SI and CI

Comparison of SI and CI engine:
SI engine
CI engine
Working cycle is Otto cycle.
Working cycle is diesel cycle.
Petrol or gasoline or high octane fuel is used.
Diesel or high cetane fuel is used.
High self-ignition temperature.
Low self-ignition temperature.
Fuel and air introduced as a gaseous mixture in the suction stroke.
Fuel is injected directly into the combustion chamber at high pressure at the end of compression stroke.
Carburettor used to provide the mixture. Throttle controls the quantity of mixture introduced.
Injector and high pressure pump used to supply of fuel. Quantity of fuel regulated in pump.
Use of spark plug for ignition system
Self-ignition by the compression of air which increased the temperature required for combustion
Compression ratio is 6 to 10.5
Compression ratio is 14 to 22
Higher maximum RPM due to lower weight
Lower maximum RPM
Maximum efficiency lower due to lower compression ratio
Higher maximum efficiency due to higher compression ratio
Lighter
Heavier due to higher pressures