What does ignition advance angle mean?

[Leroy]

Ignition advance refers to the spark plug firing before the engine piston reaches the top dead center (TDC) of the compression stroke. The angle through which the crankshaft rotates from the moment the spark plug fires until the piston reaches the TDC is called the ignition advance angle. Expanded knowledge about ignition advance angle: 1. Since it takes a certain amount of time from the spark plug firing to the flame propagation and complete combustion of the combustible mixture in the cylinder, and the engine operates at high speeds, if ignition occurs exactly when the piston reaches TDC, by the time the combustible mixture starts to burn completely, the piston will have already begun to move downward. This results in a loss of gas thrust and ultimately leads to a decrease in engine power. 2. If the spark plug fires before the piston reaches TDC, the combustible mixture can burn completely just as the piston reaches TDC. Theoretically, the highest gas pressure occurs optimally at 10°-15° after the compression TDC, which helps reduce the loss of gas thrust and enhances the engine's power output. 3. Normally, the minimum ignition advance angle should not be less than 5°, and if the ignition advance angle is -20°, it indicates a fault in the ignition advance system.