Numerical Analysis of Ammonia-Hydrogen Premixed Swirling Combustion Characteristics under Wall Effects

The research investigates the influence of wall confinement on the characteristics of ammonia-hydrogen swirl flames through numerical simulations. An increase in wall confinement size leads to an expanded recirculation zone and a higher axial center position, while reducing the redial restriction on the swirling flame, allowing more free and sufficient radial flame development in radial direction. The increase in confinement size facilitates greater radial flame spread and results in a wider flame angle relative to the combustor axis. As the wall dimension increases from 60 mm×60 mm to 100 mm×100 mm, the NO_x mole fraction at the combustor outlet decreased from 7.402 1×10^-3 (60 mm×60 mm) to 7.129 7×10^-3 (100 mm×100 mm), corresponding to a reduction of approximately 3.68%. The reduction in NO_x is attributed to the suppression of thermal NO formation and altered species conversion pathways that limit fuel NO generation. Under the 80 mm×80 mm confinement wall configuration, the NO_x concentrations initially rise before decreasing with increasing hydrogen content. As the equivalence ratio increases from 0.8 to 1.2, NO_x mole fraction decreases from 1.051 3×10^-2 to 2.158 1×10^-3, corresponding to an emission reduction of approximately 79.5%, respectively, indicating higher emissions under lean conditions and significantly reduced emissions under fuel-rich conditions.