How a four-stroke gasoline engine works
The working principle of the four-stroke engine: the four-stroke gasoline engine completes a working cycle through the intake, compression, power and exhaust strokes.
1. Intake stroke
The piston moves from top dead center to bottom dead center, the exhaust valve closes and the intake valve opens. The combustible mixture is drawn into the cylinder through the intake valve until the piston moves down to bottom dead center.
2. Compression stroke
The crankshaft continues to rotate, and the piston moves from the bottom dead center to the top dead center. At this time, both the intake valve and the exhaust valve are closed, and the cylinder becomes a closed volume. The combustible mixture is compressed, and the pressure and temperature continue to rise. When the piston reaches the top dead center point when the compression stroke ends.
3. Working stroke
During the power stroke, the intake and exhaust valves remain closed. When the piston is at the position close to the top dead center of the compression stroke (ie, the ignition advance angle), the spark plug generates an electric spark to ignite the combustible mixture. The top dead center moves to the bottom dead center, and the crankshaft rotates through the connecting rod and outputs mechanical work. Except for maintaining the continuous operation of the engine itself, the rest are used for external work. As the piston moves downward, the volume in the cylinder increases, and the gas pressure and temperature decrease. When the piston moves to the bottom dead center, the power stroke ends.
4. When the exhaust stroke is close to the end of the work, the exhaust valve is opened, the intake valve is still closed, and the free exhaust is carried out first by the pressure of the exhaust gas. When the piston reaches the bottom dead center and then moves to the top dead center, the exhaust gas continues to be forcibly discharged. To the atmosphere, after the piston crosses top dead center, the exhaust valve closes and the exhaust stroke ends.
The crankshaft continues to rotate, the piston moves from the top dead center to the bottom dead center, and the next new cycle begins. In each working cycle, the piston reciprocates four strokes at the top and bottom dead centers, corresponding to two revolutions of the crankshaft.
