Engine Terminology:
1.Top Dead Center (TDC): Position of the piston when it stops at the furthest point away from
the crankshaft.
– Top because this position is at the top of the engines (not always), and dead because the piston
stops as this point.
– When the piston is at TDC, the volume in the cylinder is a minimum called the clearance
volume.
2. Bottom Dead Center (BDC): Position of the piston when it stops at the point closest to the
crankshaft. Volume of the cylinder is maximum.
3. Stroke : Distance traveled by the piston from one extreme position to the other : TDC to BDC
or BDC to TDC.
4. Bore :It is defined as cylinder diameter or piston face diameter; piston face diameter is same
as cylinder diameter( minus small clearance).
5. Swept volume/Displacement volume : Volume displaced by the piston as it travels through
one stroke.
– Swept volume is defined as stroke times bore.
– Displacement can be given for one cylinder or entire engine (one cylinder times number of
cylinders).
6. Clearance volume : It is the minimum volume of the cylinder available for the charge (air or air
fuel mixture) when the piston reaches at its outermost point (top dead center or outer dead
center) during compression stroke of the cycle.
– Minimum volume of combustion chamber with piston at TDC.
7. Compression ratio : The ratio of total volume to clearance volume of the cylinder is the
compression ratio of the engine.
– Typically compression ratio for SI engines varies form 8 to 12 and for CI engines it varies
from 12 to 24
DIFFERENCE BETWEEN SI ENGINE AND CI ENGINE
SI ENGINES:-
1. Working cycle is Otto cycle.
2. Petrol or gasoline or high
octane fuel is used .
3. High self-ignition temperature.
4. Fuel and air introduced as a
gaseous mixture in the suction
stroke.
5. Carburettor used to provide the
mixture. Throttle controls the
quantity of mixture introduced.
6. Use of spark plug for ignition
system.
7. Compression ratio is 6 to 10.5 .
8. Higher maximum RPM due to
lower weight.
9. Maximum efficiency lower due
to lower compression ratio.
10. Lighter.
CI ENGINES :-
1. Working cycle is diesel cycle.
2. Diesel or high cetane fuel is
used.
3. Low self-ignition temperature.
4. Fuel is injected directly into the
combustion chamber at high
pressure at the end of
compression stroke.
5. Injector and high pressure pump
used to supply of fuel. Quantity
of fuel regulated in pump.
6. Self-ignition by the compression
of air which increased the
temperature required for
combustion.
7. Compression ratio is 14 to 22.
8. Lower maximum RPM.
9.Higher maximum efficiency due
to higher compression ratio.
10.Heavier due to higher pressures.
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1.Top Dead Center (TDC): Position of the piston when it stops at the furthest point away from
the crankshaft.
– Top because this position is at the top of the engines (not always), and dead because the piston
stops as this point.
– When the piston is at TDC, the volume in the cylinder is a minimum called the clearance
volume.
2. Bottom Dead Center (BDC): Position of the piston when it stops at the point closest to the
crankshaft. Volume of the cylinder is maximum.
3. Stroke : Distance traveled by the piston from one extreme position to the other : TDC to BDC
or BDC to TDC.
4. Bore :It is defined as cylinder diameter or piston face diameter; piston face diameter is same
as cylinder diameter( minus small clearance).
5. Swept volume/Displacement volume : Volume displaced by the piston as it travels through
one stroke.
– Swept volume is defined as stroke times bore.
– Displacement can be given for one cylinder or entire engine (one cylinder times number of
cylinders).
6. Clearance volume : It is the minimum volume of the cylinder available for the charge (air or air
fuel mixture) when the piston reaches at its outermost point (top dead center or outer dead
center) during compression stroke of the cycle.
– Minimum volume of combustion chamber with piston at TDC.
7. Compression ratio : The ratio of total volume to clearance volume of the cylinder is the
compression ratio of the engine.
– Typically compression ratio for SI engines varies form 8 to 12 and for CI engines it varies
from 12 to 24
DIFFERENCE BETWEEN SI ENGINE AND CI ENGINE
SI ENGINES:-
1. Working cycle is Otto cycle.
2. Petrol or gasoline or high
octane fuel is used .
3. High self-ignition temperature.
4. Fuel and air introduced as a
gaseous mixture in the suction
stroke.
5. Carburettor used to provide the
mixture. Throttle controls the
quantity of mixture introduced.
6. Use of spark plug for ignition
system.
7. Compression ratio is 6 to 10.5 .
8. Higher maximum RPM due to
lower weight.
9. Maximum efficiency lower due
to lower compression ratio.
10. Lighter.
CI ENGINES :-
1. Working cycle is diesel cycle.
2. Diesel or high cetane fuel is
used.
3. Low self-ignition temperature.
4. Fuel is injected directly into the
combustion chamber at high
pressure at the end of
compression stroke.
5. Injector and high pressure pump
used to supply of fuel. Quantity
of fuel regulated in pump.
6. Self-ignition by the compression
of air which increased the
temperature required for
combustion.
7. Compression ratio is 14 to 22.
8. Lower maximum RPM.
9.Higher maximum efficiency due
to higher compression ratio.
10.Heavier due to higher pressures.
Join fb group :- Fb group
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