ABSTRAKT

The present experimental study deals with a high-speed hydrogen jet diffusion flame ejected vertically upward from a straight circular nozzle. Consideration is given to the flame reattachment phenomenon that occurs before the flame blowout. The Schlieren technique, and an image processing method employing the high-speed video camera, are used to visualize the flame base in the vicinity of the nozzle tip and to investigate the time-history of the flame morphology. If is found that: ft) the intermittent reattachment of the flame is induced with an increase in the mass flow rate of fuel; (2) when the mass flow rates reach a critical point, a small flamelet appears in the vicinity of the nozzle exit; and (3) a further increase in the mass flow rate leads to extinguishing of the flamelet and no reattachment phenomenon takes place after that. The effect of nozzle thickness on the onset and end of the reattachment phenomenon of the flame is minor. In contrast, occurrence of the blowout is affected by the nozzle thickness.