petrol engine

Have ever wondered when you buy a new engine what engine is it? Or when you buy a new car what type of engine in it?.

If you know that great but if you don’t let me tell you there are two types of engines used in cars, petrol and diesel engines. Petrol and diesel engines are classified on the basis of the respective fuels used by these engines. The engine which uses petrol to run is called a petrol engine while the one using diesel to run is called a diesel engine.

For more information, let’s see What is Petrol and Diesel Engines and the Difference Between them.

What is the Diesel and Petrol Engines

Petrol Engine

A Petrol engine is an Internal Combustion Engine in which the spark ignition is fitted. In this engine fuel and air are usually mixed after compression. The former mixture was formerly used in a carburetor, but now it is done by electronically controlled fuel injection.

Diesel engine

A diesel engine is an ICE (Internal Combustion Engine) in which the air is compressed to a high enough temperature to ignite the diesel oil injected into the cylinder, where expansion and combustion energize a piston. The diesel engine is also known as a compression engine. It is named after Rudolf’s engine.

The diesel engine can be made to run on an alternative and renewable source of energy such as Biodiesel with little or no modification. Biodiesel generally refers to used vegetable oil that has been used for cooking and it can also be recycled and treated so that it can be used to power diesel cars.

Petrol Engines v/s Diesel Engines

Petrol Engine

  • The petrol engine works on the Otto cycle, which consists of two isochoric processes.
  • In the petrol engine the fuel is highly volatile (volatile means; the liquid solution vaporized automatically when in contact with the air).
  • The petrol engine is fitted with a spark plug.
  • Petrol engines are commonly used in lightweight vehicles such as cars, motorcycles, scooters, etc.
  • Petrol engines need repeatedly overhauling.
  • The petrol engine maintenance cost is lower.
  • The petrol engine has a lower compression ratio ( 6 to 10) so it produces less power than the diesel engine.
  • The thermal efficiency of a petrol engine is 26%.
  • In the petrol engine, the compression is about 10 bar.
  • In a petrol engine, the spark plug is generated by the spark plug into the chamber plug so the ignition is caused by a spark from an external source, hence it is called a spark ignition (SI) engine.
  • A car with a petrol engine has less efficient.
  • Due to the low compression ratio, the petrol engine has low vibrations so it produces low noise.
  • The petrol engine torque is lower than the diesel engines.
  • Petrol engines are also high-speed engines due to their lightweight and homogeneous combustion.

Diesel Engine

  • The diesel engine works on the diesel cycle.
  • Diesel is used as fuel in this engine which is a non-volatile fuel.
  • The diesel engine is fitted with a fuel injector.
  • Diesel engines are used in heavy vehicles such as buses, trucks, etc.
  • Diesel engine overhauling occurs after a very long time.
  • The diesel engine maintenance cost is expensive.
  • In the diesel engine more power is produced due to a high compression ratio (15 to 25).
  • The thermal efficiency of a diesel engine is 40%.
  • In diesel engines, the compression is about 35 bar.
  • In a diesel engine, the ignition is caused by the heat generated during the compression stroke by a high compression ratio. Hence it is called a compression ignition (CI) engine.
  • A diesel engine is more efficient, cars can get incredible mileage out of them.
  • Due to the high compression ratio, the diesel engine has large vibration so it produces a loud noise.
  • Diesel engine fuel efficiency is better than the petrol engine.
  • Diesel engine torque is high.
  • Diesel engines are also low-speed engines due to heavyweight and heterogeneous combustion.

Which is better between petrol and diesel engine?

Diesel and petrol engines are the main engines in the automobile industry nowadays, and both are internal combustion engines.

A diesel engine uses compression ignition, which can quickly ruin the gas engine because they have come from a workhorse heritage. They tend to be reliable and required less care as compared to the petrol engine. While in a petrol engine, air and petrol are mixed in the carburetor and it enters the cylinder.

The output of the diesel and petrol engines is measured in terms of horsepower and torque. Horsepower is a measure of power, while torque is the measure of an engine twisting force on the driveline. A big amount of both is great, but if you have a lot of horsepower with little torque then your vehicle is going to be slow. Its torque helps to get things moving, that is why diesel engines are used in big vehicles such as trucks.

A diesel engine takes less fuel than a petrol engine. Diesel is more dangerous from the standpoint of solid particles thrown out from diesel engines suspended in the air. The diesel engine doesn’t have a spark plug, that intakes the air and compresses it. And it injects the fuel directly into the combustion chamber which may cause some respiratory issues because it has a tendency to accumulate in our lungs. The smoothness of the petrol engine is a strong advantage, favored by people.


So, from the above article, you can get an idea about which engine is better and which one is not. Both petrol and diesel have their own advantages and disadvantages. Even though diesel has more fuel efficiency and mileage than petrol, it is costlier and required high maintenance costs. Hence, the better choice between the two fuels depends upon the user’s requirement. And needs of the customer( if your car travel is not very sustained, then you can go for a petrol engine while for a long and frequent run you can go for the diesel engine). The difference between both the fuel is considering changing over time.

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