This International Standard establishes the rating of liquid spark-ignition engine fuel in terms of an arbitrary scale of octane numbers using a standard single-cylinder, four-stroke cycle, variable compression ratio, carburetted, CFR engine operated at constant speed. Research octane number (RON) provides a measure of the knock characteristics of motor fuels in automotive engines under mild conditions of operation.This International Standard is applicable for the entire scale range from 0 RON to 120 RON, but the working range is 40 RON to 120 RON. Typical motor fuel testing is in the range of 88 RON to 101 RON.This International Standard is applicable for oxygenate-containing fuels containing up to 4,0 % (m/m) oxygen and for gasoline containing up to 25 %(V/V) ethanol.NOTE 1 Although 25 % (V/V) of ethanol corresponds to approximately 9 % (m/m) oxygen, full applicability of this test method for that oxygen range has only been checked for gasoline type of fuels.NOTE 2 Work is under way to check the possibility to use the method up to and including 85 %(V/V) ethanol.NOTE 3 This International Standard specifies operating conditions in SI units but engine measurements may be specified in inch-pound units because these were the units used in the manufacture of the equipment, and thus some references in this International Standard include these units in parenthesis.NOTE 4 For the purposes of this standard, the terms “% (m/m)” and “% (V/V)” are used to represent the mass fraction, µ, and the volume fraction, f, of a material respectively.