plant E
7
-
332
1593
0.12
0.05
0.17
Table S3: Particle emission factors calculated from the results obtained in study 4. The numbers highlighted in the
gray-shaded box, from February 5 2012, are considered unreliable and should not be trusted. This is also the case for
the data calculated based on the results from February 7 2012.
2012-02-05
BTDC (°)

Before thermodenuder
treatment
PN1 (#/GJ) PM1 (mg/GJ)
After thermodenuder
treatment
Electrical energy
efficiency
(GJ e-out./GJ cons.)
11.5
1.94
1.51x1015
194
9.42x1014
133
41.8%
11.5
1.96
1.40x1015
195
7.95x1014
119
41.7%
11.5
2.01
1.31x1015
180
7.33x1014
126
41.4%
11.5
2.08
1.22x1015
165
7.49x1014
109
40.9%
11.5
2.18
6.87x1014
104
1.47x1015
172
41.3%
2012-02-07
BTDC (°)

11.5
1.94
1.70x1016
309
6.60x1015
196
41.7%
11.5
1.96
1.32x1016
281
5.60x1015
176
41.6%
11.5
2.01
9.46x1015
236
3.96x1015
149
41.5%
11.5
2.08
1.57x1016
331
6.21x1015
183
41.4%
11.5
2.21
1.99x1016
345
5.53x1015
176
40.9%
2012-02-06
BTDC (°)

13.8
2.01
2.58x10
491
1.26x1015
287
41.8%
13.3
2.03
1.78x1015
379
1.05x1015
238
42.1%
12.5
2.05
1.78x1015
318
7.04x1014
190
42.0%
11.5
2.10
1.50x1015
288
7.42x1014
161
41.6%
10.0
2.16
1.04x1015
176
6.01x1014
116
40.6%
2012-02-08
BTDC (°)

