The Vincent Piatti Story - Twinspin Engine Consultants

Transcription

The Piatti Story
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THE PIATTI STORY
by
Ben Shannon
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The Piatti Story
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Published in electronic form 2006
All rights reserved by
Twinspin Engine Consultants LLC
Canadian Lakes, Michigan 49346
www.twinspin-ec.com
[email protected]
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The Piatti Story
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Table of Contents
I.
II.
III.
IV.
V.
VI.
FOREWORD
BACKGROUND
EXECUTIVE SUMMARY
INTRODUCTION
SIGNIFICANCE
ENGINE TEST RESULTS
•
Twin Cylinder
- High Output Version I
- Version II
•
Ford Piatti 2.3L Inline Four Cylinder Comparison
- Airflow Comparison
- Full Load Performance
- Part Load Emissions and Specific Fuel Consumption
- Full Load Performance behavior to various four valve engines
- Full Load Performance behavior to various two valve engines
•
U of M Single Cylinder Combustion Studies
HEMISPHERICAL vs TWINSPIN
- Part Load Performance - Emissions & Fuel Consumption
1580 rpm & 48 imep-psi
2370 rpm & 72 imep-psi
- Cross-sectional Fuel Consumption TwinSpin Chamber
•
Piatti - Triumph - May Combustion System
Power & Thermal Efficiency
- Part Load Performance
Fuel Economy
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TABLE
1.
ENGINE PERFORMANCE SUMMARY
ILLUSTRATIONS
Figure 1.
Figure 2.
Figure 3.
Figure 4
Figure 5.
Figure 6/7.
Figure 8.
Figure 9.
Figure 10
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15/16
Figure 17/18.
Figure 19/20.
Figure 21/22.
Figure 23/24.
Figure 25
Figure 26/27.
Figure 28.
Figure 29/30.
Figure 31/32.
Figure 33.
Figure 34/35.
Figure 36/37.
Figure 38/39.
VINCENZO PIATTI
THE UNITED STATES OF AMERICA PATENT
TWIN CYLINDER HIGH OUTPUT - Full Load Comparison
THERMODYNAMIC CONSIDERATIONS
CYLINDER HEAD DESIGN TREE
FULL LOAD PERFORMANCE - Honda - BMW - Piatti
HIGH OUTPUT TWIN CYLINDER BEING ASSEMBLED
HIGH OUTPUT TWIN CYLINDER
TWIN CYLINDER VALVETRAIN COMPONENTS
CYLINDER HEAD CROSS-SECTION - Version II
CONSIDERATIONS IN ENGINE DESIGN DEVELOPMENT
FULL LOAD PERFORMANCE VERSION II
FORD PIATTI 2.3L SOHC TWINSPIN CYLINDER HEAD
RATE OF AIRFLOW THROUGH CONDUIT.
2.3L FULL LOAD PERFORMANCE BEHAVIOR
2.3L PART LOAD EMISSIONS AND FUEL CONSUMPTION
COMPARISON OF FULL LOAD PERFORMANCE
BEHAVIOR OF VARIOUS FOUR VALVE ENGINES
COMPARISON OF FULL LOAD PERFORMANCE
BEHAVIOR OF VARIOUS TWO VALVE ENGINES
SINGLE CYLINDER COMBUSTION CHAMBER BEHAVIOR
FULL LOAD PERFORMANCE BEHAVIOR COMPARISON
PART LOAD SPECIFIC FUEL CONSUMPTION BEHAVIOR
COMPARISON OF EMISSIONS AND FUEL CONSUMPTION
FOR VARYING AIR-FUEL RATIOS, 1580 RPM, 48 IMEP,
AND 10/20% EGR
COMPARISON OF EMISSIONS AND FUEL CONSUMPTION
FOR VARYING EGR, 1580 RPM, 48 IMEP, 16:1 AND 20:1
AIR-FUEL RATIOS
COMPARISON OF COMBUSTION DURATION
COMPARISON OF MASS FRACTION BURN
COMPARISON FULL LOAD PERFORMANCE
COMPARISON PART LOAD FUEL CONSUMPTION
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Piatti and his Combustion System
The Man Who Knew
Bugatti
I. FOREWORD
Vincenzo (Vincent) Piatti’s (Figure 1.) very first job was with none other than Ettore
Bugatti and, was the first researcher to identify “Tumble” (fluid motion during the
cylinder filling process) which Piatti named (Figure 2.) “TwinSpin”. Remarkably, he is
still actively working on combustion chambers, valve mechanisms, manifolding and,
several of his Patented ideas are employed by major companies throughout the world.
