Dynamics of the in sac cavitating flow for diesel spray with split injection strategy

IC engines consume a large amount of fuel and produce plenty of emissions, thus reducing fuel consumption, and emissions are important. Nozzle internal flow which dominates spray breakup is the key to improve spray atomization and reduce fuel consumption. In this study, microscopic imaging technique was employed to investigate the effects of needle oscillation and injection strategy on the nozzle internal flow under cold (20°C) and hot (140°C) conditions. Needle oscillation was found to affect spray morphology, leading to obvious spray asymmetry under both cold and hot conditions with stronger spray radial propagation under hot condition. Cavitation in the sac appeared when needle oscillated due to enhanced turbulence. Besides, cavitation in the sac was introduced when the needle was insufficiently open due to throttling, especially under hot condition because of reduced viscosity. By contrast, when the split-injection strategy was employed, cavitation was considerably boosted because of the consistent flow transition and the resultant throttling effect. Effective injection duration of the first injection governed the corresponding peak relative cavitation area. The appearance of cavitation was delayed during the initial stage for each split injection after the fuel flows out due to laminar flow regime.