Study On The Spray Characteristics Of A GDI Engine Multy-hole Injector

Gasoline direct injection (GDI) technology is one effective measure to improve fuel economy in spark-ignition gasoline engines. The spray characteristics of injectors are important factors affecting GDI engine performances. Therefore, it is significant to investigate the spray characteristics of an injector for a GDI engine. To study the spray characteristics of a multi-hole injector, a constant volume chamber test bench, including a fuel supply system, an electronic control unit, an optical path and a pressurized nitrogen bottle and two heaters, was set up.Based on the MATLAB software, a special programme has been developed to analyze the shadow images of gasoline sprays in the constant volume chamber taken by a high speed digital camera under different conditions. Using strong, weak threshold edge detection method and morphology operation, the spray morphology can be determined accurately and conveniently. The characteristic parameters of the spray such as spray cone angle and penetration can be calculated through the spray outline. The influence of injection pressure, the back pressure and temperature in the constant volume chamber on the spray characteristic parameters of gasoline fuel was studied. The result show that:As the injection pressure increases, the spray breakup and evaporation enhances, the penetration, outline length and area of the spray occupied increase in different injection pulse width. However, the injection pressure has a little influence on spray cone angle.When the back pressure in the constant volume chamber increases, the spray penetration and geometry contour reduce sharply in different injection pulse width, the spray moves slowly in every direction, the spray evaporation is also slow. But the cone angle increases slightly with the back pressure increases.The temperature in the constant volume chamber has positive effect on the evaporation of gasoline fuel. High temperature promotes the evaporation processes of spray significantly. But it has a little influence on the change in spray cone angle and penetration, the spray cone angle and penetration decrease slightly.