Nitrogen Oxides as a By-product of Ammonia/Hydrogen Combustion Regimes

Alternative fuels are under scrutiny for mitigating carbon dioxide emissions. One of these alternatives is ammonia, which can be produced from waste sources, renewable energy and even nuclear power with potentially zero carbon emissions over most of its life cycle. The difficulties of pure ammonia combustion, partially due to its low flame speed and flammability, can be addressed by doping ammonia mixtures with hydrogen, which increases the reactivity of these blends and allows combustion features similar to those of some fossil fuels. However, NOx emissions are still a problem when burning ammonia, with some circumstances where emissions are even worse than with fossil-based systems. This is a consequence of the considerable formation of N2O, a greenhouse gas that is known to possess up to 300 times the Global Warming Potential (GWP) of carbon dioxide, making these regimes unsuitable for the purpose of fuel replacement to combat climate change. Therefore, this work shows bespoke results for unburned NH3 and NOx emissions, specifically NO, NO2 and N2O, at various conditions of operation whilst employing ammonia-hydrogen blends in a tangential swirl burner representative of industrial gas turbines. The results show a good compromise of NOx emissions at the near 1.05 - 1.2 equivalence ratio, with further understanding behind the chemistry that precludes the formation/consumption of these unwanted emissions for full deployment of ammonia-based energy systems.