柴油-甲醇混合燃料多环芳香烃形成的影响因素研究

Factors Influencing Formation of Polycyclic Aromatic Hydrocarbons for Diesel-Methanol Blended Fuel

以柴油-甲醇燃料为研究对象,探究柴油-甲醇混合燃料燃烧对多环芳香烃(PAHs)生成的影响规律。将AVL-Fire和Chemkin耦合,构建正庚烷-甲苯-PAHs化学反应动力学机理并验证,采用Chemkin中的均质零维反应模型进行仿真模拟,研究了柴油-甲醇混合燃料不同掺混比、初始温度、初始压力、当量比对多环芳香烃苯、萘、菲、芘(A_(1)~A_(4))的影响。结果表明:随着甲醇掺混比从0%增加到20%,A_(1)~A_(4)的摩尔分数峰值降幅分别为5.4%,14.6%,21.5%,28.1%,总生成率的谷值升高率分别为0.86%,18.91%,20.84%,23.54%,说明PAHs的苯环数越多,受甲醇的抑制作用相对越明显;从反应路径中可以看出,甲醇在燃烧中分解形成H_(2)、OH、H等,更多地加入到消耗PAHs的反应路径中,尤其是苯环数较多的PAHs;随着初始温度从1000 K增加到1200 K,缸内温度急剧升高的时刻提前,A_(1)~A_(4)摩尔分数峰值分别上升了0.67×10^(-5),2.43×10^(-10),5.23×10^(-14),0.93×10^(-14),说明初始温度增加有利于加速PAHs的生成;随着初始压力从0.1 MPa增加到1 MPa,A_(1)~A_(4)的峰值到达时刻均有所提前,大约提前了27 ms,提前幅度为93%,甲醇分子裂解形成的自由基与PAHs前驱体反应更加剧烈,有利于促进PAHs的生成;当量比从0.5增加到1.5,A_(1)~A_(4)的摩尔分数峰值升高率分别为1486%,1194900%,79249900%,29269900%,当量比的增加导致燃烧局部缺氧,显著地促进了PAHs的形成。

Taking the diesel-methanol blended fuel as the research object,the influence of diesel-methanol blended fuel combustion on the formation of polycyclic aromatic hydrocarbons(PAHs)was studied.The kinetic mechanism of n-heptane/toluene-PAHs chemical reaction was constructed and verified by coupling AVL-Fire and Chemkin,the simulation was conducted by using the homogeneous zero-dimensional reaction model of Chemkin,and the influences of mixing ratio,initial temperature,initial pressure and equivalent ratio on PAHs such as benzene,naphthalene,phenanthrene and pyrene(A_(1)-A_(4))were analyzed.The results show that the peak drop of A_(1)-A_(4)mole fraction are 5.4%,14.6%,21.5%,and 28.1%respectively and the valley increase of total yield are 0.86%,18.91%,20.84%,and 23.54%respectively when the methanol blending ratio increases from 0 to 20%.Accordingly,methanol has the more obvious inhibitory effect on PAHs with the more number of benzene rings.According to the reaction path,methanol decomposes into H_(2),OH,H and so on during the combustion,which enter the reaction path that consumes PAHs,especially PAHs with more benzene rings.As the initial temperature increases from 1000 K to 1200 K,the sharp rise time of in-cylinder temperature advances,the peak values of A_(1)-A_(4)mole fraction increase by 0.67×10^(-5),2.43×10^(-10),5.23×10^(-14),and 0.93×10^(-14)respectively,hence the increase of initial temperature is beneficial to accelerate the generation of PAHs.The initial pressure increases from 0.1 MPa to 10 MPa,then all the peak arrival times of A_(1)-A_(4)advance.The advancement is about 27 ms,which is equivalent to 93%.The free radicals of methanol molecular decomposition have a violent reaction with PAHs precursor,which is beneficial to promote the generation of PAHs.Besides,the peak values of A_(1)-A_(4)mole fraction increase by 1486%,1194900%,79249900%,and 29269900%respectively when the equivalence ratio increases from 0.5 to 1.5.The increase of equivalence ratio causes local hypoxia so as to promote the formation of PAHs.