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

随着野火活动的增加，人类的成本和风险也在增加，确定控制野火蔓延的关键物理过程变得越来越重要。需要这些知识来改进火灾管理人员使用的模型，以便为遏制和规定的燃烧战略提供信息。大多数基础研究只关注于研究死燃料（如死树）的燃烧行为。这种关注是有问题的，因为许多野火实际上是通过活燃料和死燃料的混合物燃烧的。活的和死的燃料的组成可能有很大的不同，例如，活的树比死的树有更高的水分含量。在这项工作中，将进行一系列实验和计算模拟，以更好地了解当存在活燃料和死燃料的混合物时燃烧是如何变化的。预计从这项研究中获得的知识将改善火灾蔓延的模型，反过来，火灾管理人员使用的工具将变得更加准确。提高模型的准确性可以帮助减少与进行规定的燃烧或控制野火有关的成本。大多数基础野火研究只关注死燃料的燃烧行为。这种关注是有问题的，因为大多数野火实际上是通过活燃料或活燃料和死燃料的混合物发生的。在此背景下，这项工作的总体目标是确定控制异质（即活的和死的）燃料着火和蔓延的关键物理和化学过程。作为这项工作的一部分，以下目标将被解决：(1)阐明导致燃料燃烧行为差异的关键物理，因为对流和辐射传热的贡献是不同的；(2)确定当活燃料和死燃料的混合物燃烧时，关键的物理和化学过程是如何变化的。实现具体目标的主要方法将是进行控制良好的实验和相应的模拟，其中系统地加热活和死燃料颗粒的混合物，直到点火并最终发生燃尽。实验将应用激光和其他诊断方法来确定燃料颗粒的温度和热解速率、当量比和停留时间。模拟将使用多物理场计算流体动力学（CFD）描述来确定关键变量（例如速度、温度、化学成分等）的时间历史和空间分布。预计通过本研究获得的知识，火灾管理者、从业人员和科学家将更好地了解活燃料和死燃料混合物的燃烧行为。这种理解可以用于更新基于物理的现场尺度火灾蔓延模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.