15
15
15
13.8
2.00
3.24x10
352
1.14x10
206
42.2%
13.3
2.01
1.72x1015
241
7.69x1014
143
41.8%
12.5
2.03
1.25x1015
170
6.35x1014
102
41.7%
11.5
2.08
127
41.5%
2.14
5.72x1014
4.11x1014
88
10.0
1.23x1015
1.21x1015
46
40.7%
84
Supplementary Figure 1
Figure S1: Normalized size segregated particle elemental compositions from Plants A (left) and E (right). Sample were
collected using ELPI and analyzed using SEM-EDX.
Figure S2: NOX as a function of changing  (bottom axis) and BTDC (top axis). Note that in the datasets on February 6
and 8, small changes in  are performed by the engine manegement software as BTDC is changed.
Figure S3: NOX, UHC, and CO concentrations measured in the flue gas as a function of  (left) and BTDC (right).
a)
b)
c)
d)
Figure S4: PM0.1, PM1, and PM2.5 data (panes a and b) and PN0.1, PN1, and PN2.5 (panes c: and d:) data recorded during
this campaign using the ELPI. Panes a and c shows the data recorded during the experiments with varying lambda, and
panes b and d shows the datasets from the BTDC experiments. The markers show the measured data points from the
two data series recorded while changing  during the field campaign, the dashed line shows the average of the two
measurement series.
a)
b)
c)
d)
Figure S5: Particle number and mass emission factors plotted against set  and BTDC angle. Panes a and c show
particle number emission factors and panes b and d show mass emission factors for Plant E as a function of  (panes a
and b) and BTDC (panes c and d).
Supplementary note 1: On air to fuel ratio and BTDC
The air to fuel ratio needed to stoichiometrically combust methane is calculated from the reaction of
methane with pure oxygen as shown in Error! Reference source not found..
2O2 + CH4  CO2 + 2H2O
Equation 1
The stoichiometric ratio for this reaction on a per mole basis is 2:1 oxygen to methane. If this number
calculated on a per mass basis from the mass of fuel (m fuel), using the mass of air (mair) taking the average
mass fraction of oxygen in the atmosphere into account, the air to fuel ratio (AFR) is 17.2:1 (see Error!
Reference source not found.).
Equation 2
The AFR is dependent on the fuel used and varies from very low numbers for oxygenated species (e.g.
AFRmethanol = 6.4) to very high numbers for completely reduced species (e.g. AFR hydrogen = 34). Natural gas
and biogas consist of a mixture of hydrocarbons along with impurities of other less combustible compounds
and consequently the AFR is not constant for these types of fuel. In order to deal with this challenge,
internal combustion engines are often equipped with an oxygen sensor in the exhaust system (-probes)
that allow real-time control of the AFR to attain a specified stoichiometric ratio. λ is defined as the ratio of
the actual AFR (AFRactual) to the stoichiometric AFR (AFRstoichiometric) as shown in Error! Reference source
not found..
Equation 3
If  > 1, the combustion is said to be lean and if  < 1, the combustion is said to be rich. The excess of air
in a lean burn engine combusts more of the fuel and emits fewer hydrocarbons. The two main reasons for
running at lean conditions is 1) that the excess air reduces the temperature of the combustion process and
this in turn reduces the amount of nitrogen oxides (NO X) produced, and 2) that since there is excess oxygen
available, the combustion process is more efficient and more power is produced from the same amount of
fuel. The downside to lean running conditions is that the accelerating power (torque) of the engine is
reduced when compared to rich running conditions. However, this is not an issue under steady state power
production in power plant applications. The gas engines investigated in these experiments are lean-burn,
four stroke, reciprocating engines and were set to run at approximately  = 2.
The Ignition timing of a spark ignition internal combustion engine is measured as the angle of the crankshaft
before it reaches top dead center (BTDC), at which a spark will occur in the combustion chamber. It is
necessary to advance the timing of the ignition due to the time it takes the flame front to propagate from
the spark plug to the rest of the fuel in the cylinder. The timing advance, measured as BTDC, is among other
factors dependent on the angular velocity of the crankshaft (rotations per minute, RPM) which lengthens or
shortens the time available before TDC is reached. Advancing the spark timing (higher BTDC) means that
the spark is energized earlier relative to the point where the combustion chamber reaches its minimum size
(at TDC, maximum mechanical compression). The purpose of the power stroke is to use the energy
produced during combustion of the fuel, to use the increased cylinder chamber pressure to push the piston
down to rotate the crankshaft and produce mechanical energy. While the flame front is propagating through
the air/fuel mixture, the pressure in the cylinder increases, due to (1) the increase in temperature, (2) the
conversion of fuel and air to exhaust gasses (complete combustion of hydrocarbons, larger than methane, to
carbon dioxide and water increases the number of moles of gasses in the cylinder, methane is a 1:1 ratio),
and (3) the compression performed by the piston (the energy needed for compressing the gasses is derived
from the energy released during previous combustion cycles). Changing the ignition timing also alters the
flame propagation velocity and consequently the heat release rate due to the altered physicochemical
properties of the air/fuel mixture as a function of crank angle caused by altered temperatures and pressures.
This alters the peak pressure in the cylinder which in turn alters the peak temperature, the combustion
chemistry, and consequently the amount of NO X produced from the process. Since higher peak temperatures
and pressures equals higher output from the engine for the same amount of fuel but also higher output of
NOX, this type of mechanical NOX control comes at a cost in the form of higher fuel consumption and higher
CO2 emissions. Ignition timing can be adjusted to meet different goal e.g. reduce pollution or increase power,
and optimal ignition timing is achieved by adjusting a number of factors like timing of the intake valves
and/or fuel injectors (determining the mixing state of the air and fuel in the cylinder), the type of ignition
system used (e.g. a pre-chamber or open chamber), the type and condition of the spark plugs, the fuel
composition, temperature, and pressure, the engine speed and load, the air and engine temperature, and
intake air pressure. Incorrect ignition timing often leads to extreme pollution, excessive vibration (BTDC too
high), and engine knocking (BTDC too low), and may lead to engine damage and failure.
Appendix 5
Artikel til Dansk Kemi nr. 12, 2013
Ultrafine partikler fra gasmotorer på danske kraftvarmeværker
Fuglsang, K.1, Rosenørn, T.1, Frederiksen, T.G.1, Kristensen, P.G.2, Jørgensen, L. 2, Andersen, S.D. 2,
Larsen, K. 3, Iversen, B.4, Norrby, T.5, Tang, J.6
1
2
3
4
5
6
FORCE Technology, Park Alle 345, Brøndby
Dansk Gasteknisk Center A/S, Dr. Neergaards Vej 5B, 2970 Hørsholm
Bergen Engines Denmark A/S, Værftsvej 23, 9000 Aalborg
Wärtsilä Danmark A/S, Jens Munksvej 1, 9850 Hirtshals, Denmark
Statoil Fuel & Retail Sweden AB, P.O. Box 194 SE-149 22 Nynäshamn, Sverige
Dansk Fjernvarme, Merkurvej 7, 6000 Kolding
Det er tidligere vist, at gasmotorer på danske kraftvarmeværker kan emittere overraskende
mange ultrafine partikler. Denne undersøgelse analyserer omfanget og årsagen til
partikelemissionen fra gasmotorer på danske kraftvarmeværker.
Baggrund
Der er i disse år stor fokus på at reducere indholdet af sundhedsskadelige partikler i udeluften. Reguleringen retter
sig i stigende grad mod ultrafine partikler. I takt med, at den fælleseuropæiske regulering har haft succes med at
reducere udledningen af disse skadelige partikler fra lette og tunge køretøjer på vejene, udgør bidraget af partikler
fra stationære kilder i nærområder en stigende andel af indholdet af små og ultrafine partikler i udeluften i Danmark.
FORCE Technology har i samarbejde med Dansk Gasteknisk Center (DGC) og Nationalt Center for Miljø og Energi
ved Aarhus Universitet (DCE)tidligere undersøgt emissionen af bl.a. ultrafine partikler fra danske
kraftvarmeværker. Der findes omkring 300 kraftvarmeværker med fjernvarmeforsyning i Danmark, og ca. 200 af
disse producerer el og varme med naturgasfyrede gasmotorer. Hertil kommer en række naturgasfyrede gasmotorer,
der anvendes på private virksomheder, herunder gartnerier. Resultatet af den tidligere undersøgelse indikerede, at
der fra gasmotorer kunne opstå emissioner af ultrafine partikler, som var højere end de emissioner, der blev målt i
røggassen efter rensning fra affaldsforbrændingsanlæg og biomassefyrede anlæg /1/. På baggrund heraf blev der i
