Derivation and application of autoignition-based simplified kinetic models of hydrocarbon oxidation for fire simulations

Abstract

The possibility of a global reaction model with temperature-dependent kinetic parameters to predict the autoignition delay times of stoichiometric fuel-air mixtures with the accuracy corresponding to that of the most comprehensive chemical mechanisms is demonstrated. These effective kinetic parameters are derived for C1-C7 alkane and two alkene (ethylene and propylene) fuels. With these parameters, complicated non-monotonic dependencies of autoignition delay time on temperature, such as those in which an interval with negative temperature dependence exists, are replicated. Using these kinetic parameters, large eddy simulations are performed for the flames produced by the FM circular burner and UMD line burner, using the subgrid combustion model SCM. The critical role of the autoignition event for the prediction of flame extinction is highlighted, and a correlation between the experimental critical oxygen concentrations and the simulated autoignition delay times is demonstrated. This modelling approach is shown to correctly replicate both experimental scenarios with different hydrocarbon fuels at oxygen mole fractions from 0.21 down to complete flame extinguishment. Compared to the detailed chemical mechanisms, use of the global reaction model offers considerable reduction of computational cost yet retaining the capability of predicting critical phenomena of flame extinction and re-ignition in under-ventilated or strained flames.