Flame Front Stratification During Quasi-Flame Flashback

During the study of premixed NH₃/CH₄ fuel mixtures, flame separation into two reaction zones was observed upon flashback into a Bunsen burner. Stable combustion regimes were obtained, with a gap between the burner rim and the upper luminous region, the size of which depended on the mixture composition and the position of the combustion zone inside the burner. The influence of the equivalence ratio and the ammonia mole fraction on the separation effect was examined. At the burner exit, temperature and gas composition profiles were measured. Flame emission was recorded at the chemiluminescence bands of OH* (308 nm) and CH* (431 nm), and emission spectra were acquired both inside and outside the burner. Spectral analysis revealed a band corresponding to NO₂ emission in the upper part of the luminous region. It is most likely that nitrogen dioxide is formed through low temperature reactions occurring when the combustion products mix with atmospheric air.