Two Stroke Cycle Engine
Merits: One power stroke in one revolution of the crankshaft
Power developed for the same engine speed theoretically twice that of a four stroke engine
Simple design and lighter in construction for the same power
Merits: Uniform torque is obtained. Hence a lighter fly wheel can be used
Design of ports is simpler. Hence initial cost is less
Mechanical efficiency is high. No moving parts like cam, follower, rocker arm valves etc.,
Merits: Starting is easy
These engines are generally air cooled
Four Stroke Cycle Engine
Demerits: One power stroke in two revolutions of the crank shaft Power developed for the same engine speed is theoretically half that of two stroke engine.
For the same power complicated design and heavier in construction.
Demerits: Non uniform torque on the crankshaft. Hence a heavier flywheel is required for balancing. Design valve mechanism is difficult. Hence initial cost is more.Mechanical efficiency is less. Power is lost due to friction caused by valve mechanism
Demerits: Starting is not so easy. These engines are generally water cooled.
COMPARISON BETWEEN FOUR STROKE CYCLE AND TWO STROKE CYCLE ENGINE (MERITS AND DEMERITS):
Two Stroke Cycle Engine
DeMerits: Consumption of lubricating oil is more, because less time is available to remove the heat More wear and tear of moving parts.
Some of the fresh air fuel mixture may escape with exhaust gases. Hence fuel consumption is more
DeMerits: Thermal efficiency is less. It produces more noise due to sudden release of exhaust gases Scavenging is poor, since exhaust port is open only for a short time
Merits: Poor scavenging leads to mixing of fresh charge with exhaust gases. This results in poor performance, slow running Used in light vehicles, like bikes, scooters, mopeds, etc.
Four Stroke Cycle Engine
Merits: Consumption of lubricating oil is less, because more time is allowed for removing heat from the cylinder. Less wear and tear of parts is less
Fuel cannot escape with exhaust gases. Hence fuel consumption is less.
Merits: Thermal efficiency is more.
Noise is less is less. Exhaust gases are released in separate stroke.
Scavenging is better, since there is a separate exhaust stroke for the removal of exhaust gases
Demerits: Better performance and efficiency is more
Used in heavy vehicles, like buses, lorries, trucks etc.
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