Spray Characteristics of an Impinged Diesel Fuel Spray

A study was conducted to investigate the spray characteristics of diesel fuel impinged on a raised target (pedestal). Two separate fuel injection systems were used with two different spray chambers. Both systems used commercial diesel fuel injectors with single hole nozzles. In the first system, the fuel impinged against the center of a raised surface (pedestal) in an atmospheric pressure spray chamber. A laser light sheet oriented along the spray axis was used to illuminate a plane of the spray. A 35 mm camera set at 90° to the light sheet captured the injection events at various times after the start of injection. The spray behavior was examined for a range of pedestal heights and diameters. The second injection system, using the same imaging scheme and a fixed pedestal size, was used in a high pressure chamber to examine the effect of ambient pressures up to 5.9 MPa and ambient densities up to 19.7 kg/m³. From the images, spray shape and penetration were determined for each of the test cases. The results presented in this paper show the effect of impingement on a liquid fuel spray. After impingement, the spray forms two distinct regions. In the first region, a large vortex forms at the edge of the pedestal and grows as injection proceeds. This vortex seems to consist of smaller, lower velocity drops that have been entrained from the main spray region. The second region consists of what appears to be higher velocity, larger diameter drops that are not affected by the vortex and spread out radially from the top of the pedestal. Although the penetration of these higher momentum drops does not seem to be affected by the pedestal geometry, the location of the smaller vortex is a function of the pedestal diameter. Under higher ambient densities, the larger diameter droplets are not visible.