Impacts of Radiation Reabsorption on the Flame Speed and NO Generation of CH<sub>4</sub>/NH<sub>3</sub>/Air Flames
Shu Zheng, Yuzhen He, Hao Liu, Yu Yang, Qiang Lü
Abstract
Partial replacement of methane with ammonia, a carbon-free fuel with promising application potential, can effectively reduce carbon emissions. In this paper, a numerical study on CH 4 /NH 3 /air one-dimensional (1D) premixed flames at different equivalence ratios was performed. The impacts on the laminar flame speed and NO generation by radiation reabsorption are discussed. It was clear that the improvement of flame speed under radiation impact showed a nonlinear tendency with an increasing equivalence ratio. The decisive factors were the preheat-induced chemical effect when ϕ = 0.6–1.2 and the direct radiation effect at ϕ = 1.2–1.5. The promotion effect on NO formation by radiation reabsorption decreased first and then increased with an increasing equivalence ratio, controlled by the reactions NH + NO ≤> N 2 O + H and NH + O 2 ≤> NO + OH in lean combustion and N + OH ≤> NO + H and NH + O ≤> NO + H in rich combustion. NH i ( i = 0, 1, 2) radicals were the main factors controlling the NO generation and conversion. The oxidation of CH 4 participated in the generation and consumption of NO by generating OH, CH i, and CO 2 .