A suite of X-Ray diagnostics has been used to characterize the geometry and internal flow of the Engine Combustion Network's "Spray C" diesel injector. X-Ray tomography has been used to determine the geometry of the internal flow passages of this single-hole injector with a spatial resolution better than 2 micrometers. X-ray phase contrast imaging has captured the three dimensional shape of the cavitation layer that is generated by the sharp inlet and cylindrical shape of this steel nozzle. Finally, time-resolved X-ray tomography has been used to measure the density distribution of the fuel as it first emerges from the nozzle, and its breakup as it moves downstream.

Measurements of the nozzle geometry reveal that the radius of curvature of the inlet corner varies significantly around the azimuthal rotation angle, with a change in radius of as much as 40%. The variation in radius of curvature strongly influences the shape of the cavitation layer that is generated just downstream. The measurements reveal that the cavitation layer inside this nozzle has a highly asymmetric shape, and that the length and thickness of the cavitation sheet are directly tied to the inlet corner radius. At some azimuthal locations, the cavitation layer extends the full length of the nozzle to the outlet, likely causing hydraulic flip and stabilization of the flow separation.

Time-resolved X-ray tomography reveals the impact that the cavitation inside this nozzle has on the fuel distribution. The fuel distribution is highly asymmetric, with a region of very low fuel density that exactly matches the location of greatest cavitation. Together, these measurements form a unique, comprehensive study of cavitation in a cylindrical steel nozzle, from its onset to its manifestation in the external spray.