正庚烷HCCI燃烧下多环芳烃生成机理与影响因素分析

Analyses of influencing factors and formation mechanism of polycyclic aromatic hydrocarbons in n-heptane HCCI combustion

通过修改化学动力学软件SENKIN,建立了正庚烷均质充量压缩点燃(HCCI)燃烧过程数值模拟的单区模型.利用此模型对正庚烷HCCI燃烧下芳烃(苯、萘、菲及芘)的生成及演变规律进行了详细分析.同时,分析了过量空气系数、进气初始压力和发动机转速对多环芳烃形成规律的影响.计算中采用了正庚烷的燃烧与分解、多环芳烃生成的详细反应机理(共包括107种组分、542个基元反应).结果表明,在低温反应阶段并没有苯(A1)、萘(A2)、菲(A3)、芘(A4)生成;当进入高温反应阶段后,苯、萘、菲、芘的浓度迅速升高至峰值,然后均陡直下降为零.随着过量空气系数的增大,苯的摩尔分数峰值降低,但菲的摩尔分数峰值变化较小.同时,苯、萘、菲的摩尔分数随进气初始压力的降低而降低;随着发动机转速的下降,苯的摩尔分数先降低后增加,萘的摩尔分数却是先增加后降低,而菲的摩尔分数却持续降低.

By amending the chemical kinetics package SENKIN,the single-zone model which can numerically simulate the homogeneous charge compression ignition（HCCI） combustion of n-heptane was built.The formation and evolvement mechanisms of the aromatic hydrocarbons（including benzene,naphthalene,phenanthrene and pyrene） in n-heptane HCCI combustion were simulated.At the same time,the effects of the excessive air coefficient,inlet pressure and engine speed on the formation of polycyclic aromatic hydrocarbons were analyzed.n-Heptane was used as fuel and the detailed reaction mechanisms of combustion of n-heptane and formation of the polycyclic aromatic hydrocarbons were adopted（including 107 species,542 reactions）.The experimental results show that there are no benzene（A1）,naphthalene（A2）,phenanthrene（A3） and pyrene（A4） formations at the reaction stage of lower temperature.However,as the combustion process goes into the reaction stage of higher temperature,the mole fractions of A1,A2,A3 and A4 increase rapidly to peak values,then decrease rapidly to zero.With the excessive air coefficient increasing,the peak value of the mole fraction of A1 decreases,but the variation of the mole fraction of A3 is little.At the same time,with inlet pressure decreasing,the mole fractions of A1,A2 and A3 decrease.Furthermore,with speed of engine decreasing,the mole fraction of A3 decreases,and the mole fraction of A1 decreases firstly and increases afterwards.However,the variation trend of the mole fraction of A2 is contrary to that of A1.