【作者】 王宁；

【导师】 周进；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2009， 硕士

【摘要】 为了满足火箭发动机燃烧机理研究的需要,本文发展了一种基于平面激光诱导荧光技术定量测量燃烧流场OH基浓度的手段。通过详细推导荧光信号公式,分析荧光强度的影响因素,发现在合理选择激发谱线及采用统一的实验参数情况下,可忽略其他因素对荧光信号的影响,使得荧光强度与OH基摩尔分数成正比。由此提出了利用PLIF技术定量测量OH基浓度的方案,即结合平面标定火焰的数值计算与实验结果,求出荧光强度与OH基摩尔分数的比例因子,然后将该比例因子应用到其他火焰中,就可通过荧光强度得到OH基绝对浓度分布。为了得到标定火焰的数值计算结果,研究了甲烷空气详细化学反应机理的简化方法,得到了19组分39方程的简化机理,并对该简化机理进行了验证,发现简化机理能够较好地预测已燃区重要组分的浓度。在此基础上,将简化机理应用到标定火焰的数值计算中,得到了轴线上的OH基摩尔浓度分布。进行了平面标定火焰的PLIF实验研究,获得了较高信噪比的OH基PLIF图像。对图像进行降噪处理及邻域平均,得到了燃烧器轴线上的荧光信号灰度值。结合标定火焰的数值计算结果,得到荧光信号灰度与OH基摩尔浓度的比例因子。采用相同的实验设置对甲烷空气扩散火焰进行了PLIF实验研究,得到了清晰的火焰结构图像,应用比例因子求出了扩散火焰中的OH基浓度分布。对部分预混火焰进行了实验研究,求出了火焰中的OH基浓度,发现随着内层预混当量比的减小,OH基浓度逐渐增加。对扰流火焰进行了PLIF实验研究,发现湍流扰动会大大增强火焰的褶皱。为了分析本文OH基定量PLIF技术的精度,对甲烷空气部分预混火焰进行了实验研究,得到了燃烧器轴线上的OH基摩尔浓度,并与耶鲁大学测量的数据进行了对比,结果表明:本文定量得到的OH基摩尔浓度值与实际值在同一量级的水平。对于OH基这类极其活泼且含量非常小的自由基,可认为已初步实现了定量测量。更多还原

【Abstract】 In purpose of studying the combustion in rocket engines, a PLIF based scheme to measure the radical mole concentration of OH component is proposed.By deducing the PLIF signal expression in detail, the influencing factors are analysed. It is found that if the OH transition lines are carefully chosen and the experiment setups are consistent, other factors can be omitted except the OH radical mole concentration and PLIF signal is proportional to the OH radical mole concentration. Thus, with the simulation and experiment results of a laminar flame, which is used for calibration, the coefficient can be determined, and then OH radical mole concentration in other flames can be determined by corresponding PLIF signals and the coefficient.A reduced reaction mechanism for methane/air combustion is obtained, with 19 species and 39 reactions considered. The rationality of it is tested and it is verified to forecast the mole concentration of important species well. On this basis, the reduced mechanism is applied to the simulation of the laminar flame, and the OH mole concentration along the axis is obtained.PLIF experimental investigations on the laminar flame provide clear OH-PLIF images, and the PLIF signals along the axis is obtained by image processing. Comparing with the simulation results of the laminar flame, the coefficient is determined.Afterwards, with the same experimental setups, PLIF experiments are carried out on methane/air diffusion flame, which clearly show the structure of the flame. OH mole fraction distribution of the flame is obtained with the forenamed coefficient. Furthermore, partially premixed flames are studied, which indicate that the OH mole fraction is increasing with the strengthening of premixing. Disturbance to flames are studied in experiments and it is found that turbulence will cause larger distortion in flames.At last, in order to analyse the precision of the presented method, OH mole fraction along the axis of a partially premixed flame is determined and contrasted with the data from Yale University, which shows that OH mole fraction determined in this presented method has the same quantitative level with the real one. This precision is acceptable for species which are very reactive and of small quantities such as OH.更多还原