Influence of air and fuel flows on gas turbine sprays at high pressures

Abstract

A single-component phase-Doppler particle analyzer (PDPA) is used to measure local variations in dropsize distributions and drop velocities in the near-nozzle region of a practical, contraswirling, prefilming airblast atomizer. The technique of laser sheet imaging is used to obtain global patterns of the spray. Measurements are taken using air pressure drops across the atomizer of 5% and 10% and ambient air pressures of 1,6 and 12 bar. The liquid employed is aviation kerosine at flow rates of up to 75 g/s. The results show that the previously observed effect of an increase in ambient air pressure in widening the spray cone angle is not a pressure effect per se but is due to the increase in fuel flow rate that accompanies an increase in air pressure at constant air-fuel ratio (AFR). For any given air pressure, it is found that spray cone angle increases gradually and continously with increase in fuel flow rate. If the fuel flow rate is allowed to remain constant, the effect of an increase in air pressure is to reduce slightly the spray cone angle. In general, spray volume increases with fuel flow rate and/or reductions in air pressure. Variations in air pressure at a constant AFR, which corresponds to the normal practical situation, have little effect on either spray volume or the distribution of drop sizes in the spray.