Spark Plug: Description and Operation

PURPOSE
The Spark Plug creates a spark to ignite the fuel/air mixture by causing the high current of the secondary circuit to jump the gap to ground.

OPERATION
Paths for this current are through the ground electrode and center electrode across the spark gap. The spark produced when the current jumps the gap ignites the air/fuel mixture in the cylinder. The temperature range of the spark plug is determined by the length of the insulator and the size of the heatsink area. The longer the insulator, the smaller the heatsink area , this allows the insulator to burn off any deposits. A short insulator and large heatsink is used for extended high speed operation where cylinder temperatures are high, helping reduce preignition. The center electrode temperature ranges from a low of 392°F (200°C) at low speeds to a high of 1472°F (800°C) at higher speeds.