Influence of Steam Dilution on Nitrogen Oxide Formation in Premixed Methane/Hydrogen Flames

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Influence of Steam Dilution on Nitrogen Oxide Formation in Premixed Methane/Hydrogen Flames

Göke, Sebastian / Paschereit, Christian Oliver

The premixed combustion of natural gas and hydrogen at atmospheric pressure is investigated over a wide range of equivalence ratios and different degrees of steam and nitrogen dilution of up to 30% in the air. Emission formation, local temperatures, OH radical concentrations, and flame shape and position are measured in gas-fired tests. The measurement results confirm that steam effectively inhibits the formation of ${NO}_{x}$ emissions, even at constant flame temperature. For both natural gas and hydrogen, ${NO}_{x}$ and CO emissions below 10 ppm were measured up to near-stoichiometric fuel concentrations at wet conditions. Nitrogen dilution does not lead to reduced emissions. A numerical analysis conducted with a reactor network shows that the influence of steam dilution on radical concentrations and ${NO}_{x}$ formation depends strongly on the degree of humidity and on the equivalence ratio. The thermal, the $N_{2} O$ , and the NNH pathway are significantly constrained at wet conditions mainly due to reduced O atom concentrations, whereas prompt ${NO}_{x}$ can be increased due to higher CH radical concentrations for the natural gas flame. Thus, the inhibiting effect of steam dilution on ${NO}_{x}$ formation is stronger at high flame temperatures.