Computational Evaluation of Nozzle Flow and Cavitation Characteristics in a Diesel Injector

The capabilities of various numerical models to accurately account for the onset and development of cavitation in diesel injector nozzles is assessed and evaluated. The numerical predictions of the models are computed, and are compared to measured experimental data and observations. The numerical predictions for actual diesel nozzle geometry have been validated with experimental measurements of the total vapor mass flow rate. This vapor flow is found to be developed along the nozzle length due to the nucleation of the cavitation bubbles inside the diesel injector. The cavitation inception criteria that is used for the quantitative cavitation calculations included vapor quality, voidage, cavitation kinetic energy and cavitation energy. The results indicate that the cavitation simulation model predicts a diffused and gradual vapor distribution inside the nozzle in agreement with the experimental data. The cavitation inception criteria used in current numerical modeling has matured to the level where it can usefully identify many of the characteristics of cavitation, and can significantly contribute to the optimization of cavitation production inside diesel injector. The calculations performed indicate that for the same model assumptions, such as the numerical implementation, discretization scheme and turbulence model, the predictions of the different cavitation sub-models are phenomenologically different. The calculations indicate that the Zwart-Gerber-Belamri model predicts a large void zone inside the injector delivery orifice and fail to capture the transition from incipient to fully developed cavitation, while the Singhal et al. model predicts a more diffused and gradual vapor distribution in agreement with the experimental model data. From the raw results, the values of the relevant parameters were computed, and the occurrence of cavitation was clearly identified. The results evidenced interesting differences in the permeability of the characteristics and strength of cavitation in nozzle under real diesel engine conditions.