A Study of the Effectiveness of a Narrow Channel Apparatus in Simulating Microgravity Flame Spread over Thin Fuels
A Study of the Effectiveness of a Narrow Channel Apparatus in Simulating Microgravity Flame Spread over Thin Fuels
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DOI：
10.2514/6.2012-3493
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发表时间：
2012-07
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影响因子：
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通讯作者：
J. M. Pepper;F. Miller;S. Olson;I. Wichman
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文献类型：
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作者：
J. M. Pepper;F. Miller;S. Olson;I. Wichman
NASA目前对非金属固体的可燃性测试方法是NASA-STD-(I)-6001A测试1。允许火焰向上传播6英寸或更多的材料不能通过可燃性测试。地面测试1中的火焰主要是向上流动的浮力气体，这不能代表微重力下的实际火焰行为，因为微重力对火焰没有浮力影响。NASA的科学家已经证明，通过在垂直方向上对水平传播的火焰进行空间限制，可以在地面火焰传播测试中将浮力降至最低。在圣地亚哥州立大学的窄通道装置(SDSU NCA)进行的可燃性测试结果与NASA的窄通道装置在1个大气压和21%氧气下的结果非常接近。SDSU NCA的优势在于，它不仅将浮力影响降至最低，而且还允许在常氧当量大气中进行易燃性测试，以便与未来的航天器舱内大气更接近。在SDSU NCA中，通过改变试验通道中的总压、反向流动氧化剂速度和氧气浓度来实现常氧条件。在我们之前的研究中，我们测量了在总压力从0.27到1.0atm，氧摩尔分数从0.77到0.21的情况下，火焰在Whatman 44无灰滤纸上的蔓延速度，沿着稀薄燃料上下5 mm的常压曲线。火焰传播速率存在显著差异，在低气压/高氧气浓度时，火焰传播速率要高得多。这篇论文扩展了这项工作，通过比较在SDSU NCA的Kimwipe®上和NASA的零重力研究设施中沿着常氧曲线的几个点进行的火焰传播测试的可燃性结果。此外，还进行了标度分析，研究了压力对某些火焰长度标尺的影响。
NASA’s current flammability testing method for non-metallic solids is NASA-STD-(I)-6001A Test 1. Materials that allow for an upward flame propagation of six inches or more fail the flammability test. The flames in the Earth-based Test 1 are dominated by the upward-flowing buoyant gases, and this is not representative of actual flame behavior in microgravity, where there are no buoyant effects on flames. Scientists at NASA have shown that by spatially confining a horizontally spreading flame in the vertical direction, buoyant forces can be minimized in an Earth-based flame spread test. Results from flammability tests conducted in San Diego State University’s Narrow Channel Apparatus (SDSU NCA) closely match results from NASA’s Narrow Channel Apparatus at 1 atmosphere of pressure and 21% oxygen. The advantage of the SDSU NCA is that it not only minimizes buoyant effects, but it also allows flammability tests to be performed at normoxic equivalent atmospheres that more closely match future spacecraft cabin atmospheres. Normoxic conditions are achieved in the SDSU NCA by varying the total pressure, opposed flow oxidizer velocity, and oxygen concentration in the test channel. In our previous research we measured the flame spread rate across Whatman 44 ashless filter paper at total pressures from .27 to 1.0 atm and oxygen mole fractions from 0.77 to 0.21 respectively, along the normoxic curve for a gap height of 5 mm above and below the thin fuel. Significant differences in the flame spread rate were found, with much higher spread rates at the low pressure/high oxygen concentrations. This paper extends that work by comparing flame spread results from flammability tests conducted on Kimwipes ® in the SDSU NCA and in true microgravity in NASA’s Zero-Gravity Research Facility at several points along the normoxic curve. Also, a scaling analysis is conducted to study the effect of pressure on certain flame length scales.