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octane number

(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.
Also called octane rating.
Origin of octane number
1930-35 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for octane number
  • To avoid engine knock, the team's engine runs on ethanol, which has a higher octane number than gasoline.
  • In general, a higher octane number means the engine can run more efficiently and will have less tendency to knock.
  • Naphtha isomerization converts the straight chains to branched, significantly raising their octane number.
  • Such a material would have a high octane number and could be a useful additive to motor gasoline.
  • Dixie also recommended that a fluoride content test be conducted to further validate the octane number results.
  • It is conceptually similar to the octane number used for gasoline.
  • The research method gives slightly higher ratings, and the octane number displayed on the pump is an average of the two methods.
  • The octane number of a fuel governs the amount of spark advance tolerated by a given engine.
British Dictionary definitions for octane number

octane number

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
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
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octane number in Science
octane number  
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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