spark plug

See also: sparkplug

English

a typical spark plug
close-up of spark plug during spark
a typical schematic portrayal of an Otto cycle, showing the spark provided by the spark plug

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    Noun

    spark plug (plural spark plugs)

    2. The part of some internal combustion engines which forms a high-voltage electric spark which ignites the fuel-air mixture to begin the power stroke. (Petrol engines have spark plugs. Diesel engines do not have them because the heat from their high compression ratios supplies the ignition.)
      Alternative form: plug (ellipsis)
      Hypernyms: plug < device, part
      Coordinate term: glow plug
      In the 21st century, it is not unusual for a set of spark plugs to last a decade or longer; gone are the days when changing the plugs annually was common.
      • 1919 January, Practical hints on running a gas engine, United States Department of Agriculture:
        With all engines using spark plugs it is comparatively easy to ascertain whether the ignition system is working properly.
    3. (figuratively) Someone who is a driving force in new endeavours.
      Synonyms: straw that stirs the drink, catalyst, instigator, mover and shaker, stimulus
      Coordinate terms: firecracker, dynamo
      Helen is a real spark plug. We're lucky she's on the team.
      • 2003, Growing for Market: News and Ideas for Market Gardeners:
        Steve Pincus, a Madison-area farmer who sells produce to L'Etoile, says admiringly of Odessa: "She's a spark plug. She's out there speaking out about sustainable agriculture and local food."
      • 2009 May 30, Al Baker, “Investigators Reviewing a Timeline of Seconds That Led to a Police Shooting”, in The New York Times‎[1], New York, N.Y.: The New York Times Company, →ISSN, →OCLC, archived from the original on 24 June 2024:
        Mr. Santiago used a sparkplug to smash the driver’s side window.
    4. (military) A rod (for cylindrical secondaries) or sphere (for spherical secondaries) of fissile material at the center of the secondary of a multistage thermonuclear weapon, which undergoes nuclear fission when compressed to supercriticality by the imploding secondary, helping to raise the secondary to the pressures and temperatures necessary to ignite nuclear fusion in the secondary's fusion fuel.

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