Prediction of Cavitation Erosion Intensity Using Large-Scale Diesel Nozzles

In the field of heavy-duty diesel engines, which require lifetime durability and high fuel efficiency, there is a growing demand for increased injection pressure and increased flow rate inside injection holes. This trend makes it important to prevent cavitation erosion of injector nozzles. This paper aims to clarify the relation between cavitation behavior and erosion damage experimentally by visualizing the flow inside diesel nozzles and to establish a new method for predicting cavitation erosion. To visualize internal flow, authors used the large-scale transparent nozzle whose Reynolds number and Cavitation number were matched with those of the actual real-size nozzle. Direct observation showed that the form of the cavitation changed from string-type cavitation to film-type cavitation with increasing needle lift. In addition, comparison between the locations where cavitation bubbles collapse and the locations where erosion occurs suggested that collapse of the film-type cavitation at high needle lift contributed significantly to the erosion damage. Furthermore, it is found that the location and intensity of erosion can be predicted by calculating the local quantity of film-type cavitation collapse.