ECN Spray G Injector: Assessment of numerical modeling accuracy

Gasoline Direct Injection (GDI) is a leading technology for Spark Ignition (SI) engines: control of the injection process is a key to design the engine properly. The aim of this paper is a numerical investigation of the gasoline injection and the resulting development of plumes from an 8-hole Spray G injector into a quiescent chamber. A LES approach has been used to represent with high accuracy the mixing process between the injected fuel and the surrounding mixture. A Lagrangian approach is employed to model the liquid spray. The fuel, considered as a surrogate of gasoline, is the iso-octane which is injected into the high-pressure vessel filled with nitrogen. The numerical results have been compared against experimental data realized in the optical chamber. To reveal the geometry of plumes two different imaging techniques have been used in a quasi-simultaneous mode: Mie-scattering for the liquid phase and schlieren for the gaseous one. Different operating conditions, in terms of temperature and pressure inside the chamber, have been tested to check the robustness of the numerical framework proposed by varying operating conditions. Results obtained show a very good agreement between the numerical results and the experimental data confirming the capabilities of the approach to describe accurately all the physical phenomena involved in the injection process. The influence of the grid size and the number of parcels has been highlighted showing the existence of threshold values for accuracy. Further investigation on the mixing characteristics of the spray have been performed looking at the turbulence generated by the spray-ambient interaction and the local ignition probability index.