Facts for Kids

Spark plug

People started using sparks to light engines in the 1800s. In 1860, Étienne Lenoir used an electric spark in one of the first piston engines. By the late 1800s, inventors like Nikola Tesla and companies in Europe were working on better plugs. Around 1902, Gottlob Honold at Robert Bosch’s company made a higher-voltage design that worked well for new cars. Later, makers such as the Champion company and the Lodge brothers improved how plugs were made so they lasted longer. In 1930, Helen Blair Bartlett helped make the ceramic parts much stronger and safer.

Spark plug

A spark plug is a small part that helps a car or lawn mower make power. It sits in the engine and makes a tiny spark that lights the mixture of fuel and air. The spark plug has a metal threaded shell that screws into the engine and a white ceramic piece called an insulator that keeps electricity from escaping. A thin metal piece called the central electrode reaches into the engine where the spark jumps to a side electrode. Wires from the ignition system carry the high voltage to the plug. Have you ever wondered how such a tiny spark can move a whole car?

Ignition coil

A spark plug makes a spark when it gets very high voltage from the ignition coil or a magneto. The voltage climbs until the air between the metal tips cannot stop the electricity. Then the electricity jumps the gap and makes a spark. The voltage can be many thousands of volts—often 12,000 to 45,000 volts. The spark is a tiny, very hot channel that lights the fuel‑air mixture, making a small, fast burn that pushes the piston. Engines time the spark carefully so the burn happens at the right moment for smooth power.

Insulator

The white part you see on a spark plug is the insulator, usually made of a hard ceramic called sintered alumina. It keeps the high voltage inside and helps move heat out to the engine. At the top is a terminal where the spark plug wire connects. A metal shell with threads lets the plug screw into the engine and also acts as the ground. Inside is the central electrode and at the end a side or ground electrode; the spark jumps between them. Tips may have thin layers of metals like platinum or iridium so they last a long time.

Spark gap

The spark gap is the space the electricity jumps across from the center electrode to the side electrode. Typical gaps are small, about 0.6 to 1.8 millimeters. A narrower gap makes a weaker spark that usually still fires; a wider gap makes a stronger spark but can cause misfires if the ignition cannot reach the voltage. Mechanics measure the gap with a special gauge. Some plugs use two, three, or four ground electrodes so the spark wears a different place and the plug lasts longer, but multiple electrodes can slightly change how well the burn starts.

Heat range

When you install a spark plug, its threaded length must match the engine so it does not stick in too far or sit too shallow. Plugs seal to the head with a crushed washer or a tapered seat, and each type needs the right torque. The plug tip works very hot—often between about 500 and 800 °C—and manufacturers make plugs with different heat ranges. A "hot" plug keeps its tip hotter to burn off deposits; a "cold" plug moves heat away faster to avoid overheating. Looking at a plug’s tip color can help a mechanic see if an engine runs too rich, too lean, or just right.