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

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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.