20-Difference Between SI Engine and CI Engine

In this article, we will discuss about the difference between SI engine and CI engine. The Spark Ignition (SI) engine, as its name indicates uses spark to ignite the fuel. In a Compression Ignition (CI) engine, the air is compressed within the cylinder and the heat of this compression air is used to ignite the fuel. Since spark and compressed air is used to ignite the fuel in these engines, so they are called as spark ignition (SI) engine and compression ignition (CI) engine.

SI Engine (Spark Ignition Engine)

Spark Ignition (SI) Engine is a type of engine in which the combustion takes place by the spark generated by the spark plug. It uses petrol as fuel and works on Otto cycle. In the spark ignition engine, the air-fuel mixture is inserted into the cylinder with the help of carburetor. The compression of the fuel takes place but it has a low compression ratio. The fuel is ignited by the spark generated by the spark plug. SI engine produces less noise and vibration and their starting is very easy. They are light in weight and have less maintenance cost. They are mostly used in light commercial vehicles such as scooters, motorcycles cars, etc.

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CI Engine (Compression Ignition Engine)

Compression Ignition (CI) Engine is an engine in which the combustion of fuel takes place by the heat of the compressed air. It uses diesel as fuel and works on the Diesel cycle. In the compressed ignition engine, only air enters into the cylinder during suction stroke. It has high compression ratio because of the high ignition temperature of the diesel fuel. The heat of the compressed air ignites the fuel. Due to the high compression ratio it produces more power. Due to incomplete combustion of the fuel, it produces more hydrocarbons which lead to air pollution. The noise and vibration problem is there in the CI engines. The maintenance cost of the CI engine is more than compared with the SI engines. They are mostly used in heavy-duty vehicles such as buses, trucks, railways, ships etc.

Difference Between SI Engine and CI Engine in Tabular Form

S.no	Parameter	SI Engine	CI Engine
1.	Definition	It is an engine in which the spark is used to burn the fuel.	It is an engine in which heat of compressed air is used to burn the fuel.
2.	Fuel used	Petrol is used as fuel.	Diesel is used as fuel.
3.	Operating cycle	It operates on Otto cycle.	It operates on Diesel cycle.
4.	Compression ratio	Low compression ratio.	High compression ratio.
5.	Thermal efficiency	High thermal efficiency.	Less thermal efficiency.
6.	Method of ignition	Spark plug is used to produce spark for the ignition.	Heat of compressed air is used for the ignition.
7.	Engine Speed	High speed engines.	Low speed engines.
8.	Pressure generated	Low pressure is generated after combustion.	High pressure is generated after combustion.
9.	Constant parameter during cycle	Constant volume cycle.	Constant pressure cycle.
10.	Intake	Air + fuel.	Only air.
	Weight of engine	Si engine has less weight.	CI engine are heavier.
12.	Noise production	It produces less noise.	It produces more noise.
13.	Production of hydrocarbon	Less Hydrocarbon is produced.	More hydrocarbon is produced.
14.	Starting	The starting of SI engine is easy.	The starting of CI engine is difficult.
15.	Maintenance cost	Low	High
16.	Vibration problem	Less	Very High
17.	Cost of engine	Less cost	High cost
18.	Volume to power ratio	Less	High
19.	Fuel supply	Carburetor	Injector
20.	application	It is used in light commercial vehicles like motorcycle, cars etc.	It is used in heavy duty vehicles likes bus, trucks, ships etc.

Conclusion

So now, I hope you have clearly understood the difference between SI engine and CI engine. If you have any confusion related to that then feel free to ask through your comments. If you find it informative or useful then share it with others.