An engine is complex unit in which different

components are assembled together, and fuel is burned

to produce power or energy. The engine

converts chemical energy (heat energy)

into mechanical energy, which is

then utilised for vehicular movement.

There are different processes of fuel

combustion. When the fuel is burned

within the engine, it is called an Internal

Combustion (IC) engine, and when it is

burned externally and the produced

steam is used for the mechanical

movement, it is called an External

Combustion (EC) engine. Nowadays,

automobile engines are quite economical

due to the developments taking place in

the field of internal combustion engine.

On the basis of the process of ignition,

the automobile engines are classified into spark ignition

engine (petrol or gas) and compression ignition engine

(diesel). In an IC engine, the reciprocating motion of the

piston is converted into rotary motion of the crankshaft

and the produced power is then transmitted to move

the vehicle. In case of a rotary engine or Wankel

engine, the rotor rotates and completes the process of

combustion and produces the power, which helps the

vehicular movement.

The spark ignition engine can be differentiated from the

compression ignition engine as per the following factors.

(i) The type of fuel used.

(ii) The way the fuel enters in the combustion chamber.

(iii) The way in which fuel is ignited.