CHARACTERISTIC MODES AND THERMAL STRUCTURE OF NONPREMIXED CIRCULAR-DISC STABILIZED FLAMES

The characteristic modes and structure of the nonpremixed circular-disc stabilized flames are experimentally studied. Using direct and schlieren photography techniques, the flames in the stability domain are systematically classified into seven characteristic modes: recirculated, transition, unsteady detached, laminar ring, developing, split flashing, and lifted. The flame behavior and the combusting and cold flow patterns in each characteristic mode are comprehensively discussed. Two stability limits which are closely related to the flow structure are found. The flame and lift-off heights are correlated to the central-to-annular jet momentum ratio. The structure and transport mechanism in the recirculation bubble dominate the flame behavior for central-to-annular jet momentum ratio lower than 7.5. For the central-to annular jet monentum ratio higher than 7.5, the combusting flow behaves like a turbulent diffusion flame. The temperature profiles are probed by a fine-wire thermocouple. The thermal structure in the recirculation area is found to be complicatedly dominated by the vortex structure in the bubble.