What will happen if we add petrol in diesel cars or vice-versa?

This is a very common doubt among people of all ages. Firstly, we should understand the common differences between petrol and diesel.

• Petrol has higher self-ignition temperature (246 °C), compared to diesel (210 °C)


• Petrol engines use spark plugs to ignite the petrol, whereas diesel self ignites due to the temperature and pressure created during compression ratio.


• Petrol is highly volatile compared to diesel.


• If petrol is ignited in a cylinder having a compression ratio exceeding 11:1, knocking becomes a common phenomenon.


• Diesel needs to be injected at a very high pressure (1000 bar to 2000 bar) so that it is atomized and readily burns when injected inside the combustion chamber. Petrol is injected or mixed with air at a very low pressure of 2 to 4 bar.

When petrol is added in a diesel engine:

The temperature and pressure created during compression stroke will be very high in diesel engines. This will result in self-ignition of petrol. It will lead to knocking creating loud thumping noises. It will put a lot of stress on piston and cylinder walls leading to damage.

When diesel is added in a petrol engine:

The engine won’t start simply because diesel is less volatile and will not mix with air to form a combustible mixture. Diesel has to be atomized to make sure it burns readily when injected. But the fuel injectors in petrol engines don’t develop enough pressure to atomize diesel. Hence, combustion doesn’t take place.