Collaborative Research: Understanding Key Processes Controlling Burning of Heterogeneous Fuel in Wildfires

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Identifying key physical processes that control the spread of wildfires is becoming increasingly important as the cost and risk to humans increase with rising wildfire activities. Such knowledge is needed to improve models used by fire managers to inform containment and prescribed burn strategies. Most fundamental studies have focused only on studying the burning behavior of dead fuels (e.g., dead trees). This focus is problematic because many wildfires actually burn through mixtures of live and dead fuels. The composition of live and dead fuels can be vastly different, for example live trees have higher moisture content than dead trees. In this work, a series of experiments and computational simulations will be conducted to better understand how burning changes when mixtures of living and dead fuels are present. It is expected that as a result of the knowledge gained from this study, models of fire spread will be improved, and in turn, the tools used by fire managers will become more accurate. Improved accuracy of models can help to reduce the costs associated with conducting prescribed burns or containing wildfires.Most fundamental wildfire studies have focused only on the burning behavior of dead fuels. This focus is problematic because most wildfires actually occur through live, or mixtures of live and dead fuels. With this background, the overall objective of this work is to identify key physical and chemical processes that control ignition and spread of fire within heterogeneous (i.e., live and dead) fuels. The following aims will be addressed as part of this effort: (1) Elucidate key physics that cause differences in burning behavior of fuels as contributions from convective and radiative heat transfer are varied, and (2) Identify how key physical and chemical processes change when mixtures of living and dead fuels burn. The primary approach to attaining the specific aims will be to conduct well-controlled experiments and corresponding simulations where mixtures of live and dead fuel particles are systematically heated until ignition and ultimately burnout occurs. The experiments will apply laser-based and other diagnostics to determine temperatures and pyrolysis rates of fuel particles, equivalence ratios, and residence times. The simulations will use a multiphysics Computational Fluid Dynamics (CFD) description to determine time history and spatial distribution of key variables (e.g., velocity, temperature, chemical composition etc.).It is expected that as a result of knowledge gained from this study, fire managers, practitioners, and scientists will be better informed about the burning behavior of mixtures of live and dead fuels. This understanding can be used to update physics-based field-scale fire spread models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.