Experimental and numerical characterization of high-pressure spray for GDI engines

Direct-injection is now widely applied in spark-ignition engines in combination with turbocharging to reduce the fuel consumption and the knock risks. This is achieved through the use of multi-hole, high-pressure injectors whose features are rather different with respect to the hollow-cone, low-pressure configurations that were adopted in the last decade. This last aspect has to be taken into account when multi-dimensional simulations of GDI engines have to be performed. In particular, suitable models are needed to describe the spray atomization and the wall-impingement processes. In this paper experimental investigations were performed using a 6-hole injector in a constant-volume vessel with optical access. Spray images were acquired by a CCD camera and processed to obtain the spray penetration and cone angles for the different tested operating conditions. The effects of injection pressure were evaluated in the range 3.0 - 20 MPa at ambient density of the gas. A flat plate was added to the experimental apparatus for investigation of the spray-wall impingement and liquid-film images were acquired. On the basis of the experimental database, a CFD methodology for gasoline spray simulations was implemented into the Lib-ICE code, developed under the OpenFOAM technology. The evolution of the resulting liquid film was also taken into account by solving the mass and momentum equations on the mesh boundary.