Electronically controlled gasoline injection system PPT/PDF notes

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.

1. Fuel delivery system
2. Air induction system
3. Sensors and air flow control system
4. 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

Click the link: to watch the video

Working of Electronically Controlled Injection system