Spray Characteristics and Wall-impingement Process with Different Piston Tops for the Multi-hole Injector of DISI Gasoline Engines

Spray characteristics and spray wall-impingement events are the key factors for the direct injection spark ignition (DISI) engines, affecting fuel/air mixture preparation and its combustion process. Thus, the spray characteristics of a multi-hole injector for DISI engines, such as spray tip penetration and spray cone angle were investigated in an optical chamber employing the high-speed shadow photography. Furthermore, the effects of the injection pressure, ambient pressure and piston top shape on the impinging spray development were studied in the optical chamber, when the impinging distance is 26.1 mm, corresponding to about 60 CAD ATDC. In addition, the SMD and wall film thickness of the spray impinging on the piston top were studied by means of CFD technique. The results showed that the ambient pressure had the greater effect on the changes of the spray penetration and spray cone angle than the injection pressure. For various piston tops, the spray patterns were changed due to different interaction between the spray and the piston top. The elevated injection pressure decreased the SMD and increased the wall film thickness; the elevated ambient pressure resulted in the increase in the SMD, while the wall film thickness decreased first and increased afterward. When the time of injection is longer than 3 ms, the SMD under the injection pressure 9 MPa is averagely 14 μm smaller and 5.5 μm larger than the ones under the injection pressure 6 MPa and 12 MPa; and the wall film under the injection pressure 9 MPa is averagely 3.9 μm thinner and 1 μm thicker than the ones under the injection pressure 12 MPa and 6 MPa. The investigations are meaningful to the injector arrangement at DISI engine design stage, and to optimizing the injector and the combustion chamber structure.