Internal Nozzle Flow Simulations of the ECN Spray C Injector under Realistic Operating Conditions 2020-01-1154
The availability of powerful computational resources has largely increased in the recent years and has been largely exploited in the field of high-fidelity numerical simulations of internal combustion engine applications. Among them, numerical modeling of the internal- and near- nozzle injection flows has attracted interest within both academic and industrial communities. The accurate reproduction of the physics occurring at the very small scales that are typical of the injector’s internal geometry can provide undoubtedly useful insights. In particular, phenomena such as fuel cavitation and hydraulic flip can be qualitatively and quantitatively assessed in order to better understand the performance of the injector under well-defined operating conditions. In this study, three-dimensional large eddy simulations were performed to study the flow inside the ECN Spray C injector which, by means of sharp radii of curvature, is specifically designed to trigger flow separation at the sac-orifice fillet location. The influence of fuel properties and injection pressure on the flow behavior as well as the effect of minimum grid size were investigated. The multiphase simulations relied on the individual species solution method, and the homogeneous relaxation model was used to predict phase change due to cavitation. Realistic injector geometry and full needle motion obtained from x-ray measurements were employed. The results agreed well with previously published experimental data of mass flow rate and discharge coefficient. The simulations correctly captured the flow separation and gas layer thickness inside the orifice that were witnessed in the experiments. It was found that flow separation at the orifice inlet was key to trigger hydraulic flip and ingestion of ambient gas into the orifice. The penetration of the ambient gas inside the orifice was closely related to the momentum of the liquid specie and correlated with injection pressure and fuel density. Fluctuations in the volume fraction of each species were observed at the start and the end of injection, implying a possible correlation with the needle motion. Finally, it was found that finer mesh resolution near the wall was key to achieve a more accurate solution of the gas layer which in turn affected the extent of the hydraulic flip.
Hengjie Guo, Roberto Torelli, Abian Bautista Rodriguez, Aniket Tekawade, Brandon Sforzo, Christopher Powell, Sibendu Som