IC Engine Fundamentals by Prof. Steve

M S Steve
Assistant professor
Dept of Mechanical Engineering
Amal Jyothi College of Engineering
1

msstevesimon@gmail.com

Heat Engines
Absorb energy in the
form of heat
Convert part of it into
work
Reject balance as heat

2


Combustion

3


Heat Engines
1.
2.

4

External Combustion Engines – steam engine
Internal combustion Engines – automobile engine



Internal Combustion Engine
 Burns fuel and air in enclosed space
 Produces hot burned gases

 Converts some of this heat into

useful work
 Allows heat to flow from hot engine to cold outside air

Nikolaus Otto
patented the 4stroke engine when
he was only 34!
5

Internal Combustion Engines are those
heat engines where the combustion of
the fuel takes place inside the engines

6


Advantages of I C Engines
1.
2.
3.
4.

7

High thermal efficiencies ( 30 to 35%)
Higher power to weight ratio
Compact and suitable for portable applications
Quick-starting and simple in construction


Disadvantages of I C Engines
1.

2.

8

Since fuel combustion occurs in the cylinder, consequent
very high temperatures of engines necessitates engine
cooling arrangements
High temperatures restrict ICEngines to be single-acting,
reducing the power strokes per revolution


Classification of IC Engines
According to:
 Fuel used
 Strokes per cycle
 Thermodynamic cycle
 Speed of engine
 Method of ignition
 Method of cooling
 Method of governing
 Arrangement of engine cylinders
 Number of cylinders
 Application
9


Arrangement of Cylinders

11


Comparison of Petrol and Diesel Engines
1.
2.

3.
4.

5.
6.
7.
8.
9.
12

PETROL ENGINE
Works on Otto Cycle
Fuel-air mixture is
admitted during suction
stroke
Spark ignition
Low compression ratios
(6 to 10)
Lower engine efficiency
Higher fuel consumption
Lower engine vibrations
and noise
High running cost
Light duty application

1.
2.
3.
4.
5.
6.
7.
8.
9.

DIESEL ENGINE
Works on Diesel Cycle
Fuel is injected at the end
of compression stroke
Compression ignition
High compression ratios
(10 to 20)
Higher engine efficiency
Lower fuel consumption
Higher engine vibrations
and noise
Low running cost
Heavy duty application


IC Engine

13


IC Engine Parts
1.
2.
3.
4.
5.

6.

15

Cylinder Head
Cylinder Block and Liner
Piston
Connecting Rod
Crankshaft
Crank Case and Sump


Cylinder head

16


Engine valves

17


Valve mechanism

18


Piston assembly

19


Crank case

20


Crank shaft assembly

21


Four Stroke and Two Stroke Engines

22


Four Stroke I C Engine
In a four stroke I C Engine, one cycle of operation is
completed in four strokes of the piston in the engine
cylinder
The strokes are:
1. Suction (Induction) stroke
2. Compression Stroke
3. Power Stroke
4. Exhaust Stroke

23


Suction (Induction) stroke

24


Compression Stroke

25


The four-stroke engine

Spark plug

Exhaust valve
Inlet valve
Cylinder

Piston

28



Inlet valve
open

INDUCTION STROKE

29



Inlet valve
open

Piston down
30


INDUCTION STROKE

Charge in
Inlet valve
open

Piston down
31


INDUCTION STROKE

Charge in
Inlet valve
open

Piston down
32


INDUCTION STROKE

Charge in
Inlet valve
open

INDUCTION STROKE

33



Exhaust valve
closed

Inlet valve
closed

COMPRESSION STROKE
Piston up
34



Exhaust valve
closed

Inlet valve
closed

Piston up

35


COMPRESSION STROKE


Exhaust valve
closed

Inlet valve
closed

Piston up

COMPRESSION STROKE
36


Exhaust valve
closed

Inlet valve
closed

BANG

POWER STROKE
37



Exhaust valve
closed

Inlet valve
closed

Piston down
powerfully

38


POWER STROKE


Exhaust valve
closed

Inlet valve
closed

POWER STROKE
39

Piston down
powerfully


Exhaust valve
closed

Inlet valve
closed

POWER STROKE
40



Inlet valve
closed

Exhaust valve
open

EXHAUST STROKE
41



Inlet valve
closed

Exhaust valve
open

Exhaust gases
out

Piston up
42


EXHAUST STROKE


Inlet valve
closed

Exhaust valve
open

Exhaust gases
out

Piston up

EXHAUST STROKE
43



Inlet valve
open

Exhaust valve
closed

INDUCTION STROKE

44


And so the
cycle
continues!!

