Four-Octane-Number Method for Predicting the Anti-Knock Behavior of Fuels and Engines

The “Four-Octane-Number Method” is a practical determination of the knock-resistance of fuels based on the autoignition delay concept and obtained through simple processing of the standard “Research” and “Motor” indices combined with two other indices specially defined.

The knocking behavior of any engine can be specified once by measuring its octane requirement with 2 fuels for which the four octane numbers are known.

The behavior of any fuel can be predicted without experimenting on all the engines thus identified if its four octane numbers are known.

Extensive controls of the method have been performed over about 1000 samples for which the road octane numbers were measured. The method's predictions are within an average accuracy of 0.5 octane point.