Link Between Cavitation Development and Erosion Damage in Diesel Injector Nozzles

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. Averaging of the simulated flow field over the injection duration has allowed estimation of nozzle wall surface flow parameters indicative of erosion. These parameters have included the bubble collapse acoustic pressure and its standard deviation. Comparison of the relative magnitude of these parameters for different nozzle designs has led to the conclusion that the range of values predicted are orders of magnitude greater for the nozzles that exhibit cavitation damage relative to those found to be erosion-free. Empirical validation of the method is achieved through manufacturing of nozzles which have computationally indicated less probability for cavitation erosion, and which after sufficient running time have been found to be free of cavitation erosion.