In a two stroke engine, the working cycle is completed in two strokes of the piston or one revolution of the crankshaft. In a four stroke engine, the working cycle is completed in four strokes of the piston or two revolutions of the crankshaft.
The following are the advantages and disadvantages of two stroke over four stroke cycle engines:
Advantages
1. A two stroke cycle engine gives twice the number of power strokes than the four stroke cycle engine at the same engine speed. Theoretically, a two stroke cycle engine should develop twice the power as that of a four stroke cycle engine.
2. For the same power developed, a two stroke cycle engine is lighter, less bulky and occupies less floor area.
3. A two stroke cycle engine has a lighter flywheel and gives higher mechanical efficiency than a tour stroke cycle engine.
Disadvantages
1. The thermal efficiency of a two stroke cycle engine is less than that of a four stroke cycle engine, because a two stroke engine has less compression ratio than that of a four stroke cycle engine.
2. The overall efficiency of a two stroke cycle engine is also less than that of a four stroke cycle engine.
3. The consumption of lubricating oil is large in a two stroke cycle engine because of high operating temperature.