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Diesel injector nozzles with different geometries have been investigated, firstly to study the effect of cavitation on the flow at the exit of the nozzle, and secondly to see its effect on the spray and the consequent flame formation. The flow at the exit of the nozzle was characterized by measuring both the injection rate and the momentum flux for a wide range of typical engine's rail and cylinder pressures. The injection rate is directly affected by cavitation and it will become choked when this phenomenon appears. The measurement of the momentum flux can be combined with the injection rate to derive the velocity at the nozzle exit. The momentum flux does not seem to be influenced by the appearance of cavitation. Apart from this hydraulic characterization, the different nozzles have also been mounted on an engine with optical access to the combustion chamber. During these tests, the spray, its vaporization and combustion were visualized and recorded with a high resolution camera.