2010 iværksat et projekt med støtte fra Energinet.dk med det formål at undersøge nærmere, hvor stor
partikelemissionen fra gasmotorer på repræsentative danske kraftvarmeværker er, og hvilke faktorer, der giver
anledning til partikelemissionerne. Projektet blev gennemført af FORCE Technology, DGC, Bergen Engines
Denmark A/S, Wärtsilä Denmark A/S, Statoil Fuel & Retail Sweden AB og Dansk Fjernvarme. Denne artikel
opsummerer projektets væsentligste resultater.
Indledning
Det primære formål med projektet var at undersøge omfanget af, og årsagen til, partikelemissioner fra de
gasmotorer, der typisk anvendes på danske kraftvarmeværker. Fem danske gasmotoranlæg blev udvalgt ud fra
motortype og størrelse, som værende repræsentative for danske, gasmotorfyrede kraftvarmeværker. Gennem et
omfattende måleprogram på disse anlæg blev omfanget af partikelemissionen vurderet. Partiklerne blev vurderet i
forhold til egenskaber og størrelse, og det blev vurderet hvilke faktorer, der kan påvirke partikeludslippet.
Måleprogram
Måleprogrammet omfattede i alt 7 feltmålinger foretaget i perioden 2011-2012 på fem danske kraftvarmeværker,
som vist i Tabel 1. En liste over værkernes motor- og smøremiddeltyper typer er vist i Tabel 1.
Tabel 1: Oversigt over de 5 udvalgte kraftvarmeværker, deres motortyper og anvendte smøreolier.
Anlæg
Motor type
(mærke)
El-effekt
(kW)
Motorolie
(mærke)
A
B
C
D
E
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
6074
3118
2066
4794
3271
Shell Mycella
Geotex PX40
Geotex PX40
Mobil 805
Q8 Mahler
1 af 7
Der blev gennemført en målekampagne på hvert af de nævnte anlæg for at undersøge variationen mellem
gasmotorerne under normal drift. Disse målinger blev udført af FORCE Technology (FT) og DGC i tæt samarbejde
med de enkelte værker. Tabel 2 opsummerer de parametre, der blev målt af hhv. FT og DGC i de enkelte
kampagner. De anvendte målemetoder er ligeledes vist i Tabel 2. Figur 1 viser målingen af ultrafine partikler i
forbindelse med en af feltkampagnerne.
Tabel 2: Oversigt over anvendte målemetoder i de enkelte målekampagner. ELPI: Elektrical Low
Pressure Impactor, TD: Thermo Denuder, Filter/XAD: Kombination af opvarmet filter og absorptionsrør
pakket med XAD ® polymer adsorbent, FID: flammeionisationsdetektor, NDIR: Non-dispersiv infrarød
detektor, CLD: Chemiluminescence Detector, ZrO2: Zirconium Oxide sensor, SEM: Scanning Electron
Microscope, EDX: Energi-røntgenfluorescens spektroskopi, AAS/ICP-MS: atomabsorptionsspektroskopi
/Ion Coupled Plasma - massespektroskopi. FT/DGC angiver om målingen er udført af FORCE
Technology eller DGC.
Test #
Anlæg
1
2
3
4
5
6
7
A
A
B
C
D
E
E
Partikel antal- og
størrelsesfordeling
ELPI
Partikel, flygtig
Olietåge
andel
TD-ELPI
Filter/XAD
FT
FT
FT
FT
FT
FT
FT
FT
FT
FT
FT
FT
DGC
FT/DGC
DGC
DGC
DGC
DGC
FT/DGC
UHC
CO
NOX
O2
FID
DGC
DGC
DGC
DGC
DGC
DGC
NDIR
CLD
ZrO2
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
DGC
Størrelsesopdelt
Røggas
Olieanalyse
elementar analyse
temperatur
SEM-EDX
AAS/ICP-MS Thermocouple
FT
FT
-
Statoil
Statoil
Statoil
Statoil
Statoil
-
DGC
DGC
DGC
DGC
DGC
DGC
DGC
Figur 1. Måling af ultrafine partikler på et gasmotorfyret kraftvarmeværk.
Resultater og diskussion
Tabel 3 viser målte gennemsnitskoncentrationer af partikler i emissionen fra de fem gasmotorfyrede
kraftvarmeværker under drift.
Tabel 3: Målte koncentrationer af partikelantal og –masse i emissionen fra de fem gasmotorfyrede
kraftvarmeværker. Anlæggenes motortype, smøreolietype og motorlast under drift er vist sammen
med olieforbruget, oplyst af de enkelte anlæg.
Anlæg
Motor type
(mærke)
A
B
C
D
E
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
Motor effekt PN1 Flygtig andel, PN1 PM1 Flygtig andel, PM1 Olieforbrug
(kW)
(g/kWh)
( #/cm³) (ved brug af TD) (mg/m³) (ved brug af TD)
6074
1.66E+06
61%
0.365
26%
0.160
3118
1.99E+06
75%
0.716
57%
0.107
2066
1.49E+06
84%
0.186
37%
0.409
4794
1.96E+07
54%
2.082
32%
0.146
3271
1.31E+06
52%
0.166
39%
0.080
Ud fra resultaterne i Tabel 3 kan der ikke påvises nogen sammenhæng mellem motortype og olieforbrug. Dette
stemmer overens med resultatet af en større spørgeskemaundersøgelse, som Dansk Fjernvarme har gennemført i
2 af 7
forbindelse med projektet. Undersøgelsen omfattede en opgørelse af olieforbrug og -type fra ca. 100 gasmotorer.
Der synes heller ikke at være nogen sammenhæng mellem motortype og emissionen af partikelmasse, partikelantal,
eller indholdet af olie i de emitterede partikler.
Resultatet af målingerne af koncentrationen af olietåge er vist i Figur 2 som funktion af den enkelte motors
olieforbrug. Olietågemålingen omfatter dels den del af olien, der er på dråbeform (opsamlet på filter), og den
gasformige del af oliekomponenterne i røggassen (opsamlet på polymeradsorbenten XAD). Emissionen af olietåge
stammer fra den anvendte smøreolie, som ikke når at blive fuldstændigt forbrændt i motorens forbrændingskammer.
Der ses her at være en klar korrelation: Jo højere olieforbrug motoren har, jo højere er koncentrationen af olietåge i
udstødningsgassen fra motoren. Det skal bemærkes, at de målte koncentrationer af olietåge er betydeligt lavere end
de koncentrationer af olietåge, der blev fundet fra gasmotorer på danske kraftvarmeværker i en undersøgelse fra
2001 /2/.
Figur 2: Den målte emissionskoncentration af olietåge som funktion af motorens samlede forbrug af
smøreolie. De åbne cirkler angiver resultater, hvor kun måletallet fra filterprøverne er inkluderet,
krydserne viser summen af filterprøver og gasformig fraktion (XAD kolonne).
Ved hjælp en thermodenuder (TD vist i tabel 2) blev partiklerne varmet op til 300 ºC og ført gennem
en absorptionsenhed inden måling i partikeltælleren (ELPI). Herved kunne det måles, hvor stor en
andel af partiklerne, der bestod af flygtige forbindelser. Det viste sig, at 50%-80% af partikelantallet
bestod af flygtige partikler. Omregnet til masse (PM1) var andelen af flygtige partikler 30%-60%. Det
antages, at den flygtige andel af partiklerne udgøres af mere eller mindre uforbrændte
smøreoliepartikler.
Typen og mængden af additiver i smøreolien oplyses ikke af producenterne, og det var derfor ikke
muligt at korrelere måleresultaterne med specifikke additiver. Additiverne består bl.a. af en række
organiske forbindelser og metaller (især calcium, zink, barium, magnesium), samt fosfor og svovl.
Partiklernes sammensætning er derfor undersøgt i forhold til en analyse af metaller i den anvendte
smøreolie. Figur 3 viser resultatet af en EDX analyse af partikelfraktioner i området fra 0,04 µm og op
til 3,0µm. Analysen er foretaget på prøver fra to forskellige kraftvarmeværker (anlæg A og E). Det er
her tydeligt, at de primære bestanddele af de mindste partikler (< 0,5 µm) er kulstof, og i mindre grad
ilt. Denne fraktion udgøres af sodpartikler, der primært består af elementar carbon (EC) og med en vis
andel af oxiderede organiske forbindelser. For de større partikler (> 1 µm) ses det, at der optræder
signifikante mængder af calcium, zink og magnesium. Disse stoffer kan korreleres direkte med
forekomsten af Ca, Zn og Mn i smøreolien. At der tillige optræder natrium og chlor i partiklerne fra
anlæg E, og ikke i partiklerne fra anlæg A, tilskrives at anlæg E ligger i et kystnært område, som
påvirkes af saltholdige partikler. Disse partikler trækkes ind i motoren via forbrændingsluften. Da
anlæg A ligger væsentlig længere fra kysten, vil denne effekt ikke ses i samme grad på anlæg A.
3 af 7
Figur 3. Resultatet af en grundstofanalyse udført ved EDX af forskellige partikelstørrelsesfraktioner. Partiklerne
er opsamlet ved hjælp af en kaskadeimpaktor (ELPI) på to af de fem undersøgte gasmotorer.
Figur 4 viser eksempler på partiklernes morfologi, analyseret ved hjælp af scanning elektronmikroskopi (SEM).
Det er tydeligt, at der er tale om partikler opstået ved helt forskellige dannelsesmekanismer. Billedet længst til
venstre viser små sodpartikler, der som nævnt oven for har et meget højt indhold af kulstof. Det midterste billede
viser en meget stor partikel, som formodes at stamme fra en forbrænding af oliedråber afrevet fra stempelvæggen
i motorens forbrændingskammer. Det højre billede viser en irregulær partikel opsamlet på anlæg E, der
formodentlig består af NaCl og muligvis en kerne af oxiderede metaller hidrørende fra mekanisk slid i motoren.
Figur 4. SEM billeder af partikler opsamlet på anlæg A. Det venstre billede viser sodpartikler, der er
dannet ud fra enkeltpartikler med en diameter på 40-60 nm; det midterste billede viser en stor, sfærisk
partikel med en diameter på omkring 1 µm - formodentlig dannet ud fra små smøreoliedråber i
forbrændingskammeret. Det højre billede viser en irregulær partikel opsamlet på anlæg E, der
formodentlig består af NaCl og oxiderede metaller hidrørende fra mekanisk slid i motoren.
Partikelemissioner ved forskellige motorindstillinger
