Soot morphology and nanostructure in complex flame flow patterns via secondary particle surface growth
Soot morphology and nanostructure in complex flame flow patterns via secondary particle surface growth
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DOI：
10.1016/j.fuel.2019.02.058
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发表时间：
2019-06-01
期刊：
影响因子：
7.4
通讯作者：
Novosselov, Igor
中科院分区：
文献类型：
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作者：
Davis, Justin;Tiwari, Kartik;Novosselov, Igor
虽然大多数研究都是在相对简单的一维火焰中探索碳烟的形成，但大多数真实世界的火焰都是由大尺度湍流涡流、循环流型和浮力效应所定义的复杂流动组成的。复杂流动对碳烟物理化学性质的影响还知之甚少。这项工作使用倒置重力火焰反应器(IGFR)来比较一维层流扩散火焰和循环火焰中碳烟生长的差异。计算流体力学(CFD)和实验观测表明，颗粒在(I)表面生长物质高度集中的富集区和(Ii)高温氧化区之间存在振荡。透射电子显微镜显示最终一次粒子直径有显著差异，一维火焰产生直径10-25 nm的一次粒子，而循环火焰产生直径25-75 nm的一次粒子。此外，来自循环火焰的较大初级颗粒既包含单核心也包含多个核心。我们认为，由于大的一次粒子的球形，二次表面生长主要是由于成熟烟尘在火焰锋面的高温环境中重新卷吸到燃料区中，随后的液层碳化过程中多环芳烃(PAH)凝聚的结果。IGFR中的循环流型和反复的颗粒生长/氧化循环可以作为森林火灾、燃煤植物等复杂流型的大尺度火焰中碳烟形成的模型。
While the majority of studies explore soot formation in relatively simple, one-dimensional flames, most real world flames consist of complex flows defined by large-scale turbulent eddies, recirculating flow patterns, and buoyancy effects. The effects of complex flow on soot physicochemical properties are poorly understood. This work employs an inverted gravity flame reactor (IGFR) to compare differences in soot growth between a one-dimensional laminar diffusion flame and a recirculating flame. Computational fluid dynamics (CFD) and experimental observations show particle oscillations between (i) a rich region with a high concentration of surface growth species, and (ii) a high-temperature oxidation region. Transmission electron microscopy (TEM) shows a significant difference in final primary particle diameter, where the one-dimensional flame produces primary particles 10-25 nm in diameter and the recirculating flame produces primary particles 25-75 nm in diameter. Additionally, larger primary particles from the recirculating flame contain both single and multiple cores. We propose that due to the spheroidal shape of the large primary particles, the secondary surface growth is primarily a result of polyaromatic hydrocarbon (PAH) condensation during re-entrainment of mature soot into the fuel rich region followed by subsequent liquid layer carbonization in the high-temperature environment of the flame front. The recirculating flow patterns in the IGFR and repeated particle growth/oxidation cycle can serve as a model for soot formation in the large-scale flames with complex flow patterns, such as forest fires, coal fire plants, and other sources.