Browse Publications Technical Papers 2001-01-1226

Influence of Mixture Fluctuations on Combustion in Direct Injection Spark Ignition Engines Simulations 2001-01-1226

Modelling small and large scale fluctuations of fuel distribution is of high interest for stratified direct injection spark ignition (DISI) engines. Homogeneous combustion models need to be extended or replaced in order to account for these fluctuations. They are presently neglected in most engine simulations. Effects of mean fuel/air equivalence ratio gradient have been recently included in previous homogeneous mixture approaches.
To account for local fluctuations of mixture composition, the new model ECFM-Z has been developed on the basis of recent Direct Numerical Simulation results and Coherent Flame Surface modelling. The model has been implemented in a CFD code (KMB) The influence of mixture fraction is integrated in the Extended Coherent Flame Surface combustion model. The model is based on a conditional approach. Unburnt hydrocarbons produced by lean flame local extinctions are taken into account.
The model ECFM-Z is applied to investigate mixture fluctuation effects in a wide spacing, DISI engine running under stratified operating conditions. A typical stratified combustion parameter, the ignition timing, is varied. Accounting for the local fluctuations in mixture composition modifies heat release estimation. Effects of partial quenching and mass burning rate modelling on the combustion efficiency are revealed.


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