Each stroke in IC engines forms a sequence of operations in one cycle of IC Engines i.e suction stroke, compression stroke, expansion stroke, and exhaust stroke.

Strictly speaking, when an engine is working continuously, we may consider a cycle starting from any stroke. We know that when the engine returns back to the stroke where it started, we say that one cycle has completed. The following sequence of operation in a cycle is widely used.

1.    Suction stroke. In this stroke, the fuel vapor in correct proportion, is supplied to the engine cylinder.

2.    Compression stroke. In this stroke, the fuel vapor is compressed in the engine cylinder.

3.    Expansion or working stroke. In this stroke, the fuel vapor is fired just before the compression is complete. It results in the sudden rise of pressure, due to expansion of the combustion products in the engine cylinder. This sudden rise of pressure pushes the piston with a great force and rotates the crankshaft. The crankshaft, in turn, drives the machine connected to it.

Exhaust stroke. In this stroke, the burnt gases (or combustion products) are exhausted from the engine cylinder, so as to make space available for the fresh fuel vapor