A Molecular Modelling Investigation of Selected Gasoline Molecules to Relate Oxidation Pathways to their Autoignition Behaviour

An adaptation of the procedure originally developed by Twu and Coon for blend octane prediction is described. The technique is based on a graded index describing an aspect of the negative temperature coefficient (NTC) autoignition behaviour of a fuel. It is further postulated that the fuel's NTC behaviour can be linked to the transition state activation energy barriers involved in the first internal hydrogen abstraction by the alkylperoxy free radical. Density-functional theory (DFT) calculations were employed to assess this hypothesis and the results were able to explain the difference between the ignition behaviour of a number of selected fuel components. The calculated NTC assignments, which were directionally consistent with the DFT results, were used successfully to determine the blend octane rating.