Inventor:
The spark plug was invented in 1903 by Dr. Robert Bosch. The spark plug is one of the most vital components of the ignition system in a gasoline or gas engine. Spark plug is the French word for Candle.
Functioning:
To create an ignition, a high voltage, amplified by the ignition coil to 30,000 volts, travels through the spark plug wire to the spark plug. Once the current reaches the spark plug, it is conducted through the central or center electrode to the lower part of the spark plug, where it sits in the combustion chamber. The center electrode is a long pin made from special materials (usually copper to dissipate heat effectively). The end of the spark plug that protrudes into the combustion chamber endures high temperatures (up to 900 degrees Celsius). Therefore, it must be made from heat-resistant material. The spark generated in the spark plug jumps between two electrodes. The spark plug must never be bumped or dropped, as this can damage the ceramic insulator, altering the electrode gap. The ceramic insulator is fitted around the central electrode (the white part by which the spark plug is held) to ensure the spark occurs between the two electrodes. Failure to do so may cause the high voltage or spark to arc. In such cases, the spark plug is defective and must be replaced.
A spark plug consists of three components:
- Porcelain insulator
- Central / Center electrode
- Metal body with a thread and a hex, to which one or more ground electrodes are attached.
Heat Rating:
It is crucial for the center electrode to maintain the correct temperature. If the temperature is too low, the spark plug will foul and the spark will not jump effectively. The temperature must not get too high either, as this will cause it to glow, making the mixture ignite before the spark occurs.
Characteristics of a Used Spark Plug:
A used spark plug can reveal the following about the engine: oil consumption, temperature, timing, ignition operation, and fuel usage.
- Coffee brown (with milk) is good.
- Soot deposits indicate low compression, malfunctioning ignition, or an excess of fuel.
- If they are wet and smell like gasoline, then the engine has poor ignition or incorrect injection quantity (possibly a defective coil or injector).
- Oil deposits indicate oil use in the combustion chamber.
- White insulator (center of the spark plug around the electrode) means the spark plugs are too hot.
- A hard, dry deposit may mean either the engine or the spark plug is not reaching the appropriate temperature. It might indicate a spark plug with incorrect heat rating has been installed.
Spark Plug Wires:
Spark plug wires ensure the conduction of current from the distributor cap or the ignition coil to the spark plugs and should not be interchanged among themselves. If an engine won’t start on a damp morning or runs rough in moist weather, damp (leaky) spark plug wires could be the cause.
More information about the type of ignition system or the control of the coil by the ECU can be found on the ignition system page.