Coupled Flame Acceleration and NOx Suppression in Ammonia Combustion Assisted by Oxygenated Ignition Fuels

Abstract

Ammonia combustion suffers from low flame speed and high nitrogen oxide emissions, limiting its practical application as a carbon-free fuel. Herein, an oxygenated-fuel ignition chamber was designed to improve ammonia premixed combustion while controlling pollutant formation. Flame propagation was recorded by high-speed schlieren imaging, and NO, NO2, N2O, and NH3 slip were quantified by Fourier-transform infrared gas analysis. At an equivalence ratio of 0.9, the ignition-assisted system increased the laminar flame propagation velocity from 7.8 to 18.6 cm s⁻¹, while reducing ignition delay by 42.5%. The peak NO concentration decreased from 612 to 438 ppm when the chamber equivalence ratio was optimized, mainly due to enhanced early-stage radical generation and more complete NHx conversion. The results clarify the interaction between ignition enhancement and pollutant pathways in ammonia combustion.