ReaxFF MD simulation of NOx/N2 formation mechanisms in ammonia-coal deep air-staged combustion

Deep air-staged NH 3 /coal co-combustion is an effective route for NO x mitigation, yet nitrogen-conversion chemistry under strongly reducing conditions remains unclear. ReaxFF molecular dynamics (ReaxFF MD) simulations were used to elucidate the nitrogen-containing species conversion network under deep air-staged conditions, and to compare it with conventional air staging and the Glarborg mechanism. Restricted oxygen supply weakens the oxidative radical pool and shifts NH 3 consumption away from direct oxidation toward reactions with nitrogen containing intermediates. This suppresses conventional NO formation pathways and promotes ·NH i cross-recombination, increasing the formation of NNH and N 2 H 2 by 2.3 times. Consequently, the NNH-mediated NO to N 2 pathway increases nearly threefold, becoming the dominant NO reduction pathway in the primary combustion zone, and lowering the total NO yield by 12.5%. Comparison with the classical Glarborg gas-phase mechanism further reveals several elementary steps whose importance is underestimated or absent under deep air-staged conditions, particularly H 2 NO formation, ·NH i recombination, and the unimolecular conversion of H 2 NO and N 2 H 2 . These results provide atomistic insight into nitrogen chemistry in strongly reducing environments and a mechanistic basis for precise NO x control in NH 3 /coal co-combustion.