Numerical study on methane heterogeneous reaction characteristics in micro catalytic combustors with orthogonal thermal anisotropic walls

This numerical study investigates the combustion characteristics of premixed methane/air in micro catalytic combustors, specifically focusing on orthogonal anisotropic walls. A two-dimensional computational fluid dynamics (CFD) model incorporates detailed methane heterogeneous (catalytic) chemical reactions over platinum catalyst, validated against experimental data with maximum deviations of 4.9 % at an equivalence ratio of 0.6. The impact of wall materials, such as pyrolytic graphite and stainless steel 316, on heterogeneous reactions (HTR) performance is explored. In addition, the effect of different wall thermal conductivities on HTR stability is also studied. The results show that pyrolytic graphite has better combustion performance and a wider range of stable combustion limits. This advantage is mainly attributed to the thermal anisotropy of pyrolytic graphite, which enhances fuel preheating and facilitates the stable combustion of methane. The reduction of transverse thermal conductivity reduces heat losses from external walls and diminishes the preheating effect on unburnt gases. Conversely, an increase in transverse thermal conductivity enhances the heat transfer performance of external walls, reduces temperature gradients, diminishes convective heat contributions from external walls, and ultimately lowers the Biot number of external walls. In summary, this research yields vital insights for designing and optimizing micro-combustors, particularly in the practical application of selecting wall materials and adjusting thermal conductivity parameters.