Fyrtaktsprincipen

Fyrtaktsprincipen, or the four-stroke principle, is a thermodynamic cycle that converts heat energy into mechanical work. It is the most common type of internal combustion engine used in automobiles and many other applications. The principle describes the operation of a piston within a cylinder through four distinct stages or strokes.

The first stroke is intake. The piston moves down, creating a partial vacuum, and the intake valve opens, drawing a fuel-air mixture into the cylinder. The second stroke is compression. The intake valve closes, and the piston moves up, compressing the fuel-air mixture. This compression increases the mixture's temperature and pressure.

The third stroke is power. At the top of the compression stroke, a spark plug ignites the compressed fuel-air mixture. The resulting explosion creates a rapid expansion of gases, forcing the piston down with great force. This downward movement is what generates the engine's mechanical power.

The final stroke is exhaust. The exhaust valve opens, and the piston moves up again, pushing the burnt gases out of the cylinder. Once the exhaust gases are expelled, the cycle repeats, beginning again with the intake stroke. This continuous cycle of four strokes allows the engine to produce sustained power. The precise timing of the valve openings and closings, as well as the ignition of the fuel-air mixture, is crucial for the efficient operation of a four-stroke engine.