Effect of hydrogen addition on combustion and heat release characteristics of ammonia flame

Abstract

As a key parameter of fuel, the heat release characteristics of ammonia (NH3) flames under hydrogen (H2)-enriched conditions constitute the emphasis of this research. The effect of H2 addition on heat release characteristics of premixed laminar NH3 flames are numerically investigated by considering the detailed chemical mechanism. The NH3, O2, H2O, NO, and N2O mole fraction distributions based on the Dagaut-Kéromnès mechanism agree well with experimental results, thereby potentially providing repeatable and accurate outcomes with NH3 flames using this mechanism. The OH × N radical positively affects the net heat release rate at various equivalence ratios and H2 addition ratios conditions. The chemical effect is evidently important at low H2 addition ratios, while the transport effect becomes dominant at high H2 addition ratios because of the high mobility of H2. For the three top endothermic elementary reactions of NH3 flames, the contribution of R236: H + O2=OH + O increases, while R171: H + NO(+M) = HNO(+M) and R240: H2O + O=OH + OH decrease with increasing H2 addition ratios. Diverse key exothermic elementary reactions of NH3 flames occur at various equivalence ratios and different H2 addition ratios. The large contribution of R128: N + NO=N2+O at fuel-rich conditions can be applied to reduce NOx emissions of the NH3 flame under pure and H2 addition conditions.