Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A substance, such as tetraethyl lead, added to gasoline to reduce engine knock.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. of an additive added to petroleum/gasoline to reduce the occurrence of engine knock.
  • n. Such a substance, usually tetraethyl lead (also MMT, MTBE and ethanol)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. any of various compounds that are added to gasoline to reduce engine knocking
  • adj. suppressing or eliminating engine knock in combustion engines

Etymologies

anti- +‎ knock (Wiktionary)

Examples

  • They replaced the last of the lead-like antiknock with ethanol in big part due toADM.

    The Volokh Conspiracy » Non-Ethanol Gas in the DC Area:

  • Distillate fuels and heavy oils were heated under pressure in large drums until they cracked into smaller molecules with better antiknock characteristics.

    Cracking

  • Moreover, cracked gasoline actually had a much better antiknock value than natural gasoline, which meant more power and allowed for higher-compression engines.

    The Prize

  • It was then discovered that cracked gasoline was actually preferable to “straight run” gasoline because it had much superior antiknock properties.

    The Prize

  • The important qualities for gasoline are octane number (antiknock), volatility (starting and vapor lock), and vapor pressure (environmental control).

    Petroleum refining

  • Tetraethyl lead, gasoline antiknock additive, produced by Thomas Midgley (1889–1994).

    5. Technological Developments

  • ATL Racing Fuel Cells, Ramsey, NJ, May 30, 2008: Most unleaded racing fuels contain "ethanol" as an antiknock, but ethanol settles out if moisture gets into your fuel cell.

    Inside Track Breaking News Blog

  • Check your car’s owner manual for the recommended fuel (unleaded gasoline versus diesel) and octane rating or antiknock index (on the yellow sticker affixed to the pump).

    How To Buy & Sell just about Everything

  • Most cars can optimize their own performance to the gas they’re fed, but only up to a certain point: Gas with too low an antiknock index causes an engine to fire prematurely and lose power.

    How To Buy & Sell just about Everything

  • Gas with an antiknock index well above the required octane level doesn’t increase performance or power, just your fuel costs.

    How To Buy & Sell just about Everything

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