L. Allocca, A. De Vita, and L. Di Angelo (Italy)
Spark Ignition Engines, GDI, Spray Evolution, Laser Diagnostic.
Experimental analyses of hollow cone sprays, generated by pressure-swirl injectors for Direct Injection Spark Ignition (DISI) engines, have been performed. Spray characteristics have been measured using a system able to gather and to process spray images. It includes a CCD camera, a frame grabber and a pulsed sheet obtained by the second harmonic of Nd-YAG laser (wavelength 532 nm, width 12 ns, thickness 100 µm). A digital image processing software has been used to analyse the collected pictures. Time- and space-evolution of transient sprays have been acquired under different operative conditions as a function of the time after the start of injection (SOI). The spray structure and the effects of the fuel injection pressure, ambient pressure and injector design have been analysed. The fuel has been injected at pressures of 7.0 and 9.0 MPa by electronically controlled injectors in an optically accessible vessel with backpressure ranging between 0.1 to 1.2 MPa. Two high-pressure swirl injectors, generating a 60° (small-angle injector) and 80° (large-angle injector) nominal spray-cone angles, have been used, respectively. A detailed spatial and temporal characterization of the emerging spray has been carried out showing interesting peculiarity of the jet for the different operative conditions. The global parameters of the spray in terms of tip penetration, cone angle and hollow-cone structure have been measured. The ambient pressure strongly affects the spray structure resulting in an isotropic contraction and a reduction of smaller droplets and vortexes zones at higher backpressure values respect to lower ones. Varying the injection pressure the global spray structure is quite similar except for the tip penetrations, which increase as the injection pressure increases.
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