FLAME STABILITY AND STRUCTURE OF TURBULENT PREMIXED FLAME IN A STAGNATION POINT FLOW

对驻点流动中褶皱层流火焰的稳定性和结构进行了实验研究。利用激光多普勒测速仪（LDV）测量来流中心线速度分布，估计来流特性。采用激光层析成像方法获取火焰前缘图像，通过图像处理器对图像进行分析，估算火焰曲率。主要结论如下：1.对于刘易斯数大于1的贫丙烷/空气火焰，由流动发散引起的火焰拉伸和由火焰弯曲引起的火焰拉伸之和所定义的总拉伸率是火焰熄灭的主要参数。另一方面，贫甲烷/空气火焰，其刘易斯数小于1，熄灭的影响下的热损失的墙壁。这表明，刘易斯数效应对火焰熄灭起着重要作用，当考虑火焰曲率效应合理估计火焰拉伸时，火焰熄灭机理可视为与层流火焰相似.从16 mm高速胶片的层析图像中，可以看到火焰前缘的运动，并得到火焰曲率的变化。结果表明，火焰到达壁面时，火焰发生局部熄灭.湍流燃烧速度取决于湍流强度和由于火焰曲率引起的火焰拉伸的乘积。

Flame stability and structure of a wrinkled laminar flame in a stagnation point flow have been studied experimentally. The characteristics of an approaching flow were estimated by measuring the centerline velocity profile with LDV. The flame front image was taken by using the laser tomographic method and the flame curvature was estimated by analyzing the tomographic image with image processor. The conclusions are as follows.1. For the lean propane/air flame, whose Lewis number is larger than unity, the total stretch rate defined as a sum of flame stretch due to flow divergence and that due to flame curvature is a primary parameter for the flame extinction. On the other hand, lean methane/air flame, whose Lewis number less than unity, is extinguished under the influence of the heat loss to the wall. These indicate that the Lewis number effect plays an important role for the flame extinction and the extinction mechanism can be treated as similar to that of the laminar flame when the flame stretch is reasonably estimated by taking into account the effect of flame curvature.2. From the tomography image of high speed 16mm films, the flame front movement is shown and the variation of the flame curvature is obtained. The result shows that the flame is locally extinguished when the flame reaches to the wall.3. The turbulent burning velocity depends on the product of the turbulent intensity and the flame stretch due to flame curvature.