富氢焦炉气/碳氢燃料扩散火焰碳烟生成机理研究

Suppression of soot formation helps reduce smog. Adding Coke-Oven-Gas(H2:55%~60%) to fuel is an effective approach to reduce PAH and soot formation during the combustion of fossil fuels. Soot formation processes are complex. The pathways and mechanism of how adding Coke-Oven-Gas affects soot formation remain unclear. The objectives of this proposed research project are to gain fundamental insights into the controlling factors, reaction pathways, and the chemical effects of Coke-Oven-Gas blending to fuel on soot formation in laminar diffusion flames of hydrocarbon fuels. By utilizing the methodology of combining laser-based diagnostics, theoretical analysis, and numerical modeling, an in-depth analysis will be conducted to gain comprehensive understanding of the effects and mechanism of Coke-Oven-Gas addition to different hydrocarbon fuels on the processes of fuel pyrolysis, PAH formation, soot nucleation, and the subsequent surface growth. The proposed research project will reveal the fundamental cause of the different chemical effects of hydrogen on soot formation when it is added to different hydrocarbon fuels and to establish the relationship between the hydrogen chemical effect and the C/H ratio of the hydrocarbon fuel. The state-of-the-art soot formation model based on the PAH collision for soot nucleation and the HACA (hydrogen abstraction acetylene addition) and CAHM (carbon addition hydrogen migration) mechanisms and PAH condensation for subsequent surface growth will be used in a fully coupled manner with detailed reaction mechanisms to predict soot volume fraction distributions in flames of different fuels and with Coke-Oven-Gas addition. Through detailed comparisons between the measured and predicted soot volume fraction distributions, the drawbacks of the soot model in soot modeling in diffusion flames of Coke-Oven-Gas -hydrocarbon blended fuels will be revealed and an improved soot model will be proposed. The outcome of this project will enrich the existing knowledge of soot formation and the chemical role of hydrogen in Coke-Oven-Gas/hydrocarbon blended fuel flames, as well as to provide much-needed theoretical guidance in effective implementation of the Coke-Oven-Gas blending approach to reduce soot formation in diffusion flames of different hydrocarbon fuels.

抑制碳烟生成是减少雾霾产生的重要途径。焦炉气富含氢气(55%~60%)，掺混焦炉气与其它碳氢气体燃烧具有抑制PAH和碳烟生成的应用前景。碳烟生成过程复杂，焦炉气与其它碳氢燃料燃烧碳烟生成机制及路径的研究尚属空白。本项目以掺混焦炉气碳氢燃料扩散燃烧火焰作为研究对象，以认知富氢焦炉气/碳氢燃料碳烟生成的关键影响因素与路径为研究目标，结合系列实验，理论分析和数值模拟，深入分析焦炉气/气相碳氢燃料火焰中PAH和碳烟生成的影响因素；探讨焦炉气在碳氢燃料热解，PAH生成，碳烟成核及随后生长过程中的作用机制；揭示焦炉气掺混到不同C/H比碳氢燃料火焰对PAH和碳烟生长的化学作用路径。应用并完善PAH碰撞成核、碳烟表面生长模型（HACA/CAHM）和PAH在碳烟颗粒表面凝结的生长的碳烟模型。明晰采用焦炉气有效抑制碳氢燃料碳烟生成的条件和物理与化学作用机制，为降低碳氢燃料燃烧碳烟生成提供理论指导。

碳氢燃料不完全燃烧生成的碳烟颗粒对人体健康和自然环境造成巨大危害，造成严重的空气污染问题，降低能源利用效率，是燃烧领域的热点问题。氢气混合碳氢燃料燃烧可以降低燃烧过程碳烟的生成，冶金炼焦产物焦炉煤气富含氢气，并含有一定比例的碳氢燃料。本课题围绕富氢焦炉煤气/碳氢燃料燃烧特性，分别采用实验、数值模拟、理论分析和分子动力学计算相结合，系统研究了氢气与甲烷/乙烯等碳氢燃料多组分混合燃烧过程中碳烟成核、长大、氧化、浓度分布、碳烟组成、形貌结构等特性。重点分析了不同比例下掺氢碳氢混合燃料碳烟生成的机理、协同作用及影响规律。研究结果表明，掺混燃料的热效应不是影响碳氢混合燃料燃烧碳烟生成的主要原因，而是稀释效应和化学效应共同作用抑制碳烟生成。甲烷和氢气比例提高，可有效抑制碳烟的生成。小比例甲烷掺混时对碳烟生成具有协同作用。乙烯燃料中掺混烷烃燃料燃烧促进碳烟的生成，且随烷烃含碳数增加协同效应增强，掺氢导致乙烯和烷烃间的协同效应减弱。甲烷掺混比例增加碳烟有序度呈现先增加后减小的趋势，低甲烷掺混比时乙烯氢气碳烟中芳香族官能团的含量明显上升，脂肪族相对含量较纯乙烯氢气中上升明显，但随甲烷掺混比增加出现先增加后减少的现象。在纯乙烯中掺混小比例甲烷，火焰根部类液滴状结构开始减少，簇状结构出现提前；在纯乙烯中掺混一定比例甲烷后，类液滴状结构已经消失，呈现出多个形状较为规则的大颗粒。掺混氢气和甲烷的协同作用促使碳烟粒径变化幅度改变。小比例掺混氢气，碳烟初始粒径有所增加，沿高度方向粒径降低幅度减慢。本研究结果全面揭示了碳氢燃料碳烟生成机理，为提高碳氢燃料燃烧效率、扩大焦炉煤气的应用渠道和降低碳烟生成的路径提供了理论支撑。