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.

Spark plug, commonly known as flame nozzle, is used to discharge the pulse high-voltage electricity sent by the high-voltage wire (flame nozzle wire), breakdown the air between the two electrodes of the spark plug, and generate an electric spark to ignite the mixed gas in the cylinder. The main types include: standard type spark plugs, edge protruding spark plugs, electrode type spark plugs, seat type spark plugs, pole type spark plugs, surface jumping spark plugs, etc.