Effects of spacing on flaming and smoldering firebrands in wildland–urban interface fires
Effects of spacing on flaming and smoldering firebrands in wildland–urban interface fires
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DOI：
10.1177/07349041221081998
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发表时间：
2022-03
影响因子：
1.9
通讯作者：
Byoungchul Kwon;Ya-Ting T. Liao
中科院分区：
文献类型：
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作者：
Byoungchul Kwon;Ya-Ting T. Liao
火种（余烬）攻击已被证明是野火蔓延到荒地-城市界面社区的关键机制之一。当引燃物落在基板材料上后，材料的引燃倾向不仅取决于材料的属性（如形状、大小和数量），还取决于引燃物的分布。为了帮助描述这一过程，本研究旨在研究间隙间距对一组木制样品燃烧行为的影响。实验用9个边长为19毫米的木立方体进行。这些样品以3 × 3的正方形排列在悬挂线上，并由底部表面的热线圈点燃。样品之间的间隙间距(s)在每次测试中变化（范围从0到30 mm）。点火后，样品被留下燃烧完成。燃烧过程用摄像机记录下来。在燃烧和阴燃过程中监测样品的质量损失和温度。结果表明，火焰高度和样品质量损失率与间隙间距呈非单调关系。当间隙减小时，由于相邻火焰对每个样品的热量输入增强，火焰高度和质量损失率首先增加。当s≤10 mm时，观察到单个样品的火焰合并成一个大火焰。随着s的进一步减小，火焰底部的空气夹带量减小，火焰中心的火焰升离距离增大，导致火焰高度增大，火焰对固体样品的热反馈减小，质量损失率减小。质量损失率的降低最终也导致火焰高度的降低。气体火焰高度与固体燃烧速率相关。对于连续火源，相关关系一般遵循先前的经验方程。对于阴燃燃烧，由于相邻燃烧样品之间的热相互作用，与单个燃烧样品相比，阴燃温度和持续时间显著增加。为了帮助解释燃烧实验的结果，热重分析也在空气和氮气中进行，导致加热速率范围从10到100 K/min。
Firebrand (ember) attack has been shown to be one of the key mechanisms of wildfire spread into wildland–urban interface communities. After the firebrands land on a substrate material, the ignition propensity of the material depends on not only the attributes (e.g. shape, size, and numbers) but also the distribution of the firebrands. To help characterize this process, this study aims to investigate the effects of gap spacing on the burning behaviors of a group of wooden samples. Experiments are conducted using nine wooden cubes, 19 mm on each side. These samples are arranged in a 3 × 3 square pattern on suspension wires and are ignited by hot coils from the bottom surface. The gap spacing (s) between the samples varies in each test (ranging from 0 to 30 mm). After ignition, the samples are left to burn to completion. The burning process is recorded using video cameras. Sample mass loss and temperatures are monitored during the flaming and smoldering processes. The results show that the flame height and the sample mass loss rate have non-monotonic dependencies on the gap spacing. When the gap spacing reduces, the flame height and the mass loss rate first increase due to enhanced heat input from the adjacent flames to each sample. When s ≤ 10 mm, flames from individual samples are observed to merge into a single large fire. As s further decreases, the air entrainment at the flame bottom decreases and the flame lift-off distance at the flame center increases, resulting in an increased flame height, decreased flame heat feedback to the solid samples, and a decreased mass loss rate. The decreased mass loss rate eventually leads to a decrease in the flame height as well. The gaseous flame height is correlated to the solid burning rate. The correlation generally follows previous empirical equations for continuous fire sources. For the smoldering combustion, compared to a single burning sample, the smoldering temperature and duration significantly increase due to the thermal interactions between adjacent burning samples. To help interpret the results of the burning experiments, thermogravimetric analysis is also performed in air and nitrogen, resulting in heating rates ranging from 10 to 100 K/min.