Four Stroke Spark Ignition Engine

In four stroke S.I engine the complete operation is done in four stroke in this each stroke has 180° of crankshaft rotation and this four stroke is completed by 720° of crank rotation.

Intake stroke:

In this stroke start when piston is at TDC and move towards BCD. In this the inlet valve is open and exhaust valve is closed. By the suction formed in the cylinder the fuel air mixture is drawn in the downward motion of piston. when piston reaches BDC the suction stroke end and inlet valve is closed.

Compression Stroke

When the piston moves to TDC upwards the compression starts and by return stroke the charge is compressed in the cylinder. In this stroke both inlet and exhaust valve are closed, the chemical energy is converted in to heat energy during the combustion of fuel, and the pressure is also increased.

Expansion

Due to high pressure of burnt gases the piston moves towards the BDC. Both inlet and exhaust valves are closed in this stroke. Pressure and temperature is increased in this power stroke.

Exhaust Stroke.

The inlet valve is remains closed and exhaust valve is opened due to which pressure of burnt gases reduced to atm level, at the end of the expansion stroke . The remaining burnt gases are forced out of the cylinder. as the piston moves towards to TDC,