Piatti is strongly drawn to this blend of the theoretical and the practical approach, saying
“I learned to be pragmatic in England. French engineering is Cartesian, very theoretical you start from first principles - but sometimes you never get to the end! So you must be
empirical - but believe in the theory!” Today, Vincent Piatti is enthusiastically pursuing
his “Twin Cylinder” engine, and once again, has identified an improved version of his
original “TwinSpin” combustion chamber which he has named “CONVERGENT
TWINSPIN” or “CONVERGENT TUMBLE”.
The high output Version I
(“Convergent TwinSpin”) Twin Cylinder engine has been tested and certified at the Piatti
test laboratory in Milano, Italy. These data have been compared to the European BMW M3 and Honda VTEC engines and, are shown in Figure 3.
Figure 1
Figure 2
Vincenzo Piatti - he came to England in 1949 and patented the TSCC idea, and on January 11, 1972
in the United States of America.
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Full Load Performance
Comparison
220
BMEP - psi
200
180
160
140
120
0
1
2
3
4
5
6
7
8
9
10
ENGINE SPEED - rpm (1000)
Figure 3 Comparison of Full Load Performance
II. BACKGROUND
Development work on the Piatti combustion system started in 1971 with a single cylinder
engine to explore the potential of various combustion chamber shapes. This work led to
the Piatti patented combustion system which was subsequently proven on a four cylinder
production block. The Piatti patents cover two fundamental aspects of the system:
1. A controlled vortex generation combustion chamber design which offers the
following advantages:
a.
Positive direction of all unburned combustible material in the combustion chamber
towards the developing flame front.
b.
Absolutely central spark plug location to ensure minimal flame paths.
c.
High thermal and combustion efficiency through the use of minimal surface-tovolume ratios for the combustion chamber.
d.
Complete combustion control to provide low octane sensitivity without recourse to
excessive flame quench areas in the combustion chamber.
e.
High volumetric efficiency and excellent scavenging efficiency to ensure very low
specific fuel consumption.
f.
Minimal stratification of the fuel-air charge in the combustion chamber, thus
lending unusual lean burn capability to the engine.
g.
Simplicity of manufacture and adaptation to production engine designs.
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2.
A novel valve actuation mechanism which provides:
¾
Large tappet area to facilitate broader latitude in camshaft profile design and
optimization of the engine aspiration processes to minimize pollution without
sacrificing power, performance and fuel economy.
¾
Simplification of the valve actuation mechanism for multiple valve operation.
The Piatti patented designs are based upon a four valve per cylinder (two inlet and two
exhaust) double hemisphere combustion chamber configuration which provides excellent
charge mixing and combustion with simplicity of manufacture and adaptation to
production engine block designs.
This unique design, which can be applied to any existing four stroke internal combustion
engine, has been tested under laboratory conditions at both an automotive manufacturer’s
facilities, University of Michigan automotive test laboratory, and subsequently in road
vehicles.
III. EXECUTIVE SUMMARY
The fast paced technology development in small internal combustion petrol engines is
expected to continue well into the 21st Century. In recent years as smaller automotive
powerplants have found increased application to more fuel efficient passenger cars, a
renewed effort to enhance the engine’s torque output throughout the speed range has
occurred. The design of the combustion chamber, induction and exhaust systems
represents a key area in which the automotive engineer can significantly influence engine
performance, fuel consumption and exhaust gas emission behavior.
