petrol engine

Do you know diesel and petrol are different fuels? Everybody knows. These fuels came out after the filtration of Crude oil. But we would not discuss the fuels here. Here we will tell you why diesel and petrol use in different 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 diesel engine.

So we like to discuss the diesel and petrol engine here and the differences between them.

Diesel and Petrol Engines

Diesel engine, any 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.

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 and petrol engines are the main engines in the automobile industry nowadays, and both are internal combustion engines. The diesel engine uses a compression ignition technology to ignite the fuel. In a diesel engine, fuel is injected into the compression chamber under high pressure and it compresses into the compression chamber.

Diesel engine uses compression ignition, which can quickly ruin the gas engine and because they have come from a workhorse heritage, they tend to be reliable and required less care as compared to the petrol engine.

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 are great, but if you have a lot of horsepower with little torque than your vehicle is going to be slow. Its torque which helps to get things moving, that is why diesel engines are used in big vehicles such as trucks.

While in a petrol engine, air and petrol are mixed in the carburetor and it enters the cylinder. In diesel engines and petrol engines, different technology uses which is called spark ignition technology. It has a spark plug, and after each compression stroke, there will be spark ignition.

A diesel engine takes less fuel than the 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 it 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.

Diesel Engines v/s Petrol Engines

  • The petrol engine works on the Otto cycle, which consists of two isochoric processes and two isentropic processes while the diesel engine works on the diesel cycle.
  • Diesel is used as fuel in this engine which is a non-volatile fuel, wherein the petrol engine the fuel is highly volatile (volatile mean; the liquid solution which vaporized automatically when it contact with the air).
  • The petrol engine is fitted with a spark plug while the diesel engine is fitted with a fuel injector.
  • Petrol engines are commonly used in lightweight vehicles such as cars, motorcycles, scooters, etc. Diesel engines are used in heavy vehicles such as buses, trucks, etc.
  • Petrol engines need repeatedly overhauling, wherein the diesel engine overhauling occurs after a very long time.
  • The petrol engine maintenance cost is lower than the diesel engine.
  • In the diesel engine more power is produced due to a high compression ratio (15 to 25) wherein the petrol engine has a lower compression ratio ( 6 to 10) so it produces less power than the diesel engine.
  • The thermal efficiency in a diesel engine is 40% and in a petrol engine, it is 26%.
  • In the petrol engine, the compression is about 10 bar and 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. 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.
  • Diesel engine is more efficient, car can get incredible mileage out of them whereas in the car with a petrol engine are less efficient.
  • Due to the high compression ratio, the diesel engine has large vibration so it produces a loud noise. Due to the low compression ratio, the petrol engine has low vibrations so it produces low noise.
  • Diesel engine fuel efficiency is better than the petrol engine.
  • Diesel engines turbocharged more easily. 
  • Diesel fuel doesn’t consist of lead and emission from regulated pollutants such as carbon monoxide. However, diesel engine does create high emission of nitrogen oxides and particulate matter as compared to the petrol car, which is considered as carcinogenic (carcinogenic simply means the thing which causes cancer). Despite the fact that diesel provides a better fuel economy, petrol burns cleaner than diesel, this is the reason why diesel cars lack behind petrol cars in terms of usage.
  • The high compression of gases within the cylinder, diesel engines are built extremely hard and will generally last longer than their petrol counterparts. They can also go longer between maintenance.
  • Diesel engines torque is high where the petrol engine torque is lower than the diesel engines.
  • Diesel engines are also low-speed engines due to heavyweight and due to heterogeneous combustion. Petrol engines are also high-speed engines due to lightweight and homogeneous combustion.


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 fuel depends upon the user 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). as the difference between both the fuel are considering changing over time.

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