Numerical simulations of burner-stabilized hydrogen-air flames in microgravity

Abstract

Detailed two-dimensional, time-dependent numberical simulations have been performed to gain understanding of the similarities and differences in the structure and stability of burner-stabilized flames in zero and earth gravity. These simulations include the effects of fluid convection, detailed hydrogenoxygen chemistry, multispecies diffusion, thermal conduction, viscosity, and heat losses to the burner. A series of simulations for a range of mixtures and inlet velocities have been performed. These simulations show the presence of cellular structures at the burner surface in both zero and earth gravity at high inlet velocities. As the inlet velocity is reduced, the flames move closer to the burner and the heat loss to the burner increases. At low inlet velocities, these cellular structures are suppressed in both zero gravity and earth gravity, indicating that increased heat loss to the burner is the primary mechanism stabilizing these flames. Downward propagating burner-stabilized flames become smoother more quickly than zero-gravity flames, indicating that gravity still plays a small part in stabilizing the flame. The simulations described here clarify the relative importance of gravity and heat losses to the burner on the stability of lean hydrogen-air flames.