Internal Combustion Engines

Transcription

Lecture-13
Prepared under
QIP-CD Cell Project
Internal Combustion Engines
Ujjwal K Saha, Ph.D.
Department of Mechanical Engineering
Indian Institute of Technology Guwahati
1
Gasoline Injection
In a multi-cylinder engine with a carburetor, it
is difficult to obtain a uniform mixture in each
cylinder. The various cylinders receive the airgasoline mixture in varying quantities and
richness. This problem is called the maldistribution and can be solved by the port
injection system by having the same amount of
gasoline injected at each intake manifold.

By adopting gasoline injection each cylinder
can get the same richness of the air-gasoline
mixture and the mal-distribution can be
avoided to a great extent.

2
Typical pattern of mixture distribution
in a multi-cylinder engine
3
Reasons for Gasoline Injection
To have uniform distribution of fuel in a
multi-cylinder engine
To improve the breathing capacity and
hence the volumetric efficiency
To reduce or eliminate detonation
To prevent fuel loss during scavenging in
case of two-stroke engines

Types of Injection Systems
Gasoline direct injection (GDI)
Port-Injection
(a) Timed
and
(b) Continuous
Manifold Injection
4
Groupings
The above fuel injection systems can be
grouped under two heads,viz., single-point
and multi-point injection. In the single point
injection system, one or two injectors are
mounted inside the throttle body assembly.
Fuel sprays are directed at one point or at
the center of the intake manifold. This type is
also known as throttle body injection.
Multipoint injection has one injector for each
engine cylinder, where fuel is injected in
more than one location. This is somewhat
more common and is often called port
injection system.
5
Continuous Injection Systems
This system usually has a rotary pump.
The pump maintains a fuel line gauge
pressure of about 0.75 to 1.5 bar. The
system injects fuel through a nozzle
located in the manifold immediately
downstream of the throttle plate. In a
supercharged engine, fuel is injected at
the entrance of the supercharger. The
timing and duration of the fuel injection is
determined by Electronic Control Unit
(ECU) depending upon the load and
speed.
6
Timed Injection Systems
This system has a fuel supply pump
which sends fuel at a low pressure of
about 2 bar when the engine is running at
maximum speed. A fuel metering or
injection pump and a nozzle are the other
parts of the system. The nozzle injects the
fuel in the manifold or the cylinder head
port at about 6.5 bar or into the
combustion chamber at pressures that
range from 16 to 35 bar. Timed injection
system injects fuel usually during the early
part of the suction stroke.
7
Gasoline injection in
four-stroke engines
8
Fuel injection
in two-stroke
engines
9
Electronic Fuel Injection System
Modern gasoline injection systems use engine
sensors, a computer, and solenoid operated fuel
injectors to meter and inject the right amount of
fuel into the engine cylinders.

These systems called electronic fuel injection
(EFI) use electrical and electronic devices to
monitor and control engine-operation.

An electronic control unit (ECU) or the
computer receives electrical signals in the from
of current or voltage from various sensors. It
then uses the stored data to operate the
injectors, ignition system and other engine
related devices. Typical sensors for an electronic
fuel injection system includes the following:

