In order to ignite air fuel mixture we need heat.In case of diesel engines (compression ignition engines) this head is achieved by the compression of gases.But in case of spark ignition engines we need to have an external source to ignite air fuel mixture because compression is not enough to ignite the mixture.
spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine.

There are two types of spark plug :

  • Hot Spark Plug
  • Cold Spark Plug

“Cold” spark plugs normally have a short heat flow path. This results in a very quick rate of heat transfer. Additionally, the short insulator nose found on cold spark plugs has a small surface area, which does not allow for a massive amount of heat absorption.

On the other hand, “hot” spark plugs feature a longer insulator nose as well as a longer heat transfer path. This results in a much slower rate of heat transfer to the surrounding cylinder head.
The heat range of the spark plug must be carefully selected in order to create an optimal thermal performance. If the heat range is not correct, you can expect serious trouble. Typically, the appropriate firing end temperature is  900-1,450 degrees. Below 900 degrees, carbon fouling is possible. Above it, overheating becomes an issue.

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