Mechanism and effect assessment of sub-atmospheric pressure and co-flow air to suppress the flicker of buoyancy-driven methane laminar diffusion flame br

To further reduce the combustion instability behavior in high-altitude areas, a synergistic suppression of buoyancy-driven methane laminar diffusion flame flicker was achieved by sub-atmospheric pressure combined with co-flow air, and the suppression mechanism was revealed through the schlieren technique. As the pressure decreases, the fluid density gradient within the shear layer decreases, slowing down the formation of vortices. When the co-flow air increases, the vortex is accelerated to rise until the vortex forms downstream of the flame and the flame flicker is completely suppressed. The suppression of flame flicker by sub-atmospheric pressure and co-flow air was nonlinear. The flicker frequency, oscillation amplitude, and flame mean height of flames were assessed for a pressure of 0.5-1.0 atm and co-flow air of 4-16 L/min. The sub-atmospheric pressure reduces the flicker frequency, which increases with increasing co-flow air. The reduction rate of oscillation amplitude at sub- atmospheric pressure varied among different co-flow air flow rates. The initial and that almost realize flame stabilization co-flow air flow rates are more effective than the intermediate flow rate in reducing the oscillation amplitude. The flame mean height decreases monotonically with decreasing pressure, but there is a small peak in the downward trend with increasing co-flow air

Automated summary

To reduce combustion instability in high-altitude areas, the combination of sub-atmospheric pressure and co-flow air effectively suppresses the flickering of buoyancy-driven methane flames. The suppression mechanism was revealed through schlieren technique, showing that decreasing pressure slows down vortex formation while increasing co-flow air accelerates it. The flicker frequency decreases with sub-atmospheric pressure but increases with increasing co-flow air.