Effect of Wall Thermal Boundary Conditions on Flame Dynamics of CH_4-Air and H_2-Air Mixtures in Straight Microtubes

摘要

Unsteady numerical simulations with detailed chemistry have been carried out for premixed stoichiometric CH4-air and H-2-air mixtures in straight microtubes to understand the flame-wall coupling and its effect on flame dynamics for a range of wall heat transfer conditions. Varying flame shapes were observed during the unsteady flame propagation mode. These flame modes are represented with flame shape angles and the corresponding flame shape is correlated to the wall heat transfer conditions. Various similarities in flame propagation characteristics have been observed for both of the fuels. A normalization technique has been adopted to establish the independence of variation of nondimensional flame propagation velocity on fuel type. It has been observed that an increase in convective heat transfer coefficient, h, though increasing the heat loss from a propagating flame, does not necessarily lead to a monotonic decrease in flame propagation speed. A transition regime where propagating flame changes its shape has been identified. The variation of mass flux in the vicinity of the propagating flame has been used to gain better understanding of flow redirection and its impact on flame shape and flame propagation behavior.