The ignition system of a car mainly consists of ignition power supply, ignition switch, ignition coil (high-voltage package), spark plug, and high-voltage wire.

The ignition coil consists of a primary coil (low voltage section) and a secondary coil (high section). Connected to the primary coil are the ignition switch, circuit breaker, and capacitor. Connected to the secondary coil are the distributor, high-voltage line, and spark plug. Turn on the ignition switch, and low voltage current flows from the battery to the primary coil of the ignition coil. The magnetic field generated around it is enhanced by the iron core in the ignition coil. Due to the action of the circuit breaker, the primary low voltage circuit is cut off, and the primary current suddenly drops to zero. The magnetic flux in the iron core also quickly disappears. At the same time, high voltage is induced in the secondary coil, and the current passes through the two poles of the spark plug to generate electric sparks, igniting the combustible mixture in the cylinder.

The original configuration of the ignition coil was a single wire harness, which was not satisfactory in terms of voltage, current, and throughput. Therefore, ignition coils that do not require high-voltage wires have been introduced one after another.

Spark plug gap and ignition coil

The electrode gap of a spark plug refers to the distance between the side electrode and the electrode. The gap of a spark plug in a car varies from 0.6mm to 1.6mm, and different engines require different gaps, which are determined by the high-voltage redundancy generated by the ignition coil.

In general, the larger the gap, the longer the arc, and the greater the ignition energy. But if the redundancy generated by the ignition coil is exceeded, it will have the opposite effect. Not only will it fail to increase the ignition energy of the spark plug, but it will also cause the spark plug to lose fire due to insufficient voltage. At the same time, the ignition coil will be overloaded for a long time, causing it to overheat and result in internal short circuits or circuit damage. The design life of most ignition coils is over 300000 kilometers. Improper use of spark plugs can lead to premature retirement, which is the main reason for many repair shops to return ignition coils.

However, a spark plug gap that is too small is also not good, as it cannot fully discharge high-voltage electricity and the heat generated by igniting the mixture is insufficient, resulting in incomplete combustion and preventing the engine's power from being fully released. Under normal circumstances, the lifespan of a spark plug is determined by the gap between the spark plugs. If the gap is too large, the breakdown voltage required will be too high, and the voltage redundancy of the ignition coil will not be sufficient, which will result in insufficient ignition.