Spark and Ignition
Ignition by electrical spark occurs because the fuel particles between the electrodes are activated by the spark to discharge, a chemical reaction (oxidation) is triggered, the heat of reaction is generated, and the flame core is formed. This heat activates the surrounding air-fuel mixture, eventually a flame core is formed that spreads the combustion to the surroundings itself.
However, if the quenching effect between the electrodes (the work of the electrodes absorbing the heat and extinguishing the flame) is greater than the flame core heat generation action, the flame core is extinguished and the combustion stops.
If the plug gap is wide, the flame core is larger and the quenching effect is smaller, so reliable ignition can be expected, but if the gap is too wide, a large discharge voltage becomes necessary, the limits of the coil performance are exceeded, and discharge becomes impossible.
Change in the discharge voltage
The ignition system normally generates 10-30 kV secondary voltage.