Drop-size distribution characteristics of spill-return atomizers

Abstract

The spray characteristics of three spill-return atomizers are examined in a pressure vessel using a standard light-scattering technique. Attention is focused on the effects of fuel-injection pressure, ambient air pressure, atomizer flow number, and the spilled fuel-flow fraction on the drop si/e distribution of the spray. The results indicate a strong dependence of atomization quality on fuel-injection pressure, while the influence of spill fuel fraction on drop-size distribution is small. They also indicate that, for nozzles having a low initial spray angle, atomization quality declines with increases in ambient gas pressure due to the contraction in the spray angle that accompanies an increase in gas pressure. A smaller range of drop sizes is obtained with nozzles of lower flow numbers. The variation of drop velocity with axial distance from the nozzle is investigated for each drop-size group, taking into account the aerodynamic drag, momentum forces, and change in spray cone angle. Its effects on drop-size distribution are examined. An alternative expression for drop-size distribution is presented and its relative merits are discussed.