For at undersøge, hvad typiske motorindstillinger betyder for partikelemissionen, blev der på anlæg E udført en
række forsøg, dels hvor motorens luftoverskud (λ) blev ændret, og dels hvor motorens tændingsvinkel blev
ændret. En ændring af λ vil – ligesom en ændring af tændingsvinklen – ændre NOX koncentrationen, og det var
formålet at undersøge, hvordan en ændring af NOX emissionen ville påvirke partikelemissionen. Figur 5 viser
gennemsnittet af to identiske forsøgsrækker, hvor partikelantallet i udstødningen er målt som funktion af NOX
koncentrationen. Den stiplede linje viser summen af faste og flygtige (olie) partikler (PN(total)), og den
sammenhængende linje viser koncentrationen af de faste partikler (PN(solid)).
4 af 7
Figur 5: Partikelantallet som en funktion af NOx koncentrationen fra en gasmotor på kraftvarmeværk E. I venstre plot ændres
NOx koncentrationen ved at variere luft / brændstof forholdet. I det højre plot indstilles NOx koncentrationen ved at variere
tændingsvinklen.
Det er tydeligt, at der er en signifikant stigning i partikelkoncentrationen, når NOX koncentrationen øges ved
ændring af tændingsvinklen, men at denne stigning ikke forekommer i samme grad, når NOX stigningen styres
ved ændring af λ. Dette er en vigtig information i forbindelse med begrænsning af partikelemissioner. En
ændring af tændingsvinklen, der halverer NOx koncentrationen fra en gasmotors normale driftspunkt vurderes jf.
figur 5 at medføre en halvering af partikelemissionen. Dette vurderes at koste op til 1 % point elvirkningsgrad.
Trods et tab i elvirkningsgraden er der for kraftvarmeværkerne et incitament til at reducere NOx emissionen ved
at ændre tændingsvinklen på gasmotorerne, idet tabet i elvirkningsgrad udlignes af en reduceret NOx afgift. Ved
ændring af tændingsvinklen har anlæggene således mulighed for både at opnå en NOx reduktion og en reduktion
i partikelemissionen.
Partikelemissioner før og efter udførelse af service på gasmotoren
På et af de fem anlæg blev der udført en målekampagne før og efter, at der blevet udført en omfattende service
på motoren. Denne service, der bliver udført af motorleverandøren efter 25.000 timers driftstid, omfatter bl.a.
udskiftning af motorens stempelringe og foringer. Målingen efter service blev først udført efter cirka 500
driftstimer for at sikre, at udskiftede reservedele var kørt ind og motorens drift dermed stabiliseret. Det totale
partikelantal fra motoren øgedes fra 1,31  106 partikler/cm³ før service til 8,81  106 partikler/cm³ efter service,
og massekoncentrationen (PM1) steg fra 0,17 mg/m³ før service til 0,26 mg/m³ efter service. På trods af, at disse
tal er markant forskellige, er de begge inden for de koncentrationsområder, der observeres under normal drift af
gasmotorer undersøgt i dette arbejde.
Figur 6 viser den gennemsnitlige partikelstørrelsesfordeling før hhv. efter service på motoren.
Figur 6. Partikelantal og masse målt som funktion af partikelstørrelse før og efter udførelsen af en omfattende
service på motoren.
Som det kan ses ud fra Figur 6, er der ikke stor forskel i partikelstørrelses populationer før og efter den udførte
service på motoren. Der synes dog at være en svag tendens til, at der opstår lidt færre store partikler (> 0,75 µm)
og lidt flere små partikler (< 0,75 µm) efter, at der er udført service på motoren.
5 af 7
Beregning af emissionsfaktorer
Den samlede emission af partikler er beregnet ud fra de målte koncentrationer og ud fra det aktuelle røggasflow.
Emissionerne er i Tabel 4 omregnet til emissionsfaktorer for PN1, PM1, NOx og UHC baseret på den indfyrede
energimængde. Beregningsmetoden følger den metode, der er anvendt i tidligere emissionsopgørelser /3/. De
viste emissionsfaktorer for NOX og UHC stemmer overens med de emissionsfaktorer, der er bestemt for danske
gasfyrede kraftvarmeværker i forbindelse med tidligere undersøgelser /3/.
Tabel 4. Beregnede emissionsfaktorer for partikelantal (PN1), partikelmasse (PM1), NOX og UHC på de fem
gasmotorfyrede kraftvarmeværker. Resultater fra anlæg D er udeladt i det beregnede gennemsnit, da motorens
drift på anlæg D viste sig at være ustabil og derfor ikke repræsentativ.
PN1
PM1
NOX
UHC
Energieffektivitet
(#/GJ indfyret) (mg/GJ indfyret) (g/GJ indfyret) (gC/GJ indfyret) (GJ produceret/GJ indfyret)
A
5.78E+14
127
103
319
43%
B
6.97E+14
252
160
480
42%
C
5.20E+14
65
165
572
41%
D
6.84E+15
726
191
357
41%
E
4.57E+14
58
138
501
40%
Gennemsnit (Ekskl. D)
5.63E+14
125
141
468
42%
Anlæg
Tabel 5 sammenligner de beregnede emissionsfaktorer for PN1 og PM1 med en tidligere undersøgelse udført af
DCE, DGC og FORCE /3/.
Tabel 5. Sammenligning mellem emissionsfaktorer bestemt for partikelantal (PN1) og partikelmasse
(PM1) i denne undersøgelse og tidligere bestemte emissionsfaktorer fra en række forskellige typer.
Antal anlæg
Gennemsnit, dette studie (Ekskl. D)
Gasfyret anlæg (naturgas)
Gasfyret anlæg under opstart (naturgas)
Gasfyret anlæg (deponigas)
Dieselfyret anlæg
Biomasseanlæg med posefilter
Biomasseanlæg med elektrostatisk udfælder
Affaldsforbrænding med posefilter
Affaldsforbrænding med elektrostatisk udfælder
4
1
1
1
1
1
1
1
1
Partikel antal
(#/GJ indfyret)
5.6E+14
1.6E+16
4.1E+17
1.6E+13
2.4E+14
5.4E+13
3.2E+14
3.6E+12
2.3E+13
RSA
18.00%
NA
NA
NA
NA
NA
NA
NA
NA
Partikel masse
(g/GJ indfyret)
0.125
2.618
13.694
0.012
0.173
0.119
0.811
0.251
0.053
RSA
Reference
72.00%
NA
NA
NA
NA
NA
NA
NA
NA
Dette studie
(DMU RAPPORT)
(DMU RAPPORT)
(DMU RAPPORT)
(DMU RAPPORT)
(DMU RAPPORT)
(DMU RAPPORT)
(DMU RAPPORT)
(DMU RAPPORT)
Tabel 5 viser, at emissionsfaktoren under normale driftsforhold varierer relativt lidt fra anlæg til anlæg. Samtidig
viser resultaterne, at der - som vist for anlæg D i Tabel 4 - kan opstå en signifikant højere partikelemission under
uregelmæssig drift. Denne undersøgelse har fokuseret på emissioner under normal motordrift. Tidligere
undersøgelser har som det fremgår af Tabel 5 desuden vist, at opstart af gasmotoren kan give kortvarige men
høje partikelkoncentrationer, såvel målt som partikelantal som -masse.
Konklusion
Undersøgelsen viser, at gasmotorer på danske kraftvarmeværker under normal drift giver anledning til
partikelemissioner, der er af samme størrelsesorden som affaldsforbrændingsanlæg eller biomassefyrede
kraftvarmeværker, der er forsynet med velfungerende filterteknologier. Under uregelmæssig drift, eller under
opstart, vil der kunne opstå højere partikelemissioner. Dog skal dog i den forbindelse nævnes at gasmotorer,
grundet deres status som relativt rene kraftværker, ofte ligger i byområder og ikke nødvendigvis har samme
skorstenshøjde som større energiproducerende anlæg. Der kunne ikke måles nogen sammenhæng mellem
partikelemissionen fra motoren og motortypen (Bergen RR og Wärtsilä), smøreolietypen, og partikelemissionen
var ikke væsentligt påvirket af, om der blev udført service på motoren.
En yderligere reduktion af partikelemissioner fra gasmotorer vil ud fra undersøgelsens resultater kunne opnås
ved at reducere tændingsvinklen. Mange gasmotoranlæg er i gang med at reducere deres NO x emissioner på
grund af NOx afgiften. Da denne reduktion blandt andet foregår ved justering af tændingsvinklen, er der
mulighed for at opnå en samtidig reduktion i partikelemissionen.
6 af 7
Referencer:
1
2
3
Fuglsang m.fl. (2009). Måling og karakterisering af ultrafine partikler fra danske kraftvarmeværker.
Dansk Kemi 91 (4), pp. 20-23.
Kortlægning af emissioner fra decentrale kraftvarmeværker (2003). Eltra projekt 3141, delrapport 4.
Måleprogram og analyse af emissioner fra gasfyrede decentrale kraftvarmeværker < 25 MWe.
Emissionskortlægning for decentral kraftvarme 2007 – Energinet.dk miljøprojekt nr. 07/1882.
Delrapport 5. Emissionsfaktorer og emissionsopgørelse for decentral kraftvarme, 2006. Faglig rapport
fra DMU nr. 781 2010.
7 af 7
Appendix 6
FORCE
TECHNOLOGY
Factors controlling condensed phase emissions from
gas engine fired combined heat and power plant (CHP)
– a field study
Measurement program
Objective
The primary objective of this study was to identify the
primary causes of fine and ultra fine particles emitted
from CHP plants using gas fired engines. Through an
extensive field measurement program, the most
important factors influencing particle emission were
assessed. To identify which operational parameters has
the greatest influence on the particulate emission from
gas engines, the measurement program included
collection of relevant engine operating parameters as
well as measurement of relevant gas and particulate
phase components.
The presented work is based on a measurement
program comprised of a total of 7 field measurement
campaigns conducted over a time span of 13 month at
5 Combined Heat and Power (CHP) plants at selected
locations in Denmark.
Volatile particle fraction
Particle concentration I
Site
Engine type
(Brand)
Engine load Engine lubricant Base oil group Oil consumption
