Analysis of the Spray Numerical Injection Modeling for Gasoline Applications

The modeling of fuel jet atomization is key in the characterization of Internal Combustion (IC) engines, and 3D Computational Fluid Dynamics (CFD) is a recognized tool to provide insights for design and control purposes. Multi-hole injectors with counter-bored nozzle are the standard for Gasoline Direct Injection (GDI) applications and the Spray-G injector from the Engine Combustion Network (ECN) is considered the reference for numerical studies, thanks to the availability of extensive experimental data. In this work, the behavior of the Spray-G injector is simulated in a constant volume chamber, ranging from sub-cooled (nominal G) to flashing conditions (G2), validating the models on Diffused Back Illumination and Phase Doppler Anemometry data collected in vaporizing inert conditions. The Discrete Droplet Modeling of the spray, in which stochastic parcels representing the fuel droplets are tracked with a Lagrangian approach and coupled with the gas phase, is used within the commercial CFD code CONVERGE. Three spray parcels initialization paradigms are compared to define a robust numerical framework for GDI applications. The well-known blob injector model, for which the parcel properties are defined according to semi-empirical models based on the nozzle properties, represents the current industrial standard approach and it is set as the basis for the study. The definition of the injected parcel properties through One-Way coupling between higher fidelity Eulerian mixture modeling simulations of the multi-phase flow inside the injector is then compared, keeping the primary breakup modeling unchanged. Moreover, droplet diameter probability functions are defined on the basis of near-nozzle X-ray radiography and Ultra-Small-Angle X-ray Scattering (USAXS) and employed to describe the spray, avoiding the jet primary breakup models. These approaches are compared against experimental data, lowering the chamber pressure to explore the behavior or super-heated fuels, typical of early pilot injections, where flash-boiling promotes the atomization and the plume expansion and mutual interaction.