Experimental Study on Ammonia Dissociation and NOx Emission Under Fuel-Rich Combustion in a Porous Burner

Fuel-rich combustion of ammonia (NH₃) in porous media to produce a H₂-rich fuel for subsequent fuel-lean combustion is proposed and experimentally examined by burning a stream of NH₃ and O₂ in Ar in a cylindrical combustion chamber filled with silicon carbide foam ceramic to appreciate the effect of flowrate (and thus the residence time) and equivalence ratio (ɸ) on flame temperature, NH₃ conversion and NOx emission. The experimental results showed that at ɸ = 1.0, NH₃ combustion produced a considerable amount of NO at ca 8,800 ppm. Increasing ɸ significantly reduced NOx emission, leading to almost zero NOx emission at ɸ = 1.4, resulting in an effluent containing 10.2% H₂ and 1.9% NH₃, in line with expectation. Meanwhile, the flame temperature (T₁) decreased from 1496°C at ɸ = 1.2 to 1440°C at ɸ = 1.4, and the degree of NH₃ dissociation also decreased by 15.89% to 80.59%. The enhancement of combustion performance at high flowrates is attributed to the elongated higher-temperature combustion zone within the porous media which improves the thermal dissociation of NH₃. It has been demonstrated that fuel-rich combustion of NH₃ can significantly reduce NOx emissions and produce high concentrations of H₂ for subsequent fuel-lean combustion.