Abstract Recently, to simulate microgravity flames in a terrestrial environment, low stretched stagnation-point diffusion flames have aroused wide interest, while the extinction behaviors of varied stretched flames at reduced oxygen concentration were scarcely investigated. This issue was accomplished by an investigation in this paper. Firstly, local and total extinction modes with ‘U’-shape boundaries were found to enlarge the unstable area in the flammability map. Furthermore, gas-phase radiation inversely proportional to stretch rate contributed to decreased critical flame temperature with dropped stretch rate. Two different power laws of critical flame standoff distance versus stretch rate existed at quenching and blowoff due to the coupling effects of boundary layer and critical oxygen concentration. Surface energy balance to evaluate the mechanisms of quenching and blowoff demonstrated that, both solid-phase conduction and surface radiation dominated at quenching, while they can be ignored at blowoff. Finally, critical burning rate was obtained from the surface energy balance and found to decrease with declined stretch rate. The similar changing tendencies of flammability and burning characteristics versus stretch rate in this work to the microgravity results implied a low-cost earth-based research method to simulate microgravity flames, and some new findings can provide instructions for fire protection in space.

中文翻译：

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不同拉伸速率下滞点扩散火焰在低氧消光极限下的可燃性和临界参数

摘要 近年来，为了模拟陆地环境中的微重力火焰，低拉伸驻点扩散火焰引起了广泛的关注，而对不同拉伸火焰在降低氧浓度下的熄灭行为却鲜有研究。这个问题是通过本文的调查完成的。首先，发现具有“U”形边界的局部和完全消光模式扩大了可燃性图中的不稳定区域。此外，与拉伸速率成反比的气相辐射有助于随着拉伸速率的降低而降低临界火焰温度。由于边界层和临界氧浓度的耦合效应，在淬火和吹气时存在两种不同的临界火焰间隔距离与拉伸速率的幂定律。评估淬火和吹气机制的表面能平衡表明，固相传导和表面辐射在淬火时占主导地位，而在吹气时可以忽略它们。最后，从表面能平衡中获得临界燃烧速率，发现随着拉伸速率的降低而降低。这项工作中的可燃性和燃烧特性与拉伸率的相似变化趋势与微重力结果类似，暗示了一种低成本的地球研究方法来模拟微重力火焰，一些新发现可以为太空防火提供指导。从表面能平衡获得临界燃烧速率，发现随着拉伸速率的降低而降低。这项工作中的可燃性和燃烧特性与拉伸率的相似变化趋势与微重力结果类似，暗示了一种低成本的地球研究方法来模拟微重力火焰，一些新发现可以为太空防火提供指导。从表面能平衡获得临界燃烧速率，发现随着拉伸速率的降低而降低。这项工作中的可燃性和燃烧特性与拉伸率的相似变化趋势与微重力结果类似，暗示了一种低成本的地球研究方法来模拟微重力火焰，一些新发现可以为太空防火提供指导。