In two strokes SI engine a cycle is completed in two stroke
of a piston or one complete revolution (360º)
of a crankshaft. In this engine the suction stroke and
exhaust strokes are eliminated and ports are used instead of
valves. Petrol is used in this type of engine.
The major components of a four stroke spark Ignition engine
It is a cylindrical vessel in which a piston makes up and
It is a cylindrical component making up and down movement in
It is the portion above the cylinder in which the combustion
of the Fuel-air mixture takes place.
The inlet port allows the fresh fuel-air mixture to enter
the combustion chamber and the exhaust port discharges the
products of combustion.
It is a shaft which converts the reciprocating motion of
piston into the rotary motion.
The connecting rod connects the Piston with the crankshaft.
The cam shaft controls the opening and
closing of inlet and Exhaust valves.
It is located at the cylinder head. It is used to initiate
the combustion process.
piston moves from bottom dead centre to top dead centre, the
fresh air and fuel mixture enters the crank chamber through
the valve. The mixture enters due to the pressure difference
between the crank chamber and outer atmosphere. At the same
time the fuel-air mixture above the piton is compressed.
Ignition with the help of spark plug takes
place at the end of stroke. Due to the explosion of the gases, the piston moves downward. When the piston
moves downwards the valve closes and the fuel-air mixture
inside the crank chamber is compressed. When the piston is
at the bottom dead centre, the burnt gases escape from the
same time the transfer port is uncovered and the compressed
charge from the crank chamber enters into the combustion
chamber through transfer port. This fresh charge is
deflected upwards by a hump provided on the top of the
piston. This fresh charge removes the exhaust gases from the
Again the piston moves from bottom dead centre
to top dead centre and the fuel-air mixture gets compressed
when the both the Exhaust port and Transfer ports are
covered. The cycle is repeated.