Experimental study on the effect of cone-shaped bluff body on lean premixed flames in a swirl burner

An experimental study was conducted to investigate the effect of conical bluff bodies on the flame dynamics and emissions from a natural gas/air swirl burner. Three bluff bodies (a disc, a 130° cone, and an 80° cone) were positioned above burner’s outlet to influence the flame dynamics and optimize emissions. The swirl burner performance in lean premixed combustion condition was evaluated at a constant swirl number of 0.87 at 0.65–0.90 equivalence ratios. The flame height and width were increased in the experiments with conical bluff bodies compared to the disc shape. Also, 130° and 80° bluff bodies enhanced the chemiluminescence of all species, as well as the uniformity of the thermal field by distributing the reaction zone. In particular, the bluff bodies impacted the flame dynamics and resulted in decreased NOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NO}}_\text{x}$$\end{document} formation by a minimum of 12.79% and 19.13% and increased CO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{CO}}$$\end{document} emissions by 22.71% and 14.18% for 130° and 80° cone bluff bodies, respectively. The equivalence ratios of blow-off and lift-off reduced and increased with conical bluff bodies compared to the disc shape, respectively. The results suggest that the conical shapes diminish the central recirculation zone (CRZ) that is responsible for a concentrated reaction zone above the burner outlet. A weaker CRZ reduces the temperature of the burner bluff body and resolves the concentrated reaction zone to reduce NOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NO}}_\text{x}$$\end{document} formation. The cone angle of the bluff body can be utilized as an optimization tool to adjust emissions and increase operational lifetime of swirl burners in industrial combustion systems.