Flame ignition and extinction modelling using infinitely fast chemistry in large eddy simulations of fire-related reacting flows

Abstract

Large eddy simulations with the use of infinitely fast chemistry, focusing on flame ignition and extinction modelling, are presented within the context of fires. A dynamic approach with respect to turbulence, combustion and radiation modelling is employed in the simulations. Flame ignition is modelled based on an ignition temperature, which varies with the local sub-grid scale strain rate, while flame extinction is modelled based on the concept of a critical flame temperature, which varies with the local mixing time scale. Validation of the approach is made by considering four different experiments, involving both no-extinction and extinction scenarios. Focus is put on the predictive capabilities of the simulations, with respect to different grid sizes, by comparison to experimental data involving both first and second order statistics, and data available in the literature for different grid sizes and for the different fuels considered. The predicted flame temperatures and combustion efficiencies with the proposed approach agree fairly well, both qualitatively and quantitatively, with the experiments and data for the limiting oxygen concentration from the literature.