Petrol Engine VS Diesel Engine Difference Clearly Explained ....

Spark Ignition (SI) Engine is a type of engine in which the combustion takes place by the spark generated by the spark plug.Where are in case of Compression Ignition (CI) Engine it is an engine in which the combustion of fuel takes place by the heat of the compressed air.

Here are the Few Major Difference Between SI Engine and CI Engine :-

S/No	SI Engine	CI Engine
1	Working cycle is Otto cycle.	Working cycle is diesel cycle.
2	SI engines are high speed engines.	CI engines have high thermal efficiency.
3	High self-ignition temperature.	Low self-ignition temperature.
4	Knocking takes place at the end of combustion.	Knocking takes place at the beginning of combustion.
5	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.
6	Homogeneous mixture of fuel, hence high pressure is generated.	Heterogeneous mixture of fuel, hence low pressure is generated.
7	Constant volume cycle.	Constant pressure cycle.
8	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.
9	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.
10	Use of spark plug for ignition system	Self-ignition by the compression of air which increased the temperature required for combustion
11	Compression ratio is 6 to 10.5	Compression ratio is 14 to 22
12	Higher maximum RPM due to lower weight	Lower maximum RPM
13	Maximum efficiency lower due to lower compression ratio	Higher maximum efficiency due to higher compression ratio
14	Lighter in weight	Heavier due to higher pressures
15	They are mostly used in light commercial vehicles such as scooters, motorcycles cars etc.	They are mostly used in heavy duty vehicles such as buses, trucks, railways, ships etc.