Combustion characteristics of ammonia-hydrogen/air swirl flames under secondary air injection in a two-stage premixed model combustor

Jae Hyun Kim, Tae Won Kim, Hyeon Woo Lee, Young Hoo Kim, Ju Han Kim and Oh Chae Kwon

Energy, 2025, vol. 335, issue C

Abstract: To enable the practical industrial application of ammonia (NH3) as a carbon-free fuel based on its thermal cracking concept, the combustion characteristics of NH3-hydrogen (H2)(-nitrogen (N2))/air swirl flames under secondary air injection in a two-stage premixed model combustor are investigated for various conditions of H2 mole fraction (xh,f), primary and total fuel-equivalence ratios (ϕp and ϕt), air injection height (Hs) and pressure (P). Rich-quench-lean (RQL) combustion is achieved through the NH3-to-H2 conversion in the primary flames and H2-dominant combustion in the secondary flames. Key parameters such as xh,f, ϕp, and P significantly affect the low NOx (nitrogen oxides) and unburned fuel (LNF) emission condition via the primary flames, while ϕt influences unburned NH3 emissions via the post-flame zone of the secondary flames. With decreasing xh,f or increasing P, the LNF emission range narrows and the optimum ϕp for LNF shifts toward fuel-leaner condition. Hs has a notable impact on unburned NH3 emissions but does not have any significant effect on NOx emissions. The widest LNF emission range at normal temperature and P is found at xh,f = 0.50, ϕt = 0.9 and the optimum ϕp of 1.2. These results provide guidance for the design of low-emission, stably-operating NH3 combustion systems.

Keywords: Ammonia; Hydrogen; Secondary air; Flame morphology; Nitrogen oxides (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:335:y:2025:i:c:s0360544225039556

DOI: 10.1016/j.energy.2025.138313

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