Correlation of spatial heterogeneity of fuel vapor concentration and turbulent vortex in evaporating intermittent spray

为探讨燃油蒸气浓度与蒸发喷雾中湍流旋涡的相关性，对间歇喷雾中燃油浓度的空间非均匀性和二维图像分析的流速测量技术进行了并行研究；在燃油浓度空间非均匀性研究中，通过对间歇非蒸发喷雾二维断面图像的高速摄影，捕捉和分析了燃油颗粒的特征运动，对喷雾结构的形成过程有了新的认识。通过激基复合体荧光法对蒸发喷雾中的燃油蒸汽浓度进行可视化，表征了蒸汽浓度的非均质性。蒸发喷雾中燃油蒸气分布的结构与非蒸发喷雾中的液滴分布结构相似，但空间尺度略大于非蒸发喷雾。在二维图像速度测量技术的研究中，提出了一种新的图像分析技术--粒子图像测速仪PIV。通过将每个粒子的图像信息压缩到其重心，将自相关平面的计算简化为每个粒子位移的比较。通过分析这种方法得到的自相关平面的第二个峰值的形状，可以对每个粒子的运动进行识别，并在一个询问点内提取数十个速度矢量。从提取的速度矢量中分析了局部湍流强度和积分长度尺度。将该PIV技术应用于高温高压条件下的蒸发喷雾，成功地得到了瞬时速度矢量图。

To explore the correlation of the fuel vapor concentration and the turbulent vortex in evaporating spray, we performed the researches on the spatial heterogeneity of fuel concentration in intermittent fuel spray and the measurement technique of flow velocity by 2D image analysis in parallel.In the study of the spatial heterogeneity of fuel concentration, the characteristic movements of fuel particles were captured and analyzed through the high speed photography of 2D sectional image of intermittent non evaporating spray, and the new knowledge for the formation process of spray structure was obtained. Through the visualization of fuel vapor concentraition in evaporating spray by the exciplex fluorescence method, the heterogeneity of vapor concentration was characterized. The structure of fuel vapor distribution in evaporating spray is similar to that of droplets distribution in non evaporating spray though the spatial scale is a little bit larger than that in non evaporating one.In the study of the measurement technique of flow velocity by 2D image analysis, a new course of image analysis technique was examined in particle image velocimetry, PIV.By condensing each particle image information into its gravity center, the calculation of auto-correlation plain was greatly reduced into the comparison of each particle displacing. Analyzing the shape of the second peak of auto-correlation plain obtained in this way, identification of each particle motion can be carried out, and several tens of velocity vectors were extracted within a single interrogation spot. The local turbulent intensity and integral length scale were analyzed from these extracted velocity vectors. By applying this PIV technique to the evaporating spray under the high pressure and high temperature condition, the instantaneous velocity vectors maps were obtained successfully.