What if you accidentally put diesel fuel in your car instead of petrol?

Answer 1

Depending on the mix (how much petrol vs how much diesel), the car will either not go at all, or may go but feel jerky. It is obviously not recommended to put ANY diesel in a petrol engine, simply because of the way a petrol engine works vs how a diesel engine works.

In a petrol engine, the fuel is made to combust only with a spark, and therefore requires a much higher pressure for combustion to take place. The higher the octane of the fuel, the more pressure is needed for the fuel to combust.

A diesel engine works in the opposite way, where it needs less pressure and no spark to combust.

If you have accidentally put diesel in a petrol engine, don't drive the car. Drain the fuel. You may have to replace to fuel filter and the spark pugs

Comment: To clarify the above logic.

CAUTION!! Diesel engines have compression ratios of 15:1 or more so that PRESSURE (not spark) ignites the fuel. Petrol engines use SPARK to ignite the fuel. The high octane rating of petrol is so that it does not PRE-IGNITE (pink) under pressure. Raise the compression ratio and you need a higher octane rating, which is why some petrolheads use Avgas (130 octane) on their high performance engines. Diesel engines need HIGH pressure to operate, petrol engines can use LOWER pressure to work, but need higher octane rated fuel if the pressure rises.