发射光谱法研究甲基环己烷燃烧时激发态自由基时间历程

Research on the Time-Histories of Exited Radicals during the Combustion of Methylcyclohexane by Emission Spectroscopy

采用三组单色仪探测系统,测量了甲基环己烷在高温反射激波作用下瞬态燃烧反应过程中三种激发态自由基OH＊,CH＊和C＊_2的特征光辐射,得到了激发态自由基时间历程和光辐射相对强度随温度的变化规律。反射激波温度1 200~1 700K,激波压力1.5atm,甲基环己烷摩尔分数0.1%,当量比1.0。在点火燃烧初始阶段三种自由基几乎同时产生,自由基持续时间随着温度的升高而变短。相同温度下CH＊和OH＊自由基持续时间大于C＊_2自由基,在1 400K以下C＊_2自由基发光消失。OH＊和CH＊自由基发光强度在T〈1 400K时对温度变化不敏感,而在T〉1 400K时CH＊自由基峰值随温度快速增长,C＊_2和OH＊峰值随温度增大比较平缓。将实验结果和化学反应机理模拟结果进行了对比,实验获得的OH＊自由基时间历程在低温时和机理预测结果吻合较好,但在高温时有一定差异。CH＊自由基时间历程在高温与机理结果吻合较好,在低温时机理预测结果 CH＊自由基持续时间要长于实验结果。实验测得的结果为含激发态物种化学反应动力学机理的验证和优化提供了依据。

By using three monochromator!detecting systems,the light emissions of excited-state OH＊,CH＊and C＊_2radicals during the transient combustion of methylcyclohexane at high temperatures behind the reflected shock wave have been measured.The dependence of the time-history and the relative intensity of excited radicals on the temperature have been obtained.The reflected shock temperatures are 1 200~1 700 K,the shock pressure is 1.5atm,the mole fraction of methylcyclohexane is 0.1%and the equivalence ratio is 1.0.At the beginning of the combustion process,these three radicals were produced at the same time.The durations of these radicals became shorter when the temperature increases.At the same ignition temperature,the durations of CH＊and OH＊are longer than that of C＊_2.The C＊_2signal disappears below 1 400 K.The emission intensities of OH＊and CH＊are not sensitive to the temperature at T〈〉1 400 K.However,at high temperature（T1 400K）,the peak intensity of CH＊increases rapidly as temperature increases,while C＊_2and OH＊increase slowly.Current results were compared to the simulation results of corresponding chemical reaction mechanism.The obtained time-history of OH＊radical matches well with the prediction of mechanism at low temperatures,but shows difference at high temperatures.The time-history of CH＊radical matches well between experimental and simulated results at high temperatures,however,the simulated durations of CH＊are longer than the experimental results at low temperatures.Current work provides experimental data to validate and optimize corresponding chemical reaction mechanism containing excited-state species.