Combustion limits and flame stabilization of lean methanol in a graded-porosity porous-media burner

Porous medium (PM) combustion offers a potential strategy for the stable and efficient combustion of lean methanol. In this work, PM with a pore-graded topological structure was applied to the combustor, and a systematic investigation was conducted on lean methanol combustion. The effects of flow rate and equivalence ratio on the stable combustion characteristics of lean methanol, as well as the influences of equivalence ratio and flow rate on the combustion temperature distribution, were systematically analyzed under two PM arrangement configurations. Meanwhile, the evolution of lean methanol combustion states under the two arrangement configurations and the flame characteristics of the combustor under different inlet conditions were clarified. The results indicated that the forward gradient-porosity arrangement (configuration I) broadened the lean combustion limit of lean methanol to an equivalence ratio of 0.45. It was further demonstrated that the reverse gradient-porosity arrangement (configuration II) produced a more uniform temperature distribution within the combustion chamber and achieved continuous stable combustion for 120 min within the low-flow-rate range of 6–9 L/min, with a peak temperature of 1037 K attained at a flow rate of 9 L/min. In addition, under Configuration I, a peak temperature of 1284 K was reached at an equivalence ratio of 0.45 and a flow rate of 9 L/min. The lean-burn stability limit of methanol can be effectively broadened by utilizing PM with a graded-pore topological structure and significantly enhance the combustion stability of lean methanol. Under configuration II, efficient and stable combustion of lean methanol was achieved, and the methanol conversion efficiency was consistently maintained above 99.68%. The high-quality flue gas generated from lean methanol combustion has an average temperature over 800 K, and the combustion system can be utilized in integrated energy utilization scenarios. This work provides an important technical reference for the clean and efficient utilization of lean methanol.