Difference between SI and CI Engines:-
The following are the main differences between SI and CI Engines:
Spark Ignition (SI) Engine
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Compression Ignition (CI) Engine
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Spark plug required
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No spark plug required
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The mixture of air and fuel is introduced into the cylinder from carburettor.
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Only air is introduced into the cylinder.
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These type of engines compresses air and fuel together in the
cylinder
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In these engines air is only compressed in the cylinder.
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No fuel pump is used.
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Fuel pump is used to inject fuel.
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Fuel is mixed with air before compression starts.
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Fuel is mixed with air once compression is complete.
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Compression ratio is low.
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Compression ratio is high.
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This type of engine makes use of highly volatile liquid fuel.
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This type of engine makes use of less volatile liquid fuel.
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Less efficient.
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More efficient.
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Fuel used in this engine is expensive.
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Cheaper fuels are used in these engines.
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Higher fuel consumption in these engines for same power.
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These engines have lesser fuel consumption for same power.
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Engines are more compact and light.
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Heavier and strong engines due to higher pressure involved
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Initial cost is less
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Initial Cost is high.
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These engines have a smooth operation
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Roughness in engine operation encountered, especially when the engine
runs at high speed and low loads.
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Difference between four stroke and two stroke engines:-
The following are the main differences between a four stroke and two stroke engines:
4-Stroke
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2-Stroke
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In four stroke
engine all the four operations i.e. suction, compression, ignition and
exhaust are completed in two revolutions of crank shaft.
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In two strokes
engine all the four operations are completed in one revolution of the crank
shaft.
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Power is
developed in every alternate revolution of the crankshaft.
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Power
is developed in every revolution of the crankshaft.
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The torque is
less uniform; hence a four stroke engine requires a heavier flywheel.
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The torque is
more uniform than in the four stroke engine hence a lighter flywheel is
necessary in a two stroke engine.
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The suction
and the exhaust are opened and closed by mechanical valves in a four stroke
engine
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In a two
stroke engine, the piston itself opens and closes the ports
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In a four
stroke engine the charge directly enters into the cylinder
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in a two
stroke engine
the charge
first enters the crankcase and then flows into the cylinder
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The crankcase of
a four stroke engine even though closed is not a pressure tight chamber.
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The crankcase
of a two stroke engine is a closed pressure tight chamber
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In a four
stroke engine the piston drives out the burnt gases during the exhaust stroke.
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whereas, in a
two stroke engine the high pressure fresh charge scavenges out the burnt
gases
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The
lubricating oil consumption in a four stroke engine is less.
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The
lubricating oil consumption in a two stroke engine is more than in four
stroke engine.
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A four stroke
engine produces less noise.
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A two stroke
engine produces more noise than a four stroke engine.
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Since the fuel
burns in every alternate revolution of the crankshaft in a two stroke engine
the rate of cooling is more than in a four stroke engine.
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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.
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A four stroke
engine cannot run in either direction.
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A
valve less two stroke engines runs in either direction
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