Abstract: In order to study the ignition characteristics of three xylene isomers and acquire time-histories of important OH,CH and C₂radicals in the combustion reaction of xylene, ignition delay times of the three xylene isomers in air were investigated behind the reflected shock waves in a chemical shock tube with a monochromator system. The ignition conditions spanned temperature of 1224~1478K and pressure of 0.18~0.21MPa with an equivalence ratio of 1.0. Time-resolved transient emission spectra of p-xylene/air in the combustion process were also obtained by using an intensified spectroscopic detector CCD system at temperature of 1440K. Experimental results illustrate that the ignition delay time of p-xylene is most sensitive to the temperature, while those of o-xylene and m-xylene are similar. The ignition delay time of m-xylene and p-xylene are close, and the time of o-xylene is the shortest at the same experimental conditions. During the p-xylene combustion reactions, the concentrations of OH, CH and C_2radicals reach their peaks once they appear, but the disappearing processes of the radicals are different. The concentration of CH radical decreases rapidly in the same trend with that of C₂ radical. Moreover, CH and C_2radicals exist in a short time while the duration of OH radical is much longer. 

Key words: Xylene; Radical; Ignition delay time; Transient emission spectrum; Shock tube

摘要： 为了研究二甲苯三种同分异构体的点火特性,获得该燃料燃烧反应重要自由基OH,CH和C₂的变化信息,在化学激波管中利用反射激波点火,点火温度1224~1478K,点火压力0.18~0.21MPa,燃料当量比1.0,由单色仪光谱系统测得了二甲苯/空气的点火延迟时间,并用ICCD瞬态光谱探测系统测得了点火温度1440K时对二甲苯/空气燃烧的时间分辨瞬态发射光谱。实验结果表明:对二甲苯点火延时对温度的敏感程度最高,邻二甲苯和间二甲苯的点火延时对温度的敏感程度相近；在相同实验条件下,间二甲苯和对二甲苯的点火延迟时间比较接近,邻二甲苯的点火延迟时间最短。在对二甲苯燃烧反应中,OH,CH和C₂自由基一旦出现很快达到其浓度峰值,但各个自由基的消失过程各不相同,CH和C₂自由基存在的时间很短,且相对浓度变化趋势几乎完全一致,而OH自由基持续时间最长。 

关键词: 二甲苯;自由基;点火延迟时间;瞬态发射光谱;激波管 