Effect of wall thermal conductivity on the stability of catalytic heat-recirculating micro-combustors

Thermal management strategies for enhancing stability of catalytic micro-combustors via heat recirculation were studied for obtaining design insights. The stability of heat-recirculating systems utilizing catalytic combustion of methane-air mixtures was studied numerically. A two-dimensional computational fluid dynamics model including detailed chemistry and transport was developed to explore the underlying mechanism by which heat recirculation enhances combustion stability. Simulations were performed over a wide range of wall thermal conductivities and flow velocities in order to gain insight in combustion stability and identify suitable ranges of operating conditions, with special emphasis on heat recirculation as a means of understanding energy management at small scales. It was shown that the wall thermal conductivity plays a vital role in determining stability, especially for that of the inner walls. Heat recirculation has little effect on extinction but strongly affect blowout. The optimal design is obtained by the use of all walls with minimal thermal conductivity. For highly conductive walls, heat recirculation does not improve stability significantly, whereas heat recirculation is effective only for low-conductivity walls. The effect of heat recirculation becomes more pronounced with decreasing wall thermal conductivity. Engineering maps that delineate combustion stability were constructed and design recommendations were finally made. (c) 2017 Elsevier Ltd. All rights reserved.