Two-stroke and four-stroke cycle engine

-:::Two-stroke and four-stroke cycle engine:::-

A two-stroke engine working cycle is completed into 2 stocks of the Piston or revolution of the crankshaft.

A four-stroke engine working cycle is completed in 4 strokes of the Piston for two revolutions of the crankshaft.

The sequence of operation in a cycle::-
Strictly speaking, when an engine working continuously we may consider a cycle starting from any stock. That the engine returned back to the stock 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 vapour in correct proportion, is supplied to the engine cylinder.
2) compression stroke:- In this stroke, the fuel vapour is compressed in the engine cylinder.

3) expansion or working stroke:- in this stroke, the fuel vapour is fired just before the compression is complete. It results in the sudden rise of pressure, due to expansion of the combustion product in the engine cylinder. This sudden rise of pressure pushes the Piston with a great force and rotate the crankshaft. The crankshaft in turn drives the machine connected to it.

Exhaust stroke:- in this stroke, the brunt gases( or combination product) exhaust form the engine cylinder, so as to make face available for the fresh fuel vapour.

Advantages and disadvantages of 2 stroke over 4 stroke cycle engine::-

The following are the advantages and disadvantages of 2 stroke over 4 stroke cycle engine,

 

Advantages::-
1) two-stroke cycle engine gives twice the number of power stroke as a 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, the 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 four-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 forced-to-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.

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