Drop-size distribution characteristics of spill-return atomizers

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-size 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 increase in ambient gas pressure due to the contraction in spray angle that accompanies an increase in gas pressure. A smaller range of drop sizes is obtained with nozzles of lower flow number. 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.