Controlled autoignition in gasoline engines is a promising concept to simultaneously reduce both emissions and fuel consumption of internal combustion engines. To describe the spatial progress of the chemical reactions in threedimensional simulations of CAI engine cycles an efficient combustion chemistry model was developed. To analyze the effects of mixture homogeneity on the progress of the reactions, thermodynamic analyses and numerical simulations of engine operation in HCCI mode have been

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... erformed based on experimental investigations with an optically-accessible single-cylinder engine. The numerical simulations were used to interpret the experimental observations in terms of mixing and reaction progress. Both experimental investigations and simulations show that injection timing is a feasible control parameter for the optimization of operating points because autoignition is influenced by the start of injection and the therewith connected temperature and mixture distribution. Furthermore spark assisted HCCI combustion at high load was investigated by thermodynamic analyses and combustion visualization. The results of the combustion visualization and heat release analyses suggest a superposition of flame front propagation and autoignition. Therefore the kinetic model to describe autoignition was coupled with a model to describe the turbulent flame propagation and three averaged cycles at different load were simulated. In all cases a good accordance between simulation and experiment can be stated. Like the results of the combustion visualization the simulations show a propagating flame front near the spark plug followed by sequential autoignition in the outer regions of the combustion chamber.