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octane number

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noun
  1. (of gasoline) a designation of antiknock quality, numerically equal to the percentage of isooctane by volume in a mixture of isooctane and normal heptane that matches the given gasoline in antiknock characteristics.
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Origin of octane number

First recorded in 1930–35
Also called octane rating.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for octane number

octane number

octane rating

noun
  1. a measure of the quality of a petrol expressed as the percentage of isooctane in a mixture of isooctane and n -heptane that gives a fuel with the same antiknock qualities as the given petrol
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

octane number in Science

octane number

  1. A numerical representation of the ability of a fuel to resist knocking when ignited in the cylinder of an internal-combustion engine. The octane number of a given fuel is determined by comparing the amount of knocking that fuel causes when combusted with the amount of knocking caused by two standard reference fuels, isooctane (which resists knocking and has an octane number of 100) and heptane (which causes knocking and has an octane number of 0). The octane number is then assigned as the percentage of isooctane required in a blend with normal heptane to match the knocking behavior of the fuel being tested.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.