Flame Image and Flame Structure of Turbulent Premixed Flames Using Simultaneous OH-HCHO PLIF Technique

In this study, using simultaneous OH-HCHO PLIF (Planar Laser-Induced Fluorescence) technique, we have obtained instantaneous two-dimensional flame images to investigate highly turbulent premixed combustion in a cyclone-jet combustor. On the phase diagram, conditions of U. < 15 m/s for 0.-0.75 and U. < 20 m/s for (6,a=0.90 belong to the flamelet regime, and those of U. > 20 m/s for ,95,n=0.75 and U.= 30 m/s for (b.=0 . 90 belong to thin reaction zones regime. In combustion field, HCHO plays an important role at relatively earlier stage of reaction and there is HCHO region mostly in preheat zone at the temperature range of 400 K to 1 400 K. On the other hand, OH exists in reaction zone or burned gas. From simultaneous images of these two species, we have discussed the local flame structure, based on flame length and number of flame regions. When the exit velocity is increased, more cusps appear on the flame front, with larger flame length. Interestingly, it is observed that the flame front is disconnected in some images, corresponding to the local flame extinction.