Four Stroke Cycle Petrol Engine

Four Stroke Cycle Petrol Engine Points : Four Stroke Cycle Petrol Engine, Suction Stroke, Expansion or Working Stroke, Compression Stroke, Exhaust Stroke it is also known as Otto cycle. It requires four-strokes of the piston to complete on cycle of operation in the engine cylinder. The work is obtained only during one stroke out of these for a single cylinder engine. These strokes are as follows: 1. Suction Stroke in this stroke, the inlet valve opens and air-fuel mixture(i.e; change) is sucked into the cylinder as the piston moves downward from Top Dead Centre(T.D.C). It continues till the piston reaches its Bottom Dead Centre (B.D.C). 2. Compression Stroke In this stroke, both the valves are closed and charge is compressed as the piston moves upwards from B.D.C to T.D.C. As a result of compression, pressure and temperature of the charge increases. This completes the one revolution of the crank shaft. 3. Expansion or Working Stroke Shortly before the piston reaches T.D.C (during compression stroke) the charge is ignited with the help of spark plug. It suddenly increases the pressure and temperature of (lie products of combustion but the volume, practically, remains constant. Due to the rise in pressure, the piston is pushed down with a great force. The hot burnt gases expand due to high speed of the piston. During this expansion, some of the heat energy produced is transformed into mechanical work. It may he noted that during this working stroke, both the valves are closed and piston move from T.D.C. to B.D.C. 4. Exhaust Stroke In this stroke, the exhaust valve is open as piston moves from B.D.C to T.D.C. This movement of the piston pushes out the products of combustion, from the engine cylinder is exhausted through the exhaust valve into the atmosphere. This completes the cycle, and the engine cylinder is ready to suck the charge once again.