10
Typical Sensors
1. Exhaust gas or oxygen sensor - senses the
amount of oxygen in the engine exhaust
and calculates air –fuel ratio. Sensor
output voltage changes in proportion to
air –fuel ratio.
2. Engine temperature sensor - senses the
temperature of the engine coolant, and
from this data the computer adjusts the
mixture strength to rich side for cold
starting.
3. Air flow sensor - monitors mass or volume
of air flowing into the intake manifold for
adjusting the quantity of fuel.
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Typical Sensors – contd.
4. Air inlet temperature sensor - checks the
temperature of the ambient air entering
the engine for fine-tuning the mixture
strength.
5. Throttle position sensor - senses the
movement of the throttle plate so that the
mixture flow can be adjusted for engine
speed and acceleration.
6. Manifold pressure sensor - monitors
vacuum in the engine intake manifold so
that the mixture strength can be adjusted
with changes in engine load.
12
Typical Sensors – contd.
7. Camshaft position sensor – senses
rotation
of
engine
camshaft/crankshaft for speed and
timing of injection.
8. Knock sensor – microphone type
sensor
that
detects
ping
or
resignation noise so that the ignition
timing can be retarded.
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The injector pulse width is an indication
of the period for which each injector is
energized and kept open. The computer
decides and controls the injector pulse
width based on the signals received from
the various sensors.
Under full load, the computer will sense
a wide-open throttle, high intake manifold
pressure, and high inlet airflow. The ECU
will then increase the injector pulse width
to enrich the mixture, which will enable
the engine to produce higher power.
14
Under low load and idling conditions, the
ECU will shorten the pulse width by which
the injectors are kept in the closed position
over a longer period of time. Because of
this, air-fuel mixture will become leaner and
will result in better fuel economy.
Electronic fuel injection system has a cold
start injector too. This is an extra injector that
sprays fuel into the center of the engine
intake manifold, when the engine is cold. It
serves the same purpose as the carburetor
choke. The cold start injector ensures easy
engine startup in very cold weather.
15
MPFI System
The main purpose of the Multi-Point Fuel
Injection (MPFI) System is to supply a
proper ratio of gasoline and air to the
cylinders. These system function under two
basic arrangements viz.,
(i) Port injection
(ii) Throttle body injection
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Port Injection
In
this system, the
injector is placed on
the side of the intake
manifold
near
the
intake port. The injector
sprays gasoline into the
air, inside the intake
manifold.
The gasoline mixes with the air in a
reasonably
uniform
manner.
This
mixture of gasoline and air then passes
through the intake valve and enters into
the cylinder.
17
Port Injection – contd.
Every
cylinder is provided with an
injector in its intake manifold. If there are
six cylinders, there will be six injectors.
Figure shows simplified view of a port or
multi point fuel injection (MPFI) system.
18
Throttle Body Injection
Figure illustrates the simplified sketch of
throttle body injection system (single point
injection). This throttle body is similar to the
carburetor throttle body, with the throttle
valve controlling the amount of air
entering the intake manifold.
19
Remark
As
already
mentioned,
fuelinjection systems can be either timed
or continuous. In the timed injection
system, gasoline is sprayed from the
injectors in pulses. In continuous
injection system, gasoline is sprayed
continuously from the injectors.
20
Remark
The port injection system and the
throttle-body injection system may be
either pulsed systems or continuous
systems. In both systems, the amount of
gasoline injected depends upon the
engine speed and power demands.
In some literature MPFI systems are
classified into two types viz.,
D-MPFI and L-MPFI.
21
D-MPFI System
The D-MPFI system is the manifold fuel
injection system. In this type, the vacuum in
the intake manifold is first sensed. Further, it
senses the volume of air by its density. Figure
shows the block diagram regarding the
functioning of the D-MPFI system.
Air
Intake manifold
vacuum sensor
Mixture of
air and gasoline
Engine
Gasoline
Injection into
intake manifold
Injector
Injection
volume control
ECU
RPM sensor
22
D-MPFI System – contd.
As air enters into the intake manifold, the
manifold pressure sensor detects the intake
manifold vacuum and sends the information
to the ECU. The speed sensor also sends
information about the rpm of the engine to
the ECU.
The ECU in turn sends commands to the
injector to regulate the amount of gasoline
supply for injection. When the injector
sprays fuel in the intake manifold the
gasoline mixes with the air and the mixture
enters the cylinder.
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L-MPFI System
The L-MPFI system is a port fuelinjection
system. Here, the fuel metering is regulated
by the engine speed and the amount of air
that actually enters the engine. This is called
air-mass metering or air-flow metering. This
block diagram of L-MPFI system is shown.
Air
Air flow sensor
Gasoline
Mixture of
fuel and air
Engine
RPM
sensor
Injection
near port
Injector
Injection
volume control
ECU
24
L-MPFI System – contd.
As air enters into the intake manifold, the
air flow sensor measures the amount of air
and sends information to the ECU. Similarly,
the speed sensor sends information about
the speed of the engine to the ECU.
The
ECU processes the information
received
and
sends
appropriate
commands to the injector to regulate the
amount of gasoline supply for injection.
When injection takes place, the gasoline
mixes with the air and mixture enters the
cylinder.
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Functional Divisions of
MPFI System
The MPFI system can be functionally
divided into the following there main
components:
(i) Electronic Control System
(ii) Fuel System
(iii) Air Induction System
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MPFI Electronic Control System
Sensors
(Input)
Air flow meter
cold start injector
time switch
To cold start injectorr
To injectors
(Output)
Ignition signal
Electronic control unit (ECU)
The MPFI- electronic control system is shown in
the above block diagram. The sensors that
monitor intake air temperature, the oxygen, the
water temperature, the starter signal and the
throttle position send signals to the ECU.

