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Two-Stroke Cycle Petrol Engine

Two-Stroke Cycle Petrol Engine Points : Two-Stroke Cycle Petrol Engine, Suction, Compression, Expansion, Exhaust There is one working stroke in one cycle of four-stroke cycle engines i.e.; in two revolutions of crank shaft. The desire to have one working stroke pr cylinder for every revolution of the crankshaft has led to the development of two stroke cycle engines.
A two stroke cycle engine was devised by Duglad Clerk in 1880. In this cycle the suction, compression, expansion and exhaust takes Place during two strokes of piston. It means that there is one working stroke after every revolution of the crankshaft. A two stroke engine has ports instead of valves. All the four stages of two stroke petrol engine are described below:
1. Suction In this stage, the piston while going down, uncovers the inlet port (I.P) and fresh air-fuel mixture flows into the engine cylinder from the crank case(C.C). 2. Compression In this stage, the piston, while moving up, first covers the inlet port and then exhaust port. After that the fuel is compressed as the piston moves upwards. In this stage, the inlet port opens also and fresh air-fuel mixture enters in the crank case due to the vacuum created by the upward motion of the piston during compression stroke. 3. Expansion Shortly before the piston reaches T.D.C (during compression stroke) the charge is ignited with the help of a spark plug (SP). It suddenly increases the pressure and temperature of the products of combustion. But volume practically remains constant. Due to rise in pressure, the piston is pushed down wards 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. 4. Exhaust In this stage exhaust valve is opened as the piston moves down wards. The products of combustion, from the engine cylinder are exhausted through the exhaust valve into the atmosphere. This completes the cycle and the engine cylinder is ready to suck the charge once again.

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