Combustion of NH₃/CH₄/Air and NH₃/H₂/Air Mixtures in a Porous Burner: Experiments and Kinetic Modeling
2019
Rocha, Rodolfo C. | Ramos, C Filipe | Costa, Mario | Bai, Xue-Song
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.
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