Instrumentation Development of Compact Laser Diagnostic Systems for the Combustion Experiments under Microgravity

研制了适用于微重力条件下燃烧过程实验研究的小型激光诊断系统。研制了一种小落轴，实现了0.8 S期间的微重力燃烧实验。用阴影图观察了球形火焰和烟壳的结构。将平面激光散射技术应用于液滴火焰中碳烟浓度二维分布的可视化研究。用连续激光或脉冲激光照射静止气体环境中燃烧的液滴，通过带通滤光片用面阵摄像机测量散射光强图像，用平面激光诱导荧光法测量液滴火焰中的氢氧化物浓度分布。以脉冲激光的二次谐波泵浦的染料激光为光源，通过带通滤光片，利用与入射激光成直角的带门像增强器的CCD摄像机进行检测。这使得成功地显示了液滴火焰中OH浓度的二维分布。激光诱导荧光被用于远程探测被包络火焰包围的液滴的温度。对掺入少量萘和TMPD的燃料液滴进行了氮气激光辐照。用光学多道分析器检测合成的荧光强度，用CCD相机拍摄发蓝光的液滴。通过测量两个不同波长的荧光强度之比来确定液滴的温度。

The instrumentation development has been made of compact laser-based diagnostic systems which is applicable for the experimental study of the combustion processes under microgravity.A small drop shaft was newly developed which enabled the combustion experiments under microgravity during the period of time 0.8 s. The structure of the spherical flame and the soot shell were observed by using shadowgraph. Planar laser light scattering was applied for the visualization of two dimensional soot concentration profile in the droplet flame. A droplet burning in quiescent gaseous environment was irradiated with the sheet of an incident cw Argon laser or a pulsed YAG laser and the image of the scattered light intensity was detected with the use of a CCD camera via a band pass filter.OH concentration profile in the droplet flame was measured by using planar laser induced fluorescence. A sheet of an incident dye laser pumped with the second harmonic of a pulsed YAG laser was utilized as a light source and the fluorescence intensity was transmitted through a band pass filter, being detected by using a CCD camera with a gated image intensifier which was installed at the right angle to the incident laser light. This resulted in the successful visualization of two dimensional profile of OH concentration in the droplet flame.Laser induced fluorescence was applied for the remote probing of the temperature of the droplet surrounded by an envelope flame. A fuel droplet doped with a small amount of naphthalene and TMPD was subjected to the irradiation of the incident nitrogen laser. Resultant fluorescence intensity was detected by using an optical multichannel analyzer and the droplet fluorescing blue was photographed by a CCD camera. The droplet temperature was determined by measuring the ratio of the fluorescence intensities at two different wavelengths.