2012 Volume 54 Issue 170 Pages 269-278
To clarify the stabilization mechanism of coaxial oxygen-jet diffusion flames at high pressure, experiments on flame lifting and blowout for pure-oxygen jet diffusion flame for two types of double tube burners were performed under the conditions of various jet and co-flow velocities and various methane mole fractions in co-flow diluted with nitrogen. At high pressure of 0.5 MPa, the flame stability was significantly enhanced in comparison with that at atmospheric pressure. Flame was formed in co-flow side at atmospheric pressure, while at high pressure the flame position moved to the jet-flow side. At atmospheric pressure, the flame base located close to the lip and then moves downstream of the lip with increase in methane mole fraction in co-flow and increase in jet velocity. In contrast, at high pressure, the flame base located close to the lip regardless of methane mole fraction in co-flow and approached the lip with increase in jet velocity. According to the observation results of stream line near the lip, at atmospheric pressure, the characteristic length scale of the recirculation zone was small and the flame base was located downstream of the recirculation zones, indicating that the oxygen-jet diffusion flame was stabilized by the balance between the local gas velocity and burning velocity of the premixed gas formed by diffusion. In contrast, at high pressure, the recirculation zone was formed in almost all experimental conditions, its characteristic length scale being larger than that at atmospheric pressure, and flame base located in the recirculation zones in some cases. This means that the stabilization of the flame base at high pressure is dominated by the existence of the recirculation zone. Therefore, the stabilization mechanism of the coaxial oxygen-jet diffusion flame changes depending of the ambient pressure and stability of the flame base is enhanced at high pressure.
