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A predictive, quasi-dimensional simulation of combustion in a spark ignition engine has been coupled with a chemical kinetic model for the low temperature, pre-flame reactions of hydrocarbon fuel and air mixtures. The simulation is capable of predicting the onset of autoignition without prior knowledge of the cylinder pressure history. Near-wall temperature gradients were computed within the framework of the engine cycle simulation by dividing the region into a number of thin mass slices which were assumed to remain adjacent to the combustion chamber surfaces in both the burned and unburned gas. The influence of the near-wall turbulence on the temperature field was accounted for by means of a boundary layer turbulence model developed by the authors. Fluid motion in the bulk gases has been considered by the inclusion of a turbulence model based on k - ε theory while the flame propagation rate was predicted using a fractal flame model.

A new type of model has been developed to predict near wall temperature gradients and local instantaneous heat fluxes in a “motored” engine. The unburnt charge in an existing “phenomenological” model is divided into a number of discrete masses which are assumed to be “stacked” adjacent to the cylinder surfaces. A sub-model based on the one-dimensional Enthalpy Equation is applied to the system of discrete masses in order to predict the near wall temperature distribution. Predicted temperature profiles are compared with those measured by other researchers and show good agreement under both low and high swirl conditions. Local instantaneous heat fluxes are calculated from the near wall temperature gradients, and these also show good agreement with measured results. Near wall velocity and turbulence data have been used in modelling turbulent eddy transport processes rather than using conventional boundary layer theories.