1. Intake Stroke: In the first stroke, the piston moves down the cylinder, creating a low-pressure area. This draws a mixture of air and fuel (in the case of gasoline engines) or air (in the case of diesel engines) into the cylinder through an open intake valve.
2. Compression Stroke: During the second stroke, the piston moves back up the cylinder, compressing the air-fuel mixture. This compression increases its temperature and pressure, making it more combustible.
3. Power Stroke (Combustion): This is where combustion occurs. In a gasoline engine, just before the piston reaches the top of the cylinder, a spark plug ignites the compressed air-fuel mixture, causing it to burn rapidly. This rapid expansion of gases creates high pressure, driving the piston down the cylinder forcefully. In a diesel engine, the high compression alone causes the fuel to spontaneously ignite, without the need for a spark plug.
4. Exhaust Stroke: In the final stroke, the piston moves back up the cylinder, expelling the burnt gases through an open exhaust valve. These gases are then released from the cylinder and out of the engine through the exhaust system.
So, combustion is a crucial part of the four stroke cycle, specifically during the power stroke. It is the combustion of the air-fuel mixture or the diesel fuel that generates the force that drives the piston down, creating the power needed to operate the engine.
