Experimental Investigation of the Structure and NO Emissions from Swirling Lean Premixed NH3/CH4/Air Flames and Their Correlation with OH

Ammonia/methane fuel blends have gathered interest as a promising solution for the development of a low-carbon energy system. In that pursuit, this work focused on the effects of turbulent intensity (u′ = 1.3–2.6 m/s), ammonia contents (XNH3 = 0.0–1.0), and equivalence ratios (ϕ = 0.5–0.9) on the flame structure and NO emissions of bluff-body swirl-stabilized premixed flames of ammonia/methane/air as well as their links to hydroxyl planar laser-induced fluorescence (OH-PLIF) intensity. Three swirling flame shapes are distinguished, which are jointly determined by the ammonia content and equivalence ratio. The normalized OH-PLIF intensity (Iaverage/SL) of all XNH3, u′, and ϕ can be collapsed well onto one unified correlation as a function of the normalized turbulent intensity u′/SL. The flame surface density (FSD, marked as Σ) of confined swirling flames was rarely reported before, and the FSD in a V shape increases obviously when transiting to a M shape as the ammonia content reduces. The turbulent flame area ratio (AT/AL) derived from the FSD is increasing as u′/SL increases; however, it decreases first and then increases as ϕ increases. Then, a new description of the link between NO, OH, and XNH3 was provided, which improves the correlation performance more than the previous studies only considering the link between NO and OH.