Combustion of NH3/CH4/Air and NH3/H2/Air Mixtures in a Porous Burner: Experiments and Kinetic Modeling

Ammonia (NH3) is currently in the spotlight because of its potential in serving as an energy resource devoid of carbon. Combustion of NH3, however, presents several drawbacks, such as high ignition temperature, low flame speed, and high NOx emissions. Furthermore, although dual-fuel approaches may provide a solution for some of these problems, scarcity of information on the resulting emissions inhibits a large-scale adoption. Therefore, the present work is focused on studying gaseous pollutants, namely, NOx, CO, and unburned NH3, emitted from premixed flames of mixtures of NH3 and either CH4 or H2 as combustion enhancers in a porous media burner. An inert alumina–zirconia porous media-based burner fueled with NH3/CH4/air and NH3/H2/air mixtures was employed. Temperatures and concentrations of NOx, CO, and NH3 were measured as a function of the NH3 molar fraction in the fuel mixture for both type of mixtures. The experimental data were compared to results from simulations performed with recently developed chemical kinetic mechanisms, updated with the latest nitrogen chemistry submechanisms. The experimental results for NH3/CH4 mixtures showed that the NOx emissions peak at a NH3 molar fraction in the fuel mixture of around 0.5, while for NH3/H2 mixtures, the NOx emissions present maxima at NH3 molar fractions in the fuel mixture of 0.5 and 0.8. The CO emission data indicated complete combustion of CH4, but the presence of unburnt NH3 in the flue gas reveals its incomplete oxidation for the studied conditions. The kinetic simulations showed similar NOx emission patterns but significantly overpredicted the experimental data in most cases.