The gasoline direct injection (GDI) passenger car engine market is undergoing rapid and significant growth after the “diesel gate” event in September 2015. This growth trend will continue in coming years since light-duty diesel urban vehicles will be progressively replaced by gasoline-powered cars. GDI engine exhaust emissions strongly rely on the fuel injector design and the spray performance. A major challenge in development is to avoid injector tip coking, which often causes high PN/PM emission and impacts engine performance stability over its lifetime. This problem is linked to the highly complex multiphase flow phenomenon occurring at injector closing. Until now, there has been no effective measurement technique available for the characterization of vortex structure, dynamics and interaction with cavitation inside the injection nozzle and their direct impact on spray formation. State-of-the-art diagnostic techniques only have very limited access to the flow and spray phenomenon during the injector opening and closing process, and have trouble in resolving the details of the flow around the injector nozzle tip, in the spray hole and in the counter bores of the nozzle.
Combining the volume of fluid (VOF) method for interface tracking with high-resolution, large-eddy-simulation (LES) in a VOF LES approach can resolve turbulence scales, their interaction with cavitation and the near-nozzle spray structure. Therefore, the simulation results can provide a locally refined diagnostic for the nozzle flow and spray formation process. This knowledge is required for nozzle design tailoring and spray control. In combination with moving mesh simulation, the VOF LES approach can provide a corresponding diagnostic for dynamic needle operation conditions at the start and end of the injection process. Many phenomena, including the sac-filling and sac-evacuation process, near-nozzle gas entrainment and fuel suction phenomenon after needle closure, can be investigated. All these processes have a key impact on engine emission and emission stability over an engine’s lifetime.
The moving-mesh VOF LES simulation approach provides a better alternative to the available advanced measurement techniques for the diagnostic of GDI nozzle flow, cavitation and spray dynamics for an entire injection event. This tool has been applied to support nozzle development, innovation and customer projects. The high-resolution LES technique is able to provide physical understanding and identify effective evaluation criteria for the product design. After this step, a design of experiments and optimization software package in combination with CAE tool integration and simulation workflow automation can be applied to speed up the product development process.