STRUCTURE OF AIRBLAST SPRAYS UNDER HIGH AMBIENT-PRESSURE CONDITIONS

A single-velocity-component phase Doppler particle analyzer is used to survey and measure local variations in drop-size distributions and dr op velocities in the near-nozzle region of a practical, contraswirling , prefilming airblast atomizer. The technique of laser sheet imaging i s used to obtain global patterns of the spray. All measurements are ta ken with a constant pressure drop across the atomizer of 5 percent, at ambient air pressures of 1, 6, and 12 bar. The liquid employed is avi ation kerosine at flow rates up to 75 g/s. The results show that incre asing the air pressure from 1 to 12 bar at a constant air/fuel ratio c auses the initial spray cone angle to widen from 70 to 105 deg. Farthe r downstream the spray volume remains largely unaffected by variations in atomizer operating conditions. However, the radial distribution of fuel within the spray volume is such that increases in fuel flow rate cause a larger proportion of fuel to be contained in the outer region s of the spray. The effect of ambient pressure on the overall Sauter m ean diameter is small. This is attributed to the fact that the rapid d isintegration of the fuel sheet produced by the contraswirling air str eams ensures that the atomization process is dominated by the ''prompt '' mechanism. For this mode of liquid breakup, theory predicts that me an drop sizes are independent of air pressure.