This paper presents the consensus of not only Twinspin A.G. but also of many wellknown researchers and engine design designers throughout the world.
Alternative engines such as stratified charge, TDI diesel, rotary and two stroke cycle, are
not expected to capture significant shares of the small car market segment by the year
2010. The diesel share in Europe is expected to grow faster than in the U.S.. For high
volume small cars the dominant engine will continue to be the conventional gasoline
engine with an I-4 configuration. The combustion chamber will feature both faster and
more consistent combustion, and high torque (NM/L) capabilities throughout the speed
range.
The Piatti “TWINSPIN” designs are based upon a four valves per cylinder double
hemispherical combustion chamber configuration which provides excellent charge
mixing and combustion with simplicity of manufacture at low cost and adaptation to
production engine block design. The advantages of both faster and more consistent
combustion with “TWINSPIN” has produced excellent results running air-fuel ratios as
lean as 25:1 and showing EGR tolerance at rates up to 40 percent on an I-4 engine
configuration. This is achieved through reduced inter-cyclic variation without the
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disadvantages of excessive flame quench and high rates of heat-loss which are usually
associated with conventional high swirl systems.
Recently, Piatti has improved the “TWINSPIN” combustion chamber. This latest
technology “CONVERGENT TWINSPIN” or “CONVERGENT TUMBLE” has shown
remarkable results with specific fuel consumption numbers in the diesel class and,
requires substantially (15 @ MBT) less spark advance than other combustion systems.
In summary, the specific output of the Piatti “TWINSPIN” system is outstanding
throughout the speed range compared to any competitive engines tested to date; it also
demonstrates excellent specific fuel consumption, both fast and more consistent
combustion, resulting in ultra lean mixture strengths and showing high EGR tolerance.
Practical operation is made possible of a lean-burn engine with fuel economy comparable
with that of diesel engines, and with low levels of exhaust emissions as shown, without
exhaust gas treatment.
IV. INTRODUCTION
During the last three decades, combustion engine research and development have
concentrated on reducing the emissions of noxious exhaust components and improving
fuel economy, while maintaining its integrity at full load performance. These objectives
though with changed priority combined with measures for noise reduction will continue
to influence engine development in the foreseeable future.
Reductions of fuel consumption between 15 and 30 percent can be obtained by focusing
the entire engine design on maximum (global) efficiency. In the development of a new
engine the so-called design parameters, i.e.

displacement
number of cylinders
compression ratio
stroke to bore ratio
combustion chamber layout
having a decisive influence on the actual character and behavior of an internal
combustion engine. These design parameters must be selected in a way so as to improve
fuel economy, exhaust emissions and specific output throughout the speed range of the
engine. Shown in Figure 4 are an interaction between different parameters and
combustion chamber shape.
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THERMODYNAMIC CONSIDERATIONS
. Power Density
. Torque Characteristics
. Quality of Operation
. Number of Valves
. Valve Size
. Valve Arrangement
. Valve Lift Control
. Valve Timing Control
. Stroke/bore Ratio
. Connecting Rod Length
. Compression Ratio
. Fuel Consumption
. Exhaust Emissions
. Spark Plug Location
. Squish Area
. Squish Location
. Squish Clearance
. Intake Port
Arrangement
. Swirl Type
. Charge Mixing
COMBUSTION CHAMBER SHAPE
. Dish in Piston
. Bath Tub
. Wedge
. Hemi-Spherical
. Pentroof
. Twinspin
Figure 4 Thermodynamic Considerations
Since the properties of a combustion engine are largely dependent on the combustion
process the design of the combustion chamber, which is the core of any engine, is of
paramount importance.
In the history of combustion engines, the effects of the combustion chamber shape have
been repeatedly investigated mainly with view to optimizing the combustion efficiency.
