Electronically controlled gasoline injection system for SI
engine
Limitations of carburetor or necessity of petrol fuel
injection
In
multi cylinder engines, it becomes very difficult for a single carburetor to
supply uniform quantity and quality. Since, the induction passage are of
unequal length.
The
carburetor has many wearing parts. After wear, it operates less efficiency.
There
is a loss of volumetric efficiency due to restricted flow of mixture in various
parts such as choke tubes, jets,
throttle valves, inlet pipe bends.
Venturi
throat of the carburetor causes a restriction in the passage of air flow to the
engine.
All of above
limitations of carburetor may be avoided by introducing the fuel through
injection rather than carburetion.
Types of gasoline injection system
In a petrol injection system,
the fuel is injected into the intake manifold through fuel injection valves.
There are two
basic gasoline injection arrangements.
(i) Multi point
fuel injection (MPFI)
(ii) Mono point
fuel injection
Working of Electronically controlled gasoline injection
system
In
electronically controlled gasoline injection system for SI engines, fuel supply
and timing are controlled by electronic means.
It
has developed with the development of solid state electronic devices such as
diodes and transistors.
These
systems are commonly used as they function quickly and respond automatically to
the change in manifold air pressure, engine speed, crank shaft angle and many
other secondary factors.
Developed
by Robert Bosch Corporation.
ž It
consists of following four units.
- Fuel delivery system
- Air induction system
- Sensors and air flow control system
- Electronic control unit
(i) Fuel
delivery system
This
system consist of an electrically driven fuel pump which draws fuel from
the tank through filter and forces it into the pressure line.
At the
end of the pressure line, a fuel pressure regulator is placed.
The
fuel pressure regulator is connected to the intake manifold.
The
pressure difference between fuel pressure and manifold pressure is kept
constant by this regulator so that the quantity of fuel is injected
dependent only on the injection open time.
(ii) Air Induction
system
The
incoming air from atmosphere flows initially through air filter and then
through air flow sensor.
This
air flow sensor measures the amount of air flow in the manifold and generates a
voltage signal which is dependent on the amount of air flow.
The
air flow meter consists of a rectangular plate which turns in a rectangular
shaped channel to a defined angular position dependent on the pressure from
flowing air.
(iii) Sensors and air flow control system
1.Air flow sensors
2. Intake air temperature sensor
3. Exhaust gas oxygen (EGO) sensor
4. Manifold absolute pressure sensor
5. Speed/ crankshaft sensor
6. Engine temperature sensor
7. Crankshaft position sensor
8. Knock sensor
(iv) Electronic control unit (ECU)
(Heart
of a fuel injection system)
This
unit contains number of printed circuit boards on which a series of
transistors, diodes and other electronic components are mounted.
The
data measured in the form of signals by various sensors are transmitted to the
electronic control unit.
This
unit computes the air fuel ratio required for the best performance of the
engine during each cycle and it sends signal to the injection valve and other
parts of the system.
ECU
cannot be adjusted or serviced.
Advantages
Increases
the volumetric efficiency and it also increases speed and torque.
It
reduces specific fuel consumption
Design of manifold is simple
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