Physics-based modeling of fire spread in small-scale fuel beds using multiple-reaction pyrolysis kinetics

Background Physics-based models often use single-step reaction schemes for thermal pyrolysis. However, more detailed schemes may be needed to accurately represent fuels such as pine needles that are composed of multiple chemical components. To this end, a multi-reaction kinetic scheme accounting for lipids, digestives, hemicellulose, etc. content was evaluated. Aims Validate the scheme against previous thermogravimetric analysis (TGA) experiments and assess its impact in physics-based modeling. Methods Analytical and numerical solutions were obtained for the scheme under TGA conditions. It was implemented in Fire Dynamics Simulator (FDS) to physically model previous ignition and fire spread experiments in two setups including small scale fuel beds. Key results Analytical and numerical mass loss rates matched perfectly and agreed with TGA data. In the first fuel bed setup, simulated ignition time, mass loss and mass loss rates aligned well with experiments. In the second setup, simulations in general overestimated temperatures and heat fluxes but performed better than those using a single-step scheme. Conclusions The multi-reaction scheme reproduced TGA data accurately and improved the physics-based modeling predictions for ignition and fire spread in small-scale fuel beds. Implications Multiple-reaction pyrolysis schemes may be needed to improve the physical modeling of various fire scenarios.