Abstract

This study numerically investigates the combustion characteristics of four catalytic micro-burners with different channel geometries: a straight-channel burner (Burner 1), a symmetric U-bend burner (Burner 2), and two asymmetric U-bend burners with either a wider inlet channel (Burner 3) or a wider recirculating channel (Burner 4). A steady-state, two-dimensional mathematical model accounting for gas-phase and catalytic reactions of propane on Pt/Al2O3 is employed. The results show that U-bend configurations significantly reduce the ignition equivalence ratio compared to the straight-channel design, with Burner 4 exhibiting the lowest value of 0.45. At an equivalence ratio of 0.85, Burner 4 achieves the highest maximum temperature and the most upstream flame location, attributed to enhanced heat recirculation and prolonged residence time in the wider recirculating channel. Temperature and propane mass fraction distributions reveal strong thermal coupling between the inlet and recirculating channels in asymmetric designs. The contribution of catalytic reactions to total heat release remains within a narrow range across the examined equivalence ratios for all U-bend burners, whereas Burner 1 shows a much higher catalytic contribution (~87%) due to suppressed gas-phase reactions. The U-bend geometries also exhibit lower heat loss ratios than the straight channel. The maximum wall temperature gradient increases with equivalence ratio, and the ranking among the three U-bend burners varies with operating conditions, indicating that geometry-specific thermal stress should be considered in practical design.

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