An Investigation Of Anomalies Identified Within The ASTM Research And Motor Octane Scales

This paper describes the preliminary findings arising from a project to develop a blend-property model for gasoline. An engine model was used in conjunction with various auto-ignition models, including the Shell model, to analyze engine test results and the ASTM guide curves that link octane number to compression ratio. Good correlation for both RON and MON was achieved for 40<ON<120 provided that a non-linear pressure dependency was included in the auto ignition model. This was regarded as a possible indication of molecular cage formation. The results confirmed that physical factors such as the rate of normal combustion and fuel evaporative cooling have a significant impact on the measured octane number and are thus critical for inclusion in any model that purports to predict the autoignition point.