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Cavitation formation and development inside Diesel injector nozzles suffering from erosion damage has been investigated using enlarged transparent nozzle replicas and computational fluid dynamics (CFD) simulations. Cavitation erosion has been observed at different locations within the nozzle. These have included the top surface inside the nozzle hole next to its entry, the 3o'clock and 9c'clock hole side-inlets as well as at the needle seat area. Instantaneous and time-averaged high-speed CCD images of cavitation have verified that cavitation erosion sites are found in areas of cavitation bubble collapse. This has been further supported by CFD predictions obtained using the measured injection pressure and needle lift traces, both for the pilot and main injection events. The cavitating flow regimes associated with these erosion sites correspond to geometrically-induced hole cavitation, the string cavitation and the needle seat cavitation, respectively.

Vortex flow realized inside the sac volume and the injection holes of automotive and heavy duty injectors plays an important role in the formation and development of cavitation and the near-nozzle structure of the emerging fuel sprays. Large-scale vortical flow structures are mainly induced by the geometric details of the injector. Vortex flow may be also induced by eccentric needle opening as well as the manufacturing tolerances of locations critical to the nozzle geometry such as the hole entry shape. The present paper assesses the predictive capability of a Large Eddy Simulation model against LDV measurements of the flow velocity obtained inside a transparent nozzle replica. Model predictions are compared also with RANS model predictions obtained using the standard k-ε model.