octane ratings are determined by using a standardized setup (engine)
and procedure. The fuel in question is run. The "octane rating" is
percentage of iso-octane
in a iso-octane/octane (both C8H18 but different molecular structure) mixture
that knocks at the same point as the fuel in question. For example a
fuel with an octane rating of 93 performs the test like a mixture of
93% iso-octane and 7% octane. In the US two tests are used: RON and
MON. The RON (higher rating) is an older test. MON (lower rating) is
newer and tests things that the MON test did not show well. The rating at
the pump (US) is the average of these two tests.
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