Fuel System of an Automobile

The fuel system of an automobile supplies the fuel to the engine. It consists of the following parts:

(a) Fuel tank: It is used for storing the fuel.

(b) Fuel gauge: It is used to measure the quantity of fuel present in the storage tank.

(c) Fuel pump: It is used to draw the fuel from the tank and deliver to the carburetor (or injector).

(d) Carburetor (Throttle body): It is a device, which mixes the air and fuel, and supply the mixture so formed, in correct proportions, for proper combustion, to the engine cylinder under all conditions of load, speed etc. Despite mixing the fuel with air in correct proportion, it also automatically provides a richer mixture (i.e. more fuel and less air in proportion) for starting, idling and acceleration, and a leaner mixture (i.e., less fuel and more air in portion) for part throttle operation. In order to accomplish all these tasks, a carburetor has a variety of fixed and adjustable jets, ports, pump and passages arranged in the systems.

In some petrol engines, electronically controlled fuel injection system is used instead of carburetor. In this system, the volume of incoming air is detected, a computer uses the information to determine the volume of fuel required to give a predetermined air-fuel (A/F) ratio, and the fuel is supplied forcefully through injectors which are located in intake manifold, just at the back of intake valve. It may be noted that in comparison to the carburetor-type fuel system, the fuel injection system has many advantages like improved fuel economy, improved emission, higher power and higher response.

Note: In petrol engines, fuel is injected during suction stroke in the air stream in intake manifold whereas in diesel engine, it is injected directly into the combustion chamber near the end of compression stroke.