4-Stroke and 2- Stroke cycle engine: a comparative study

4- Stroke engine:

1.        Lower fuel consumption:

The scavenging (exhaust) port in the 2- stroke engine being in the midway of the full stroke of the piston, some amount of unburnt gas escapes along with exhaust gas. But there is no such scope in the 4- stroke engine and as such, the total fuel consumption is lower in 4- stroke engine.

2.        Smooth Low speed operation:

In 2- stroke engine the exhaust gas cannot be fully expelled, whereas it can be fully expelled in the 4- stroke engine. Thus the 4-stroke engine runs smoothly particularly in low speed.

3.        Better Balanced:

In 4-stroke engine, because of all the four strokes of the piston being independent and full is better balanced. Because of the same reason, the engine is less over heated.

4.        More Noise:

Because of a large number of valves and other movable parts of the 4-stroke engine, it is a bit noisy.

5.       The number of combustion and explosions being less (1/2 of 4-stroke) the 4-stroke engine requires more number of cylinders (multi cylinders) for smooth running and better performance.

 

2-stroke engine:

1.        Smooth crankshaft rotation

In 2-stroke engine, the number of explosions being more (double) than 4-stroke engine, the crankshaft  rotation is more uniform and smooth. With the same displacement as a 4-stroke engine, the power output of a 2-stroke engine is higher.

2.        Low Cost:

Number of frictional or movable parts being less (no valve at all), the construction cost of 2-stroke engine is low. And at the same time its reliability is high.

3.        Incomplete Exhaust and Environment Pollution:

The exhaust port being in the halfway, the cylinder and piston get more overheated, resulting in lubrication problem. This causes more wear and tear of the piston rings and other parts. Moreover, incomplete combustion causes environmental pollution.

4.        Slight fluctuation at Low Speed:

The intake of charge (air + fuel in gasoline engine and only air in Diesel engine) is usually controlled from outside and hence; particularly at low speed the engine performance is a bit fluctuating.