Numerical Studies on Flame Stabilization Behavior of Premixed Methane-Air Mixtures in Diverging Mesoscale Channels

Abstract

The propagation of a laminar premixed flame front in two-dimensional diverging channels with no-slip wall conditions and various wall heat transfer conditions has been reported in the present work. Momentum, energy and species conservation equations are solved and steady solutions are obtained with a single-step reaction model for stoichiometric methane-air mixtures. Finite volume method with an adaptive grid is applied to investigate the flame stabilization characteristics in diverging channels of various angles. These investigations show that an increase in the flow velocity changes the flame shape from a mushroom-type flame to a tulip-shaped flame in diverging channels for finite heat transfer rate through solid walls. It was also observed that an increase in the divergence angle led to transition of the propagating flame front from mushroom-shaped flame to tulip-shaped flame due to increased mass flux from the center of the channel. For isothermal channels, local recirculation near the wall plays a significant role in stabilizing a flame. However, for adiabatic channels, the role played by flow recirculation in stabilizing the flame is minimal. Substantial flow redirection in radially outward direction is observed and it is more pronounced for isothermal channels compared to adiabatic channels. The flame position depends on the channel divergence angle for channels having divergence angle less than 10°. It remains independent of divergence angle for channels having divergence angle greater than 10°. Therefore, a minimum divergence of 10° degrees along the flow path is recommended for an efficient design of microcombustors.

Keywords:

• Divergent channels
• Flame stabilization
• Laminar flame propagation