3-D PIV Analysis of Structural Behavior of D.I. Gasoline Spray

Three-dimensional behaviors of direct injection (D.I.) gasoline sprays were investigated using 2-D and 3-D particle image velocimetry (PIV) techniques. The fuel was injected with a swirl type injector for D.I. gasoline engines into a constant volume chamber in which ambient pressure was varied from 0.1 to 0.4 MPa at room temperature. The spray was illuminated by a laser light sheet generated by a double-pulsed Nd:YAG laser (wave length: 532 nm) and the succeeding two tomograms of the spray were taken by a high-resolution CCD camera. The 2-D and 3-D velocity distributions of the droplet cloud in the spray were calculated from these tomograms by using the PIV technique. The effects of the swirl groove flows in the injector and the ambient pressure on the structural behavior of the droplet cloud in the spray were also examined. In the vertical tomograms of the spray including the spray axis, large-scale vortices are found in the peripheries of the spray and their scales are decreased with an increase in the ambient pressure. In the horizontal tomograms of the spray normal to the spray axis, it was found that the spray did not penetrate uniformly in the radial direction, and the irregular shape of the spray periphery is supposedly related to the swirl groove flows in the injector. The PIV results show that the spray flow consists of irregular flows including forward and reverse flow areas, which are not the simple rotating bulk motion.