Ignition propensity of structural materials exposed to firebrand in wildland-urban interface (WUI) fires

该项目将描述由火种攻击引起的材料的点火过程，这是野火蔓延到荒地-城市界面（WUI）社区的关键机制。火种是由火焰羽升起的小燃烧块，并由周围的风传播。虽然火种很小，但它们可以成群结队地从火场走很远的距离。这些火种可以在远离野火本身的WUI社区的建筑物上淋浴，因此对人类生命和财产构成严重威胁。在这个项目中，将使用实验室规模的实验和计算模型来系统地研究这些现象。通过更好地了解燃烧弹攻击，该项目将促进建筑规范和材料新测试标准的发展。这项工作将有助于提高荒地-城市界面结构的安全性，例如优化结构的几何形状以减轻火灾风险。对于受外部加热的可燃固体，点火不仅取决于总能量输入，而且取决于加热的空间分布。对于燃烧物攻击点火，燃烧物的分布及其各自的形状、大小和与目标结构的接触面积将决定结构表面热流密度的分布。环境条件（例如，背景辐射加热和空气流速）也对燃烧的燃烧物的动力学以及燃烧物与目标结构之间的相互作用有显著影响。本研究的目的是获得这些参数如何影响结构材料的点火倾向的基本理解。将使用实验室规模的实验和计算模型的结合。实验将涉及在气流和外部辐射加热的影响下燃烧的火焰。温度，燃烧持续时间，燃烧品牌的热释放率，以及基材的温度，将被分析。燃料床的着火倾向将根据燃烧物属性和环境因素进行表征。还将开发一个燃烧模型，用于模拟燃烧物攻击各方面的热动力学过程。模拟结果将提供燃烧过程中气体和固体的详细信息，从而便于对实验观察结果的解释。数值模拟还将允许对这些过程的基本物理进行调查。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。

This project will characterize the ignition process of materials caused by firebrand attacks, a key mechanism of wildfire spread into Wildland-Urban Interface (WUI) communities. Firebrands are small burning pieces lofted by flame plumes and transported by ambient winds. Although they are small, firebrands can travel in large groups for long distances from the fire front. These firebrands can shower unto structures in WUI communities far from the wildfire itself and therefore pose serious threats to human lives and properties. In this project, lab-scale experiments and computational modeling will be used to systematically study such phenomena. By providing a better understanding of firebrand attacks, this project will promote the development of new testing standards for building codes and materials. This work will contribute to the effort in increasing the safety of structures at the wildland-urban interface, such as optimal geometry of structure for mitigating fire risks.For a combustible solid subjected to external heating, ignition depends not only on the total energy input but also on the spatial distribution of the heating. For ignition due to firebrand attack, the distribution of firebrands and their individual shapes, sizes, and contact areas with the target structure will determine the distribution of heat flux on the structure surface. Environmental conditions (e.g., background radiant heating and air flow speed) also have a significant effect on the kinetics of the burning firebrands and the interactions between firebrands and the target structure. The goal of this study is to obtain a fundamental understanding of how these parameters affect the ignition propensity of a structure material. A combination of lab-scale experiments and computational modeling will be used. The experiment will involve firebrands burning under the influence of air flow and external radiant heating. Temperatures, burning durations, and heat release rates of the burning brands, as well as the temperature of the substrate, will be analyzed. The ignition propensity of the fuel bed will be characterized according to firebrand attributes and environmental factors. A combustion model will also be developed for simulating the thermo-kinetic process of each aspect of the firebrand attack. The simulation results will provide detailed information about gases and solids during the combustion process, thus facilitating the interpretation of the experimental observation. The numerical simulation will also allow the investigation of the underlying physics of these processes.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.