27
MPFI Electronic Control System
– contd.
The air-flow sensor sends signals to the
ECU regarding the intake air volume. The
ignition sensor sends information about
the engine speed. The ECU processes all
these signals and sends appropriate
commands to the injectors to control the
volume of the fuel for injection. When
necessary the cold-start injector timing
switch off the ECU operates the cold start
injector which is a part of the fuel system.
28
MPFI Fuel System
Here, fuel is supplied by
the fuel pump. At the time of
starting,
the
cold
start
injector is operated by the
cold start
injector time
switch.
The
cold
start
injector injects fuel into the
air intake chamber, thus
enriching the air-fuel mixture.
The
pressure
regulator
regulates the pressure of the
fuel. The injectors receive
signals from the ECU and
inject the fuel into the intake
manifold.
29
MPFI Air Induction System
Here,
the
air
cleaner, the air-flow
meter, the throttle
body and the air
valve supply a proper
amount of air to the
air intake chamber
and intake manifold.
The quantity of air
supplied is just what is
required for complete
combustion.
30
References
Crouse WH, and Anglin DL,
DL (1985), Automotive Engines, Tata McGraw Hill.
2. Eastop TD, and McConkey A, (1993), Applied Thermodynamics for Engg.
Technologists, Addison Wisley.
3. Fergusan CR, and Kirkpatrick AT, (2001), Internal Combustion Engines, John
Wiley & Sons.
4. Ganesan V, (2003), Internal Combustion Engines, Tata McGraw Hill.
5. Gill PW, Smith JH, and Ziurys EJ, (1959), Fundamentals of I. C. Engines, Oxford
and IBH Pub Ltd.
6. Heisler H, (1999), Vehicle and Engine Technology, Arnold Publishers.
7. Heywood JB, (1989), Internal Combustion Engine Fundamentals, McGraw Hill.
8. Heywood JB, and Sher E, (1999), The Two-Stroke Cycle Engine, Taylor & Francis.
9. Joel R, (1996), Basic Engineering Thermodynamics, Addison-Wesley.
10. Mathur ML, and Sharma RP, (1994), A Course in Internal Combustion Engines,
Dhanpat Rai & Sons, New Delhi.
11. Pulkrabek WW, (1997), Engineering Fundamentals of the I. C. Engine, Prentice Hall.
12. Rogers GFC, and Mayhew YR,
YR (1992), Engineering Thermodynamics, Addison
1.
Wisley.
13. Srinivasan S, (2001), Automotive Engines, Tata McGraw Hill.
14. Stone R, (1992), Internal Combustion Engines, The Macmillan Press Limited, London.
15. Taylor CF, (1985), The Internal-Combustion Engine in Theory and Practice, Vol.1 & 2,
The MIT Press, Cambridge, Massachusetts.
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Web Resources
1.
2.
3.
4.
5.
6.
7.
8.
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10.
11.
12.
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22.
23.
http://www.mne.psu.edu/simpson/courses
http://me.queensu.ca/courses
http://www.eng.fsu.edu
http://www.personal.utulsa.edu
http://www.glenroseffa.org/
http://www.howstuffworks.com
http://www.me.psu.edu
http://www.uic.edu/classes/me/ me429/lecture-air-cyc-web%5B1%5D.ppt
http://www.osti.gov/fcvt/HETE2004/Stable.pdf
http://www.rmi.org/sitepages/pid457.php
http://www.tpub.com/content/engine/14081/css
http://webpages.csus.edu
http://www.nebo.edu/misc/learning_resources/ ppt/6-12
http://netlogo.modelingcomplexity.org/Small_engines.ppt
http://www.ku.edu/~kunrotc/academics/180/Lesson%2008%20Diesel.ppt
http://navsci.berkeley.edu/NS10/PPT/
http://www.career-center.org/ secondary/powerpoint/sge-parts.ppt
http://mcdetflw.tecom.usmc.mil
http://ferl.becta.org.uk/display.cfm
http://www.eng.fsu.edu/ME_senior_design/2002/folder14/ccd/Combustion
http://www.me.udel.edu
http://online.physics.uiuc.edu/courses/phys140
http://widget.ecn.purdue.edu/~yanchen/ME200/ME200-8.ppt 32