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.

利用美国宇航局格伦研究中心的5.18 s下降塔，进行了微重力实验，以研究并发流火焰散布在一系列薄纤维素基燃料样品上。样品段在样品架上均匀分布，并通过气隙隔开。每个样品段的暴露宽度为5厘米。测试了两个段的长度，分别为0.5 cm和1 cm。间隙大小在不同的测试中有所不同，范围从0.5到5 cm。在所有测试中，都会施加低速气流（30 cm / s），并且最上游的燃油段会通过电点火线点火。点火后，火焰传播由两台摄像机从前视角和侧视图记录下来。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。类似于连续燃料，火焰散布在离散的燃料上是一个持续的着火过程。燃烧的离散燃料段在被消耗之前，需要点燃随后的段，以使火焰在间隙中传播。在此过程中，样品之间的较大间隙会降低有效燃料负荷，从而增加表观火焰扩散速率。但是，较大的间隙也会减少相邻样品之间的传热，从而降低样品燃烧率。结果，随着间隙尺寸的增加，火焰蔓延速率增加，但是燃烧速率降低。在相同的间隙尺寸下，较短的测试样品段的火焰蔓延率较高。当考虑相同燃料比的样本配置（燃料长度超过燃料总长度和间隙长度）时，扩散率相似。这种趋势一直保持到达到临界间隙大小并且火焰无法在整个样本阵列中传播为止。对于两个测试的样品段长度，临界间隙尺寸相似，并且怀疑由火焰长度确定。