Difference Between Petrol and Diesel Engine

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Difference Between Petrol and Diesel Engine

Editing Date：2026-04-15

Before starting to discuss about the Difference Between Petrol and Diesel Engine let us first understand about both types of engines individually.

What is a Petrol Engine?

As the name suggests, a Petrol engine is an engine where we use petrol as fuel to produce power. Generally, Petrol Engines are called SI Engine. The full form of SI is Spark Ignition. We need a spark plug to burn or ignite the petrol, that’s why it is called the spark-ignition engine.

What is a Diesel Engine?

An engine where we use diesel as fuel to produce the power is called as a diesel engine. Diesel Engines are called CI Engine, which stands for Compression Ignition engine. In the case of a Diesel Engine, only air is sucked in the suction stroke and then the air is compressed to a very high temperature and pressure.

Then an injector sprays the atomized diesel inside the compressed air chamber. Within seconds after coming in contact the fuel is burned to generate power. As the ignition is happened by the compression of air, that’s why this type of engine is called a compression ignition engine.

Difference Between Petrol and Diesel Engine

PETROL ENGINE

DIESEL ENGINE

The Petrol engine works on the principle of the Otto cycle.

The Diesel engine works on the principle of the Diesel cycle.

In Petrol engine carburetor is fitted with the cylinder.

In Diesel engine carburetor is not fitted with the cylinder. Instead of a carburetor, we use a fuel injector and fuel pump to supply the fuel.

Both Air and fuel mixture is drawn into the cylinder in the petrol engine.

Only air is drawn into the cylinder in the diesel engine.

In Petrol Engine Spark Plug is fitted with the cylinder.

In the Diesel engine, the Fuel Injector is fitted with the cylinder.

The compression ratio for a petrol engine is generally 7:1.

In case of a diesel engine, the compression ration is 16:1.

In the petrol engine, less power is developed.

In the diesel engine, more power is developed.

The construction of flywheel is light.

In this case, the flywheel construction is heavy.

The petrol engine is used for lighter vehicles.

The Diesel engine is used for heavier vehicles.

In Petrol Engine Battery is essential for generating the spark.

In Diesel, engine Battery is essential only for lighting purpose.

Maintenance cost is higher for Petrol Engine.

The maintenance cost is low in the Diesel engine.

Due to the lower compression ratio the size of the petrol engine is small.

Due to the higher compression ratio the size of the diesel engine is bulky.

FAQs

List conditions under which combustion can take place.

The conditions required for combustion to take place are:

1. Fuel: Presence of a fuel

2. Air: Oxygen is must for combustion to occur

3. Ignition temperature: The minimum temperature at which a substance catches fire.

Explain how the use of CNG in automobiles has reduced pollution in our cities.

Combustion of fuels like petroleum causes the addition of many harmful pollutants like un-burnt carbon, particulate matter, and many fume gases enter the air and cause respiratory diseases.

Compressed Natural Gas (CNG) produces these harmful products in very little quantity.
It is a comparatively cleaner fuel. Therefore, the use of CNG has reduced pollution in our cities.

Give reasons : LPG is a better domestic fuel than wood.

LPG is a better domestic fuel than wood as
	It does not produce smoke and unburnt carbon particles, which cause respiratory problems.
	It has a low ignition temperature.
	It is easy to store.

Name the unit in which the calorific value of a fuel is expressed.

The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg).

Explain how CO2 is able to control fires.

CO2 is a non-combustible gas and it is also a non-supporter of combustion. It extinguishes fire in two ways:

Since it is heavier than oxygen, it covers the fire like a blanket around the burning material and cuts off the contact between oxygen and fuel.

In cylinders, CO2 is kept in liquid form. When released, it expands enormously and cools down. This brings down the temperature of the fuel, which helps in controlling the fire.