spark plug

1. a device designed to fit in each cylinder of a gasoline-powered internal-combustion engine and to produce the electric spark for igniting the mixture of gasoline and air.

2. Informal. a person who leads, inspires, or animates a group.

[1900-05]

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Device that fits into the cylinder head of an internal-combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, creating a spark and igniting the fuel.

The electrodes and the insulator separating them must withstand high temperatures, as well as an electric stress of up to several thousand volts. Spark-gap length affects the energy of the spark, and the shape of the insulator affects the temperature of operation.

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▪ electronic device

also called  Sparking Plug,  

      device that fits into the cylinder head of an internal-combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, to form a spark for igniting the air–fuel mixture. The electrodes must be able to resist high temperatures, and the insulator separating them must withstand high temperatures and also an electric stress up to several thousand volts. Spark-gap length affects the energy of the spark, and the shape of the insulator affects the temperature of operation. When too cool, operation leads to carbonization and short-circuiting of the gap; when too hot, there may be preignition.

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