In a two-stroke cycle CI engine, there is one working stroke after every revolution of the crankshaft. All the stages of the two-stroke cycle are discussed.
(i) Suction Stage - In the suction stage, the transfer port and the exhaust port are open while the piston moves toward BDC. The fresh air flows into the cylinder from the crankcase.
(ii) Compression Stage - In this stage, the piston moves toward the top dead center (TDC) while moving up, first covers the transfer port and then the exhaust port. After that, the air is compressed as the piston moves upward. In the compression stage, the inlet port opens and the fresh air enters into the crankcase.
(iii) Expansion Stage - Before the piston reaches the TDC during compression stroke, the fuel oil is injected in the form of fine spray into the engine cylinder through fuel injection valve. At this moment, temperature of the compressed air is sufficiently high to ignite the fuel. It suddenly increases the pressure and temperature of the products of combustion. Due to increased pressure, the piston is pushed with a great force. The hot burnt gases expand due to high speed of the piston. During the expansion, some of the heat energy produced is transformed into mechanical work.
(iv) Exhaust Stage- In exhaust stage, the exhaust port is opened and the piston moves downwards. The products of combustion from the engine cylinder are exhausted through the exhaust port into the atmosphere . This completes the cycle, and the engine cylinder is ready to suck the air again.
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