Stable Combustion of Ultra-Low-Concentration Methane in a Dual-Channel Counterflow D-TPMS Porous Burner: A Pore-Scale Numerical Study

At ultra-low methane concentrations, limited heat release makes it difficult to preheat the incoming mixture sufficiently to sustain stable combustion. This study employs three-dimensional pore-scale simulations to investigate a porous burner based on a Diamond-type triply periodic minimal surface (D-TPMS). The burner comprises two interpenetrating flow-channel networks separated by a solid wall, allowing co-current operation with both streams flowing in the same direction or counterflow operation with the streams flowing in opposite directions. Under counterflow operation, fresh methane–air mixtures enter the two channels simultaneously from opposite ends of the burner and undergo preheating and combustion within their respective channels. Hot combustion products in each channel transfer heat through the separating wall to the incoming mixture in the adjacent channel, enabling continuous mutual heat recovery without direct mixing or periodic flow reversal. Under co-current operation, stable combustion of a mixture containing 4.0 vol.% CH4 was maintained at an inlet velocity of 0.10 m s−1, whereas flame blow-off occurred at 0.15 m s−1. In contrast, under counterflow operation, a 48 mm D-TPMS medium sustained stable combustion at 0.40 m s−1 with methane concentrations as low as 1.6 vol.%. At the same inlet velocity, increasing the medium length to 98 mm provided a longer axial region for inter-channel heat exchange, and stable combustion was sustained at methane concentrations as low as 1.0 vol.%. These findings indicate that continuous mutual heat recovery enabled by counterflow operation within the dual-channel D-TPMS structure substantially extends the stable operating range of ultra-low-concentration methane combustion.