Influence of Inlet Flow Configurations on Low-Swirl Combustion Characteristics of Ammonia-Hydrogen Fuel

As a promising zero-carbon fuel, ammonia has attracted considerable attention in recent years. However, the challenge of NOx emissions during its combustion remains a significant limitation to its practical application. Low-swirl combustion chambers are known to offer distinct advantages in reducing NOx formation. In this study, the flow characteristics and combustion behavior in a low-swirl ammonia-hydrogen combustor under six different inlet configurations were investigated through numerical simulation. Key parameters including velocity, turbulent kinetic energy (TKE), temperature, NOx emissions, flame strain rate, and vortex structures were systematically analyzed. The results reveal that the inlet configuration plays a crucial role in shaping the combustion flow field. When the central jet consists of air or premixed fuel/air gases, rather than pure fuel, a stable inner recirculation zone (IRZ) forms near the combustor head. In these cases, the average central-sectional temperature exceeds 1000 K, and the fuel utilization rate remains above 90%. The flame exhibits strong radial stretching, and the resulting vortex structures are more coherent, indicating that air or fuel/air premixed central jets enhance backflow induction and shear mixing, thereby improving flame anchoring and intensifying chain reactions. Among the air or fuel/air premixed cases, the configuration with an NH3/air central inlet yields the highest average TKE of 4.65 m2/s2. The NH3/H2/air configuration achieves the highest average central temperature and fuel utilization rate, reaching 1070.6 K and 96.91%, respectively. Meanwhile, the H2/air case results in the lowest NOx emissions at 257.2 ppm. The pure air group exhibits the highest average flame strain rate, reaching 347.52 s−1. In contrast, configurations utilizing pure fuel as the central jet achieve relatively low NOx emissions of 79.5 ppm and 124.7 ppm, respectively.