Zhang Pengyuan, Kang Yinhu, Huang Xiaomei, Peng Shini, Cui Kaiqi, Lu Xiaofeng
School of Civil Engineering, Chongqing University, Chongqing 400044, China.
Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, Ministry of Education of China, Chongqing University, Chongqing 400044, China.
ACS Omega. 2020 Aug 19;5(34):21579-21592. doi: 10.1021/acsomega.0c02222. eCollection 2020 Sep 1.
Flame extinction is one of the most essential critical flame features in combustion because of its relevance to combustion safety, efficiency, and pollutant emissions. In this paper, detailed simulations were conducted to investigate the effect of H addition on dimethyl ether spherical diffusion flame in microgravitational condition, in terms of flame structure, flammability, and extinction mechanism. The mole fraction of H in the fuel mixture was varied from 0 to 15% by 5% in increment. The chemical explosive mode analysis (CEMA) method was employed to reveal the controlling physicochemical processes in extinction. The results show that the cool flame in microgravitational diffusive geometry had the "double-reaction-zone" structure which consisted of rich and lean reaction segments, while the hot flame featured the "single-reaction-zone" structure. We found that the existence of "double-reaction-zone" was responsible for the stable self-sustained cool flame because the lean zone merged with the rich zone when the cool flame was close to extinction. Additionally, the effect of H addition on the cool flame was distinctively different from that of the hot flame. Both hot- and cool-flame flammability limits were significantly extended because of H addition but for different reasons. Besides, for each H addition case, the chemical explosive mode eigenvalues with the complex number appeared in the near-extinction zone, which implies the oscillation nature of flame in this zone which may induce extinction before the steady-state extinction turning point on the -curve. Furthermore, as revealed by CEMA analysis, contributions of the most dominated species for extinction changed significantly with varying H additions, while contributions of the key reactions for extinction at varying H additions were basically identical.
火焰熄灭是燃烧过程中最基本的关键火焰特征之一，因为它与燃烧安全、效率和污染物排放相关。本文进行了详细的模拟，以研究在微重力条件下添加氢气对二甲醚球形扩散火焰的影响，涉及火焰结构、可燃性和熄灭机理。燃料混合物中氢气的摩尔分数以5%的增量从0变化到15%。采用化学爆炸模式分析（CEMA）方法来揭示熄灭过程中控制的物理化学过程。结果表明，微重力扩散几何形状中的冷火焰具有由富反应段和贫反应段组成的“双反应区”结构，而热火焰具有“单反应区”结构。我们发现“双反应区”的存在是冷火焰稳定自持的原因，因为当冷火焰接近熄灭时，贫区与富区合并。此外，添加氢气对冷火焰的影响与对热火焰的影响明显不同。由于添加氢气，热火焰和冷火焰的可燃极限都显著扩展，但原因不同。此外，对于每种添加氢气的情况，在接近熄灭区域出现了带有复数的化学爆炸模式特征值，这意味着该区域火焰的振荡性质，这可能在曲线的稳态熄灭转折点之前导致熄灭。此外，正如CEMA分析所揭示的，随着氢气添加量的变化，对熄灭起主要作用的物种的贡献显著变化，而不同氢气添加量下对熄灭起关键作用的反应的贡献基本相同。
