Characterization of initial spray from a DI gasoline injector by holography and laser diffraction method

In the injection of a high-pressure swirl injector for direct-injection (D.1.) gasoline engine use, an initial spray (also called a leading spray or a preswirl spray [1]) is generated from the fuel downstream of the swirl grooves in the initial stage of the injection. This initial spray is almost unaffected by tangential forces, it has feeble swirl velocitiy and it atomizes poorly. The initial spray has different characteristics and behavior than the main spray, such as larger droplet size, farther penetration distance, and irregular shape. Therefore, the air-fuel mixing process of the initial spray is quite different from that of the main spray. In this study, the structure of the initial spray y a high-pressure swirl injector for D.I. gasoline engine use is analyzed from observation of the reconstructed images of a hologram, The origins of the initial spray are clarified by observing the spray structures with and without cleaning the injection hole, and by comparing the volume of the initial spray with those of the injector interior, such as the annular volume and tangential grooves. The droplet size distributions in the initial spray at different imaging times are investigated The spatial distribution of the droplet size in the initial spray is clarified, as are the effects of ambient pressure on the characteristics of the in initial spray. Finally, the temporal variations of droplet size of the whole spray at fixed position is studied by a laser diffraction based method, and the results are compared to the holographic results.