Difference between SI Engine and CI Engine [Notes & PDF]

Table of Contents

The main differences between SI and CI engine are the fuel petrol used in SI engine and Diesel fuel used in CI engine.

Here I have listed 19 points on difference between SI and CI engine in detail.

Before moving to study or discuss in-depth let’s know little overview on SI and CI engine first.

SI Engine:

SI engine is known or called Spark Ignition engine. In this engine, the combustion of fuel are done by Spark Plug.

CI Engine:

CI engine is called a combustion Ignition engine. In this engine, the combustion of fuel are done by injection of fuel into the hot compressed air.

Difference between SI Engine and CI Engine:

Sl No.	SI Engine	CI Engine
1.	SI engine is known as the Spark Ignition engine.	CI engine is known as the Combustion Ignition engine.
2.	The fuel used here is Gasoline or Petrol.	In CI engine the fuel used is Diesel.
3.	The compression ratio is 6 to 9.	The compression ratio is high around 15 to 20.
4.	This is light in weight because of the low pressure developed here.	This is heavy in weight because of the high pressure developed here.
5.	Low vibration and Noise here.	Here more vibration and noise.
6.	SI engine works on the Otto cycle.	CI engine works on the Diesel cycle.
7.	The speed is higher in the SI engine.	The speed is low in the CI engine.
8.	Thermal efficiency is low or average.	Thermal efficiency is high.
9.	Air and fuel are used during the intake process	but here only air is used during the intake process.
10.	This is kind of cheaper in price.	This we get higher in price.
11.	This is also called a constant volume cycle.	This is called a constant pressure cycle.
12.	Petrol fuel has a high self-ignition temperature.	Diesel fuel has a self-ignition temperature but it’s low.
13.	Knocking takes place at the end of the combustion.	Knocking takes place at the beginning of the combustion.
14.	A homogenous mixture of fuel.	A heterogeneous mixture of fuel.
15.	Petrol fuel is used in aerospace and automobiles.	Diese fuel used in heavy vehicles such as lorries, buses, and trucks, more.
16.	SI engine fitted with carburetor and spark plug.	CI engine fitted with injection or fuel injected pump.
17.	Here ignition of air-fuel mixtures takes place by an electric spark produced by a spark plug.	But here air-fuel take place by injection of fuel into the hot compressed air.
18.	Temperature range here 250 to 300-degree celsius.	In CI engine Temperature 600 to 700 degree celsius.
19.	In the SI engine, Specific fuel consumption is more.	Here in the CI engine, the specific fuel consumption is less.