Detailed Experimental and Numerical Investigation of the Spray Structure in a GDI High-Pressure Swirling Injector

The paper reports a detailed experimental and numerical investigation of the spray evolution, in terms of flow pattern and droplets size, of a gasoline hollow-cone spray generated by a high-pressure swirl injector for Gasoline Direct Injected (GDI) engine applications. Experiments were carried out, injecting the fuel in a chamber at ambient temperature and atmospheric pressure, in the range of injection pressures between 6 and 10 MPa by means of a common rail injection system, a commercial swirled type injector with a nozzle diameter of 0.50 mm and a cone angle of 67°. A 2-D imaging technique was used to follow the global evolution of the spray as function of the injection time in order to estimate the jet development, the morphology of the spray, and the instantaneous velocity field of fuel droplets by Particle Image Velocimetry (PIV). Images of the spray and PIV shots were captured, firstly, aligning the light sheet to the vertical axis of the spray; then, experiments were also taken with the light sheet placed through the cross section of the spray in order to explore the structure and velocity field at different distances from the nozzle.A PDA system was used to acquire, simultaneously, the droplets velocity as well the droplets size (D10). The system, equipped with an argon-ion laser, was set in forward scattering mode at an off-axis of 30°. Measurements of the axial velocity component and size of droplets were performed, at the same operative conditions as for the PIV ones, close to the nozzle exit (distances of Z=7.5 and 10 mm) and at different radii over 100 injection cycles. As a result, for each measurement, a data set with a minimum of about 40,000 valid data were collected and analyzed, off-line, using the ensemble averaging technique.CFD computations are simultaneously carried out by means of the STAR-CD software. Fuel jet atomization and break-up are evaluated by means of a user-implemented set of models. A preliminary evaluation of the fuel droplet velocity at the injector exit is performed in order to define an instantaneous mass flow rate, aiming at capturing the spray temporal evolution throughout the injection process.