3D-CT MEASUREMENT OF INSTANTANEOUS DENSITY DISTRIBUTIONS OF HIGH-SPEED PREMIXED TURBULENT BURNER FLAMES WITH A MULTI-DIRECTIONAL SCHLIEREN CAMERA (EFFECTS OF FLOW VELOCITY ON 3D FLAME FRONT SHAPE)
In present study, in order to provide a suitable technique for 3D observation of high speed turbulent flames, non-scanning 3D-CT technique using a multi-directional quantitative schlieren system with flash light source, is proposed for instantaneous density distribution of unsteady premixed flames. This "Schlieren 3D-CT" is based on (i) simultaneous acquisition of flash-light schlieren images taken from numerous directions, and (ii) 3D-CT reconstruction of the images by an appropriate CT algorithm. For simultaneous schlieren photography, in this experiment, the custom-made 20-directional schlieren camera has been constructed and used. Target flames are located at the center of the camera. The image set of 20 directional schlieren images are processed by MLEM CT-algorithm to obtain the 3D reconstruction of instantaneous density distribution. In this investigation, the target turbulent flame is high-speed burner flames. The burner has a nozzle exit of 4.2 mm diameter. The average flow velocity of the propane-air mixture of equivalence ratio of 1.1 is set to be 4, 6, 8 and 10 m/s. The burner is equipped with a turbulence promoting orifice in the burner tube. In order to anchor the high-speed flame on the burner nozzle, the burner tip has 4 holes for introducing the pilot flames. Results of the 3D-reconstructions indicates that the distributions show the complicated shape of the high speed turbulent flames. It is also found that the flame structure of higher speed flame has fine scale corrugations. This corresponds to the "corrugated flamelets regime" of the Borghi & Peters diagram for premixed turbulent combustion well.