Investigation of Mixing Models and Conditional Moment Closure Applied to Autoignition of Hydrogen Jets

The present paper is focused on performing a thorough investigation of first order Conditional Moment Closure (CMC) including an inhomogeneous turbulent mixing model for the conditional scalar dissipation rate to predict autoignition. Autoignition of a hydrogen and nitrogen fuel mixture in a heated coflow of air is examined. A sensitivity analysis is proposed for the autoignition length with respect to the mixing field, as well as a comparison of the effects of the inhomogeneous turbulent and Amplitude Mapping Closure (AMC) mixing models. The choice of turbulence constants only change predicted ignition length by approximately 5 % when applied to the AMC mixing model. Predictions of ignition length performed by the inhomogeneous model are lower than that of the AMC model by up to 15 %. The current ignition predictions are in reasonable agreement with the experimental data and previous simulation results. Two of the four regimes observed experimentally are reproduced qualitatively. Further improvement may be gained by using large eddy simulation and a gradient model for the conditional velocity in the inhomogeneous turbulent mixing model.