45


1.

Induction Stroke

 Engine pulls piston out of cylinder
 Low pressure inside cylinder
 Atmospheric pressure pushes fuel

and air mixture into cylinder
 Engine does work on the gases
during this stroke

47


Engine – Stroke 1

Fuel and air mixture
after induction stroke:
Pressure
Temperature

48

= Atmospheric
= Ambient


2. Compression Stroke
 Engine pushes piston into

cylinder
 Mixture is compressed to high
pressure and temperature
 Engine does work on the gases
during this stroke

49


Engine – Stroke 2

Fuel and air mixture
after compression stroke:
Pressure
Temperature

50

= High
= Hot


3. Power Stroke
 Mixture burns to form hot gases
 Gases push piston out of cylinder
 Gases expand to lower pressure and

temperature
 Gases do work on engine during this
stroke

51


Engine – Stroke 3

Burned gases after ignition:
Pressure
Temperature

52

= Very high
= Very hot


Engine – Stroke 4

Burned gases after power stroke:
Pressure
Temperature

53

= Moderate
= High


4.

Exhaust Stroke

 Engine pushes piston into cylinder
 High pressure inside cylinder
 Pressure pushes burned gases out of

cylinder
 Engine does work on the gases during
this stroke

54



Two Stroke Engines

55

Two Stroke I C Engine
In a two stroke I C Engine one cycle of operation is
completed in two strokes of the piston in the engine cylinder
Stroke 1: Scavenging and Compression
Stroke 2: Power and Exhaust

58



Scavenging and Compression

59

Advantages of Two Stroke engines
1.

2.
3.
4.
5.
6.

62

One power stroke every revolution of crankshaft results in high
power to weight ratio
Torque is more uniform needing lighter flywheel
Simpler in construction due to absence of valves and valve gear
Friction loss is less giving higher mechanical efficiency
Lower initial cost
Easier starting


Disadvantages of Two Stroke engines
Overall efficiency is less due to:
a) Inadequate scavenging as some combustion products remain in
cylinder
b) Loss of fresh charge during scavenging
c) Less effective compression ratio for same stroke length
2. Engine overheating due to power stroke in every revolution
3. High lubricating oil consumption
4. Exhaust is noisier
1.

63


Comparison of Four Stroke and Two Stroke Engines
FOUR STROKE ENGINE
1.

2.

3.

4.
5.
6.
7.
64

One cycle in 4 strokes of
piston or 2 revolutions of
crankshaft
Valves are used for charge
admission and exhaust
One power stroke in two
revolution causing torque
fluctuations needing heavy
flywheel
Low power to weight ratios
Higher overall efficiency
Complex construction due to
valve gear
Heavy duty applications

TWO STROKE ENGINE
1.
2.
3.

4.
5.
6.
7.

One cycle in 2 strokes of piston
or one revolution of crankshaft
No valves but ports are used
for admission and exhaust
One power stroke in one
revolution causing smoother
torque and consequent lighter
flywheel
Higher power to weight ratios
Lower overall efficiency due to
loss of fresh charge
Simpler construction
Light duty applications


I C Engine Systems
1.
2.
3.
4.
5.

