Studies on the Near-Wall Micro-Structure of Turbulent Propagating Flame of Premixed Mixtures

为了弄清湍流预混火焰的微观结构，人们进行了大量的研究。由于微结构对湍流质量燃烧速度有很大的影响，研究者负责人等人提出了一个考虑褶皱层流火焰区与分布岛火焰区燃烧分数比的湍流燃烧区模型，并对预混湍流火焰在强稳定湍流场中的传播进行了燃烧实验。在本实验中，湍流火焰仅沿燃烧室的一个方向传播。湍流火焰的纹影图像从垂直和平行于传播方向拍摄。通过中心轴附近和壁面附近的离子探针检测小火焰的电浮动电位。从火焰传播方向拍摄的纹影图像显示出非常复杂的条纹，并且测量的连续条纹之间的平均距离随着湍流强度的增加而迅速减小，随着层流火焰厚度的减小而缓慢减小。在一张照片中测量的连续条纹之间的平均距离显示出在壁附近比在中心轴附近更小的值。靠近壁的离子信号峰的数目大于靠近中心轴的离子信号峰的数目。用双离子探针法对层流燃烧速度小、湍流强度大的混合物进行了湍流火焰区厚度大于70mm的测量。由于该燃烧室可从两个方向进入，因此，除上述纹影法外，激光多普勒测速法和激光片光法也可方便地应用于湍流传播火焰的测量。

In order to make clear the micro-structure of premixed turbulent flame, many studies have been carried. Because, the micro-structure has large influence on the turbulent mass burning velocity.The head investigator et al. proposed a turbulent combustion zone model which considered the burned fraction ratio of the wrinkled laminar flame zone to the distributed-islands flame zone.Combustion experiments were carried out for premixed turbulent flame propagating in strong and steady turbulence field. The turbulent flame propagates only in one direction of the combustion chamber in this experiment. Schlieren-images of the turbulent flame were photographed from both normal and parallel to the propagating direction. The electrical floating potential of the flamelets was detected by ion probes near the central axis and near the wall. The obtained schlieren-images photographed from flame propagating direction show very complicated fringes and the measured average distance between successive fringes decreases rapidly with increasing the turbulence intensity and slowly with decreasing the laminar flame thickness. The measured average distance between successive fringes in one photograph shows smaller value near the wall than near the central axis. The number of peaks of ion signal near the wall is larger than near the central axis. These results suggest that the micro-structure of turbulent propagating flame is strongly influenced by the wall.More than 70mm of turbulent flame zone thickness was measured by a double ion-probe method for mixtures with small laminar burning velocity at strong turbulence intensity. This value of zone thickness is high enough to analyze the micro-structure of premixed turbulent flame.Since this combustion chamber is accessible from two directions, laser-doppler anemometry and laser-sheet optical method in addition to the schlieren method mentioned above can be easily applied for measurement of turbulent propagating flame.