Lifted flame structure of coannular jet flames in a triple port burner

Abstract

In this study, we investigated the combustion field in a triple port burner. The coannular burner consists of three concentric tubes, where air flows in both inner (central) and outer tubes, and fuel flows in the annulus between these air tubes. In order to investigate the combustion characteristics in the triple port burner, the liftoff height and concentrations of soot and NOx were experimentally examined. A numerical simulation was also conducted to discuss the flame structure in detail. Since two non-premixed flames are formed in the boundaries of fuel and air, there are four flame configurations, consisting of attached flames, inner attached/outer lifted flames, inner lifted/outer attached flames, and twin lifted flames. By increasing the external air flow velocity, unique flame behaviors are observed, including (1) inner flame re-attachment and (2) flip-flop between inner and outer flames. When the flame is lifted, the maximum soot concentration and NOx emission are decreased. Based on the flame index, the attached flame is mainly a diffusion flame. When the inner or outer flame is lifted, the so-called triple flame structure is observed. Interestingly, in the case of twin lifted flames, two rich premixed flames are merged each other.