What will happen if diesel is used in petrol car?

Diesel fuel ignites on compression alone, an ignitioin spark won't work.

Your petrol engine does not have anywhere near a high enough compression ratio, so all you'll do is to flood the engine, pump injection system and fuel lines with a useless fuel. If there is petrol already in the system then as the diesel mixture starts coming through your engine will misfire and then stop; the misfiring can cause damage and can ruin your catalytic converter.

If you want a diesel vehicle then sell yours and buy one. There are no guarantees that diesel will remain cheaper and in some countries (such as the UK) it's already far more expensive than petrol. The most economical modern petrol vehicles can, if driven carefully, match diesels for fuel economy. What you save in fuel costs in a diesel car may be outweighed by the need for more frequent servicing and oil/filter changes compared to a petrol car. Petrol cars with manual transmissions can also be push started in an emergency, but you cannot usually do that with a diesel. The added weight of a diesel engine also usually causes heavier wear on the tyres, suspension, steering rack and CV joints.

The internals of Petrol and Diesel engines are different. If you were to use Diesel in a Petrol engine, the engine will seize and start. To make it work on petrol will require an engine overhaul and cost you a lot. Instead I recommend to convert your petrol car to CNG/LPG. You will to buy only a petrol to LPG/CNG conversion kit for your car.

You and your car will have a long lasting relationship with a mechanic.

Try it for yourself and SEE what happens........

Here's a hint: the result will not make you happy or save you any money.

Please refer any joke's book written on Santa and Banta...