Flame radiation fraction behaviors of sooty buoyant turbulent jet diffusion flames in reduced- and normal atmospheric pressures and a global correlation with Reynolds number

Abstract

This paper reports new experimental observations on flame radiation fraction of sooty turbulent buoyant jet diffusion flames in a reduced atmospheric pressure (at high altitude in Tibet) and corresponding scaling theoretical interpretations. A global correlation of the flame radiation fraction with Reynolds number is proposed for both the reduced- and normal pressures. Experiments are carried out in both Hefei (altitude: 50m) with atmospheric pressure of 100kPa and Lhasa (altitude: 3650m) with atmospheric pressure of 64kPa. The turbulent buoyant jet diffusion flames are produced by nozzles with diameters of 4, 5, 6, 8 and 10mm using propane as fuel at different flow rates. The emitted thermal radiation fluxes by the flames, for both attached condition and lifted off condition, are measured by a water-cooled radiometer. The flame radiation fraction change due to pressure reduction is clarified. Results show that the flame radiation fraction changes little with atmospheric pressure. A dimensional scaling theory is proposed to interpret this pressure dependency behavior. The flame radiation fraction for attached flame is found to be higher than that for lifted-off flame, decreasing in both cases with increasing nozzle fuel velocity or turbulent mixing at the flame base. Such decreasing behavior is found to be well fitted globally by a negative power law function on source Reynolds number (χR∼Re−0.32) of the discharged fuel flow at the nozzle.