Spark Plug: Description and Operation

PURPOSE
Spark plugs produce the sparks that ignite the air/fuel mixture in the combustion chambers.

CONSTRUCTION
The spark plug consists of a metal rod, called an electrode, surrounded by a ceramic insulator. The lower end of the insulator is encased in a threaded metal shell that is screwed into the combustion chamber of the cylinder head. Another electrode is welded to the shell. It is separated from the center electrode by a small air gap.

OPERATION
High voltage current from the distributor flows down to the center electrode and jumps the air gap in the form of a spark.