Effect of heat and mass transfer on the combustion stability in catalytic micro-combustors

Abstract

The combustion characteristics of methane-air and propane-air mixtures in catalytic micro-combustors was studied numerically in order to clarify the importance of transport in combustion stability. The primary focus is on heat and mass transfer as a means of understanding energy management at small scales. A two-dimensional computational fluid dynamics model including detailed gas-phase and surface chemistry and multicomponent transport was developed for obtaining design insights. The effect of typical operating variables and design parameters was studied. Different performance measures were evaluated to assess the operability of the system. Engineering maps denoting combustion stability were constructed and design recommendations were also made. It was shown that in practical engineering design, heat and mass transfer plays a critical role in the process of catalytic combustion, and transport properties are usually key factors in determining combustion stability. Heat and mass transfer between the catalytic surface and gas phase depends strongly on the flow velocity and wall thermal conductivity. The operation of the system is limited by the heterogeneous reaction at low flow velocities and by mass transfer at high flow velocities. In the range of moderate flow velocities, combustion stability is determined by heat and mass transfer at low wall thermal conductivities and by transverse heat transfer within the system at high wall thermal conductivities. Finally, the role of combustor dimension in enhancing transport rates was illustrated, and the fuel transport properties were evaluated to assess the effect of mass transfer.