The spark plug is first used in a gas engine in 1860 by Lenoir. Later, there were so many developments happen in spark plugs. The spark plug delivers the electric current to combustion chamber from an ignition system. In this article, we will discuss the components of a spark plug.
- Terminal: The outer end of the spark plug contains a terminal. This terminal is connected electrically to the ignition system. The terminal construction depend upon the spark plug usage.
- Seals: The spark plug seals the engine’s combustion chamber when it is installed. It should be kept air tight so that there will be no leakage from combustion chamber. These are usually made with compressed metal powder or glass. While the plugs replaced or removed these seals also replaced.
- Metal case: The metal case is also called jacket. It removes the heat from insulator and and pass that heat to the cylinder head. To tighten the spark plug, it withstands the torque or provide the structural strength.
- Insulator: The outside metal case of insulator is made from sintered alumina or aluminum oxide ceramic. It helps tolerate the electrical voltage and heat. It mechanically supports the central electrode.
- Plug gap: The same spark plug can be used in different engines. The gap settings might be different. So it is important to check with the manual for specifications when fitting for the first time.
It plays a critical role in the performance of engine. If the gap is improper it will effect on the engine in a way to reduce fuel efficiency and the engine power. If the gag is too wide, the plug may fail to produce spark. Also, small gap may affect the air and fuel mixture.
- Center electrode: This is the hottest part of the spark plug. With an internal wire, the central electrode connect to the terminal. The tip of the center electrode can be made of a combination of nickel-iron, chromium, copper or noble metals. In the late 1970s, the engines development reached to a heat range which is unable to cope by the solid nickel alloy center electrodes. So the manufacturers are making a center electrode with copper cored which carry the heat of combustion away from the tip more effectively than the nickel alloy.
- Side or ground (or earth) electrodes: The electrode is made of high nickel steel and is hot forged or welded to the side of the metal shell. On projected nose plugs the side electrode runs very hot than the normal. The center electrode does not overlap in multiple side electrodes designs.
Each component has a special way of delivering the electric current to the combustion chamber. Mostly the material used in the spark plug is to bear the heat and to supply the electric current uninterruptedly.