A VISUAL STUDY OF THE STRUCTURE OF TURBULENT NONPREMIXED FLAMES NEAR JET EXIT

Abstract

An experimental study is made of the structure of turbulent nonpremixed flames in the vicinity of the exit of hydrocarbon jets. The jets are issued upward from a circular tube which is located inside a coflowing low-velocity air stream. Schlieren-direct and TiO2 scattering-direct synchronized photography is used to visualize the flame zone and various boundaries. A stable flame zone is seen to exist at the exterior of the boundary of fuel jet. The location of the flame zone is found to be influenced by the diffusion velocity of fuel in addition to the stoichiometric volume ratio and entrainment of reactants. The presence of a stable laminar flame region near the burner tip is experimentally confirmed. However, in the core region near the tip, the flow is turbulent from the entrance and eddies grow to large sizes in the downstream direction. A schematic characterization is proposed which illustrates the basic structure of the turbulent nonpremixed flame in the near field.