Non-premixed combustion characteristics and thermal performance of a catalytic combustor for micro-thermophotovoltaic systems

Micro-combustors with reliable flame stability and high surface temperature are crucial for micro-thermophotovoltaic devices. Recently, we verified the feasibility of catalytic combustion for non-premixed CH4/air in an asymmetrical planar micro-combustor. The upper limit of operational average velocity is 1.2 m/s and the maximum combustion efficiency is 52.4%. In the present work, a symmetrical configuration was proposed to improve the performance of the prototype combustor. Numerically investigation shows that the symmetrical combustor can be operated at an average velocity above 9 m/s, and the maximum combustion efficiency and surface radiation efficiency are 98.5% and 25.9%, respectively. In addition, as the average velocity is increased, the combustion efficiency decreases monotonically while the radiation efficiency and radiant energy output increase first and then decrease. Moreover, the combustion efficiency achieves its peak value under stoichiometric ratio. The accumulation of O2 near the Pt surface under fuel lean condition causes a sharp increase in O(s) coverage and a decrease in heat release rate. Furthermore, a larger wall thermal conductivity leads to more uniform wall temperature distribution and better heat recirculation effect on the incoming gases. However, a medium thermal conductivity of 1–10 W/(m·K) favors a larger radiant energy output.