Methodology and Tools to Predict GDI Injector Tip Wetting as Predecessor of Tip Sooting 2018-01-0286
With upcoming emission regulations particle emissions for GDI engines are challenging engine and injector developers. Despite the introduction of GPFs, engine-out emission should be optimized to avoid extra cost and exhaust backpressure. Engine tests with a state of the art Miller GDI engine showed up to 200% increased particle emissions over the test duration due to injector deposit related diffusion flames. No spray altering deposits have been found inside the injector nozzle.
To optimize this tip sooting behavior a tool chain is presented which involves injector multiphase simulations, a spray simulation coupled with a wallfilm model and testing. First the flow inside the injector is analyzed based on a 3D-XRay model. The next step is a Lagrangian spray simulation coupled with a wallfilm module which is used to simulate the fuel impingement on the injector tip and counter-bores. Lower injection pressures and a rounded edge at the nozzle inlet due to hydro-erosive grinding are increasing the wallfilm on the injector. The simulations are verified with measurements including high speed microscopic video analyzes of the injector tip during injection. The simulated wallfilm on the injector tip matches well with the measurement results.
As a last step, the tested engine is simulated in one operating point including the injector nozzle geometry for a full 720° CrA cycle. Variations of charge motion, injector and fuel temperatures are investigated to reduce the tip wetting and improve fuel evaporation. An increased fuel temperature and high tip temperatures show a promising reduction of the injector tip wallfilm. Further simulations performed with multi-component fuels allow a prediction of tip wetting for region based different gasoline distillation curves.