Difference between 2-Stroke and 4-stroke engines.

Difference between Four Stroke Engine &  two-stroke engine

 Four Stroke EngineTwo Stroke Engine
1.It has one power stroke for every two revolutions of the crankshaft.It has one power stroke for each revolution of the crankshaft.
2.Heavy flywheel is required and the engine runs unbalanced because the turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft.Engine design is simple due to the absence of valve mechanism.
3.Engine design is complicated due to the valve mechanism.The engine is heavy. Power to weight ratio is low
4.Less output due to mixing of fresh charge with the hot burnt gases. mep is lowThe engine is light. Power to weight ratio is high
6.Less mechanical efficiency due to more friction on many parts. More wear and tear. More maintenance is requiredMore mechanical efficiency due to less friction on a few parts. Less wear and tear. Less maintenance is required
7.More output due to full fresh charge intake and full burnt gases exhaust.mep is highLess output due to mixing of fresh charge with the hot burnt gases.mep is low
8.Power developed is lessPower developed is more (almost double)
9.Gear box [to reduce speed & reversing] is connected between engine and propeller shaftEngine directly connected to propeller shaft. Engine is reversible
10.Engine consists of inlet and exhaust valve.Engine consists of inlet port and exhaust port/valve.
11.More thermal efficiency.Less thermal efficiency, as effective compression ratio is less
12.Separate cylinder L.O is not requiredSeparate cylinder L.O is required
13.High speed & Short Stroke – Costly fuel of better ignition quality should be usedSlow speed & Long Stroke – effective scavenging and cheap fuel of low ignition quality can be burnt

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