Experimental and numerical characterization of a direct solenoid actuation injector for Diesel engine applications

In the present paper, a non-conventional Diesel injection system is analyzed by means of a detailed numerical and experimental investigation. The analyzed system, the Magneti Marelli DDI Diesel direct injection, is based on a direct-actuation solenoid injector. The DDI system operates up to 60.0 MPa injection pressure, with a multi-hole nozzle resulting in a conventional fuel spray plumes distribution inside the combustion chamber, which suites the requirements of small industrial and automotive Diesel applications. In the present research activity, the hydraulic behavior of the DDI system was analyzed in terms of injected volumes and injection rate time-histories varying the injection pressure from 30.0 MPa to 60.0 MPa with a back pressure of 2.0 MPa. The resulting injection process was also analyzed in terms of spray global shape evolution along with droplet sizing and velocity in a pressurized (1.0 MPa) test vessel in quiescent and room temperature conditions. In order to investigate and to validate the capability of adopted CFD models to reproduce the spray behavior at such non-conventional injection pressure levels for Diesel applications, an experimental and numerical comparison was performed, in terms of liquid spray morphology, tip penetration and droplet sizing. A numerical methodology, based on a preliminary Eulerian Steady Simulation of the nozzle, has been developed in order to gain correct flow rates and turbulence data at each of the nozzle holes exit. Then the Lagrangian spray simulations have been carried out by means of a new atomization approach able to take into account the cavitation phenomena and the turbulence effects. A tuning campaign has been performed in order to validate the secondary KH-RT breakup model, and a grid sensitivity analysis has been carried out.