Concurrent-flow flame spread over thin discrete fuels in microgravity
Concurrent-flow flame spread over thin discrete fuels in microgravity
复制标题
微重力下稀薄离散燃料上的并流火焰传播
DOI：
10.1016/j.combustflame.2020.12.005
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发表时间：
2021
影响因子：
4.4
通讯作者：
Ferkul, Paul
中科院分区：
文献类型：
--
作者：
Carney, Ama;Li, Yanjun;Liao, Ya-Ting;Olson, Sandra;Ferkul, Paul
利用美国宇航局格伦研究中心的S落塔，进行了微重力实验，研究了顺流火焰在一系列薄薄的纤维素燃料样品上的传播。样品段均匀地分布在样品支架上，由气隙隔开。每个样品段的裸露宽度为5厘米。测试了两个管段长度，0.5厘米和1厘米。在不同的测试中，间隙大小各不相同，从0.5厘米到5厘米不等。在所有测试中，施加低速气流(30厘米/S)，并通过电子点火导线点燃最上游的燃料段。点火时，由两个摄像机从前视和侧视角度记录火焰传播过程。使用自定义视频处理代码提取传播速率、火焰长度和燃烧持续时间。与连续燃料类似，火焰在离散燃料上的传播是一个连续的点火过程。燃烧的离散燃料段在被消耗之前，需要点燃随后的段，以便火焰在缝隙中传播。在这一过程中，样品之间较大的间隙降低了有效燃料负荷，增加了表观火焰传播率。然而，较大的间隙也会降低相邻样品之间的换热，从而降低样品的燃烧速度。结果表明，随着缝隙尺寸的增大，火焰传播速率增大，燃烧速率减小。在相同间隙尺寸下，被测样品段越短，火焰传播率越高。当考虑相同燃料比(燃料长度与间隙长度之和的燃料长度)的样本配置时，散布率是相似的。这一趋势一直保持到达到临界间隙大小，火焰不能在整个样品阵列中传播。对于两个测试样品段长度，临界间隙大小相似，并且怀疑由火焰长度决定。
Microgravity experiments are performed to study concurrent-flow flame spread over an array of thin cellulose-based fuel samples, using NASA Glenn Research Center's 5.18 s drop tower. Sample segments are distributed uniformly, separated by air gaps, on a sample holder. The exposed width of each sample segment is 5 cm. Two segment lengths, 0.5 cm and 1 cm, are tested. The gap sizes are varied in different tests, ranging from 0.5 to 5 cm. In all tests, a low-speed air flow (30 cm/s) is imposed and the upstream-most fuel segment is ignited by an electrical ignition wire. Upon ignition, the flame spread is recorded by two video cameras from the front and side-view angles. Spread rates, flame lengths, and burning durations are extracted using a custom video processing code. Similar to continuous fuels, flame spread over discrete fuels is a continual process of ignition. A burning discrete fuel segment, before it is consumed, needs to ignite the subsequent segment in order to have flame propagation across the gap. During this process, larger gaps between samples reduce the effective fuel load, increasing the apparent flame spread rate. However, larger gaps also reduce the heat transfer between adjacent samples, decreasing the sample burning rate. As a result, as the gap size increases, the flame spread rate increases but the burning rate decreases. At the same gap size, the flame spread rate is higher for the shorter tested sample segments. When considering sample configurations of the same fuel ratio (fuel length over the summation of the fuel and gap lengths), the spread rates are similar. This trend remains until a critical gap size is reached and flame fails to propagate across the entire array of samples. The critical gap sizes are similar for the two tested sample segment lengths and are suspected to be determined by the flame length.
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DOI：
10.1115/imece2019-11908
发表时间：
2019-11
期刊：
Volume 8: Heat Transfer and Thermal Engineering
影响因子：
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作者：
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