Confined combustion of polymeric solid materials in microgravity
Confined combustion of polymeric solid materials in microgravity
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DOI：
10.1016/j.combustflame.2021.111637
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发表时间：
2021-12
影响因子：
4.4
通讯作者：
Yanjun Li;Ya-Ting T. Liao;P. Ferkul;Michael C. Johnston;C. Bunnell
中科院分区：
文献类型：
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作者：
Yanjun Li;Ya-Ting T. Liao;P. Ferkul;Michael C. Johnston;C. Bunnell
采用微重力实验研究了约束对高分子固体材料燃烧行为的影响。扁平的100 × 22 × 1 mm的PMMA样品在国际空间站上的一个小管道内的同步气流中燃烧。检查了三种不同的燃烧场景，双面，单面和平行样品。在前两种情况下，单个样品分别在两侧和一侧燃烧。平挡板平行于样品放置，以限制燃烧的可用空间。在不同的试验中，挡板与试样之间的距离(H)是不同的。在每个测试中，施加的流量逐步减少，并且在每个流量速度下实现稳定的火焰蔓延，直到火焰熄灭。结果表明，在相同的约束条件下，稳态火焰长度和蔓延速率与测试范围内的流速成正比。当约束增大（或H减小）时，火焰蔓延速度和火焰长度先增大后减小。淬火流动速度随h的减小先减小后增大，表明限制可以根据不同的条件提高或降低固体燃料的可燃性。在第三种燃烧场景中，两个PMMA样品彼此平行放置，间隔距离为H.观察到双火焰，燃烧被限制在两个样品之间。在三种测试燃烧场景中，在相同约束水平(H)下，双火焰的火焰长度和燃烧速率最大。这是因为双火焰之间的热相互作用增强了对固体燃料的热反馈，减少了对周围流动管道的相对热损失。在相同挡板-试样距离下，将单面火焰与双面火焰进行比较，单面火焰的传播速度略小于双面火焰的一半。这是由于一半的热解区暴露在火焰和热损失在样品的背面。氧气向火焰的最佳输送也起着作用。
Microgravity experiments are performed to study the effects of confinement on the burning behavior of polymeric solid materials. Flat, 100 × 22 × 1 mm PMMA samples are burned in concurrent air flow in a small flow duct aboard the International Space Station. Three different burning scenarios are examined, double-sided, single-sided, and parallel samples. In the first two scenarios, single samples are burned on both sides and on one side, respectively. Flat baffles are placed parallel to the sample to confine the available space for combustion. The distance between the baffle and the sample (H) is varied in different tests. In each test, imposed flow is reduced in steps and steady flame spread is achieved at each flow speed until the flame quenches. The results show that at the same confined condition, steady state flame length and spread rate are proportional to flow speed over the range tested. When confinement increases (or H decreases), the flame spread rate and flame length increase first and then decrease. In addition, the quenching flow speed decreases and then increases with decreasing H. These results suggest that the confinement can increase or decrease solid fuel flammability depending on conditions. In the third burning scenario, two PMMA samples are placed parallel to each other separated by a distance H. Twin flames are observed and combustion is confined between the two samples. Among the three tested burning scenarios, twin flames have the largest flame length and burning rate at the same confinement level (H). This is because the thermal interaction between the twin flames enhances the heat feedback to the solid fuel and reduces the relative heat loss to the surrounding flow duct. Comparing single- and double-sided flames with the same baffle-sample distance, the spread rate of a single-sided flame is slightly less than half of that of a double-sided flame. This is due to the halved pyrolysis area exposed to the flame and heat loss on the back side of the sample. Optimal transport of oxygen to the flames also plays a role.