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Spark Ignition (SI) engine can be compared with Compression Ignition (CI) engine system in 7 aspects. Those 7 aspects are engine speed, cycle efficiency, fuel used, time of knocking, cycle operation, pressure generated and constant parameter during cycle.



Spark Ignition Engine

Compression Ignition Engine


Engine speed

SI engines are high speed engines.

CI engines are low speed engines.


Cycle efficiency

SI engines have low thermal efficiency

CI engines have high thermal efficiency.



Fuel used

Petrol is used as fuel, which has high self ignition temperature.

Diesel is used as fuel, it has low self ignition temperature.


Time of knocking

Knocking takes place at the end of combustion.

Knocking takes place at the beginning of combustion.


Cycle operation

SI engine works on otto cycle.

CI engine works on diesel cycle.


Pressure generated

Homogeneous mixture of fuel, hence high pressure is generated.

Heterogeneous mixture of fuel, hence low pressure is generated.


Constant parameter during cycle

Constant volume cycle.

Constant pressure cycle.



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