Importance of Geometrical Factors on Spray Characteristics of Spill-Return Atomizers

Abstract

An experimental investigation into small pressure-swirl spill-return atomizers was made to determine the effect of the entry port number, swirl-chamber shape, spill-line design, and the manufacturing precision on the spray quality and stability. The atomizers were studied using phase-Doppler anemometry, high-speed visualization, and mechanical patternation. Jet A-1 fuel was sprayed at inlet pressures of 0.5, 1.0, and 1.5 MPa and for spill-to-feed ratios of 0, 0.4, and 0.8. The chamber shape influenced the spray characteristics of the simplex atomizers only moderately with no systematic effect of conical chambers to the others. The spray was found to be circumferentially heterogeneous; its uniformity improved with increase in the pressure, while the effect of swirling port number was negligible. Atomizers with axial spill orifice demonstrated strong spray pulsations at a spill-to-feed ratio of zero. A periodic decay of the air core was identified as a possible reason for the pulsations. Atomizers with off-axis spill orifices always produced a stable spray. Atomizers with tangential inlet ports provided a finer spray than those with helical ports. Manufacturing precision, axial symmetry, and matching of the surfaces of connected parts were found important for the spray symmetry and homogeneity.