Effect of swirl on lean flame limits of pilot-stabilized open premixed turbulent flames

Abstract

Increased combustion activity and the undesirable effects on our ecosystem resulting from the primary and secondary combustion emissions are major concerns with regard to maintaining a clean and green environment. This has driven combustion engineers to employ combustion methods or postcombustion techniques for achieving acceptable emission levels in burner systems. Among the methods developed, lean premixed combustion has gained importance as an effective measure for reducing combustion emissions. However, lean premixed burner flames are severely affected by reduced flame stability. It is known that burner stability can be improved by using swirling flow [1,2]. In recent years, a novel concept of lowswirl burners [3] has gained momentum as an effective combustion emission control strategy and for operating stable lean premixed flames and increased combustion efficiency. Chan [3] et al. developed a low-swirl burner operating with lean premixed flames stabilized at a certain distance above the burner exit, defying the long-held notion that lifted flames are inherently unstable. Several studies [3–6] have reported stability limits of lean premixed flames in different burner configurations. A study on unsteady flame dynamics [4] relating to a lean-premixed swirl-stabilized combustor revealed that the operating parameters, viz. inlet temperature and equivalence ratio, are the two major factors that