66

Air & Exhaust System
Fuel Systems
Ignition Systems
Cooling Systems
Lubrication Systems


AIR SYSTEM FOR PETROL
ENGINE

67


AIR SYSTEM FOR PETROL ENGINE

AIR FROM ATM

AIR FILTER

Carburettor

Product of combustion to atm

68


Engine

SILENCER

FUEL SYSTEMS

 Petrol Engines
 Diesel Engines

69


Fuel Systems
Petrol Engines
Correct quantity of petrol is mixed with air in carburettor before
being admitted into cylinder during suction stroke

70


FUEL SYSTEM FOR PETROL ENGINE

AIR FROM ATM

AIR FILTER
combu
stion

Fuel storage
tank
71

Fuel Pump

Fuel Filter


Carburettor

Engine

FUEL SYSTEM FOR PETROL
ENGINE

72


FUEL SYSTEM FOR DIESEL ENGINE
AIR FROM ATM

Low
pressure
pump

filter

filter

AIR
FILTER
High
pressure
pump

Fuel storage
tank

Fuel Injector

Product of combustion to atm

SILENCER

Engine
73


 It pumps fuel from storage tank to carburetor
 Actuated by cam, it is in touch with rocker arm
 As the link is pulled downwards diaphragm will move down

and fuel will enter the chamber
 Inlet and Exhaust valves are one way valves

75


One-way
Inlet Valve

One-way
Outlet Valve

Diaphragm

Driving Cam

76

Diaphragm Pump

Air
Filter

Carburettor

Cockpit
Gauge
Inlet

Tank
Pump

77

PETROL ENGINE – Carburettor Fuel System

Exhaust

JET

VENTURI

FLOAT NEEDLE VALVE

AIR VENT

FUEL
LEVEL
FLOAT

FLOAT CHAMBER

80

SIMPLE CARBURETOR WORKING

FUEL
FEED @
PUMP

 Major function of carburetor is to provide air fuel mixture
 Basic principle : When a volatile fuel is placed in the passage

of high velocity air, the fuel gets vaporized at a faster rate
 Arrangement:
•
•
•
•
•

81

Jet and fuel nozzle
Venturi tube & venturi throat
Float chamber
Throttle valve
Float , float needle, air vent


Working
1.

2.

Petrol is pumped into the float chamber, level of petrol is
maintained by a float arrangement
Suction stroke of engine causes air flow through venturi tube.

3. VELOCITY of air at throat will increase & PRESSURE will
decrease at JET point(will be less than Atm. Pressure)
4. In float chamber the pressure acting is Atm. Pressure, due to this
pressure difference fuel will flow from FLOAT CHAMBER to
the JET
5. Function of throttle is to control speed and power to engine,
more the throttle is closed flow of air & fuel mixture to the
cylinder is less
82


FUEL
FLOW

AIR FLOW

AIR FLOW

AIR/FUEL
MIXTURE
FLOWS TO
ENGINE

AIR IS SUCKED THROUGH VENTURI …..
A PISTON MOVING DOWN ON SUCTION STROKE
THE LOWER AIR PRESSURE PULLS FUEL THROUGH THE JET

FUEL LEVEL DROPS

MOVING AIR HAS LOWER PRESSURE
83


FUEL LEVEL DROPPING LOWERS FLOAT

PULLING AIR INTO FLOAT CHAMBER

FUEL LEVEL DROPS

84


FUEL LEVEL DROPPING LOWERS FLOAT
FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED
AND ALLOWS FUEL TO ENTER FLOAT CHAMBER FROM PUMP

FUEL LEVEL DROPS

85


FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED

FUEL IS PULLED OUT OF THE FLOAT CHAMBER

ONLY WHEN PISTON IS ON THE INDUCTION STROKE
86


We now need to look at controlling
the air/fuel mixture flowing into the
engine
Controlling the air/fuel mixture
means controlling the engine
The carburettor part which controls
the flow is….

THE THROTTLE
87


THROTTLE
VALVE

88


THROTTLE VALVE
THIS WOULD BE A HIGH THROTTLE SETTING OR ‘FULL –POWER’

OPEN THROTTLE ALLOWS VENTURI TO WORK AT MAXIMUM EFFICIENCY

89


LOW THROTTLE SETTING - CALLED ‘IDLE’ OR ‘TICK-OVER’
ALMOST CLOSED THROTTLE MEANS THE VENTURI DOES NOT WORK VERY
WELL
LOW AIR FLOW MEANS VERY LITTLE OR NO FUEL/AIR MIXING IN THE
VENTURI
SO AN ALTERNATIVE AND EFFECTIVE VENTURI NEEDS TO BE FOUND

90


LOW THROTTLE SETTING - CALLED ‘IDLE’ OR ‘TICK-OVER’

EDGE GAPS BECOME THE VENTURI FOR THE LOW AIR FLOW
AT IDLE - SLOW RUNNING JET CONTROLS FUEL FLOW
T

91


LIMITATIONS OF CARBURETTOR
• Distribution of air /fuel mixture to cylinder is not uniform
• Construction of venturi causes low volumetric efficiency
• There is a loss of volumetric efficiency also due to restricted
flow of mixture in various parts such as chokes, tubes, jets,
throttle valve, inlet pipe bends, etc.

