Structures of inverse jet flames stabilized on a coaxial burner

Abstract

In this study we investigate different parameters used for mapping global flame structures and identify the most universal in terms of comparing flames emerging from different geometrical burner arrangements. Simultaneously the study was carried out to determine the discharge conditions yielding the blue flame of a high degree of partial premixing, and to examine the instantaneous local flame structures and mixing in the blue torch area under these conditions. In order to decouple velocity ratio and global equivalence ratio (referring to the mass flow rate of air and methane), as well as the jet velocity and Reynolds number, two different centre air nozzle diameters were studied. The results clearly indicated that the centre jet Reynolds number and global equivalence ratio are more universal parameters for inverse flame characterization than jet velocity and velocity ratio. OH-PLIF (planar laser-induced fluorescence), hot- and cold-flow acetone-PLIF were performed to provide additional information on instantaneous local flame structures and mixing in the blue torch area of the flame resembling a partially premixed flame. The PLIF results indicated that in the area of the blue torch, air and gas are well mixed by shear layer-generated vortices, and turbulences, which at this position are strongly present.