Difference between two stroke and four stroke engine

Differences between two stroke and four stroke engine

Two-stroke and four-stroke engines are two distinct types of internal combustion engines. Despite sharing the goal of converting fuel into mechanical energy, they differ in their operating cycles and characteristics. In this discussion, we will explore the differences between these engine types, shedding light on their respective designs and working. By the end, you will gain a clear understanding of how these engines vary and their significance in various industries.

Fig: Two stroke engine
Difference between two stroke and four stroke engine
Fig: Four stroke engine

Differences between two stroke and four stroke are:

Two stroke Four stroke
The whole cycle (suction, compression, expansion, exhaust) is completed in 2 strokes of the piston.The whole cycle (suction, compression, expansion, exhaust) is completed in 4 strokes of the piston.
Horse power output (theoretically) of a 2 stroke engine is twice that of 4 stroke but in actual practice it is 1.5 to 1.8 times.Horse power output is less than that of a 2 stroke engine.
Higher pressure and temperature at the starting of a compression stroke, hence thermal stress on the combustion chamber wall.Lower pressure and temperature as compared to 2 strokes, hence less thermal stresses.
Less volumetric efficiency and poor scavenging, hence less efficient.More volumetric efficiency and better scavenging, hence more efficient.
More fuel consumption.Less fuel consumption.
More headroom required.4 stroke trunk piston requires less head room.
Torque produced is more regular, hence the flywheel is smaller.Torque produced is irregular and hence heavier flywheel required in comparison with a 2 stroke engine as the number of operating cycles in a 2 stroke engine is twice that in a 4 stroke engine.
2 strokes are used in low speed high powered diesel main propulsion.4 strokes are used in medium speed power generation.
One power stroke takes place at every revolution of the crankshaft.One power stroke takes place every two revolutions of the crankshaft.
Camshaft to crankshaft ratio is 1:1.Camshaft to crankshaft ratio is 1:2.
2 stroke low speed engine can burn fuel of cheaper quality because of the very long stroke which adds more time for scavenging and exhaust process.4 stroke engine faces trouble in burning cheaper low quality fuel.
Lube oil costs less.Lube oil cost more than 2 stroke engines of equivalent power.
Higher power to weight ratio.Less power to weight ratio.

Are 2 stroke engines more efficient than 4-stroke engines?

A four-stroke engine is more efficient than a two-stroke engine. Since fuel is consumed once every four strokes in a four stroke engine, fuel is less consumed, as opposed to every two strokes in a two stroke engine.


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