All the above limitations of carburettor can be avoided by introducing the fuel
through injection rather than the carburettor
93

FUEL INJECTION PUMP
A fuel injection pump is used to supply precisely metered
quantity of diesel under high pressure to the injectors at the
correct time.

94


FUEL PUMP
Spring
Delivery valve

Fuel overflow port
Inlet port

Barrel
Rack

plunger

98


barrel
 Barrel houses the inlet port and fuel overflow port

99

Plunger
 Plunger driven by cam & tappet
 Plunger reciprocates in a barrel & fuel enters thru inlet port
 Plunger have a vertical and helical groove which help in

determining the amount of fuel supplied to the fuel injector

100


•

Delivery valve is a non return valve,
kept in position by a spring.
When the Pr. In the barrel exceeds a
predetermined value and valve opens
against the compression of the spring
and the pressure of the fuel above.

Fuel pump is connected to the fuel
injector through a passage

101


Working
 When the plunger is at bottom the fuel inlet & overflow





102

ports are uncovered and filtered fuel is forced into the barrel
Both ports are covered when the plunger moves upwards
Fuel will get compressed when the plunger moves further
forward
The high pressure lifts the delivery valve and fuel flows out
thru the delivery valve
With further rise of the plunger the overflow port is
uncovered by the plunger and pressure drops


 The quantity of fuel pumped can be varied by the angular

position of the helical groove relative to the inlet port

103

Diesel Fuel Pump
 Plunger reciprocates on a barrel(hollow cylinder like





105

arrangement)
A rectangular helical groove in the plunger which extends
from top to another helical groove
When the plunger is at bottom -- fuel inlet and overflow port
are open,--fuel will come inside the barrel
When the plunger moves up– both ports are closed –and fuel
inside the barrel get compressed
Due to the high pressure of compressed fuel delivery valve
will get opened

FUEL INJECTOR

106


FUEL INJECTOR
A fuel injector is used to inject the fuel in the cylinder
in atomised form and in proper quantity. Fuel
injectors are available in several designs. Main
components of fuel injectors are : NOZZLE
VALVE
BODY
SPRING
The nozzle is its main part which is attached to the
nozzle holder. Entry of fuel in the injector is from the
fuel injection pump.

107


FUEL INJECTION NOZZLE

109


PARTS OF FUEL INJECTOR
1.
2.
3.
4.
5.

6.
7.
8.
9.
111

Nozzle valve
Nozzle body
Spring
spindle
Adjusting screw
Lock nut
Passage
Nozzle
Leak of connection

 Nozzle valve is fitted in a nozzle body.
 The spring retains the valve in its seating through a spindle.
 Adjusting screw and lock nut- to adjust the lift of the nozzle

112


Working
 High pressure fuel from the fuel pump enters the injector

through the passage and lift the nozzle valve
 Fuel travels down the nozzle and is injected into the engine
cylinder in the form of fine spray
 When the fuel pressure drops the spring force overcomes the
fuel pressure and the valve get closed
 Any leakage of the fuel at the end of the compression is fed
back to the fuel pump suction chamber by the leak off pipe

113


FUEL INJECTOR

114


 Nozzle valve is held on its seat by a spring which exerts

pressure through a spindle
 Fuel from fuel pump enters the passage and lifts the
nozzle valve
 then the fuel will sprayed through the nozzle and is injected
into the engine
 When pressure drops the nozzle valve will occupy in its
seat under the compression of the spring

115


Ignition Systems
 Ignition

process in Petrol Engines requires an electric spark
produced at the spark plug.

 This spark is generated by an electric discharge produced by the

ignition system.

