Abstract
<title>Abstract</title> <p>Stabilizing ultra-lean methane-air flames at high throughput remains a central challenge in porous media combustion of low-concentration coal mine methane (CMM). Here, we experimentally and numerically examine how imposed inlet-velocity non-uniformity affects flame-front morphology, velocity redistribution, heat recirculation, stability limits, and emissions in a homogeneous packed-bed burner. A double-layer distributor with spatially non-uniform flow resistance was used to generate alternating high-velocity regions (HVR) and low-velocity regions (LVR). Cold-flow simulations based on the measured viscous and inertial resistance coefficients showed that the inlet velocity modulation was gradually smoothed within the packed bed by lateral momentum exchange and stronger resistance in the high-velocity channels. During start-up, co-firing low-concentration CMM reduced high-grade methane consumption, reaching a 75% saving when the co-fired methane concentration was 5%. Under stable operation, the non-uniform inlet produced a laterally modulated wavy flame. The reaction zone in the HVR shifted downstream, whereas that in the LVR remained closer to the distributor. The HVR-LVR interface formed a persistent thermal anchoring zone that promoted lateral heat recirculation and delayed flame detachment as Darcy velocity increased. Compared with a uniform-intake planar flame, the wavy flame increased the effective reaction surface and widened the stable operating window, thereby raising the blow-off limit. CO concentrations at methane concentrations of 3.5%, 4.0%, 4.5%, and 5.0% were 14, 2, 0, and 0 mg/m³, respectively, and NOx emissions were limited to 3–15 mg/m³. These results identify inlet-velocity modulation as a passive route to stable and low-emission CMM combustion in porous media burners.</p>