Octane number
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octane number
(′äk′tān ′nəm·bər)
(engineering) A rating that indicates the tendency to knock when a fuel is used in a standard internal combustion engine under standard conditions; n-heptane is 0, isooctane is 100; different test methods yield other values variously known as research octane, motor octane, and road octane.
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Octane number
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Octane number
A standard laboratory measure of a fuel's ability to resist knock during combustion in a spark-ignition engine, A single-cylinder four-stroke engine of standardized design is used to determine the knock resistance of a given fuel by comparing it with that of primary reference fuels composed of varying proportions of two pure hydrocarbons, one very high in knock resistance and the other very low. A highly knock-resistant isooctane (2,2,4-trimethylpentane, C8H18) is assigned a rating of 100 on the octane scale, and normal heptane (C7H16), with very poor knock resistance, represents zero on the scale. Octane number is defined as the percentage of isooctane required in a blend with normal heptane to match the knocking behavior of the gasoline being tested. See also Spark knock.
For fuels with a rating higher than 100 octane, the rating is usually obtained by determining the amount of tetraethyllead compound that needs to be added to pure isooctane to match the knock resistance of the test fuel.
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McGraw-Hill Science & Technology Dictionary
McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved.
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