Homogeneous Fuel-NO Mitigation during Flameless Oxy-Combustion of CH<sub>4</sub>/NH<sub>3</sub> Mixtures
Shichao Zhu, Pengfei Li, Yan Gao, Guodong Shi, Fan Hu, Zhaohui Liu
Abstract
In oxy-fuel combustion systems aimed at carbon capture, reducing the level of NO x emissions is critical for corrosion mitigation and CO 2 utilization. Previous studies mostly focused on NO x mechanisms in traditional flame oxy-combustion, while experimental evidence regarding the homogeneous fuel-NO reduction benefits of flameless oxy-combustion is lacking. To fill this gap, this study provides the first systematic investigation into homogeneous fuel-NO formation in flameless oxy-combustion of CH 4 /NH 3 mixtures, combining experimental data with validated numerical simulations. The impacts of combustion mode (flameless vs flame oxy-combustion), initial oxygen concentration ( X O 2 ), and equivalence ratio (Φ) are thoroughly investigated. The experiments indicate that at Φ = 0.8 and X O 2 = 30%, flameless oxy-combustion reduces homogeneous fuel-NO by 56.8% in comparison with flame oxy-combustion and by 15.8% compared to flameless air combustion. Notably, across varying initial X O 2 (25–40%) and Φ (0.6–0.9), the effectiveness of fuel-NO reduction under flameless oxy-combustion remains largely unchanged. Finite-rate combustion modeling with an optimized skeletal mechanism and reaction pathway analysis further reveal that under flameless oxy-combustion of CH 4 /NH 3 mixtures, homogeneous fuel-NO formation through N 2 O → NO, CN → NO, and NCO → NO pathways is inhibited, whereas the primary NO destruction route, NH 2 → N 2, is promoted. This research delivers pioneering experimental evidence of the efficacy of flameless oxy-combustion in reducing fuel-NO emissions and offers critical insights into the underlying mechanisms.