FUEL DELIVERY IN A PORT FUEL INJECTED SPARK-IGNITION ENGINE

The goal of tills study was to investigate the effects of injector cha racteristics and injection timing on fuel mass delivery to the valve i n a fired spark ignition engine. The relationship between injection ti ming and fuel arrival at the intake valve must be known for designing an injection system for increased liquid entrainment into the gas phas e and minimized fuel wetting of the port walls. Fuel spray behavior fr om a conventional injector design and prototype vacuum-assist and air- assist injector designs is investigated by measuring fuel drop size an d velocity at the intake valve using phase Doppler interferometry. The results of this study indicate the amount of time required for the fu el spray to reach the intake valve is constant and independent of inje ction timing. However, the width of the temporal fuel spray arrival di stribution is a strong function of injection timing. injection timing and the corresponding gas-phase dynamics have the strongest impact on the smallest drops, resulting in a redistribution of tile drops with r espect to size. In addition, the fuel spray behavior was investigated at the start of tile intake valve event when hot cylinder gases flow i nto the intake port. The arithmetic mean diameter of the fuel film ato mized off the back of the intake valve during this period was found to range from 55 to 65 mu m.