Cars are driven by their engines, which is the heart and soul of the car. These engines work either on diesel or petrol. So What would happen if you fill diesel in a petrol car? Let's find out.

What would happen if you fill diesel in a petrol car? | The Mechanical post

Note: It is highly advisible to NOT to try these things.
First and foremost let us understand the difference between the two engines ie. Petrol & Diesel.

Petrol Engine :

Petrol is a fluid which has a lower flash point.Which means that it takes a comparatively low temperature for petrol to detonate or burn. Thus the compression ratio of petrol is low (about 6 to 10.5) ie. in short the volume of the cylinder which houses the piston is less, resulting in less pressure development during compression. 

As petrol engine's compression ratio is low, during compression the petrol and air mixture doesn't ingnite. Thus a Spark plug is used to ignite the air fuel mixture.

Diesel Engine : 

Diesel unlike petrol has a higher flash point. Thus it takes higher temperature for diesel to detonate or burn. 

Diesel engines are constructed with higher compression ratio (around 14 to 22) which means the cylinder which houses the piston has more volume and the stroke lenght of the piston is more.Therefore during the compression cycle of the engine, the heat due to compression only, becomes so intense that the air and fuel mixture gets ignited without the need of  spark plug.

Now let's analyse the situation if we fill diesel in a petrol car:

If diesel is filled in the tank of your petrol car, your car would run for a while normally until all the previous petrol in the tubes is consumed. 

Then as the diesel would start entering the engine, your car would stop. How ?? let's see.

As mentioned above, petrol engines have low compression ratio and diesel has a high flash point so the diesel would not get enough heat to ignite. Thus there would be no combustion and there car won't run.

However, you would need to remove all the diesel from the tank ,tubes and the engine to get your car working. This process would cost you a lot, you might need to change your engine which by no means comes cheap.

Thus, never ever fill your car with the wrong fuel.