(kW)
(Brand)
(API definition)
(g/kWh)
Jelling
Christiansfeld
Aså
Frederikssund
Brønderslev
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
6074
3118
2066
4794
3271
Shell Mycella
Geotex PX40
Geotex PX40
Mobil 805
Q8 Mahler
2
3
3
3
3
0.160
0.107
0.409
0.146
0.080
The particle number concentration was measured
usinge an electrostatic low pressure impactor (ELPI,
Dekati). The mass concentration was then subsequently
inferred using asumptions on density andparticle shape.
Particle volatile fraction vs. NOX concentration
Particle mass and number vs. NOX concentration
75%
40%
60%
30%
45%
20%
30%
10%
15%
0%
300
350
400
450
500
550
NOx mg/m (n, ref)
600
650
2/7/12
2/5/12
Average WO/TD
2/7/12
2/5/12
Average W/TD
2.5E+07
2.0E+07
1.5E+07
1.0E+07
5.0E+06
2.00E+07
1.50
1.50E+07
1.00
1.00E+07
0.50
5.00E+06
350
400
450
500
550
NOx mg/m (n, ref)
600
650
1.95
2
2.05
2.1
Lambda
2.15
2.2
2.25
2/7/12
2/5/12
Average WO/TD
2/7/12
2/5/12
Average W/TD
4.0E-01
2.50E+07
2.00
0.00
300
0%
700
PN1 #/cm (n,ref O2)
1.9
Changing lambda, Mass based ( g/m )
Particle mass
50%
PM1 mg/m (n, ref O2)
2.50
PN1 #/cm (n,ref O2)
90%
PM1 mg/m (n, ref O2)
Mass fraction (PM1)
Number fraction
Number Fraction (PN1)
Mass fraction
Changing lambda, Number based (#/cm )
0.0E+00
Using a Thermodenuder (Dekati), all volatile species in
the gas phase were stripped from the extracted aerosol
sample at 300 °C before being passed on to the analysis
equipment.
60%
Particle concentration II
The NOX concentration can be controlled either by changing the
air to fuel ratio (Lambde) or by changing the crank angle at
which the spark initiated the combustion (measured as before
top dead center (BTDC).
Particle number
Thomas Rosenoern1, Karsten Fuglsang1, Lars Jørgensen2, Per G. Kristensen2,
Kim Larsen3. Bent Iversen4, Thomas Norrby5, John Tang6
3.0E-01
2.0E-01
1.0E-01
0.0E+00
1.9
1.95
0.00E+00
700
2
2.05
2.1
Lambda
2.15
2.2
2.25
Changing BTDC, Number based (#/cm )
Oil mist measurements
Number based
Field test #
Oil consumption NOx mg/m³ UHC mgC/m³ PN1 #/cm³
(g/kWh)
(n, ref)
(n, ref)
(n,ref O2)
Oil fraction
(PN1)
Mass based
1
0.160
327
1016
1.66E+06
61%
0.36
3%
42%
0.35
0.29
0.64
Jelling
2
-
-
-
-
-
-
-
-
0.11
0.07
0.18
Christiansfeld
3
0.107
503
1511
1.99E+06
75%
0.72
57%
74%
0.26
0.22
0.48
Aså
4
0.409
524
1812
1.49E+06
84%
0.19
37%
42%
0.76
0.98
1.74
Frederikssund
5
0.146
606
1135
1.96E+07
54%
2.08
32%
48%
0.43
3.85
4.28
Brønderslev, before
6
0.080
438
1589
1.31E+06
52%
0.17
39%
60%
0.14
0.29
0.43
Brønderslev, after
7
-
332
1593
8.81E+06
49%
0.26
39%
46%
0.12
0.05
0.17
Oil mist vs. lubricant consumption
Oil mist on filter mg/m (n, ref O2)
2.00
y = 4.0916x + 0.0488
R = 0.99361
0.75
1.50
y = 1.71x + 0.0792
R = 0.92595
0.50
1.00
0.25
0.50
0.00
0.0
0.1
0.2
0.3
Oil consumption (g/kWh)
0.4
0.5
0.00
Oil mist on filter+XAD mg/m (n, ref O2)
Oil mist on Filter and XAD
1.00
Average W/TD
3.0E+06
2.0E+06
1.0E+06
9
10
11
12
13
BTDC angle (°)
14
15
Oil mist
PM1 mg/m³ Oil fraction Oil fraction Oil mist on filter Oil mist on XAD Oil mist on filter+XAD
(n, ref O2)
(PM1)
(PM10) mg/m³ (n, ref O2) mg/m³ (n, ref O2)
mg/m³ (n, ref O2)
Jelling
Oil mist on Filter
Average WO/TD
2/6/12
0.0E+00
The graph shows the correlation between measured oil mist in the stack gas and the lubricant consumption. The
open circles indicate results where only the filter samples are included; the crosses also include the fraction
collected on the XAD column. A strong correlation between oil mist measured and engine lubricant consumption was
found, with the stronger correlation found when the gas phase was included. No other significant correlations were
found between the oil mist results and other measured parameters in this work.
Changing BTDC, Mass based ( g/m )
2/8/12
2/6/12
Average WO/TD
2/8/12
2/6/12
Average W/TD
6.0E-01
Particle mass
Site
2/6/12
2/8/12
4.0E+06
Particle number
The table shows the average of the results from the 7 individual campaigns which comprised a total of 20 separate
oil mist samples. The samples were collected on heated (120 °C) glass fiber filter followed by a condencer and a
absorption column packed with Amberlite XAD-2 resin beads. The collected samples are subsequently extracted
and the collected amount of oil is determined using GC-FID analysis. The fraction collected on the filter is used
primarily for data analysis in this work. However, in some instances, the fraction collected on the XAD column has
also been considered in order to provide a more thorough analysis. Shown in the table is also measured values for
oil consumption, NOX, unborned hydrocarbons (UHC) along with particle number and mass concentration. The
results shown in light shaded boxes indicate that the values were not measured simultaneously with the oil mist
samples, but during the following day of the same campaign. The result show in the dark grey shading is
considered to be an outlier.
2/8/12
5.0E-01
4.0E-01
3.0E-01
2.0E-01
1.0E-01
0.0E+00
9
10
11
12
13
BTDC angle (°)
14
15
Main findings
No correlation between PM10/PN10 and NOX level
No correlation between PN1 and NOX level
Some correlation between PM1 and NOX level
No/weak correlation between PM1/PN1 and Lambda (fuel to air
ratio)
Strong correlation between PM1/PN1 and BTDC (before top
dead center)
Strong correlation between oil mist and consumption
No other correlation was found to oil mist measured
1: FORCE Technology, Brøndby, Denmark; 2: Danish Gas Technology Centre, Hørsholm, Denmark; 3: Bergen Engines Denmark A/S, Aalborg, Denmark; 4: Wärtsilä
Danmark A/S, Hirtshals, Denmark; 5: Statoil Fuel & Retail Sweden AB, Nynäshamn, Sweden; 6: Danish District Heating Association, Kolding, Denmark
Appendix 7
Factors controlling condensed phase emissions from gas engine fired combined heat and power
plant (CHP) – a field study
1
1
2
2
3
4
5
Thomas Rosenoern , Karsten Fuglsang , Lars Jørgensen , Per G. Kristensen , Kim Larsen . Bent Iversen , Thomas Norrby , John Tang
1
2
6
3
FORCE Technology, Brøndby, Denmark, Danish Gas Technology Centre, Hørsholm, Denmark, Bergen Engines Denmark A/S, Aalborg, Denmark,
Wärtsilä Danmark A/S, Hirtshals, Denmark, 5Statoil Fuel & Retail Sweden AB, Nynäshamn, Sweden, 6Danish District Heating Association, Kolding, Denmark
4
As increasing evidence of the effects of fine and ultrafine particles on human health and climate is mounting,
greater focus has been directed to potential sources. Among these, stationary sources with low stack heights that
are situated in or near urban areas, are identified as potentially problematic. This study focuses on one such group
of plants, namely the gas fired Combined Heat and Power (CHP) plants. Recent studies have shown that a
relatively high number of fine and ultra fine particles are emitted from gas fired CHP plants. Since combustion of
Natural gas, which for the main part is methane, is not expected to produce significant numbers of particles, it is
expected that the particulate emissions originate from the engine lubrication oil.
Results will be presented from: 1) A study comparing emissions from gas engines at five different CHP plants
2) An investigation of the effect of gas engine service (including change of cylinder liners and piston rings) on the
emissions 3) An exploration of the change in emissions as a result of changing the air/fuel mixing ratio and the
ignition timing.
Particle number concentrations were measured using an Electric Low Pressure Impactor (ELPI) after a dilution
and drying system. The volatile fraction of the condensed phase was probed using a thermo denuder in front of
the ELPI. A number of gas phase parameters have also been measured for use in the data analysis.
In depth analysis of correlations between engine parameters, gas phase concentration, and particle number
and mass concentrations, show that a number of parameters may be contributing factors with respect to particle
emission abatement. The Figure below show an example of the correlation found as part of this study, particularly
between particle number concentrations and NOX levels in the exhaust stream from a CHP gas engine selected for
extensive studies.
Figure 1: Particle number concentration as a function of NOX concentration. In the left plot the NOX concentration is controlled by varying the air/fuel
mixing ratio, in the right plot the NOX concentration is set by altering the ignition timing.
A clear correlation is seen between particle number concentrations and measured NOx level when the NOx
production is changed by changing the ignition timing (right graph). The same close correlation is not seen when
NOx production is controlled by changing the air/fuel mixing ratio (left graph). The figure also shows the general
trend of a drop in particle number concentration of approximately 50% when measurements are performed using
