Abstract
An experimental and kinetic modeling study was performed to investigate the influence of NO(2) addition on the autoignition characteristics of NH(3)/O(2)/Ar mixtures. Ignition delay times were measured using a shock tube at temperatures of 1450-2200 K, pressures of 0.14 and 1 MPa, equivalence ratios of 0.5, 1.0, and 1.5, and NO(2) concentrations from 0 to 2000 ppm. The results show that NO(2) addition significantly promotes NH(3) autoignition, with the enhancement strongly dependent on temperature, pressure, equivalence ratio, and NO(2) concentration. The effect is particularly pronounced at intermediate temperatures (1450-1700 K) and higher pressure, and exhibits a nonlinear relationship with NO(2) concentration. The updated Shrestha and Glarborg mechanisms accurately reproduced the experimental IDT data. The evolution of key species indicates that NO(2) addition significantly promotes NH(3) consumption, along with the formation of NO and the radicals OH and NH(2). Flux analysis reveals that NO(2) addition introduces a novel ammonia consumption pathway via NH(3) + NO(2) = NH(2) + HONO, facilitating rapid NH(2) radical production. HONO decomposition further accelerates OH radical formation. Reaction rate analysis confirms that NO(2) promotes OH generation through NO(2) + H = NO + OH, especially in the early stages of NH(3) oxidation. Moreover, NO(2) addition significantly alters NH(2) consumption pathways, with both NO(2) and NO participating in reactions with NH(2), not only accelerating its consumption but also suppressing NH(2) self-recombination and other radical-consuming channels.