How Automotive Engines WorkAlthough they can operate with either diesel or gasoline, all automotive engines operate on the principle of internal combustion. Additionally, most engines are 4-stroke engines refers to the fact that the piston in the engine moves up and down four times in two full revolutions – intake then compression and power then exhaust – during one full combustion cycle.
The first revolution in a gasoline engine is made up of the intake and compression strokes. During the intake stroke the piston moves to the bottom of the cylinder and a fuel-air mixture is forced into the cylinder and the intake valve then shuts. During the compression stroke the piston moves towards the top of the cylinder compressing the fuel-air mixture into the combustion chamber where the temperature is several hundred degrees hotter.
The second revolution in a gasoline engine is made up of the power and exhaust strokes. During the power stroke the piston is forced to the bottom of the cylinder when the fuel-air mixture is ignited by a spark plug creating forceful downwards pressure. During the exhaust stroke the piston rises to the top of the cylinder once more and the exhaust valve opens allowing the used fuel-air mixture to exist the cylinder via the tailpipe.
An automotive diesel engine differs from a gasoline engine in that in a gasoline engine fuel is mixed with air, compressed, and then combusted but in a diesel engine there is no fuel-air mixture, only air, and this air is compressed first and then fuel (in a vapor mist form) is injected. Because air’s temperature rises under compression the fuel then ignites without the use of a spark plug.