SPRAY CHARACTERISTICS OF A PRESSURE-SWIRL FUEL INJECTOR SUBJECTED TO A CROSSFLOW AND A COFLOW

An analysis of fuel spray was conducted using flow visualization and phase Doppler particle anemometry (PDPA) in an experimental facility housed at the Propulsion Directorate of the US Air Force Research Laboratory (AFRL). In order to model typical real-world aircraft engine conditions, this test facility was equipped with a pressure-swirl injector in combination with heated crossflow air normal to the fuel (JP-8) injection and, optionally, with coflow air parallel to the primary direction of fuel injection. Results are presented for fixed fuel rate (Reynolds number for the liquid flow of 9200 and a liquid jet Weber number of 7100) and varied crossflow velocity for four momentum flux ratios. Flow visualization and coherent structure velocimetry clearly demonstrated how the crossflow reoriented the conical spray pattern and led to large spatial variation in the measured Sauter mean diameter. At locations downstream of the injector, the PDPA data demonstrated that the vertical component of velocity was relatively low for small droplets and high for large drop sizes. This bimodal behavior may be rationalized by considering the initial propagation direction of the spray, the residence time of the fuel droplets, and the shear of the surrounding flow field. The addition of a coflow stream of air to the system led to significant reductions in Sauter mean diameter of the droplets in the region of the spray cone downstream of the fuel injector. The coflow also tended to disrupt the bimodality of the drop size distribution.