汽油压燃发动机中燃烧化学动力学特性的模拟

Numerical Simulation of Chemical Reaction Kinetics in Gasoline Compression Ignition Combustion

利用PRF70掺混燃料作为汽油表征燃料进行仿真研究,将三维计算软件CONVERGE和Chemkin结合,研究了汽油压燃燃烧反应过程的主要放热反应并对其进行了相关的化学反应路径分析。结果表明:在汽油压燃燃烧反应过程中,不同反应对总放热率的贡献不同,由HCO+O_2CO+HO_2、CH2O+OHHCO+H2O、CH2CCH2OH+O_2CH2OH+CO+CH2O是燃料燃烧过程中对放热贡献最大的3个反应,其放出的热量远大于其他反应;汽油压燃燃烧反应过程中参与夺氢反应的自由基主要有4种,分别是HO_2、OH、H、O,在不同曲轴转角处上述4种自由基参与夺氢反应的重要性不同,HO_2夺氢反应所占比例始终领先其他3种,H、O参与的夺氢反应所占比例随曲轴转角的增加而增加,相应的OH参与夺氢反应所占比例减少;汽油压燃燃烧反应过程中,随着曲轴转角的变化,缸内温度升高,异辛烷发生高温裂解的比例增加。

The main exothermic reactions in gasoline compression ignition(GCI)combustion were studied and the important elementary reaction paths were analyzed by adopting PRF70 blended fuel as indicated gasoline fuel and by combining the CONVERGE,a three-dimensional calculation software,and the Chemkin,a zero-dimensional calculation software.The results show that different reactions in the GCI combustion contribute differently to the total heat release rate.HCO+O2■CO+HO2,CH2O+OH■HCO+H2O and CH2CCH2OH+O2■CH2OH+CO+CH2O are the three main reactions contributing most to heat release rate compared with other reactions.The four radicals HO2,OH,H and O are involved in hydrogen(H)abstracting reaction.The H abstracting reaction by HO2 dominates in the GCI combustion,the H abstracting reactions by H and O increase with the crank angle,while the H abstracting reaction by OH decreases with the increase of crank angle.With the advance of the combustion,the temperature in cylinder goes up,and iso-octane cracking at high temperature increases.