A fundamentally based model of knock in the gasoline engine

A mathematical model has been developed to simulate the occurrence of knock in the gasoline engine. A rapid-compression machine was used to obtain experimental information on the autoignition characteristics of a suitable range of sensitive and non-sensitive reference fuels. A generalised chemical reaction scheme which embodies the essential kinetic features of the degenerate branched chain reactions responsible for autoignition was then refined to give an accurate simulation of these observations. When incorporated in a computerised engine cycle simulation this chemical model predicts the development of end-gas reactions and the occurrence of knock. The model has been used to investigate the origin of severity in the CFR engine. In confirming that high end-gas temperatures are of major importance in de-rating sensitive fuels under ‘severe’ engine conditions this study gives us confidence in our approach to engine simulation, and especially in the chemical aspect of the model.