碳烟颗粒是碳氢燃料不完全燃烧或热解的产物，会引发大气污染和全球气候变暖等问题，对人体健康造成威胁；但其又有不少工业应用价值。因此，理解碳烟生成机理对于控制燃烧源颗粒物排放，以及指导工业炭黑材料的合成具有重要意义。本工作选择了准一维的且具有良好边界条件的乙烯层流预混滞止火焰开展研究；结合了实验与模拟手段详细地研究了碳烟生成过程中的一些关键子过程，以及二茂铁的添加对碳烟生成各个子过程的影响机制，以加深对碳烟生成机理的理解。 首先，对于碳烟颗粒的成熟过程，本工作通过分析碳烟成熟度与颗粒尺寸的关系，分别考察了在不同温度和当量比条件下碳烟颗粒的成熟路径。结果表明：火焰温度较低时，虽然颗粒尺寸有所增长，成熟度却不显著增加，说明了表面氢提取碳加成反应被抑制。火焰温度较高时，碳烟成熟度会随着颗粒尺寸增加而增加。在尺寸相同时，较低当量比火焰产生的碳烟颗粒要更成熟，是因为其在火焰中停留时间更长。 其次，对于芳烃分子在碳烟颗粒表面的沉积过程，本工作通过分子动力学模拟揭示了沉积效率与温度和芳烃分子质量的依赖关系，并发现碳烟表面的脂肪链的存在会阻碍芳烃分子在其表面的沉积。本工作提出的沉积模型可很好地改进对串联射流搅拌反应器和流动管反应器内的碳烟生成的预测。 最后，本工作考察了二茂铁掺混的火焰的碳烟生成特性。结果表明，ppm量级的二茂铁的添加对于火焰温度以及气相碳氢前驱体组分浓度均影响不大；然而二茂铁可以显著地促进碳烟成核和长大，使得碳烟产量增多；还会降低碳烟的成熟度。二茂铁对碳烟颗粒尺寸增长的促进很可能是因为颗粒中的铁促进了颗粒间的碰撞凝并。为了支持这一推测，本工作利用分子动力学手段模拟了掺混铁的晕苯二聚体之间的碰撞；发现铁的掺混可以增加晕苯二聚体之间的碰撞凝并效率，使得晕苯团簇长大的过程加快。 本工作通过实验和模拟的手段考察了碳烟成熟过程，芳烃分子在碳烟表面沉积的过程，详细分析了二茂铁对碳烟生成机理的影响，加深了对碳烟生成机理的理解，促进了铁与碳烟相互作用的认知。
Soot particle, generated from the in-complete combustion or pyrolysis of hydrocarbon fuels, can lead to air pollution, accelerate global warming and damage human health. However, it is also a widely used industrial material. Therefore, the fundamental understanding of soot particle formation process is significant for reducing the combustion-source particle emission and controlling the industrial synthesis of carbon black. The quasi-one-dimension laminar premixed burner-stabilized stagnation ethylene flames with well-defined boundary conditions is chosen as target, and some key subprocesses in soot formation as well as the influence of ferrocene on each subprocess are investigated by various experimental and computational methods, to help the understanding of soot formation mechanism. Soot maturation is studied by investigating the relationship between the soot maturity and particle size. It can help isolate two maturation pathways and analyze their contribution under different flame temperatures and equivalence ratios conditions. The results show that at lower flame temperature conditions, although particle size increases, soot maturity is almost unchanged, indicating that surface hydrogen-abstraction-carbon-addition reaction is inhibited. At higher flame temperature conditions, soot maturity would increase with particle size. Soot particles generated from lower-equivalence ratio flames are less mature, when the particle sizes are similar, since their residence time in flames are longer. Meanwhile, molecular dynamics simulation is employed to investigate the condensation of gas-phase aromatic molecules on soot surface. The dependence of condensation efficiency on temperature and aromatic molecular mass is revealed, and the presence of aliphatic chains on soot surface is found to inhibit the condensation of PAH molecules. The condensation sub-model proposed in this work can improve the prediction of the soot formation in jets-stirred reactor in tandem with plug flow reactor. The soot formation in ferrocene-doped laminar premixed burner-stabilized stagnation ethylene flames is also investigated, for revealing the influence of ferrocene, a commercial ferric fuel-additive, on soot formation mechanism. The results show that neither flame temperature nor the concentrations of small gas-phase soot precursors can be influenced by the addition of ferrocene at ppm level. However, ferrocene can promote soot inception and size growth, resulting in the increasing of soot yield. The maturity of soot particles will also be lowered by ferrocene addition. The promotion of ferrocene addition on soot particle size growth is inferred to be contributed by the enhanced particle coagulation. To support this inference, molecular dynamics simulations are performed to study the binary collision between iron-doped coronene dimers. Coagulation efficiency is found to be increased by iron addition, and correspondingly, the size growth of coronene clusters via coagulation is accelerated by iron addition. By investigating the subprocesses during the soot formation and the influence of ferrocene addition on each subprocess, the fundmental understanding of soot formation mechanism and the interaction between iron and soot can be enhanced.
