Lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched premixed combustion mode.

Compared with pure NH 3 fuel, the lower NO emission conditions of NH 3 –H 2 mixtures under the oxygen-enriched combustion mode have been identified quantitatively. Furthermore, the effects of the H 2 addition on the NO productions of premixed oxygen-enriched NH 3 –H 2 flames are studied numerically, while the major reactions responsible for the variation of total NO are identified. Results show that the H 2 addition is eligible to reduce the NO emissions of the oxygen-enriched NH 3 combustion if the laminar burning velocity is fixed to a larger value (>23 cm/s). The quantitative equations are obtained to determine the optimum oxygen-enriched conditions of the NH 3 –H 2 mixture, aiming to achieve lower NO emission and similar or improved combustion stability compared to pure NH 3 fuel by restricting the minimum and maximum O 2 percentages for the NH 3 –H 2 mixtures. Based on the rate of production (ROP) analysis, for the oxygen-enriched NH 3 –H 2 combustion, R144 (HNO + H<=>H 2 +NO) is consistently the most significant NO production reaction, while R85 (NH + NO<=>N 2 O + H) and R91 (N + NO<=>O + N 2) play significant roles in the NO consumption. When the laminar burning velocity (S L) is kept to a lower value, the increased total NO of the oxygen-enriched NH 3 flames with the H 2 addition is ascribed to more efficient suppressions on the NO consumption reactions of R85, R91 and R77 (NH 2 +NO<=>NNH + OH). In contrast, thanks to the extra impact of the higher O 2 percentage on the H/O/OH radical pool at larger S L , the NO production reactions begin to suffer stronger suppressions of the H 2 addition, resulting in the reduced total NO of NH 3 –H 2 mixtures. Furthermore, R144 is identified as the key reaction influencing the variation trend of total NO at both lower and higher S L values. • NO emissions of oxygen-enriched NH 3 –H 2 combustion are investigated. • Lower NO emission conditions of NH 3 –H 2 mixture than NH 3 are identified. • H 2 addition leads to opposite change of NO emission at small and large S L. • Effects of H 2 addition on NO formations are analyzed at different S L. • R144 plays a decisive role in determining the opposite change of NO emission. [ABSTRACT FROM AUTHOR]