The stabilization mechanism of highly stabilized partially premixed flames in a concentric flow conical nozzle burner

Many practical combustion systems are based on the mode of partially premixed flames where the interaction between lean and rich pockets improves the flame stability. In our recent work a highly stabilized concentric flow conical nozzle burner has been designed and developed for partially premixed flames. Flow field, temperature and OH radical measurements were conducted outside the cone. The early region of the flame within the cone affects the stability of the flame. So, the aim of the present work is to study the stabilization mechanism inside the cone based on two dimensional measurements of the flow field and temperature field. Five turbulent partially premixed flames have been investigated at Reynolds numbers range between 8.3 × 103 and 14.5 × 103 and equivalence ratio ranges between 2.5 and 4. The turbulent flow field inside and outside the conical quartz nozzle were obtained using a three-dimensional PIV system. The flow filed at the near region inside the cone shows a recirculation zone suggesting air entrainment along the cone wall. This stream of air is likely to be heated by the flame and thus improves the flame stability. Thus, the stabilization mechanism of the conical nozzle burner is mainly affected by the flow pattern inside the cone. This flow field structure improves the stability significantly as compared to similar partially premixed flames without cone. The mean temperature field indicated two distinctive regions at early axial distances, the first of a lower central flame temperature and a second region of a higher flame temperature, which located at a shifted radial distances. These two regions are associated with four distinctive regions of temperature fluctuations. The jet equivalence ratio has a limited effect on flow fields and has relatively milder effect on the temperature field.

► Study the stabilization mechanism of highly stabilized partially premixed flames.
► The temperature field is measured for different highly stabilized flames.
► The conical nozzle improves the stability as compared to normal nozzle burner.
► Recirculation, entrainment of heated air and expanding flow enhance the stability.