I want to know deep about petrol and diesel engine ao what will happen
As others have explained putting petrol in a diesel engine will lead to incomplete combustion definitely in case of a cold start however things might be different in case of higher temperature say in a IDI engine
the engine will not start because the self ignition temperature of petrol is high then diseal so it need an external source like a spark plug to ignite it
explosion may happen as the compression ratio of both fuels differ.
It will prove that you're an idiot.