IP 236: Petroleum products - Determination of knock characteristics of motor and aviation fuels - Motor method

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  • Method adopted/last revised:
  • Method reapproved: 2019
  • Status: Current
  • First printed in STM books: 2018

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. Motor octane
number (MON) provides a measure of the knock
characteristics of motor fuels in automotive
engines under severe conditions of operation. The
motor octane number provides a measure of the
knock characteristics of aviation fuels in aviation
piston engines, by using an equation to correlate
to aviation-method octane number or performance
number (lean-mixture aviation rating).
This International Standard is applicable for the
entire scale range from 0 MON to 120 MON,
but the working range is 40 MON to 120 MON.
Typical motor fuel testing is in the range of 80
MON to 90 MON. Typical aviation fuel testing is
in the range of 98 MON to 102 MON.
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 for gasoline containing up to 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, φ, of a
material respectively.
NOTE 5 When determining conformance with
specified limits in this standard, an observed or
calculated value shall be rounded to the nearest
unit in the last right-hand digit used in expressing
that limit in accordance with the rounding method
of ASTM Practice E29

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