Despite numerous investigations and forecasts, the classical reciprocating engine will
continue to prevail as a principle propulsion system for motor vehicles. This means that
there will not be any substantial modifications to the basic concept of an internal
combustion engine, and the known fundamental features of the combustion chamber
design will be maintained. Combustion chamber development (Figure 5) will be focused
on working out a more efficient compromise between the requirements of specific power
throughout the speed range, fuel consumption and exhaust emissions. Reducing fuel
consumption respectively improving engine efficiency will play a predominant role in the
future.
Coming engine generations will have to be equipped with combustion chambers ensuring
knock-free operation with relatively high compression ratios and lean air-fuel mixtures.
Completely new prospects for combustion chamber layout are offered by “Convergent
TwinSpin” configurations. Investigations on single cylinder research engines have
shown, fuel consumption as well as HC and NOX emissions can be substantially reduced
as compared to other combustion chamber configurations, provided that combustion
chamber shape, valve timing and compression ratio are correctly tuned.
The refinement must begin with the combustion process and that design evaluation must
work outwards from the centre, but without increasing total system cost, service
requirements or gross additional investment; i.e., design priorities must be considered in
the following order:
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Combustion process.
Inlet ports, manifolds, exhaust ports and manifolds.
Camshaft profiles
Carburetion / fuel injection and ignition.
Fuel type
Total harmonization of the system to provide ultimate engine
efficiency and exhaust gas cleanliness.
These design priorities (PROCESS) will enable the engine researcher to achieve an
outstanding global (Kj/dm3) efficiency throughout the speed range and, hence, the
smallest possible (displacement) powerplant for a given vehicle weight, which will then,
achieve additional vehicle fuel consumption.
Cylinder Head Design Tree
Power - Torque - Speed
BSFC - HC & Nox
EMISSIONS
INTAKE PORT DESIGN
COMBUSTION
AIR FLOW - SWIRL & TUMBLE
INTAKE TURBULENCE
LEAN LIMIT - BURN RATE
OCTANE REQUIREMENT
?
TWO VALVES
THREE VALVES
Two Intake
or
Two Exhaust
Canted
Paralled
FOUR VALVES
Two Inlake
&
Two Exhaust
MULTI VALVES
Intake 2 or 3
Exhaust 2 or 3
Shannon
1983
Figure 5 Cylinder Head Design Considerations
V. SIGNIFICANCE
In the demanding world of automotive design the powerplant in the future will play more
of an important role, especially in small sub compact automobiles. During the past three
decades engine technology has made major steps, and it is a perfectly reasonable and
rational belief that technology will continue, well into the 21st Century.
The Piatti designs are based upon a four valve per cylinder (two inlet and two exhaust)
and, an unique double hemisphere combustion chamber configuration which provides
excellent charge mixing and combustion with simplicity of manufacture and adaptation to
production engine block designs. The fitting of this “CONVERGENT TUMBLE”
cylinder head and piston provides more power throughout the speed range, greater engine
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flexibility with extended gasoline mileage, and lower emission levels than possible with
standard cylinder head designs.
This unique combustion chamber design, which can be applied to any existing four stroke
engine cycle petrol engine, has been tested under laboratory conditions at an automotive
manufacturers facility, and at a major University laboratory.
Vincenzo Piatti has spent a life long career designing and developing the combustion
chamber for an internal combustion engine. As previously stated, Piatti was the first
researcher to identify “TUMBLE”, while other researchers within the automotive
industry openly stated that there was no such thing, and that it was not possible to
maintain this type of vertical swirl within the combustion chamber. It was not until
Ricardo, years later, identified “TUMBLE” did the automotive world except this type of
vertical swirl as being superior over the conventional swirl rotation around the cylinder
axis. An internal combustion engine requires fluid motion during the cylinder filling
process and, hence, higher turbulent intensity with improvement in EGR tolerance,
specific fuel consumption and specific power output.
Piatti identified “TUMBLE” three decades ago, and today he has identified
“CONVERGENT TUMBLE” which is an improvement over his original combustion
chamber, showing improvement in combustion and specific fuel consumption.
