Experimental and numerical study of CH₄/air porous media combustion with topology gradation at elevated pressure

Industrial heavy-duty gas turbines are facing the risks of flame blow-off and thermoacoustic oscillations, while submerged combustion within porous media effectively broadens the flammability limits and suppresses thermoacoustic instabilities. However, keeping a stable flame submerged within the porous media under pressurized and high-velocity gas turbine conditions remains a significant challenge. The porous media burners reported in previous studies are adapted for low-speed operation, with a maximum cross-sectional velocity of 8 m/s at atmospheric pressure and 0.5 m/s under pressurized conditions. To adapt porous media combustors for gas turbine applications, this study investigates the effects of “V-graded” pore size gradient topology on flame temperature, stability, and emissions under pressurized (0.1–0.5 MPa) and high-velocity (5–25 m/s) conditions. The results demonstrate direct observation of excess enthalpy flames within the porous media reaching temperatures near 2000 °C. The Λ-graded structure exhibits stronger heat recirculation efficiency and higher flame temperatures, while the V-graded structure achieves a wider flammable limit with the lowest fuel-lean equivalence ratio below 0.3. At high velocities, three structures maintain NO and CO emissions below 50 ppm@15%O₂, with the V-graded structure demonstrating superior performance in controlling the total emissions of NO and CO. The V-graded structure with high flow resistance exhibits stronger vibration amplitudes compared to other structures. Significant deformation occurs in foam ceramics located within the high-temperature region of the combustion zone, whereas the ordered ceramics exhibit excellent thermal shock resistance.