Characteristics of Sub/Supercritical Gasoline and Iso-Octane Jets in High Temperature Environment 2019-01-0289

Based on the temperature and pressure in the cylinder of GDI (Gasoline Direct Injection) engines under the common operating conditions, jets´ characteristics of gasoline and iso-octane at different fuel temperatures under the high ambient temperature were studied by means of high-speed photography and striation method. It is found that the supercritical gasoline jet shows the morphological collapse of jet center and the protrusion of the front surface, but the iso-octane jet doesn´t. Meanwhile, as the fuel temperature rises, the flash boiling and the interference between adjacent plumes affect the gasoline jet, and cause the center of the jet to form a high-speed and low-pressure zone, hence the air entrainment in this region contributes to the collapse of jets. The collapse and convergence of jets´ morphology are the main reasons for the change of penetration and cone angle. In the subcritical stage, the thermal motion of the fuel molecules, the internal turbulence of the jet, and the heat exchange between the jet and the high temperature environment as well as the exchange of momentum increase the jet´s projected area, but vary the contour circumference with the fuel temperature rising. In the supercritical stage, the diffusion effect dominated by the thermal motion of fuel molecules allows the projected area and the circumference of the contour to change regularly. Therefore, this study provides an insight into morphological differentia between gasoline and iso-octane jets, and reveals that the fuel temperature has a significant impact on jet characteristics, but the degree of influence varies between gasoline and iso-octane at high ambient temperature.