Two vs. Four Strokes

Difference Between Two and Four Strokes

The combustion engines are categorized as two and four strokes engines. Two and four stroke refers to the numbers of times the piston moves up and down the cylinder to complete one combustion cycle. It is called Otto Cycle. There is one upward and downward stroke in the two stroke engine. On the other hand there are total four strokes in its combustion cycle in the four stroke engines.

Two Strokes

The compression stroke and the return make two strokes in the engine. When there is compression stroke the mixture of air-fuel- oil mixture is compressed followed by the explosion of the fuel. The exhaust is forced out through a bypass in the return stroke. At the same time the cylinder sucks a new mixture.

Two stroke engine is easier and less expensive. It makes twice the power of a four stroke engine of the same size. It is of small size and may be used scooter, motor bikes, chain saw and lawn movers etc. It is also used in marine ships and diesel trains. It does not contain a separate lubricating system. So, its parts are worn faster as compared to the four stroke engine. The oil is mixed with fuel. So it causes more pollution.

Four Strokes

There is one compression an done exhaust stroke in the four stroke engines. They are followed by return stroke to complete the combustion cycle. The combustion takes place at the top dead centre when compression stroke compresses the fuel mixture. During the second upward movement, the exhaust valve gets open. It is called exhaust stroke. The brunt fuel emits through this valve. The valve is closed during the second stroke and intake valves are open to suck the mixture of the cylinder.

A four stroke engine has a proper lubricating system. It has a different mechanism to control the valves. It produces one power stroke for two revolutions of the crankshaft. It is a costly engine compared to the two stroke engine. It is more fuel efficient than a two stroke engine. As the oil is not mixed in fuel, it causes less pollution.

Difference between two strokes and four strokes

The number of strokes in each types of engine creates a difference between the two. Both the engines are based on internal combustion. But they have differences in their mechanisms. They have their own advantages and disadvantages. Two stroke engines are less expensive and have simple construction. On the other hand four stroke engines are more expensive and complicated mechanism involved. But they are less pollutant and more fuel efficient than two stroke engines.


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