Spark Plug: Description and Operation

Spark Plug Construction:

PURPOSE
Provides a path for the high current of the secondary circuit to flow 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 10 m.p.h. to a high of 1472°F (800°C) at 80 m.p.h..