 Ignition systems in petrol engines are classified as :

1.Battery ignition system.
2.Magneto ignition system
• The difference between the two systems is in the source of
primary voltage.
116


Ignition systems
 Basic requirements of an ignition systems
 A source of electrical energy
 A device for boosting the low voltage to produce high voltage
 A device for timing and distributing the high voltage to each

spark plug

117


Battery ignition system
 It is also called coil ignition system.
 The source of energy to the primary windings is a 6V or

12V battery.
 As the number of windings in the secondary is 50 to 100

times more than that of the primary , the output voltage
induced will be of the order of 10000v to 20000V.

119


Magneto ignition system
 The source of energy is either rotating magnets with fixed

coils or rotating coils with fixed magnets.
 The rapid collapse and reversal of magnetic field induces a
very high voltage in the secondary winding.
 It is generally employed in racing cars, motor cycles etc.

121


Spark plug
TaskThe spark plug ignite the suctioned and compressed fuel-air
mixture due to arcing between the electrodes.

FunctionThe ignition voltage travels to the spark plug from directly
Connected ignition coils or over the ignition lines from the
Ignition coils causing arcing in the air gap between the center
and ground electrodes.

122


The Spark Plug
Spark plug is located in the cylinder head,
it ignites the air and fuel mixture.
Has centre and side electrodes,
with an air gap between them.

Terminal

Insulator
Hex

Centre electrode receives coil voltage.
Metal
shell

Side electrode is grounded.
High voltage jumps the
air gap, creating a spark.
Insulator prevents high voltages
from shorting to ground.
123

Gasket
Thread
Side
electrode

Centre
electrode
Gap
Next >

Lubricating Systems
Purpose:
1. To reduce friction and wear
2. To provide sealing between piston and cylinder
3. To cool piston heads, valves, etc.
4. To wash away carbon and metal particles

124


Lubrication Systems:
Petroil lubrication
Wet sump lubricating system

1.
2.
1.

2.

3.

125

Splash lubrication
Pressure lubrication

Dry sump lubricating system


Petrol Lubrication System
 This system of lubrication is used in scooters and motor

cycles.
 About 3% to 6% of lubricating oil is added with petrol in the
petrol tank.
 The petrol evaporates when the engine is working. The
lubricating oil is left behind in the form of mist.
 The parts of the engine such as piston cylinder walls,
connecting rod are lubricated by being wetted with the oil
mist.

126


Wet sump lubrication system
 The splash

system is used only on small four-stroke-cycle

engines.
 As the engine is operating, dippers on the ends of the connecting rods
enter the oil supply, pick up sufficient oil to lubricate the connectingrod bearing, and splash oil to the upper parts of the engine.
 The oil is thrown up as droplets, or fine spray, which lubricates the
cylinder walls, piston pins and valve mechanism.
 In the pressure-feed system, oil is forced by the oil pump through

oil lines and drilled passageways.
 The oil, passing through the drilled passageways under pressure, supplies
the necessary lubrication for the crankshaft main bearings, the
connecting-rod bearings piston-pin bushings, camshaft bearings, valve
lifters, valve push rods, and rocker studs.
127


Splash lubrication
 Simplest of all types, used only for small capacity engines.

128



Pressure lubrication

129

Dry Sump Lubrication System
 In a wet sump, the oil pump sucks oil from the bottom of the

oil pan through a tube, and then pumps it to the rest of the
engine.
 In a dry sump, extra oil is stored in a tank outside the
engine rather than in the oil pan. There are at least two oil
pumps in a dry sump -- one pulls oil from the sump and
sends it to the tank, and the other takes oil from the tank and
sends it to lubricate the engine. The minimum amount of oil
possible remains in the engine.

130


Dry sump lubrication
• The supply of oil is from an external tank.
•

131

An oil pump is employed to circulate the oil under pressure
,from the tank to various bearings of the engine.

Functions of a Lubricant
 Lubricant reduces friction between moving part.
 It reduces wear and tear of the moving parts.
 It minimizes power loss due to friction.
 It provides cooling effect. While lubricating it also carries

some heat from the moving parts and delivers it to the
surroundings through the bottom of the engine (crank case).
 It helps reduce noise created by the moving parts.

