The following are the main differences between a
four stroke and two stroke engines.
1. In a four
stroke engine, power is developed in every alternate revolution of the crankshaft
whereas; in a two stroke engine power is developed in every revolution of the
crankshaft.
2. In a two
stroke engine, the torque is more uniform than in the four stroke engine hence
a lighter flywheel is necessary in a two stroke engine, whereas a four stroke
engine requires a heavier flywheel.
3. The suction
and the exhaust are opened and closed by mechanical valves in a four stroke
engine, whereas in a two stroke engine, the piston itself opens and closes the
ports.
4. In a four
stroke engine the charge directly enters into the cylinder whereas in a two
stroke engine the charge first enters the crankcase and then flows into the
cylinder.
5. The
crankcase of a two stroke engine is a closed pressure tight chamber whereas the
crankcase of a four stroke engine even though closed is not a pressure tight
chamber.
6. In a four
stroke engine the piston drives out the burnt gases during the exhaust stroke,
whereas, in a two stroke engine the high pressure fresh charge scavenges out
the burnt gases.
7. The
lubricating oil consumption in a two stroke engine is more than in four stroke
engine.
8. A two
stroke engine produces more noise than a four stroke engine.
9. Since the
fuel burns in every revolution of the crankshaft in a two stroke engine the
rate of cooling is more than in a four stroke engine.
10. A valve
less two stroke engines runs in either direction, whereas a four stroke engine
cannot run in either direction.
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