Difference Compression ignition and Spark Ignition engine~Automobile

What is the difference between a CI engine and an SI engine-

Spark Ignition

The spark Ignition (SI) engine, as its name indicates uses spark to ignite the fuel. And in 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.

Fig 1.1-P-V Diagram of SI

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 help of carburetor. The compression of the fuel takes place, but it has 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.

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 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 fuel is ignited by the heat of the compressed air. Due to 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 as compared with the SI engines. They are mostly used in heavy duty vehicles such as buses, trucks, railways, ships etc.

Fig 1.2-P-V Diagram of CI

Let us study in details (Compare between SI & CI)

1) Definition of SI

It is an engine in which the spark is used to burn the fuel.

CI

It is and engine in which heat of compressed air is used to burn the fuel.

2) Fuel used

Petrol is used as fuel (SI)

Diesel is used as fuel. (CI)

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.

11) 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

Starting of SI engine is easy.

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.