RANS simulations on combustion and emission characteristics of a premixed NH3/H2 swirling flame with reduced chemical kinetic model

Ammonia (NH3) is considered as a potential alternative carbon free fuel to reduce greenhouse gas emission to meet the increasingly stringent emission requirements. Co-burning NH3 and H-2 is an effective way to overcome ammonia's relative low burning velocity. In this work, 3D Reynolds Averaged Navier-Stokes (RANS) numerical simulations are conducted on a premixed NH3/H-2 swirling flame with reduced chemical kinetic mechanism. The effects of (A) overall equivalence ratio Phi and (B) hydrogen blended molar fraction X-H2 on combustion and emission characteristics are examined. The present results show that when 100%NH3-0%H-2-air are burnt, the NO emission and unburned NH3 of at the swirling combustor outlet has the opposite varying trends. With the increase of Phi, NO emission is found to be decreased, while the unburnt ammonia emission is increased. NH2 -> HNO, NH -> HNO and HNO -> NO sub-paths are found to play a critical role in NO formation. Normalized reaction rate of all these three sub-paths is shown to be decreased with increased Phi. Hydrogen addition is shown to significantly increase the laminar burning velocity of the mixed fuel. However, adding H-2 does not affect the critical equivalence ratio corresponding to the maximum burning velocity. The emission trend of NO and unburnt NH3 with increased Phi is unchanged by blending H-2. NO emission with increased X-H2 is increased slightly less at a larger than that at a smaller Phi. In addition, reaction rates of NH2 -> HNO and HNO -> NO sub-paths are decreased with increased X-H2, when Phi is larger. Under all tested cases, blending H-2 with NH3 reduces the unburned NH3 emission, especially for rich combustion conditions. In summary, the present work provides research finding on supporting applying ammonia with hydrogen blended in low-emission gas turbine engines. (C) 2021 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.