Autoignition in SI engines is an abnormal combustion mode and may lead to engine knock in SI engines. Knock may cause damage and it is a source of noise in engines. It limits the compression ratio of the engine and a low compression ratio means low fuel conversion efficiency of the engine. In this paper a multi zone model based on an existing two zone model Hajireza et al., [1 and 12] and Stenla˚a˚s et al., [30] is developed and validated against the experimental results. The validation is done by using the same detailed chemical mechanism consisting of 141 species and about 1405 reactions under the same conditions. The model is a zero dimensional model capable of simulating a full engine cycle. The two zone combustion model consists of a burned and an unburned zone, separated by a thin adiabatic flame front. The multi zone model differs in the handling of the burned gas. In the multi zone case a number of burned zones are present. The number of zones is decided by the temperature difference between the flame front and the last generated burned zone. The detailed chemical mechanism is taken into account in each zone, while the propagating flame front is calculated from the Wiebe function. Each zone is assumed to be a homogeneous mixture with a uniform temperature, mole and mass fractions of species. The spatial variation of the pressure is neglected, i.e., it is assumed to be the same in the whole combustion chamber at every instant of time. Autoignition is handled by the chemical kinetic model. As the unburned zone is assumed homogeneous the effect of auto ignition is a single pressure peak. The model is not designed to predict the pressure oscillations seen in engine knock.

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