Exploration of Cavitation-Suppressing Orifice Designs for a Heavy-Duty Diesel Injector Operating with Straight-Run Gasoline

The occurrence of cavitation inside injectors is generally undesirable since it can cause material erosion and result in deviations from the expected injector performance. Previous numerical work employing an injector geometry measured with x-ray diagnostics and operating with a high-volatility straight-run gasoline (SRG) has shown that: (1) most of the cavitation is generally observed at low needle lifts, (2) needle motion is responsible for asymmetric structures in the internal flow as well as large pressure and velocity gradients that trigger phase transition at the orifice inlets, and (3) cavitation affects the injector discharge coefficient and distribution of injected fuel. To explore the potential for material damage within the injector orifices due to cavitation cloud collapse, the cavitation-induced erosion risk assessment (CIERA) tool has been applied for the first time to the realistic geometry of a heavy-duty injector using the CONVERGE software. Predictions from a large eddy simulation indicated critical locations with high erosive potential in specific injector orifices. These locations matched qualitatively well with x-ray scans of an eroded injector sample that underwent a durability test with SRG. This motivated a computational fluid dynamics exploration of a series of orifice design modifications, using a nominal reconstruction of the realistic geometry and an automated procedure for fast generation of modified surface files. The influence of orifice K-factor, inlet edge radius of curvature, and inlet ellipticity on the intensity and duration of cavitation structures was investigated using an unsteady Reynolds-averaged Navier-Stokes formulation. Quantitative and qualitative analyses highlighted the relative importance of each parameter in limiting or suppressing cavitation inside the injector orifices and provided useful insights and design guidelines for injectors operating with high-volatility fuels.