On the Stability of a Turbulent Non-Premixed Methane Flame

This paper presents an experimental qualitative assessment of the stability of a turbulent, non-premixed methane flame. The burner consists of a central fuel nozzle surrounded by an annulus of co-airflow with varying swirl strength. Two distinct nozzle geometries having similar exit cross-sectional areas but different internal/orifice geometry-a rectangular and a contracted circular nozzle-were tested. They are referred to in this paper as RN and CCN, respectively. The main focus of the present study was on determining the flame liftoff and blowout velocities as well as the liftoff height and flame length, all of which can be used as indicators of the stability of non-premixed methane flame. The experimental data revealed that the blowout velocity of the RN nozzle's flame is remarkably higher than that of the CCN nozzle, and the liftoff velocity of the CCN is only slightly higher than that of the RN nozzle for identical swirl strength. In addition, the flame length of the RN nozzle is overall shorter than that of the CCN nozzle for identical test conditions, and the liftoff height of the CCN flame is higher than that of the RN flame. LDV velocity measurements were performed to determine the reacting flow overall dynamic along the centerline plane for typical jet and co-flow exit velocities. These results aimed at helping to explain the difference in flame stability between the two different nozzles' geometries in conjunction with the co-flow swirl strength.