The images shown are photographs of ethylene/air/nitrogen diffusion flames stabilized behind a bluff centerbody. The two images on the top show the centerbody flame photographed from the side (top left) and top views (top right). The blue regions are associated with the flame front and the other colors of the flame are largely due to blackbody radiation from the soot. The intense yellow radiation is from soot trapped in a tight ring vortex downstream of the stabilizing bluff body. The motion of the soot trapped in the vortex can be seen in the longer exposure photograph taken from the top.
The bottom two images are of a centerbody flame with the same inlet flow velocities as the case shown above but with higher nitrogen content in the feed gases. The image on the lower left shows a blue ring flame that forms around the main flame immediately downstream of the centerbody. This blue ring flame exhibits a slight oscillation in the vertical direction. The image on the lower right shows the region downstream of the ring flame for the same conditions. The disturbances in the downstream region of the flame are amplified as it passes through the tube, resulting in the large structures shown in the short exposure (0.8 ms) photo.
Credit: Scott Stouffer, Garth Justinger (University of Dayton Research Institute), Mel Roquemore, Amy Lynch, Vince Belovich, Joe Zelina, Jim Gord (Air Force Research Laboratory, Wright Patterson Air Force Base), Keith Grinstead, Vish Katta and Kyle Frische (Innovative Scientific Solutions Incorporated)