A spark plug is a critical engine component that provides the spark that ignites the air-fuel mixture that drives an engine. A spark plug operates by directing electrical current to flow through a centre electrode, forming a spark across an electrode (or air) gap, completing the circuit to a ground electrode. The centre electrode is surrounded by a ceramic insulator which is non-conductive preventing current leakage and ensuring electricity flows in the desired direction.
A spark plug functions in the combustion chamber of an engine under severe condition. For example, the temperature of the combustion chamber reaches about 2,500°C and the pressure reaches 5MPa. Additionally , a spark plug is exposed to sudden changes temperature and pressure , from the high temperature of burned gases to the relatively low temperatures of the air/fuel mixture. Moreover it must endure high voltages , mechanical vibrations and the chemical corrosion of the combustion gases.