Flame holding is an essential technology for Scramjet combustors especially under low Mach flight conditions, under which the airflow temperature is low. An interesting technique for the flame holding is the utilization of shock waves. Experiments in a supersonic wind tunnel showed that the incident shock waves made possible the stable flame holding in Mach 2.5 supersonic airflow within air total temperature of 360K through 900K. The objective of this study was to investigate the flame-holding characteristics depending on air added to hydrogen fuel jet and to understand the mechanism of the flame-holding stabilized by shock wave. The flame-holding limits of hydrogen flow rate with various fuel/air ratio showed that both diffusion- and premixed-type flame-holding existed. In the diffusion-type flame-holding, the hydrogen flow rate of the flame-holding limit decreased as the added air flow rate increased. Increasing the added air flow rate further, the hydrogen flow rate limits turned to increase. To elucidate the mechanism of the flame-holding, visualization of OH species by laser-induced fluorescence and measurements of temperature and hydrogen concentration in the wake were also conducted. They showed that the addition of air suppressed the mixing of fuel and shrank the recirculation flow.
