Impact of the Primary Break-Up Strategy on the Morphology of GDI Sprays in 3D-CFD Simulations of Multi-Hole Injectors

Abstract

The scientific literature focusing on the numerical simulation of fuel sprays is rich in atomization and secondary break-up models. However, it is well known that the predictive capability of even the most diffused models is affected by the combination of injection parameters and operating conditions, especially backpressure. In this paper, an alternative atomization strategy is proposed for the 3D-Computational Fluid Dynamics (CFD) simulation of Gasoline Direct Injection (GDI) sprays, aiming at extending simulation predictive capabilities over a wider range of operating conditions. In particular, attention is focused on the effects of back pressure, which has a remarkable impact on both the morphology and the sizing of GDI sprays. 3D-CFD Lagrangian simulations of two different multi-hole 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). Numerical results are compared against experiments in terms of liquid penetration and Phase Doppler Anemometry (PDA) data of droplet sizing/velocity and imaging. CFD results are demonstrated to be highly sensitive to spray vessel pressure, mainly because of the atomization strategy. The proposed alternative approach proves to strongly reduce such dependency. Moreover, in order to further validate the alternative primary break-up strategy adopted for the initialization of the droplets, an internal nozzle flow simulation is carried out on the Spray G injector, able to provide information on the characteristic diameter of the liquid column exiting from the nozzle.

3D-CFD Simulation of a GDI Injector Under Standard and Flashing Conditions

“…Droplet characteristics at the nozzle exit have a large impact on spray penetration and morphology, as well as on the distribution of diameters and velocities along the envelope of the jet. A possible approach to evaluate droplet initial conditions involves Eulerian Multiphase nozzle internal flow simulations, as described in [40][41]. Since the internal nozzle geometry was not available for the investigated injector, an alternative approach developed at the SprayLAB of the University of Perugia was exploited, which is based on experimental momentum measurements as described in [42][43].…”

Impact of Grid Density on the Analysis of the In-Cylinder Flow of an Optical Engine

“…Areas of low MI are the vortex cores and recirculation areas in the proximity of cylinder walls. As for the AP indicator also for the MI a plane averaging and a weighted averaging is performed, respectively defined as in Eq (6) and (7).…”

“…Thermo-physical processes taking place in the cylinder are extremely complex and they strictly influence the engine efficiency, both in terms of pollution and performance [1]. Using a CFD tool it is possible to study a multitude of ICE phenomena, among which fuel/air entrainment and mixing [2][3][4][5][6][7][8][9][10], combustion [11][12][13], heat transfer [14][15][16][17][18] and pollutant formation [19][20][21][22][23]. The available literature acknowledges the remarkable potential of Large Eddy Simulation (LES) as opposite to the more standardized Reynolds Averaged Navier Stokes (RANS) to simulate the turbulent nature of engineering flows [24].…”

Comparison Between Experimental and Simulated Knock Statistics Using an Advanced Fuel Surrogate Model

“…To reduce modelling uncertainties, a high degree of accuracy in describing the six-hole full-cone spray evolution is required. Therefore, the spray is modelled following the approach described in [18,19,20,21,24,25] for multi-hole GDI injectors. Commercial RON95 gasoline is used as a reference fuel targeting the lambda value measured at the test bench (1.11).…”