VI. ENGINE TEST RESULTS
Twin Cylinder - High Output Version I
Recently, a Twin Cylinder was designed with a bore and stroke of 78.40 mm by 72.00
mm, respectively. Figure 6 graphically depicts the brake mean effective pressure and
shows the specific output (PS/L) of the Piatti Twin Cylinder engine as compared to the
BMW - M3 with variable intake camshaft phasing, and the Honda VTEC powerplants.
The specific output of the Piatti Twin Cylinder engine with “Convergent Tumble”
compares favorable to these competitive engines tested. In addition, the Twin Cylinder
shows outstanding bmep throughout the speed range and demonstrates and excellent
specific fuel consumption as shown in Figure 7.
Comparison
220
BMEP - psi
200
180
160
140
120
0
1
2
3
4
5
6
7
8
9
10
ENGINE SPEED - rpm (1000)
Figure 6 Comparisons of brake mean effective pressure
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Comparison
TWINSPIN
BMW
HONDA
Figure 7 Comparison of brake specific fuel consumption
The Piatti engine build laboratory in Milano, Italy (Figure 8) showing Piatti building his High
Output Twin Cylinder engine, Figures 9/10 depict Twin Cylinder with carburetion and valvetrain
components, respectively.
Figure 8
Twin Cylinder being Assembled
Figure 9
High Output Twin Cylinder
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Figure 10 Twin Cylinder Valvetrain Components
VII. ENGINE TEST RESULTS
Twin Cylinder - Version II
More recently, version II cylinder head was designed for the 45 hp insurance class. The
cylinder head and valvetrain as shown in Figure 11 was designed for high volume
production, keeping in mind low cost and taking into account considerations in engine
design as shown in Figure 12.
Figure 11 Version II Cylinder Head Cross- Section
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LOW EXHAUST GAS EMISSIONS
LEGISLATIVE
REGULATIONS
LOW FUEL CONSUMPTION
LOW NOISE LEVEL
HIGH POWER DENSITY
& COMPACTNESS
COMPETITION
LOW WEIGHT
HIGH ACCELERATION
& GOOD DRIVEABILITY
GOOD TRANSIENT OPERATION
CUSTOMER
INTEREST
and
DESIRES
CORPORATE
GOOD STABILITY / DURABILITY
LOW MAINTENANCE COSTS
LOW MANUFACTURING COSTS
Figure 12 Considerations in engine design development
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
100
"CONVERGENT TUMBLE"
IN-CYLINDER FLUID MOTION
90
80
70
60
50
40
30
Specific Output - hp per litre
Specific Torque - NM per litrel
Figure 13 depicts the full load performance throughout the speed range. This build
(Version II) shows outstanding specific torque and specific horsepower, showing 102
NM/L and 74 hp/L, respectively.
20
NM/L
10
hp/L
0
0
1
2
3
4
5
6
Engine Speed - rpm [1000]
Figure 13. Full Load Performance Version II
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2.3L Inline Four Cylinder
An investigation has been carried out on both SOHC and DOHC “TWINSPIN” spark
ignition engines to assess the performance, economy and exhaust emission behavior. The
work included comparing the “TWINSPIN” concept to various other four and two valve
engines.
The full load performance comparison shows that the “TWINSPIN” build (Figure 14.)
produced a higher maximum power output on 91 RON fuel and significantly higher bmep
throughout the speed range.
Although not shown graphically in this report, the “TWINSPIN” requires substantially
(18 @ MBT ) less spark advance when compared to the baseline engine.
In terms of a trade-off between fuel economy and emissions the “TWINSPIN” four valve
chambers was considerably lower than either the DATSUN or baseline chambers.
The “TWINSPIN” combustion system variants are well suited to achieve a high specific
power output in combination with high torque throughout the speed range, low fuel
consumption, reduced HC and NOX emissions and running air-fuel ratios as lean as 25:1
and showing EGR tolerance at rates to 40 percent on an 1-4 engine configuration.
