ANATOMY OF A SPARK PLUG

Spark plugs are simple in their construction and placement within the engine. A wire connects to the top, and sparks come out at the bottom. In between are a few functional materials on the outside and inside.

OUTSIDE OF A SPARK PLUG

The smooth, shiny metal part at the top of the spark plug is the terminal, which is where a spark plug wire connects. Underneath this, on the outside of the plug, is a ceramic insulator. This houses and insulates the center electrode. The ceramic insulator extends down to the hex nut, which is what a wrench grabs when installing or removing the plug. Under the nut is typically a gasket, which helps keep the plug seated and sealed in place. Below that is the body of the spark plug, which is threaded so the plug screws into the cylinder head. A small part of the center electrode protrudes out of the bottom of the body, and at the very bottom end is the ground electrode.

INSIDE OF A SPARK PLUG

When an electrical spark occurs, radio frequencies are released. If this burst of frequencies is too strong, then it can interfere with other electronic elements in the car. To prevent this from happening, the spark plug terminal connects to a graphite resistor inside the ceramic insulator. This resistor connects to the insulated center electrode, which is made of copper, iridium, or other highly conductive metal. The center electrode is what protrudes from the bottom of the plug opposite the ground electrode, which is commonly made of nickel alloy, platinum, or other metal, inside the engine's combustion chamber.

FUNCTIONS OF A SPARK PLUG

A combustion engine starts by way of a small, controlled explosion, which is caused by a spark from the spark plug. However, this is not the spark plug's only purpose. It is also an important element of the cooling system.

IGNITION

In the engine's combustion chamber, a piston lowers, causing valves to allow a mixture of fuel and air inside. Meanwhile, electric current is sent through the spark plug with a voltage that increases until it is strong enough to jump (or spark) from the center electrode to the ground electrode. The piston rises back up and compresses the fuel/air mixture, and at the last second, the spark from the spark plug ignites it. The force caused by this little explosion pushes the piston back down. The pistons are attached to a crankshaft, which translates the up-and-down motions into a rotation. This not only keeps the pistons moving, but also turns the engine over during ignition.

COOLING

Both the ceramic insulation inside a spark plug and the metal insulation of the center electrode serve to transfer some of the heat out of the combustion chamber and into the engine's cooling system. Serious damage can result if not enough heat is drawn out of the cylinder, so this function is almost as important as the spark itself.

LONGEVITY OF A SPARK PLUG

Modern spark plugs last longer than older models, but no spark plug lasts forever. The longevity of spark plugs depends partly on the type of fuel as well as basic maintenance, but the materials used in the plug itself also play a part.

Iridium and platinum are not as efficient or conductive as copper, and both of these metals are prone to overheating. As long as they do not overheat, they do last longer than copper spark plugs. Although copper has the shortest lifespan, it is generally considered the best material for a central electrode because of its excellent conductivity.