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A correct prediction of the initial stages of the combustion process in SI engines is of great importance to understand how local flow conditions, fuel properties, mixture stratification and ignition affect the in-cylinder pressure development and pollutant formation. However, flame kernel growth is governed by many interacting processes including energy transfer from the electrical circuit to the gas phase, interaction between the plasma channel and the flow field, transition between different combustion regimes and gas expansion at very high temperatures. In this work, the authors intend to present a comprehensive, multi-dimensional model that can be used to predict the initial combustion stages in SI engines. In particular, the spark channel is represented by a set of Lagrangian particles where each one of them acts as a single flame kernel.

Combustion in engines involves very complicated phenomena (including flame propagation and knocking), which are strongly affected by engine speed, load and turbulence intensity in the combustion chamber. The aim of this study was to develop a flame propagation model and a knocking prediction technique applicable to various engine operating conditions, including engine speed and in-cylinder turbulence intensity. A flame propagation model (UCFM) has been developed that improved the Coherent Flamelet Model by considering flame growth both in terms of the turbulent flame kernel and laminar flame kernel. A knocking prediction model was developed by implementing the Livengood-Wu integral as the autoignition model. The combined model allows evaluation of both where and when autoignition occurs in a real shape combustion chamber. A comparison of the measured and calculated time for the occurrence of knocking shows good agreement for various operating conditions.