A numerical study on premixed micro-combustion of CH4–air mixture: Effects of combustor size, geometry and boundary conditions on flame temperature

A numerical study on CH4–air premixed combustion in micro-combustors was undertaken by solving the 2D governing equations. The effects of combustor size and geometry, inlet velocity profile and slip-wall boundary condition on the flame temperature were investigated. The simulation results showed that a larger combustor (d = 2 mm) gives higher flame temperature only when the flow velocity is below a certain level. With regard to the combustor geometry, a 2D planar channel (H = 1 mm) represents higher flame temperature than a cylindrical tube with d = 2 mm (equal hydrodynamic diameter), over the velocity range covered by the present study. In addition, it was noted that the flame temperatures in the cylindrical tube and 2D planar channel are quite close when H = 0.65d is satisfied. The fully developed velocity profile applied at the inlet plane was found to have the flames anchored further from the entrance than the uniform profile, but no remarkable difference in terms of flame temperature (≤3 K) was observed. A simple analysis of the competing time scales (axial convection and radial diffusion) was presented to address the difference of flame structure between the methane–air and hydrogen–air mixtures. Finally, it was shown that in a combustor with d = 1 mm the effects of slip-wall boundary are negligible, compared to the bulk velocity and gases temperature.