What does the ignition advance angle of a car mean and what does it mean to the engine?

① Basic ignition advance angle: (as shown in the figure below)

② Correction value of ignition advance angle: The electronic control unit further optimizes the basic ignition advance angle according to certain correction characteristics according to sensor signals such as engine intake temperature, coolant temperature, throttle opening, air-fuel ratio of mixed gas, starting switch and air-conditioning switch and related switch signals, so as to optimize the ignition performance of the engine.

Let me say it in vernacular:

First of all, the ignition advance angle refers to the angle of the crankshaft axis when the spark plug starts to ignite during the piston compression stroke. Pay attention to why it is "advance angle", because the ignition is not ignited when the piston is completely compressed, but when the compression is not completed. (I don't know if this can move)

Then, the ignition advance angle has two laws:

① According to the significance of engineering design, calculate air intake, temperature, fuel quantity, ecu analysis, etc. And get a basically fixed ignition time.

(2) When the environment or working conditions change, according to which change, the ignition timing should be adjusted appropriately. For example, if knocking occurs, the ignition time will be pushed back, that is, the ignition advance angle will be smaller, so as to prevent the premature high temperature, high pressure and unburned mixture from forming spontaneous combustion and producing knocking. For another example, according to the power demand of different road conditions, adjust the power output to improve fuel economy. At this time, different intake time and injection time are needed, so the ignition time will change accordingly.

Knowledge point: Theoretically, ignition occurs when the compression stroke piston reaches the top dead center.

In fact, before the piston moves to the top dead center, the spark plug ignites. Why? Because it takes time for gasoline to burn. This is the ignition advance angle.

The advance angle varies with the engine speed, and the higher the engine speed, the greater the advance.

If you have played with an old-fashioned car with a fire head, you will understand that old drivers often do one thing "tune the fire head". If the ignition is early, the engine will knock, if the ignition is late, the sound will be dull, and if it is serious, it will shoot (that is, the car will burn outside the cylinder). In both cases, the engine will be weak.