a thermo denuder, indicating that a large fraction of the particulate emissions are due to semi volatile compounds
that have the potential for re-equilibration and subsequent reaction in the ambient atmosphere.
Appendix 8
Artikel til Dansk Fjernvarme
Ultrafine partikler fra gasmotorer på danske kraftvarmeværker
Det er tidligere vist, at gasmotorer på danske kraftvarmeværker kan emittere overraskende
mange ultrafine partikler. Denne undersøgelse analyserer omfanget og årsagen til
partikelemissionen fra gasmotorer på danske kraftvarmeværker.
Baggrund
Der er i disse år stor fokus på at reducere indholdet af sundhedsskadelige partikler i udeluften. Reguleringen retter
sig i stigende grad mod ultrafine partikler. I takt med, at den fælleseuropæiske regulering har haft succes med at
reducere udledningen af disse skadelige partikler fra lette og tunge køretøjer på vejene, udgør bidraget af partikler
fra stationære kilder i nærområder en stigende andel af indholdet af små og ultrafine partikler i udeluften i Danmark.
FORCE Technology har i samarbejde med Dansk Gasteknisk Center (DGC) og Nationalt Center for Miljø og Energi
ved Aarhus Universitet (DCE) tidligere undersøgt emissionen af bl.a. ultrafine partikler fra danske
kraftvarmeværker. Der findes omkring 300 kraftvarmeværker med fjernvarmeforsyning i Danmark, og ca. 200 af
disse producerer el og varme med naturgasfyrede gasmotorer. Hertil kommer en række naturgasfyrede gasmotorer,
der anvendes på private virksomheder, herunder gartnerier. Resultatet af den tidligere undersøgelse indikerede, at
der fra gasmotorer kunne opstå emissioner af ultrafine partikler, som var højere end de emissioner, der blev målt i
røggassen efter rensning fra affaldsforbrændingsanlæg og biomassefyrede anlæg. På baggrund heraf blev der i 2010
iværksat et projekt med støtte fra Energinet.dk med det formål at undersøge nærmere, hvor stor partikelemissionen
fra gasmotorer på repræsentative danske kraftvarmeværker er, og hvilke faktorer, der giver anledning til
partikelemissionerne. Projektet blev gennemført af FORCE Technology, DGC, Bergen Engines Denmark A/S,
Wärtsilä Denmark A/S, Statoil Fuel & Retail Sweden AB og Dansk Fjernvarme. Denne artikel opsummerer
projektets væsentligste resultater.
Indledning
Det primære formål med projektet var at undersøge omfanget af, og årsagen til, partikelemissioner fra de
gasmotorer, der typisk anvendes på danske kraftvarmeværker. Ud fra motortype og størrelse blev fem danske
gasmotoranlæg valgt som værende repræsentative for danske, gasmotorfyrede kraftvarmeværker. Gennem et
omfattende måleprogram på disse anlæg blev omfanget af partikelemissionen vurderet. Partiklerne blev vurderet i
forhold til deres egenskaber og størrelse, og det blev vurderet hvilke faktorer, der kan påvirke partikeludslippet.
Figur 1. Måling af ultrafine partikler på et gasmotorfyret kraftvarmeværk.
Resultater og diskussion
Tabel 1 viser målte gennemsnitskoncentrationer af partikler i emissionen fra de fem gasmotorfyrede
kraftvarmeværker under drift.
1 af 3
Tabel 1: Målte koncentrationer af partikelantal og –masse i emissionen fra de fem gasmotorfyrede
kraftvarmeværker. Anlæggenes motortype, smøreolietype og motorlast under drift er vist sammen
med olieforbruget, oplyst af de enkelte anlæg.
Anlæg
Motor type
(mærke)
A
B
C
D
E
Wärtsilä 18V34SG
RR type K
RR type K
Wärtsilä 18V34SG
RR type K
Motor effekt PN1 Flygtig andel, PN1 PM1 Flygtig andel, PM1 Olieforbrug
(kW)
(g/kWh)
( #/cm³) (ved brug af TD) (mg/m³) (ved brug af TD)
6074
1.66E+06
61%
0.365
26%
0.160
3118
1.99E+06
75%
0.716
57%
0.107
2066
1.49E+06
84%
0.186
37%
0.409
4794
1.96E+07
54%
2.082
32%
0.146
3271
1.31E+06
52%
0.166
39%
0.080
Ud fra resultaterne i Tabel 1 kan der ikke påvises nogen sammenhæng mellem motortype og olieforbrug. Dette
stemmer overens med resultatet af en større spørgeskemaundersøgelse, som Dansk Fjernvarme har gennemført i
forbindelse med projektet. Undersøgelsen omfattede en opgørelse af olieforbrug og -type fra ca. 100 gasmotorer.
Der synes heller ikke at være nogen sammenhæng mellem motortype og emissionen af partikelmasse, partikelantal,
eller indholdet af olie i de emitterede partikler.
Partikelemissioner ved forskellige motorindstillinger
For at undersøge, hvad typiske motorindstillinger betyder for partikelemissionen, blev der på anlæg E udført en
række forsøg, dels hvor motorens luftoverskud (λ) blev ændret, og dels hvor motorens tændingsvinkel blev ændret.
En ændring af λ vil – ligesom en ændring af tændingsvinklen – ændre NOX koncentrationen, og det var formålet at
undersøge, hvordan en ændring af NOX emissionen ville påvirke partikelemissionen. Figur 2 viser gennemsnittet af
to identiske forsøgsrækker, hvor partikelantallet i udstødningen er målt som funktion af NOX koncentrationen. Den
stiplede linje viser summen af faste og flygtige (olie) partikler (PN(total)), og den sammenhængende linje viser
koncentrationen af de faste partikler (PN(solid)).
Figur 2: Partikelantallet som en funktion af NOx koncentrationen fra en gasmotor på kraftvarmeværk E. I venstre plot ændres
NOx koncentrationen ved at variere luft / brændstof forholdet. I det højre plot indstilles NOx koncentrationen ved at variere
tændingsvinklen.
Det er tydeligt, at der er en signifikant stigning i partikelkoncentrationen, når NOX koncentrationen øges ved
ændring af tændingsvinklen, men at denne stigning ikke forekommer i samme grad, når NOX stigningen styres
ved ændring af λ. Dette er en vigtig information i forbindelse med begrænsning af partikelemissioner. En
ændring af tændingsvinklen, der halverer NOx koncentrationen fra en gasmotors normale driftspunkt vurderes jf.
figur 2 at medføre en halvering af partikelemissionen. Dette vurderes at koste op til 1 % point elvirkningsgrad.
Trods et tab i elvirkningsgraden er der for kraftvarmeværkerne et incitament til at reducere NOx emissionen ved
at ændre tændingsvinklen på gasmotorerne, idet tabet i elvirkningsgrad i et vist omfang vil kunne udlignes af en
reduceret NOx afgift. Ved ændring af tændingsvinklen har anlæggene således mulighed for både at opnå en NOx
reduktion og en reduktion i partikelemissionen.
Partikelemissioner før og efter udførelse af service på gasmotoren
På et af de fem anlæg blev der udført en målekampagne før og efter, at der blev udført en omfattende service på
motoren. Denne service, der bliver udført af motorleverandøren efter 25.000 timers driftstid, omfatter bl.a.
udskiftning af motorens stempelringe og foringer. Målingen efter service blev først udført efter cirka 500
driftstimer for at sikre, at udskiftede reservedele var kørt ind og motorens drift dermed stabiliseret. Det totale
partikelantal fra motoren øgedes fra 1,31  106 partikler/cm³ før service til 8,81  106 partikler/cm³ efter service,
2 af 3
og massekoncentrationen (PM1) steg fra 0,17 mg/m³ før service til 0,26 mg/m³ efter service. På trods af, at disse
tal er markant forskellige, er de begge inden for de koncentrationsområder, der observeres under normal drift af
gasmotorer undersøgt i dette arbejde.
Figur 3 viser den gennemsnitlige partikelstørrelsesfordeling før hhv. efter service på motoren.
Figur 3. Partikelantal og masse målt som funktion af partikelstørrelse før og efter udførelsen af en omfattende
service på motoren.
Som det kan ses ud fra Figur 3, er der ikke stor forskel i partikelstørrelses populationer før og efter den udførte
service på motoren. Der synes dog at være en svag tendens til, at der opstår lidt færre store partikler (> 0,75 µm)
og lidt flere små partikler (< 0,75 µm) efter, at der er udført service på motoren.
Konklusion
Undersøgelsen viser, at gasmotorer på danske kraftvarmeværker under normal drift giver anledning til
partikelemissioner, der er af samme størrelsesorden som affaldsforbrændingsanlæg eller biomassefyrede
kraftvarmeværker, der er forsynet med velfungerende filterteknologier. Under uregelmæssig drift, eller under
opstart, vil der kunne opstå højere partikelemissioner. Det skal dog i den forbindelse nævnes at gasmotorer,
grundet deres status som relativt rene kraftværker, ofte ligger i byområder og ikke nødvendigvis har samme
skorstenshøjde som større energiproducerende anlæg. Der kunne ikke måles nogen sammenhæng mellem
partikelemissionen fra motoren og motortypen (Bergen RR og Wärtsilä), smøreolietypen, og partikelemissionen
var ikke væsentligt påvirket af, om der blev udført service på motoren.
En yderligere reduktion af partikelemissioner fra gasmotorer vil ud fra undersøgelsens resultater kunne opnås
ved at reducere tændingsvinklen. Mange gasmotoranlæg er i gang med at reducere deres NO x emissioner på
grund af NOx afgiften. Da denne reduktion blandt andet foregår ved justering af tændingsvinklen, er der
mulighed for at opnå en samtidig reduktion i partikelemissionen.
3 af 3
1.4
Utilization of project results
The results of the project will be transferred to:

