Zhang Rui, Yang Shenghua, Zhou Xun, Liu Dong
MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China.
Advanced Combustion Laboratory, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China.
ACS Omega. 2022 Jul 12;7(29):25087-25093. doi: 10.1021/acsomega.2c01362. eCollection 2022 Jul 26.
Cool flames have been studied for more than three centuries since the first observation. However, there are few achievements on the effects of the pressure on cool flames. In this work, a diffusion cool flame has been for the first time established using a counterflow configuration under a wide range of pressures. Dimethyl ether is used as the fuel because its low-temperature chemistry has been well tested. The pressure range of the experiments is from 0.05 to 0.15 MPa. The extinction limits, flame temperatures, and combustion products have been measured and simulated. In general, the reactivity of cool flames is stronger with increasing pressure. Specifically, at a fixed fuel mass fraction, the cool flame has a higher extinction strain rate, temperature, and concentration of products under higher pressure. However, the enhancement effect decreases with the increase of pressure. Interestingly, it was observed that the flame became thicker when the pressure increased. Moreover, the cool flame would deflagrate and transform to a hot flame when the pressure exceeds a certain value. The model captures the trends well but underpredicts the extinction limits and overpredicts the flame temperatures and product concentration. Path flux analyses and heat release rate analyses were carried out. It was found that the main heat release reactions are the reactions with CHOCH radicals under low pressure, and CO prefers to form CO indirectly through HOCHO radicals. The study advances the understanding of cool flames in a wide range of pressures and provides experimental data for the improvement of the models.
自首次观测以来，冷火焰已被研究了三个多世纪。然而，关于压力对冷火焰影响的研究成果却很少。在这项工作中，首次使用逆流配置在广泛的压力范围内建立了扩散冷火焰。使用二甲醚作为燃料，因为其低温化学性质已得到充分测试。实验的压力范围为0.05至0.15MPa。测量并模拟了熄火极限、火焰温度和燃烧产物。一般来说，随着压力增加，冷火焰的反应活性更强。具体而言，在固定的燃料质量分数下，冷火焰在较高压力下具有更高的熄火应变率、温度和产物浓度。然而，增强效果随着压力的增加而减小。有趣的是，观察到压力增加时火焰会变厚。此外，当压力超过一定值时，冷火焰会爆燃并转变为热火焰。该模型能较好地捕捉趋势，但低估了熄火极限，高估了火焰温度和产物浓度。进行了路径通量分析和热释放率分析。发现主要的热释放反应在低压下是与CHOCH自由基的反应，并且CO更倾向于通过HOCHO自由基间接形成CO。该研究推进了对广泛压力范围内冷火焰的理解，并为模型改进提供了实验数据。
