The spark plug as an important component of the engine is used to deliver electric current. This electric current is supplied from a car ignition system to the car combustions unit of the spark-ignition engine. The spark plug mechanism I so unique. It connected to a high volt that has been generated by an ignition coil. Electrons that flow through the coil cause a voltage to develop between the side and central electrodes. Ordinarily a current should not flow because of the presence of fuel and air which act as insulators however, as the voltage produced between side and central electrons continue to rise the gas structure changes and once the dielectric strength of the gas is reached and exceeded, the gas gets ionized thus becoming a conductor and allowing the flow of current across its gap.
Spark plugs usually fire properly when given volt of about 12,000 – 25,000 and in some cases rise up to 45,000 volts.
As the current of the electron produced in the ionized gas passes through the plug gap, the temperature of the spark plug is risen to 60,000k. This severe heat in the spark channel causes a quick expansion of the ionized gas like a small explosion. This results in a thunder and lightning like click observed when an engine is ignited