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The effects of fuel temperature on both the geometry and the droplet size and velocity of a GDI swirled injector spray were investigated by means of visualizations and PDA measurements. Isooctane was used as model fuel and was injected in a quiescent bomb at injection pressure of 7 MPa. Bomb pressure ranged from 40 kPa to 800 kPa with injector nozzle temperature ranging from 293 K to 393 K. A drastic change in spray geometry was observed when conditions above the vaporization curve were reached. The temperature increase has two macroscopic effects on the spray geometry: at the nozzle exit the liquid flash boiling strongly enlarges the spray angle, at a certain distance from the nozzle the air entrainment collapses the spray. Raising the fuel temperature up to flash boiling conditions causes a significant decrease of the average droplet size.

Different laser based techniques were applied to investigate the effect of gas density on the penetration of a Diesel Spray and the entrainment of the surrounding air. The experiments were conducted in a constant volume chamber under quiescent conditions. Gas density was varied in a wide range (from 1.17 kg/m3 to 40 kg/m3) while keeping temperature constant at ambient conditions. Spray penetration was measured by different techniques: Laser Doppler Velocimetry (LDV), Laser Beam Extinction (LBE) and Laser Sheet Visualisation (LSV). The results were compared to estimate the level of agreement among the techniques. A comparison with existing penetration models was also performed and an empirical law is proposed to better correlate the results. The two-dimensional gas velocity field generated by the spray was measured by LDV and compared to PIV results evidencing different peculiarities of the two techniques in describing the structure of the flow field.

The air entrainment in a transient diesel spray was studied using laser Doppler anemometry to provide information on the effect of gas density and temperature. The spray was injected vertically into a confined quiescent atmosphere and the entrained mass flow rate was evaluated by measuring the air velocity component normal to a cylindrical geometric surface surrounding the spray, and extending to about 200 nozzle diameters (50 mm). The experimental results, relative to a density range from 0.84 to 7.02 kg/m3 and a temperature range from 293 to 473 K, indicate that the non dimensional entrainment rate, averaged in time over the main injection period, depends on the distance from the nozzle and both gas density and temperature. A first analysis, based on the available data, allowed to quantify the dependence and provided a correlation with such variables.