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

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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.