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.