Why diesel engines have more torque than petrol? [with Pdf]

The diesel engines have more torque than the petrol engine since the Compression ratio of the diesel engines is higher for the auto-ignition of fuel while in the petrol engines compression ratio is lower than the diesel engines because, in petrol engines, the air-fuel mixture is ignited by the spark plug.

Diesel vs petrol torque:

The diesel engines have more torque than petrol engines due to the following reasons:-

1] Compression ratio:-

The compression ratio of the diesel (Compressed ignition) engine is higher than the petrol (Spark Ignition) engine since, in the diesel engines, the air is compressed to high pressure to fuel gets auto-ignites when sprays into hot air while in petrol engines, the spark plug is used to ignite the air-fuel mixture.

Hence to compress the air to high pressure, the diesel engines have more compression ratio which is around 18:1 to 23:1. Therefore due to the high compression ratio in diesel engines as compared to petrol engines, more output torque is obtained in diesel engines.

2] Combustion speed:-

As in the case of petrol engines, when the air-fuel mixture is compressed by the piston, the spark plug produces the spark which ignites the fuel, the combustion flame steadily progresses from the spark plug to the downside.

But in diesel engines, the air is compressed to high pressure, so when the fuel injector sprays the fuel into the engine, immediately the fuel attains its self-ignition temperature and quickly combustion takes place which applies a large force on the piston so the piston fastly moves from TDC to BDC.

Therefore, in such a way, due to the high combustion speed in diesel engines, the high torque is obtained.

3] Stroke length:-

The stroke length of the diesel engines is more than the petrol engines. So with more stroke length, the crank radius of the diesel engines is also more Therefore due to the more crank radius and more force on the piston in diesel engines resulting (as per torque equation, Torque = Force x radius ) in more output torque is obtained.

Stroke length is more >> Crank radius is more >> More Torque obtained

4] Turbocharger:-

The turbocharger technology is commonly used in diesel engines which provides compressed air to the engine. Hence due to more quantity of air, fuel properly burns and the high torque is obtained at the output.

Hence these are the reasons due to which diesel engines have more torque than petrol engines.


Pratik is a Graduated Mechanical engineer. He enjoys sharing the engineering knowledge learned by him with people.

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