7.1 What is the Octane Number Requirement of a Vehicle?
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
7.1 What is the Octane Number Requirement of a Vehicle?
The actual octane requirement of a vehicle is called the Octane Number
Requirement (ONR), and is determined by using series of standard octane fuels
that can be blends of iso-octane and normal heptane ( primary reference ),
or commercial gasolines ( full-boiling reference ). In Europe, delta RON
(100C) fuels are also used, but seldom in the USA. The vehicle is tested
under a wide range of conditions and loads, using decreasing octane fuels
from each series until trace knock is detected. The conditions that require
maximum octane are not consistent, but often are full-throttle acceleration
from low starting speeds using the highest gear available. They can even be
at constant speed conditions, which are usually performed on chassis
dynamometers [27,28,111]. Engine management systems that adjust the octane
requirement may also reduce the power output on low octane fuel, resulting
in increased fuel consumption, and adaptive learning systems have to be
preconditioned prior to testing. The maximum ONR is of most interest, as that
usually defines the recommended fuel, however it is recognised that the
general public seldom drive as severely as the testers, and so may be
satisfied by a lower octane fuel [28].
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