In the present study a LES numerical modeling is carried out for a GDI using KIVA-4 CFD code. Thereby a comprehensive model for the fuel injection process as encountered in IC engine injectors is integrated in a Eulerian-Lagrangian framework. The injector represents a continental piezoinjector with outwardly opening nozzle. The model includes atomization, collision, evaporation and SGS turbulence models. The atomization is described with a combined primary and secondary atomization model. For the primary atomization, a LISA model is used, which is based on the assumption of formation of unstable hollow sheet close to nozzle exit, while a TAB based model is used for the secondary atomization. A new appropriate collision-coalescence model that is independent of mesh size and type is suggested and integrated into the spray model. It accounts for different regimes of droplet-droplet interactions (e.g. bouncing separation, stretching separation, reflective separation and coalescence). The resulting spray model is coupled to a LES of the carrier phase based on a Smagorinsky model. The simulation results are compared satisfactory with experimental data with respect to velocity profile, spray penetration depth, spray visualization image and droplets distribution profile.