Predicting the fire spread rate of a sloped pine needle board utilizing pyrolysis modelling with detailed gas-phase combustion

•The large eddy simulation approach was associated with a pyrolysis model.•Detailed kinetics combustion model was coupled with a C2H2 based soot model.•The fire spread over a pine needle fuel bed under different slope angles is studied.•Comprehensive description of the generation process of chemical by-products.•Temperature field and fire spread rate were well predicted against experimental data. A novel Large Eddy Simulation (LES) based fire field model that incorporates pyrolysis modelling has been developed. This model is specifically designed for flame propagation of wildland fire scenarios. It uniquely embraces the radiation heat feedback from the flame, gaseous combustion and soot products towards the fuel bed surface. It also considers the detailed chemical kinetics for combustion, primary soot incipient and oxidant for soot formation, turbulent microscopic fuel–air mixing which are fully coupled, interactive and non-linear. Numerical simulation has been performed to study the effect of slope angle on the flame propagation characteristic of pine needle fuel beds. The fire spread rate and temperature predictions are within 12% accuracy in comparison to experimental data. Owing to the unbalanced air entrainment drew by the flame combustion for the inclined slope angle cases, it can be observed from the visualised flame that it was tilted to the unburned portion of the board. This behaviour strongly promotes the radiative heat transfer from the flame onto the fuel bed, which led to a rapid increase in pyrolysis rate thus accelerated the overall flame spread on the board surface. This physical phenomenon was successfully captured by the pyrolysis model and was found to be significantly more accurate in predicting the fire spread rate for slope angles higher than 20° (error of 11.12%) when compared to empirical flame tracking methods (error of 87.19%).