NOx reduction and stability enhancement in high-pressure ammonia swirling combustion through multiphysical fields collaboration

This study investigates the effects of pressure variations on NOx emissions during ammonia combustion in a stratified swirling vortex-tube combustor, utilizing stratified vortex combustion (SVC) technology. The results reveal a significant inverse correlation between rising pressure (from 0.1 to 2.0 MPa) and emissions of NOx, NH₃, and H₂, with NOx concentrations decreasing from 0.103 to 0.066 g/kg for NO and from 0.880 to 0.540 g/kg for N₂O. Peak formation rates of nitric oxide (NO) and nitrous oxide (N₂O) also decline substantially from 39.95 to 10.15 mol/(kg s) and 27.85 to 21.45 mol/(kg s), respectively, while their reduction rates shift from −6.15 to −3.03 mol/(kg s) for NO and −38.57 to −31.48 mol/(kg s) for N₂O. The SVC technology enhances NO reduction, suppresses N₂O formation, and inhibits ammonia conversion to nitroxyl (HNO)—a key NO precursor—through the synergistic optimization of multiphysics fields (e.g., velocity, temperature, and composition fields) under elevated pressures. The observed reduction in peak NO concentration is driven by lower temperatures (e.g., from 1808 to 1756 K at peak NO formation zones) and decreased levels of reactive intermediates (e.g., OH drops from 4.67 × 10⁻⁴ to 1.40 × 10⁻⁴, HNO from 1.3 × 10⁻⁴ to 9.623 × 10⁻⁵) in the NOx formation zone. Notably, while NH₂ and H concentrations decline at higher pressures, the high-temperature region in the NO and N₂O reduction zones expands by approximately 20% at 1.5 MPa, providing a larger domain for effective emission reduction. These findings, supported by chemical kinetics analysis, demonstrate SVC's potential for stable, efficient, and low-emission ammonia combustion across varying pressure conditions, offering critical insight for its industrial application as a clean fuel technology.