Dual-interface heat transfer in discontinuously packed porous combustion of ultra-low concentration methane

Ultra-low concentration methane (ULCM) combustion requires effective internal heat recirculation because weak heat release makes stable combustion sensitive to heat losses. This study investigates the effects of reaction zone length and downstream heat storage in a discontinuously packed porous burner (DPPB), in which straight channel honeycomb ceramic sections form an upstream preheating zone (PZ) and a heat storage zone (HSZ), separated by an open reaction zone (RZ). Stability limit experiments were conducted for DPPBs with RZ aspect ratios of ζ = 0.1–0.8 and a non-heat-storage burner (NHSB), together with validated pore scale simulations. The experiments show that the HSZ can extend the stable operating range, depending on equivalence ratio and RZ aspect ratio. The simulations show that the PZ-RZ transition produces jet expansion and local recirculation, while the flame and main heat release region remain close to this interface under stable conditions. The interface between PZ and RZ provides the main upstream heat transfer pathway, whereas the HSZ modifies thermal redistribution through the downstream interface. Increasing ζ produces only small changes in the flame and heat release rate peak locations but weakens interfacial heat transfer. The lean stability advantage at smaller ζ is accompanied by stronger interfacial heat transfer, whereas removal of the HSZ reduces upstream thermal feedback.