Article
Article
Octane number
Article By:
Lane, John C. Research and Development Department, Research Laboratories, Ethyl Corporation, Ferndale, Michigan.
Last reviewed:January 2020
DOI:https://doi.org/10.1036/1097-8542.465200
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
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