Spray and atomization of a common rail fuel injector with non-circular orifices

This paper presents an experimental study on diesel sprays from non-circular orifices in ambient air. The non-circular geometry includes rectangular, square, and triangular shapes. The obtained spray characteristics were compared with those of a circular orifice. The injection pressures were varied from 300 bar (30 MPa) to 1000 bar (100 MPa). Macroscopic spray characteristics like spray cone angle and spray width were measured using a high speed camera. A laser diffraction technique was used to measure the droplet size, i.e. Sauter mean diameter, of the sprays at different axial locations. Spray behavior was measured from different orientations of the non-circular geometric shapes, including edges and corners. Spray widths measured along the spray length clearly demonstrated the presence of axis-switching phenomenon in high pressure diesel sprays obtained from non-circular orifices even at injection pressures as high as 1000 bar. They also exhibited larger widths and hence, larger surface areas, greater cone angles than sprays from a circular orifice. Thus, sprays from non-circular geometric shapes are expected to achieve better air entrainment and hence, mixing than the circular orifices. Droplet size obtained depended on the location of measurement and injection pressure and different behaviors were observed at different locations. It was noticed that non-circular orifices could induce greater instabilities in the diesel sprays thereby leading to faster atomization. As a result, an improvement in the spray characteristics can be achieved using non-circular geometries. Axis-switching phenomenon is expected to play an important role in improving the spray characteristics and the non-circular geometry may provide a cost effective approach for passively controlling the spray characteristics.