Internal Combustion Engines

7th SEMESTER, B.E. MECHANICAL ENGINEERING

Prepared by:

Mr. Sanjeev Vishwakarma

Assistant Professor (TEQIP)

DEPARTMENT OF MECHANICAL ENGINEERING

Jorhat Engineering College, Jorhat
Internal Combustion Engines
Prepared by:
Mr. Sanjeev Vishwakarma
Assistant Professor (TEQIP)

Petrol Injection System

 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 air-
gasoline mixture in varying quantities and
richness. This problem is called the mal-
distribution 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.
Typical pattern of mixture distribution in a
multi-cylinder engine
 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
 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.
 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
downstre am of the throttle plate. In a
supercharged engine, fuel is at
the entrance of the supercharger. The
injected
timing and duration of the fuel injection
determined by Electronic Control Unit
is
(ECU) depending upon the and
load speed.
 Timed Injection Systems
This system has a suppl pump
whic fuel sends fuel at a lowy pressure
h
about 2ofbar 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 bar or
6.5 combustion into the at
rangechamber
from 16 to 35 bar. Timedpressures
injection
that
system injects fuel usually during the early
part of the suction stroke.
Gasoline injection in four-stroke
engines
 Fuel
injection
in two-
stroke
engines
 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:
 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.
 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.
 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.
Electronic Fuel Injection System
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.
Electronic Fuel Injection System
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.
 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

1
6
 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.
 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.
 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.
 Remark
As already mentioned, fuel-
injection 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.
 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.
 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 Gasoline

Mixture of Injection into

air and gasoline Injector
intake manifold
Injection
volume control
Engine
EC
U
RPM sensor
 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.
 L-MPFI System
The L-MPFI system is a port fuel- injection
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 Injector
Injection
near Injection
Engi port volume control
ne
RPM EC
sensor U
 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 informatio
the received and sends n
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.
 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
 MPFI Electronic Control System
Sensors To
(Input) To cold start injectorr
injectors
(Output)

Air flow meter Ignition signal

cold start injector Electronic control unit

time switch (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.
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.
 MPFI Fuel System
 Here, is supplied by
thefuel
fuel pump. At the time of
starting, cold star
the
injector is operated t
cold start injecto by
switch. r
The
injector cold
injects the
fuel into air time
intake
enriching the chamber,
air-fuel mixture.
The pressure regulator start
regulates the pressure of the the
fuel. thus
injectors receive
The
signals from the ECU and
inject the fuel into the intake
manifold.
 MPFI Air Induction System
 Here, the
cleaner, air air-
the flow
meter, and thethrottl
body air
the supply a proper
valve e
amount of air to the
air intake chamber
and
intake
The quantitymanifold
of air
. what is
supplied is just
required for complete
combustion.