How does petrol engine works?

I will explain on a 1 cylinder engine. This makes it easier to under stand. Inside the cylinder is a piston that moves up and down tight to the side walls of the cylinder. Connected to the bottom of the piston is a rod. The rod connects to a shaft called a crankshaft at the bottom of the engine. The crankshaft is connected to the transmission. When the piston is moved downward it turns the crankshaft, also fuel is either pulled in through a carbuerator (cars pre-1986) or pumped in through electronic fuel injection system (callel EFI) above the piston. The crankshaft is still turning and momentum pushes the piston back up. The fuel and air above the piston are compressed (at least 120psi for gasoline, 500psi for diesel I will explain later.) In a gasoline engine the compressed mixture is ignited by a spark plug located at the top of the cylinder, forcing the piston down and continuing the cycle. In a diesel engine the diesel/air mix is compressed more to create heat. The heat becomes so intense that it ignites and forces the piston downward.