Figure14 Ford Piatti 2.3 L SOHC Cast Iron Cylinder Head
Figure 15 to 22 illustrates the findings of both an European car manufacturer and
“TWINSPIN” A.G. when a “TWINSPIN” {SOHC) combustion Chamber was evaluated
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on their standard production engine block. Figure 13 depicts the rate of airflow through
the inlet conduit of the 2.3 litre 2-valve engine with that of the 4-valve engine, one can
see that the 4-valve design achieves an increase of 32 percent when comparing average
flow coefficients Cav. A similar improvement is achieved also in the exhaust conduit as
shown in Figure 16, which results in the gas cycle work being reduced, and an
improvement in Cav of 29 percent.
Figure15/16 Rate of Airflow through conduit
Figure 17/18 depicts the full load performance comparison characteristics of the 2.3 litre
(SOHC) 2-valve engine with that of the (SOHC) “TWINSPIN” 4-valve engine. The
results with the Piatti TwinSpin were excellent and not only showed a 47% power
improvement at 5500 rpm, but also torque (36% @ 4000 rpm) and specific fuel
consumption (10% @ 2500 rpm) improvement over the complete rpm range.
Figure 17/18 Comparison of 2.3L Full Load Performance
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Figure 19/20 depicts the part load fuel economy and exhaust emission characteristics.
Figure 19 shows that the BSFC vs. BSNOX curve of the 2.3 litre (SOHC) “TWINSPIN”
is substantially below the baseline 2.3 litre engine and in close proximity to the Datsun
fast burn engine which has higher mechanical efficiency. Figure 20 shows a similar
improvement in BSHC vs. BSNOX. A BSFC advantage of 4 percent is attributed to the
lower friction levels of the Datsun engine.
Figure 19/20 Comparison of BSFC, BSNX, BSHC at 1500 rpm, 38 BMEP
Figure 21/22 depicts the full load performance comparison characteristics of both SOHC
and DOHC 4-valve engines. Five back-to-back assessments were conducted on 91 RON
fuel with mixture strength setting for LBT and ignition timing for MBT. These settings
were adjusted for maximum power at each increment of speed. The result with the Piatti
TwinSpin concept was excellent (Figure 21) when compared to the conventional Pentroof
4-valve combustion chamber design. The results with the three “TWINSPIN” chambers
showed excellent bmep improvement over the whole rpm range. A similar improvement
is achieved in specific fuel consumption (Figure 22) when compared to the Pentroof 4valve chamber design.
Figure 21/22 Comparison of brake mean effective pressure and brake specific fuel consumption for
four valve engines
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Figure 23/24 depicts the full load performance comparison characteristics of SOHC 2valve engines. For comparison with the baseline engine two Japanese fast burn engines
were evaluated. Both Japanese engines showed excellent bmep (Figure 23) improvement
over the baseline engine. The major reason for the improved bmep of the Japanese
engines is the volumetric and mechanical efficiency characteristics. Figure 24 shows a
similar improvement in specific fuel consumption for the Datsun when compared to the
baseline engine. A bsfc advantage of 4 percent is attributed to the lower friction levels of
the Datsun engine.
Figure 23/24 Comparison of brake mean effective pressure and brake specific fuel consumption for
two valve engines
Summarizing the results, they showed:
1. The overall results with the Piatti “TWINSPIN” combustion chamber, shown in
Table 1. were excellent when compared to other 4-valve and 2-valve engine. It
should be noted; the 2.3 litre Ford Piatti TwinSpin achieved its objectives on the
first Full Load Performance and Part Load Performance test. These data were
obtained at Ford Motor Company’s dynamometer testing facility at Dearborn,
Michigan without further development by Ford Motor Company.
2. Confirmation of high burn rates with the “TWINSPIN” system, i.e. maximum
power spark advance was reduced by 18 deg. Crank angle when compared to the
baseline engine.
