Numerical Prediction of Erosive Cavitating Flows in Injection Equipment

The paper demonstrates the capability of the commercial Computational Fluid Dynamics (CFD) code AVL FIRE to predict erosive effects due to cavitation. Such flows are of interest within the automotive and other internal combustion (IC) related industries using fuel injection components. Ability to predict such internal flows through CFD allows for improved engine efficiency, decreased emissions and shorter development cycles. Accurate modeling of cavitating flows is a prerequisite for the prediction of erosion effects and is described here. Driving force for erosive damage are the implosions of the bubbles generated due to cavitation and thereafter collapsing on the surface of the exposed material. Therefore, prediction of vapor generation and accurate transport of the bubbles are crucial. Investigated injector featured a single injector body in combination with two different needle (i.e. plunger) designs. The shape of the needle governed the nature of the flow through the injector. The fluid flow through the two different setups investigated in this study portrayed strong variance in flow aggressiveness leading to substantially differing erosion probability. First needle design showed practically no erosion damage on the needle surface, whereas the other showed strong damage. As a direct consequence, the durability of the first needle was proven superior to the latter. Presented numerical results are consistent with the experimental evidence for both, needle surface and injector body surface. Good agreement proves the applicability of the utilized numerical tool in the early design stage of injection components to distinguish between “safe” and “un-safe” component designs in terms of erosion probability. Consequently durability, efficiency and the emissions of considered engine configurations can be controlled.