Spark plugs are installed on the side or top of the engine. In the early days, spark plugs were connected to the power distributor through cylinder wires. In the past decade, engines in small cars have mostly been changed to have ignition coils directly connected to spark plugs. The working voltage of the spark plug is at least 10000V, and the high-voltage electricity is generated by the ignition coil from 12V electricity, which is then transmitted to the spark plug.

The working principle of a spark plug is that the insulation skirt of a standard spark plug is slightly shrunk into the end face of the housing, and the side electrode is outside the end face of the housing, making it the most widely used type. The insulation skirt of the edge protruding spark plug is longer and protrudes beyond the end face of the housing. It has the advantages of large heat absorption and good anti fouling ability, and can be directly cooled by the intake air to lower the temperature, so it is not easy to cause hot ignition, so the thermal adaptation range is wide.