COMPUTATIONAL ANALYSIS OF FLOW PATTERNS IN ELLIPTICAL DIESEL NOZZLES AT HIGH INJECTION PRESSURES

The use of an elliptical diesel nozzle has been considered as a potential method for improving the airfuel mixing quality as well as diesel engine performance. The present paper focuses on the internal flow patterns for circular and elliptical orifices with the same cross-sectional area under real diesel engine operating conditions. The Schnerr and Sauer cavitation model and large eddy simulation method were adopted and validated by comparing with experimental results. The results show that the cavitation inside the circular orifice was axisymmetric, while the cavitation inside the elliptical orifice was nonaxisymmetric. Moreover, the circular orifice had a larger vapor volume fraction than that of the elliptical orifices, which indicated that the use of an elliptical orifice could inhibit the generation of cavitation inside the orifice. Also, the number of turbulent vortex structures of the circular orifice was more than that of the elliptical orifices. The turbulent vorticity at the outlet of the elliptical nozzle with an aspect ratio of 1:8 was the largest, and the circular orifice held the smallest turbulent vorticity. Meanwhile, the mass flow rate and discharge coefficient of the elliptical orifice was always higher than that of the circular orifice. The elliptical orifice, with an aspect ratio of 1:4, has the largest discharge coefficient and mass flow rate under the condition of cavitation. Another important point is that the cavitation inception occurred inside the elliptical orifice at a lower cavitation number as compared to the circular orifice. In addition, when the cavitation incepted inside the orifice, the velocity coefficient increases with the decrease of cavitation number, and the velocity coefficient of the circular orifice was always larger than that of the elliptical orifice. The elliptical orifice with an aspect ratio of 1:4 has the maximum area coefficient among three geometrical orifices.