Macrostructure and ultraviolet chemiluminescence of NH₃/H₂/Air swirling micromix flames

This study investigates the macrostructure and ultraviolet chemiluminescence of NH₃/H₂/Air flames using a novel single-nozzle micromix swirl burner at relatively wide ranges of hydrogen mixing ratio (30 %≤X_H2≤70 %) and equivalence ratio (0.4≤φ≤1.3). The transition of flame macrostructure and its relationship with the ultraviolet spectrum is revealed in detail. The flame macrostructure transition was observed as the equivalence ratio increased at different hydrogen mixing ratio studied in this work. The chemiluminescence intensity and intensity ratios of selected emission peaks within the wavelength range of 200∼400 nm showed that the Overlap part (275–302 nm) is important for indicating the characteristics of NH₃/H₂/Air micromix flames. The normalized peak height at wavelength of 296 nm in the Overlap part is quite sensitive to the NH₃/H₂ mixing fraction and insensitive to the equivalence ratio, making it a useful indicator for predicting the hydrogen ratio in the NH₃/H₂ mixed fuels. The NO*/Overlap and NH*/Overlap ratios can be used to predict the equivalence ratio of NH₃/H₂/Air micromix flames when the hydrogen ratio is known. Additionally, turning points were found along the chemiluminescence intensity ratio curves (as a function of equivalence ratio), which could well match the critical equivalence ratio for the macrostructure transition from “V” to “M” at different hydrogen ratios.