132


THE COOLING SYSTEM

133


Purpose of cooling
 To regulate the engines internal temperature
 To remove excess heat from the engine
 To prevent heat to the passenger compartment
 To Control temperature of hot combustion,4000 degree

temps. could seriously damage engine parts.
 Cool Trans fluid & Oil

134


Cooling Systems
 Intense heat is generated during the combustion of fuels

inside the engine cylinder.
 30% of heat generated is converted into mechanical
work & 40% is carried away by exhaust gases to the
atmosphere.
 The remaining part of heat (30%) will be absorbed by
the engine parts which leads to overheating of these
parts.
 In order to avoid the problem of overheating it is
essential to provide some kind cooling systems.
135


 The two important characteristics of cooling systems for

the efficient working are:
(i)It should not remove more than 30%
of heat
generated.(larger amount of heat removal reduces the
thermal efficiency)
(ii)The rate of cooling should not be constant.(the rate
of cooling should increase with increase in heat
generated)
136


 Two types of cooling systems used in IC engines are:

1.Air cooling system
2.water cooling system

137


Air cooling
 The heat is dissipated directly in to the atmospheric air

by conduction through cylinder walls.
 The rate of cooling is increased by increasing the outer

surface area of the cylinder by providing radiating fins &
flanges.
 Normally it is used for the engines of motor cycles ,

scooters etc.
138


 To increase the surface area exposed fins are provided
 In some cases blower is provided to increase the heat tr. rate

139


Air cooling
 Heat is dissipated to the surrounding air around the cylinder
 Basic principle- to have continuous flow air around parts

which are to be cooled
 The heat dissipated depends on :
 The surface area of the metal, in contact with the air flow
 The Temp difference between the surface & the air
 Thermal Conductivity of the metal

141


Advantages of Air-cooled Engines:
 Air-cooled engines are smaller and lighter because they don’t
need to house any of those parts like the Water cooled engines
 In some climates, water has the tendency to freeze and this is a
problem for water-cooled engines.
 Air-cooled engines warm up quickly and are easy to maintain.
Disadvantages of Air-cooled engines:
 The cooling tends to be uneven and leads to cylinder distortion.
 It is almost impossible to manage with air-cooling if the number

of cylinders increases beyond two.
 The fins vibrate sometimes leading to a lot of noise.
142


Water cooling system.
 It is also called thermosyphon system of cooling .
 Water is circulated through water jackets around each of the

combustion chambers.
 The circulating water is cooled by the air drawn through

radiator by a fan

143


Liquid cooling (water cooling)
 Cooling medium – water
 Water circulated through the passages

around the main components
 Passages – water jackets
 Water circulation- pump or by gravity

force

144


 Water after passing through the jackets flows to a radiator.
 Radiator cools hot water with the help of moving air around the

radiator tubes
 Fans are provided to increase the heat transfer rate
 This system also uses a thermostat to control the flow of the
coolant
 Antifreeze added to avoid freezing of coolant- ethylene glycol

145


Water cooling system

146


Water Jackets

 Surrounds the cylinders

with water passage.
 Absorbs heat from the

cylinder wall.
 Pump move water to

radiator where heat is
exchanged to the air.
147



Radiators
 A radiator is a heat

exchanger.
 Tube and fin style the

most popular.
 Made of copper and

brass or aluminum and
plastic.
148

 Its job is to block the flow of coolant to the radiator until the

engine has warmed up.
 When the engine is cold, no coolant flows through the
engine. Once the engine reaches its operating temperature
(generally about 200 degrees F, 95 degrees C), the
thermostat opens.
 By letting the engine warm up as quickly as possible, the
thermostat reduces engine wear, deposits and emissions.

