Transient dynamics of formation and extinction of methane- and ethylene-fueled flames above the flat porous burner in an oxidizing atmosphere is numerically investigated. The simulated scenarios replicate the experimental conditions of the BRE (Flamenco) project of the ACME program focusing on combustion research in microgravity. The 3D unsteady model includes the multi-step and multi-component chemical mechanisms of fuel oxidation, formation and oxidation of soot, and the radiative transfer. The model is validated for the methane-fueled jet laminar diffusion flame in normal gravity and for the ethylene flame developing in short-duration free-fall microgravity in the drop tower. The microgravity flames are then simulated at longer times, and the range of fuel mass fluxes characteristic of solid and liquid combustibles is explored. In all the cases considered, combustion is essentially unsteady, in spite of the constant fuel supply rate. During the initial stage of flame growth, the temperature in the reaction zone persistently decreases due to the radiative losses down to the level causing local extinction, oscillations, and complete extinguishment of the flame. The effect of fuel type and mass flux at the burner surface on the flame lifetime and on its disintegration dynamics is demonstrated. The sensitivity of the results to the chemical mechanism used in the simulations is examined. The radiative fraction in the microgravity flames is found to be by an order of magnitude higher than that in the normal gravity flames produced by the same burner. The radiative losses are shown to be the reason for extinction and instability in the microgravity flames considered in this work.

中文翻译：

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微重力条件下扁平多孔燃烧器上方层流扩散火焰的辐射消光：计算研究

数值研究了氧化气氛中扁平多孔燃烧器上方甲烷和乙烯燃料火焰的形成和熄灭的瞬态动力学。模拟场景复制了 ACME 计划的 BRE（弗拉门戈）项目的实验条件，该项目专注于微重力下的燃烧研究。3D非定常模型包括燃料氧化、烟尘的形成和氧化以及辐射转移的多步骤和多组分化学机制。该模型在正常重力下以甲烷为燃料的喷射层流扩散火焰和在下降塔中在短持续时间自由落体微重力下产生的乙烯火焰进行了验证。然后在更长的时间内模拟微重力火焰，并探索固体和液体可燃物的燃料质量通量范围。在所有考虑的情况下，尽管燃料供应速率恒定，但燃烧基本上是不稳定的。在火焰生长的初始阶段，由于辐射损失，反应区的温度持续降低，导致火焰局部熄灭、振荡和完全熄灭。证明了燃烧器表面的燃料类型和质量流量对火焰寿命及其分解动力学的影响。检查结果对模拟中使用的化学机制的敏感性。发现微重力火焰中的辐射分数比相同燃烧器产生的正常重力火焰高一个数量级。