Structure of opposed jet premixed flame and transition of turbulent premixed flame structure

Abstract

A distributed reaction zone was achieved successfully in the laboratory by an opposed jet burner. This burner consists of two opposed mixture supply tubes with water-cooled disks. An annular turbulent premixed flame is produced around the impinging mixture jets. In the present paper, the structure of the opposed jet flame was characterized and, by comparing with the tube burner flame, the transition mechanism from wrinkled laminar flame to distributed reaction zone was discussed. On the unburned gas side of the opposed jet burner flame, the essential feature of the temperature pdf is bi-modal with relatively high probability of intermediate temperature. In this region, a thick wrinkled (not laminar) flame structure is found in which small dissipative eddies are embedded. In the middle and the burned gas regions, the probability of unburned mixture disappears and that of intermediate temperature increases, which suggests that the flame zone consists of the small eddies of completely burned and partially reacted gases. By velocity measurements with an LDV and a hot wire anemometer, it was found that, for low turbulence Reynolds numbers, a fully developed wrinkled laminar flame is produced by increasing the Damkohler number. Also it was found that, for nearly constant Damkohler numbers, the fully developed wrinkled laminar flame structure changes to the distributed reaction zone with increasing the turbulence Reynolds number.