149


TYPES OF CI INJECTION SYSTEMS

152

COMMON RAIL DIRECT INJECTION (CRDI)

153


Working
 HP fuel pump maintains fuel in the common rail at a pressure

of about 200 MPa.
 Common rail branches off to ECU controlled injector valves
 Valve contains precision machined nozzles and a plunger
driven by solenoid valves
 ECU controls the timing and quantity of fuel injected
depending on the load conditions

156


Advantages of CRDI
 Higher efficiency due to variable injection timing
 Better combustion at low speeds
 Better power balance- reduced vibration
 Lesser moving parts
 Compact engine

157


AIR FURL SYSTEM IN SI (PETROL)
ENGINES

159

Gasoline direct injection
 Petrol Direct Injection or Direct Petrol

Injection or Spark Ignited Direct Injection
(SIDI) or Fuel Stratified Injection (FSI)

160


Components of GDI engine
 Pumping element
 Metering element
 Mixing element
 Mixture control
 Distributing element

 Ambient control

162


MULTI POINT FUEL INJECTION
 Petrol vehicles used carburettor for supplying the air fuel mixture in

correct ratio to cylinders in all rpm ranges.
 Carburettor achieves this by breaking up fuel into minute particles and

mixing it with air.
 But this process may not always be perfect and might reduce the

performance of the engine.
 Therefore, multi point fuel injection system (MPFI) is used, which can

assure proper air fuel ratio to an SI engine.
164


MPFI
 MPFI stands for multi-point fuel injection
 It allows more efficient combustion of fuel, thereby

producing more power with less emissions
 It is similar to CRDI in diesel engines
 All modern petrol engines use MPFI systems

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MPFI System
 MPFI does the same function as the carburettor
 It has injectors which spray correct quantity of fuel for each

cylinder
 The fuel and air are mixed in the intake manifold before
admission to the cylinder

167


Components of MPFI
 Electronic Control Unit (ECU)- sometimes called Engine

Control Module (ECM)
 High Pressure Pump Module-pump, filter, pressure
regulator, common rail, sensor
 Injector for each cylinder, also controlled by ECU

168


ECU
The function of ECU is to receive inputs from
various sensors, compare them with pre-loaded
engine and throttle parameters and send control
signals to the actuators.

Sensors: Sense different parameters
(Temperature, Pressure, Engine Speed etc.) of the
engine and send signal to ECU.
Actuators: Receive control signal from ECU and
actuates pump and injectors
170


ECU Inputs
For the Inputs, the microprocessor (or ECU) reads a number of
sensors:
Ambient temperature
Engine RPM
Coolant temperature
Vehicle road speed
Exhaust temperature
Crankshaft position
Exhaust oxygen content
Camshaft position
Inlet manifold vacuum
Outside air pressure
Throttle position
Pressure on throttle
Based on all these inputs from the sensors, the computer in the
MPFI system decides what amount of fuel to inject, when, for what
duration, and into which cylinder. It then sends signals to actuators
for injection of correct quantity of fuel.
171


Thus it makes the engine cleaner, more responsive, ensures
complete combustion, and uses less fuel as it knows what
amount of petrol should go in.
Modern cars’ ECUs have memory, which will remember
your driving style and will behave in a way so that you get the
desired power output from engine based on your driving
style.
For example, if you have a habit of speedy pick-up, car’s
computer will remember that and will give you more power
at low engine speeds by putting extra petrol, so that you get a
good pick-up. It will typically judge this by the amount of
pressure you put on accelerator.
172


 A multi-point injection system, also called port injection, has an

injector in the port (air-fuel passage) going to each cylinder.
Gasoline is sprayed into each intake port and toward each intake
valve. Thereby, the term multipoint (more than one location)
fuel injection is used.

175

Advantages of MPFI:
 More uniform fuel-air mixture will be supplied to each cylinder.

Thus the power developed by different cylinders will be more
uniform.
 More appropriate fuel-air mixture will be supplied, which will

increase the combustion efficiency.
 Cold starting can be improved.
 Immediate response in case of sudden acceleration and

deceleration.
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ADVANTAGES OF MPFI SYSTEMS OVER
SPFI SYSTEM
MPFI

Better power

Low power

Better refinement of engines

Lesser refinement of engines

Better control over the process

Lesser control over the process

Longer life due to lesser load per injector

Lesser life due to higher load

Cleaning not required frequently

Frequent cleaning is required

No delay in response

Delay in response

No difference in delivery to each cylinder
177

SPFI

Difference in delivery to each cylinder

Thank you…!!

178


IC Engine Fundamentals by Prof. Steve

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