SI Engine & CI Engine

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.

S.no	Aspect	Spark Ignition Engine (SI engine)	Compression Ignition Engine (Ci engine)
1	Engine speed	SI engines are high speed engines.	CI engines are low speed engines.
2	Cycle efficiency	SI engines have low thermal efficiency	CI engines have high thermal efficiency.
3	Fuel used	Petrol is used as fuel, which has high self ignition temperature.	Diesel is used as fuel, it has low self ignition temperature.
4	Time of knocking	Knocking takes place at the end of combustion.	Knocking takes place at the beginning of combustion.
5	Cycle operation	SI engine works on otto cycle.	CI engine works on diesel cycle.
6	Pressure generated	Homogeneous mixture of fuel, hence high pressure is generated.	Heterogeneous mixture of fuel, hence low pressure is generated.

And this is a simple Comparison show the main Difference between S.I & C.I engine