Impact of different droplets size distribution on the morphology of GDI sprays: Application to multi-hole injectors

The scientific literature focusing on the numerical simulation of fuel sprays is plenty of atomization and secondary break-up models, all aiming at simulating GDI sprays under possibly any engine condition in terms of injection pressure and cylinder back pressure. However, it is well known that the predictive capabilities of even the most diffused break-up models are affected by injection parameters, especially backpressure. As a consequence, model constants require usually substantial tuning based on the specific operating conditions. In this manuscript, an alternative atomization methodology is proposed for the 3D-CFD simulation of GDI sprays, aiming at reducing case-to-case tuning of the model constants for variations of the operating conditions. In particular, attention is focused on the effects of back pressure, which has a huge impact on both the morphology and the sizing of GDI sprays. 3D-CFD Lagrangian simulations of two different multi-hole GDI injectors are presented. The first injector is a 5-hole GDI prototype unit operated at ambient conditions. The second one is the well-known Spray G, characterized by a higher back pressure (up to 0.6 MPa). Results are compared against experimental data in terms of liquid penetration, PDA (Phase Doppler Anemometry) data of droplet sizing / velocity and imaging. CFD results are demonstrated to be highly sensitive to the spray vessel pressure, mainly because of the atomization strategy. The proposed alternative approach proves to strongly reduce such dependency. To confirm the improvements, such approach is combined to two different well-known secondary break-up models, namely Reitz's model and the KHRT one.