MASS FLUX, MASS FRACTION AND CONCENTRATION OF LIQUID FUEL IN A SWIRL-STABILIZED FLAME

Mass flux, mass fraction and concentration of kerosene droplets have b een measured by a phase-Doppler instrument in a swirl-stabilized burne r during inert and reacting flow. In the reacting flow, the flame was supported by natural gas added through the fuel stalk, while the keros ene was added to and atomized by the combusting air. The bulk mean vel ocity of the combustion air was 30.4 m/s, corresponding to a Reynolds number of 30,000, and the swirl numbers were 0.48 and 0.29, respective ly, upstream and downstream of the kerosene injection. The equivalence ratios were 0.45 and 2.11 for the natural gas and the kerosene, respe ctively. The results show that the minimum swirl necessary for flame s tability caused fuel to centrifuge from the region of combustion, so t hat only 8 kW of energy could be released out of the available 37.4 kW of the kerosene fuel. An important conclusion is that an optimum swir l number will exist with every atomization and burner arrangement of a liquid-fuelled flame and will be different from that associated with the corresponding gas-fuelled flame. The measurement techniques approp riate to regions where the flow instantaneously reverses are described and the existence of large droplets, which moved towards the injector inside the recirculation zone and supplied fuel to the base of the fl ame, are explained in terms of a ''fountain effect'' based on the mean drag between the gas phase and the droplets. Sources of uncertainties of the mass flux and concentration measurements with the phase Dopple r instrument are considered in detail.