研究主碳链长度对于脂肪酸甲酯的同轴层流扩散火焰中碳烟的生成及其演变规律的影响.针对丁酸甲酯、辛酸甲酯及癸酸甲酯扩散火焰，采用激光诱导炽光法，结合热泳探针取样后的透射电子显微镜图像，分析火焰中碳烟体积分数的2维分布及碳烟颗粒的形貌特征.实验结果表明：随着主碳链长度的增加，脂肪酸甲酯扩散火焰的碳烟体积分数增大，碳烟的生成与积聚更为提前，表面生长速率更快；通过化学反应动力学模拟3种脂肪酸甲酯的热解氧化反应，验证了激光诱导炽光法的实验结果；随着主碳链长度的增加，脂肪酸甲酯的热解起始温度有所降低，C2H2、C2H4等中间物质的产生有所增加，多环芳香烃的生成速率更快；通过对苯环生成路径的敏感性分析可知，在丁酸甲酯热解中，第1个苯环的形成主要为C4+C2的生成路径，而辛酸甲酯、癸酸甲酯热解中苯的形成有C4+C2、C3+C3两种生成路径，且C3+C3生成路径占主导地位.
The effect of main carbon chain length on soot formation and evolution of fatty acid methyl esters (FAMEs) diffusion flames were studied in this work. Laminar coflow diffusion flames of methyl butyrate, methyl octanoate and methyl decanoate were selected as target flames. Laser induced incandescence (LII) and thermophoretic sampling particles diagnostics (TSPD) were adopted as experimental methods to analyze the soot volume fraction and soot particle morphology evolution in tested flames. Transmission electron microscopy (TEM) analysis was applied to obtain morphology information of soot particles sampled by TSPD. The results show that as the length of main carbon chain in FAMEs increases, soot volume fraction along the centreline of laminar diffusion flames increases too. Soot formation is also enhanced with earlier soot inception process and faster surface growth and aggregation. Chemical kinetic simulations of FAMEs decomposition and oxidation are employed to verify and illustrate the experimental results. It can be observed that FAMEs with longer main carbon chain are decomposed at lower temperature and intermediate species such as C2H2 and C2H4 are produced more in the decomposition and oxidation process, which enhances the formation of polycyclic aromatic hydrocarbon. Sensitivity analysis of benzene production suggests that the first aromatic ring in methyl butyrate decomposition mainly forms in C4+C2 pathway. While in methyl octanoate and methyl decanoate decomposition, benzene is produced in both C4+C2 and C3+C3 pathway and C3+C3 pathway takes the lead.
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