In wildland and other flame spread scenarios a spreading fire front often forms an elliptical shape, incorporating both forward and lateral spread. While lateral flame spread is much slower than forward rates of spread, it still contributes to the growth of the overall fire front. In this work, a small-scale experiment is performed to investigate the mechanisms causing this lateral spread in a simple, small-scale configuration. PMMA strips with thicknesses ranging from 1 mm to 3.1 mm and widths of 5 cm and 10 cm were ignited under forced flow in a laminar wind tunnel. Unlike traditional concurrent or opposed flame spread experiments, flames were allowed to progress from one side of the sample to the other, perpendicular to the wind direction. An infrared camera was used to track the progression of the pyrolysis front by estimating the surface temperature of the PMMA. The flame spread rate, depth of the burning region, thermal diffusion length, and radiant heat flux were determined and analyzed. Based on a theory of heat and mass transfer for a laminar diffusion flame, a thermal heat transfer model was developed for the preheating region to predict the lateral flame spread rate. Results show that the thermal diffusion length decreases with wind velocity, ranging from 4.5 mm to 3 mm. Convection dominates the flame-spread rate, accounting for more than 80% of the total heat flux. The theoretical flame spread rate agrees well with experimental data from all but the thinnest samples tested, overpredicting the lateral flame spread rate for 1 mm thick samples. The resulting model for lateral flame spread under concurrent flow works for forced-flow dominated flame spread over thermally-thin fuels and helps provide physical insight into the problem, aiding in future development of two-dimensional, elliptical fire spread models.

中文翻译：

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在强制气流下横向火焰蔓延在 PMMA 上

在荒地和其他火焰蔓延场景中，蔓延的火锋通常形成椭圆形，包括向前和横向蔓延。虽然横向火焰蔓延比向前蔓延速度慢得多，但它仍然有助于整体火锋的增长。在这项工作中，进行了一个小规模的实验，以研究在一个简单的小规模配置中导致这种横向传播的机制。在层流风洞中在强制流动下点燃厚度为 1 mm 至 3.1 mm、宽度为 5 cm 和 10 cm 的 PMMA 条。与传统的并行或反向火焰蔓延实验不同，允许火焰从样品的一侧蔓延到另一侧，垂直于风向。红外相机用于通过估计 PMMA 的表面温度来跟踪热解前沿的进展。确定并分析了火焰蔓延速率、燃烧区深度、热扩散长度和辐射热通量。基于层流扩散火焰的传热传质理论，建立了预热区的热传热模型，用于预测横向火焰蔓延率。结果表明，热扩散长度随风速减小，范围从 4.5 mm 到 3 mm。对流主导着火焰传播速率，占总热通量的 80% 以上。理论火焰蔓延速率与除测试的最薄样品以外的所有样品的实验数据非常吻合，高估了 1 毫米厚样品的横向火焰蔓延速率。