Ammonia-Methane Flames Stabilized in an Ordered Porous Media Burner

Ammonia, a carbon-free fuel, faces combustion challenges, including low flame stability, weak radiative heat transfer, and high NOx emissions. Porous media burners (PMBs) help to address the issues through enhanced heat recirculation and improved radiative output. However, unlike hydrocarbon flames where porous media effectively suppress thermal NOx, ammonia combustion in PMBs retains high fuel NOx emissions. This study experimentally investigates flame stability and emission characteristics of CH4/NH3 blends and pure NH3 combustion in a PMB. Spatially resolved gas sampling within the porous structure reveals the kinetic evolution of NH3 oxidation and NOx formation. Results demonstrate that air-staged combustion with 20-25% secondary air effectively reduces NOx emissions by 82.5%, suppresses unburned NH3 (<20 ppm), and eliminates N2O (not detectable). Numerical simulations using a chemical reactor network further clarify nitrogen transformation pathways and C-N interactions, providing further kinetic insights. These findings advance the fundamental understanding while establishing operational guidelines for implementing ammonia PMBs in industries.