Stakeholders in the field of engine manufacturers via
o An article in a Danish journal (Dansk Kemi, draft article in appendix 5)
o An international journal article (Environmental Science and Technology, draft
article in appendix 4).
o The project report

The research community in the field of aerosol science and engine design via
o The international journal article (appendix 4).
o Presentation of the project results on the 17th ETH-Conference on Combustion
Generated Nanoparticles, June 23th – 26th 2013, Zürich. (poster presentation, see appendix 6).
o Presentation of the project results on Electric Power Research Institute (EPRI)
Workshop: Air Quality Impacts of Natural Gas Combustion for Electricity
Generation, August 26 - 27, 2013, Palo Alto, CA, USA (oral presentation, paper presentation: See appendix 7).

The owners and operators of the Danish CHP plants via a Danish article (in the member’s journal “Dansk Fjernvarme”) (draft article attached in appendix 8).

The Danish EPA through the updated emission factors calculated for particle emissions from gas engines at Danish CHP plants.

The Danish laboratories and consultants performing emission measurements through
a presentation on the annual “Referencelaboratoriets workshop”, which will be held
on 4 Nov. 2013 at FORCE Technology, Brøndby.
It is expected that gas engine manufacturers will benefit from the recommended actions for
particle emission reduction, given in this project report, e.g. regarding the findings on the
possibility to reduce particle emissions through adjustment of ignition timing.
FORCE Technology intends to use the knowledge obtained in the project in further assistance
to engine manufacturers on emission control and reduction. The results will be marketed
through direct contact to engine manufacturers and manufacturers of particle reduction
technologies, and through publication of articles and presentation on conferences.
The articles for publication in Environmental Science and Technology and Dansk Kemi have
been submitted and are attached in draft form to this report as appendix 4 and 5. The ETH
Conference poster and EPRI abstract paper are attached as appendix 6 and 7.
1.5
Project conclusion and perspective
The results obtained showed that:

