Difference between Two Stroke and Four Stroke Engine
Four stroke engine
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Two-stroke engine
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Working cycle is divided into 4 phases,
two turns (720°) of crankshaft required to complete one cycle.
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Working cycle is divided into 2 phases,
one turn (360°) of the crankshaft to complete a full cycle. Intake and power
stroke, as well as compression and exhaust strokes, are merged.
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One power stroke per two revolutions,
low power as compared to the 2-stroke
engine. Turning momentum is not uniform, so heavier flywheel required.
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One power
stroke per one revolution; gives high power to the
volume ratio. So the uniform power
output and they need a lighter flywheel.
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They use valves for control gas flow. Involved complex valve actuating
mechanism.
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They use port instead valves. So they
do not need a heavier valve actuating mechanism.
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Oil sump is used to
lubricate the crankcase.
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No oil sump, lubrication is done by using petroil. So they can be employed in all positions.
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Lesser cooling and lubrication are needed.
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Greater cooling and
lubrication are required.
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Clean combustion and low pollution.
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Incomplete combustion and burning of
lubricating oil cause high pollution.
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Very little noise.
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High vibration and noisy
operation.
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Low volumetric efficiency.
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High volumetric efficiency due to more
time for induction.
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Thermal
efficiency is high, better part load efficiency.
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Low
thermal efficiency, poor part load efficiency.
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Long
lifespan compared to the 2-stroke engine.
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More
fragile and wear out.
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Piston
crown is flat or dome shaped.
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A
deflector provided on the crown of the piston for better scavenging.
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Heavier,
expensive.
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Lighter,
simple and cheaper.
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Used were
efficiency important; it is widespread more than 90% engines are 4-stroke.
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Used
where efficiency not necessary, and better compactness required, e.g.,
motorcycle
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-Working of the Two-Stroke engine with P-V diagram
- Comparison between SI engine and CI engine
