Spray characteristics of spill-return atomizers

Abstract

The spray characteristics of three spill-return atomizers are studied by inserting each nozzle into a cylindrical vessel which is pressurized to the desired level using gaseous nitrogen supplied from a large liquid nitrogen storage/evaporation system. The nozzle under test is located centrally at the top of the cylinder and sprays downward into the vessel. Two diametrically opposite windows are fitted to the cylinder which allow mean drop sizes in the spray to be measured using a light-scattering technique. The apparatus is used to study the effects of spill fuel fraction, fuel-injection pressure, ambient gas pressure, and nozzle flow number on mean drop size. The results show that the influence of spill fuel fraction on spray quality is small. They also indicate that spray quality may improve or decline with increases in ambient gas pressure depending on the initial spray angle. If this is larger than around 75 deg, spray quality improves with increases in gas pressure. For initial spray angles smaller than around 65 deg spray quality declines with increase in gas pressure. The extent to which a change in fuel injection pressure affects mean drop size is also found to depend on initial spray angle. An explanation for these phenomena is provided. Measurements to determine the influence of nozzle flow number (FN) on mean drop size (SMD) show that SMD oc FN 025.