A MODEL FOR THE EFFECTS OF MIXING ON THE AUTOIGNITION OF TURBULENT FLOWS

Modelled transport equations for the conditional mean and r.m.s. tempe rature increments theta before autoignition in a turbulent non-premixe d flow have been developed. The model is based on the recent finding t hat a well-defined mixture fraction, f(MR), first ignites and the conc ept that the conditional scalar dissipation rate, chi\f(MR), controls the hear losses and hence the ignition time. By introducing the fluctu ations of chi\f(MR) and by modelling the conditional correlation coeff icients between chi and theta from results from Direct Numerical Simul ations, the model is closed and calculates autoignition times in good agreement with DNS results. Extensions to complex chemistry and the re lationship with the more rigorous Conditional Moment Closure are discu ssed. Finally, the model is incorporated in a Favre-averaged k - epsil on code (KIVA-II) to predict autoignition of a transient fuel jet in h ot air with promising results.