3. Specific fuel consumption was excellent over a wide range of engine operation.
4. The bmep curves were outstanding throughout the speed range.
5. Emissions were low.
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Table 1
2.3L SOHC BASELINE
2.3L SOHC TWINSPIN
2.0L SOHC DATSUN
2.4L SOHC TOYOTA
2.0L DOHC TWINSPIN
1.6L DOHC TWINSPIN
2.0L SOHC TRIUMPH
2.5L DOHC FORD
ENGINE PERFORMANCE SUMMARY
No. Valves
MAXIMUM MAXIMUM MINIMUM
per Cyl.
C.R.
bmep @ rpm
bhp @ rpm
bsfc @ rpm
2
9.0:1
133 @ 3000
96 @ 5000
206 @ 2500
4
8.7:1
173 @ 4000
138 @ 5300 186 @ 2500
2
8.5:1
151 @ 2500
92 @ 5200
196 @ 2500
2
8.5:1
144 @ 3000
107 @ 5000 203 @ 3500
4
9.3:1
160 @ 3000
127 @ 5500 184 @ 3000
4
10.0:1 173 @ 5000
125 @ 6000 178 @ 3500
4
9.5:1
157 @ 4500
122 @ 5500 209 @ 4500
4
9.0:1
154 @ 4500
156 @ 6000 211 @ 4500
Mixture strength - LBT and Ignition timing - MBT.
Adjusted for maximum power at each increment of speed.
FUEL
SYSTEM
CARB.
CARB.
CARB.
CARB.
CARB.
INJ.
CARB.
INJ.
University of Michigan Single Cylinder Combustion Studies
Compact combustion chambers for petrol engines are desirable for many reasons.
Combustion efficiency and fuel consumption are optimized, while knock resistance is
improved; and hydrocarbon emissions are reduced due to the low surface/volume ratio of
the chamber. Compact combustion chambers are achieved by designing engines with
low bore/stroke ratios. However, in the past, due to the practical sizes of engine cylinders
and intake valves, long strokes have compromised the engine breathing and maximum
power so that average bore/stroke ratios have been greater than one. If four valve
cylinder heads were adopted instead of two valves per cylinder, the breathing limitation
would be removed; and bore/stroke ratios could be reduced below one. The final result
could show advantages for the four valve head in a number of areas.
1. Better fuel consumption for the four valve head due to reduced heat transfer losses to
the cylinder head and a higher compression ratio.
2. Lower hydrocarbon emissions due to a reduced surface/volume ratio of the
combustion chamber and a larger proportion of the combustion chamber not in direct
contact with the coolant.
3. A reduction in engine friction due to lower forces on the reciprocating and rotating
components. Also, a reduction in engine friction due to reduction in pumping losses
with improved breathing.
4. The four valve engine is reputed to have a higher misfire air-fuel ratio. If this is
proved to be correct, the engine could have gains in Nox and CO emissions under
vehicle driving conditions.
5. Bore/stroke ratios below one improve low end torque due to higher volumetric
efficiencies at the lower speeds.
The combustion chamber is the heart of the engine. The world-famous combustion
expert, Westlake, even designs them in the shape of a heart in the early 1940’s.
However, despite the millions spent on combustion research during the past three decades
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sto find the ideal shape, there is still no conformity. We can, at least, formulate a set of
rules that can eliminate poor designs. The major factors that influence the knocking
behavior of an engine, the mechanical octane’s that the designer can build into his engine,
are as follows:
(a) The path to be traversed by the flame-front must be as short as possible.
(b) The distance between the spark plug and the exhaust valve must be kept short.
(c) The end-gas must be in the coolest part of the chamber.
(d) The correct amount of turbulence and the type of turbulence must be designed
into the head.
Therefore, an investigation to study various combustion chambers shapes was conducted
at the University of Michigan. The combustion chamber shapes were as follows:
o
o
o
o
Wedge Combustion Chamber
Hemispherical Combustion Chamber
Pentroof Combustion Chamber
Twinspin Combustion Chamber
The full load performance of the
Four combustion chamber, are
Shown in Figure 25
Combustion Chamber Comparison
University of Michigan
TWINSPIN CHAMBER
PENTROOF CHAMBER
HEMISPERICAL CHAMBER
WEDGE CHAMBER
Figure 25 Comparison of various combustion chamber shapes.
