In the United States the "octane" rating of a gasoline is based on the anti-knock index (AKI). This reflects the tendency of the fuel to burn in a controlled manner. The greater the tendency to burn in a controlled manner, the less the amount of engine knocking and the greater the engine's efficiency.
Parameters:
(1) Research Octane Number (RON)
(2) Motor Octane Number (MON)
The RON and MON compare a fuel to a mixture of iso-octane and heptane under different conditions (RON performed at 600 rpm and MON at 900 rpm, plus other differences).
In both scales a 0 is equivalent to 100% heptane and 100 is equivalent to 100% iso-octane.
Usually the RON is 8-10 points higher than the MON.
anti-knock index =
= ((RON) + (MON)) / 2
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