No significant differences could be found between the particle emissions from the two
involved engine types (Bergen Engines and Wärtsilä).

When an engine is well maintained and service checks are performed regularly,
overall particle mass and number emissions do not vary strongly before and after the
performance of an engine service. This study also indicates that for a given engine
type and design there is a lower limit to the level of particle mass and number emissions attainable, beyond which no further reduction of particle emission can be
achieved by engine tuning. This minimum “base level” is assumed to depend highly
on the efficiency of parts that ensure a minimum loss of lubrication oil to the combustion chamber or through crankcase ventilation (such as gaskets, and piston
rings).
166

For the four different lubrication oils that were used at the five different plants, no
significant correlation could be found between the particle emissions and the type or
age of lubrication oil.

Due to the lack of information on additives in the lubrication oil, it was not possible
to correlate the measured particle emissions to specific additives in the lubrication
oil. However, results from analyses of metals in lubrication oil samples could be well
correlated with metals analyzed in the particles emitted from the engine. This confirms that e.g. Ca, Mg and Si in lubrication oil additives will occur in particles emitted
from the engine. A weak correlation was found between the density and viscosity of
the lubrication oils and the measured emission of uncombusted hydrocarbons (UHC)
– the higher the density (and the higher the viscosity) of the lubrication oil, the lower
the emitted concentration of UHC. It is concluded that for engines that are properly
maintained, and for lubrication oils that are controlled within the required specifications, lubrication oil type and composition seem to have a minor effect on particle
emissions.

Measurements showed that 50% - 80% of the number of particles emitted consisted
of volatile material, most likely deriving from uncombusted lubrication oil components. This share is equivalent to 30% - 60% of PM1.

From oil mist measurement at the five plants, it is concluded that during normal operation, the majority of the oil consumed by the engine is combusted in the engine
(or trapped in the exhaust system), and that only a minor fraction of the oil consumed will appear in the exhaust gas as vapor or liquid oil particles. The measured
emissions of oil mist was significantly lower than that found in studies from Danish
CHP gas engines in 2001 /ELTRA rapport/. The reason for this may partly be a reduced oil consumption in the engines, and partly due differences in measurement
procedures for determination of oil mist.

A silicon carbide (SiC) filter would probably be highly efficient for removal of ultrafine
particles, but due to the financial implications, SiC filters are not seen as an immediate solution for gas engines on CHP plants. Silicon carbide filters have been developed for use in diesel engines, and particles from CNG engines have a lower PM level
and a higher ash level as compared to diesel engines. Therefore, back pressure effects, and type and frequency of regeneration of the filter should be investigated before a SiC filter can be installed at a gas engine fired CHP plant.

The effect of the adjustment of lambda (surplus air ratio) on particle emissions is
limited. No significant effect on was found on neither PN nor PM during an extensive
4 day measurement program at plant E.

It is possible to reduce particle emissions from gas engines by adjusting the ignition
timing. By adjusting BTDC, particle emissions can be reduced by up to a factor of 5.
In this study, it is concluded that through a change in BTDC, a reduction in the NOx
concentration by about 50% (from e.g. 600 mg NOx/m³ to 300 mg NOx/m³), a simultaneous reduction in both PN and PM emissions by ~50% will be obtained. This was
obtained by reducing BTDC from about 13.5 to 11.5 on the plant E engine. The required adjustment in BTDC for this reduction in NOX and particle emissions will cost
about 1% loss in the engine efficiency. For a CHP plant gas engine, the loss in electricity production may to a certain extent be counterbalanced by a gain in heat production. However, this has not been investigated in this study.

Due to the recently introduced levy on NOX emissions introduced by the Danish government, a number of the CHP plants are currently adjusting their gas engines in order to reduce lower NOX emissions. This NOX reduction is typically obtained through
167
an adjustment of ignition timing and the surplus air ratio (lambda). The extent to
which the ignition timing is adjusted is dependent on the economy, i.e. the engine
operation will be adjusted in order to minimize the loss in efficiency. It may be concluded that CHP plants that are presently reducing their NOX emissions will most
probably also obtain a significant reduction in particle number and mass emissions.
From the results in this study, it is expected that the reduction in particle emissions
will depend on the extent to which NOX reduction is obtained through the adjustment
of ignition timing.
1.6
Updating Financial Appendix and submitting the final report
The Financial Appendix will be updated with the financial numbers for the entire project
within a period of 6 weeks from the finalization of the project, upon which the financial numbers will be uploaded at www.forskel.dk. This project report has also been submitted on
www.forskel.dk.
168

Emissions of particles from gas engine powered CHP

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