Fundamental flame characteristics of premixed H2–air combustion in a planar porous micro-combustor

Abstract

Micro-/meso-scale combustion represents a great potential in generating portable power in an efficient way. Heat recirculation is regarded as the most important factor that influences the combustion process in micro-combustors. Adding porous medium to a free flame micro-combustor is able to enhance thermal energy transport, thus allowing more heat recirculation. A CFD study on fundamental flame characteristics of premixed H2–air combustion in a planar porous micro-combustor is carried out. Thermal radiation is not considered in order to focus on the contribution of enhanced thermal conduction. The effects of flow conditions and properties of the porous medium on the wall temperature, species concentration, flame temperature, flame location, and flame speed are examined individually. The numerical results indicate that a porous micro-combustor gives a higher wall temperature and a lower flame temperature than a free flame counterpart. In the presence of porous medium, temperature distribution as well as species (OH) concentration becomes more uniform. Flame locations in a porous micro-combustor exhibit a U-shaped pattern against the change of the inlet flow velocity. Choosing the porous material properly to have the effective thermal conductivity and the wall thermal conductivity in the same order of magnitude is helpful to localize flames. Finally, the flame speed is found to be in a linear relation with the inlet flow velocity. It is noted that the blocking effect incurred by the solid matrix renders some conclusions of free flame micro-combustors ineffective in explaining the results of the porous micro-combustor, which requires further studies or more sophisticated models.