A Simulation Methodology to Lower GDI Soot Emissions by Reducing Nozzle Tip Wetting

The Particulate Number (PN) is the most complex emission component of Gasoline Engines both in view of measurement tools, conditioning, repeatability tolerance sensitivity, validation, stability and diagnostics as well as simulation development methodology. A comprehensive simulation methodology and consistent simulation tool chain are key prerequisite to significant contribution to develop cost and CO2 efficient low PN solutions. Mastering deposit formation and long-term stability of mixture formation as well as handling real driving emissions (RDE) requirements are key for low real world Particulate Numbers. Gasoline particle filter (GPF) reduces risks in PN log term stability and RDE, however shows negative CO2 impact especially in RDE thus reduction of PN-Engine out still is a key target. In the present paper the simulation and measurement of GDI tip wetting as a predecessor of tip sooting is employed. The simulation chain (within AVL FIRE) used consist of transient injector multiphase simulations, a fuel spray simulation considering fuel atomization and wall film formation as well as testing. Moreover, synchrotron X-Ray micro-tomography was used to identify the real nozzle configuration as a simulation input to ensure consistent nozzle geometry for both measurement and simulation. One injector type with step hole geometry was observed (BOSCH HDEV5). Variation of conditions which accelerate fuel evaporation from wall film formed on the nozzle tip surface were carried out. The simulations were verified with measurements including high speed microscopic video analysis of the injector tip during injection.