Zhang Pengyuan, Kang Yinhu, Huang Xiaomei, Peng Shini
School of Civil Engineering, Chongqing University, Chongqing 400045, China.
Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education of China, Chongqing University, Chongqing 400044, China.
ACS Omega. 2020 Sep 15;5(38):24654-24665. doi: 10.1021/acsomega.0c03227. eCollection 2020 Sep 29.
This paper makes a comparative study on the normal diffusion flame (NDF) and inverse diffusion flame (IDF) characteristics of dimethyl ether (DME) in microgravitational spherical diffusion flame geometry by simulations with detailed fuel chemistry and a transport model. It is found that there always existed two combustion modes (i.e., hot flame and cool flame) in either NDF or IDF condition. The combustion progress of hot flames was controlled by diffusive mixing, while that of cool flames was controlled by low-temperature competing kinetics. The cool-flame structure dynamics were far away from the chemical equilibrium. The low-temperature branching rate of DME was positively dependent on the oxygen level, while its termination rate was enhanced with the increasing temperature. Being rather distinct from the NDF counterpart, DME IDFs had the oxygen-enriched combustion feature in either hot- or cool-flame condition. Furthermore, DME hot-flame extinction was induced by thermal radiative loss, while the cool-flame extinction was induced especially by the decrease of the low-temperature branching rate. Compared with hot NDFs, it would be of less effectiveness to control the hot IDF combustion process by positive measures. However, combustion in the latter configuration was much more stable than the former. In either NDF or IDF geometry, the cool-flame chemistry could help to extend the fuel flammability range considerably, and the two-reaction-zone structure of cool flame was responsible for cool-flame stability. In addition, the IDFs had much better ignition performance than the NDF counterpart.
本文通过采用详细的燃料化学和输运模型进行模拟，对微重力球形扩散火焰几何结构中二甲醚（DME）的正常扩散火焰（NDF）和反向扩散火焰（IDF）特性进行了对比研究。研究发现，在NDF或IDF条件下总是存在两种燃烧模式（即热火焰和冷火焰）。热火焰的燃烧进程由扩散混合控制，而冷火焰的燃烧进程由低温竞争动力学控制。冷火焰结构动力学远离化学平衡。DME的低温分支速率与氧含量呈正相关，而其终止速率随温度升高而增大。与NDF不同，DME的IDF在热火焰或冷火焰条件下都具有富氧燃烧特征。此外，DME热火焰熄灭是由热辐射损失引起的，而冷火焰熄灭尤其是由低温分支速率的降低引起的。与热NDF相比，采取积极措施控制热IDF燃烧过程的效果较差。然而，后一种构型的燃烧比前一种稳定得多。在NDF或IDF几何结构中，冷火焰化学有助于显著扩展燃料的可燃范围，冷火焰的双反应区结构决定了冷火焰的稳定性。此外，IDF的点火性能比NDF好得多。
