Effect of H2O dilution on NOx emissions from the oxidation of NH3/H2 fuel mixture

During NH3/H-2 combustion, reactant jets entrain the burnt gas, resulting in a combustion zone diluted with H2O. Therefore, the effect of H2O dilution on NOx formation should be carefully examined. In this study, NH3/H-2 oxidation with N-2 and H2O dilutions was investigated in a jet-stirred reactor (JSR). A systematic experimental analysis was conducted to investigate the effects of different factors, including temperature (T), equivalence ratio (Phi), and H2O volume fraction (XH2O). A numerical simulation was conducted using a modified mechanism to interpret the measured results and examine the kinetic pathways. NO formation is enhanced as T increases but inhibited as Phi increases. The effect of H2O dilution on NO formation is related to T and Phi. Under fuel-lean conditions, NO generation is hindered by H2O dilution. NO formation is reduced by 43 % at T = 1375 K and Phi = 0.5. In contrast, under fuel-rich conditions (Phi > 1), H2O dilution promotes NO formation at high temperatures (e.g., T > 1300 K at Phi = 2.5). The N2O concentration peaks at approximately 1250 K in cases of N-2 dilution, and 25 % H2O dilution increases the T of the peak N2O concentration by approximately 100 K. At 1375 K, the promoting effect of H2O on N2O generation is significant at XH2O = 10 %. This study provides new insights into the effect of H2O dilution on NOx formation characteristics during NH3/H-2 oxidation.