Spark plugs — general information (Audi A4 B6)

The task of the spark plug is to ignite the fuel-air mixture in the combustion chamber. This creates a temperature of about 2500 degrees and a pressure of up to 60 bar. In order to ensure that the spark nevertheless jumps reliably between the spark plug electrodes, the spark plug contact rod is surrounded by a ceramic insulator. In addition, the middle electrode and the spark plug rod are located in a conductive glass mass, which is designed to rigidly fasten and seal these parts. When the appropriate ignition voltage is reached, an electric spark jumps between the middle and side electrodes, which ignites the fuel particles in the combustion chamber.

Heat rating

For the spark plug to work accurately, it must heat up to the self-cleaning temperature of approximately 400 degrees immediately after starting the engine, otherwise combustion products will settle on the insulator's thermal cone. At full load, the temperature should not exceed approximately 800 degrees. Of course, the conditions in which spark plugs operate in different engines are not the same. The only way to determine whether spark plugs and a specific engine are compatible is by looking at the heat rating. For example, if you use spark plugs with a heat rating that is too high, the insulator's thermal cone may become very hot. This may lead to uncontrolled glow ignitions, which may even destroy the engine. On the contrary, if you select spark plugs with a heat rating that is too low, the spark plugs will not reach the self-cleaning temperature, and the insulator's thermal cone will become dirty. The heat rating is set by the vehicle manufacturer.

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