Figure 26/27 The Full Load Performance - TWINSPIN vs HEMISPERICAL
Combustion Chamber Behavior
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Figure 28 Comparison of Part Load Specific Fuel
Consumption, 2000 rpm, varying BMEP
Figures 29/30 Comparison of emissions and fuel consumption for varying air-fuel ratios,
1580 rpm, 48 IMEP, and 10/20% EGR.
Figures 31/32 Comparison of emissions and fuel consumption for varying EGR,
1580 rpm, 48 IMEP, 16 and 20:1 air-fuel ratios.
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Figure 33 Comparison of combustion duration (10-90%),
1580 rpm, 48 IMEP, MBT spark advance
and 0.92 Equivalence ratio.
Figures 34/35 Comparison of mass fraction burned curves for TWINSPIN vs HEMISPHERICAL
combustion chambers, for varying EGR, 1580 rpm,48 IMEP, 0.92 Equivalence ratio.
Piatti Combustion System - Triumph - May Combustion System
For comparative studies the Piatti TwinSpin combustion system was investigated in 1976.
The three engines were as follows:
- Triumph Dolomite
9.5:1 C.R.
- Saab “Piatti Combustion System”
9.3:1 C.R.
- VW “May Fireball Combustion System” 16.0:1 C.R.
Figures 36/37 graphically depict the specific output (HP/in3) and thermal efficiency of the
above engines. The Piatti TwinSpin Combustion System shows greatly improved
specific output throughout the speed range, while similar thermal efficiency to the “May
Fireball Combustion System” at 16.0:1 compression ratio.
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The Piatti Story
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40
1.2
Brake Thermal Efficiency - %
Specific Horsepower - hp / cu. in.
38
1
0.8
0.6
0.4
0
34
32
30
28
26
24
Piatti SAAB - 9.3:1 C.R.
Triumph Dolomite 9.5:1 C.R.
May Combustion Process 16:1 C.R.
0.2
36
Piatti SAAB - 9.3:1 C.R.
Triumph Dolomite 9.5:1 C.R.
May Combustion Process 16:1 C.R.
22
20
0
1
2
3
4
5
6
0
7
1
2
3
4
5
6
7
Engine Speed - rpm [1000]
Engine Speed - rpm (1000)
Figure 36/37 Comparison of Specific Output and Thermal Efficiency
Figure 38 graphically depict the part load fuel economy of the above powerplants. The
specific fuel consumption (Lb/obhp-hr) shows an improvement of 8.2 percent at 2000
rpm when compared to the Triumph engine and comparable to the May Combustion
System at 16.0:1 compression ratio. Also, Piatti’s engine shows an improvement
(specific fuel consumption) of 11.6 percent at 4000 rpm when compared to the Triumph
powerplant, and comparable to the higher compression ratio May Combustion System.
PART LOAD FUEL ECONOMY
Piatti SAAB - 9.3:1 C.R. [2000 & 4000 rpm]
Triumph Dolomite 9.5:1 C.R. [2000 rpm]
May Combustion Process 16:1 C.R. [2000 rpm]
BSFC - Lb / obhp-hr
Triumph Dolomite 9.5 C.R. [4000 rpm]
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
4000 rpm
2000 rpm
4000 rpm
0
10
20
30
40
50
60
70
BMEP - psi
Figure 38 Comparison of Part Load Fuel Economy
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The Piatti Story
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0.8
PART LOAD
FUEL ECONOMY
Piatti Saab
BSFC - Lb / obhp-hr
Triumph Dolomite
May VW
0.7
0.6
0.5
2000 rpm
26.5 bmep - psi
3000 rpm
38.7 bmep - psi
4000 rpm
57.9 bmep - psi
0.4
Figure 39 Comparison of Part Load Fuel Economy
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