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The heated fuel injectors are designed to bring up fuel temperature so as to reduce HC and CO emissions during cold start. The heated injectors are similar to regular injectors except heaters are placed near the injector inlet and outlet. The heaters, which has the ability to regulate temperature at 180 °C, transform the thermal energy to heat up the liquid fuel through the injector body. The heated injectors are required to heat up fuel to the operating temperature (e.g., 120 °F or 48.9 °C) as quickly as possible and to maintain that fuel temperature for about three minutes. However, test results indicate it takes more than two minutes for the fuel temperature to reach the desired operating temperature. Objective of this work is to find out the mechanisms controlling the slow heating process through CFD analysis. The computational domain covers the whole injector, from inlet to exit, since the heaters located near the top and bottom of the injector.

The disk-type gasoline injector uses a flat disk with a seal ring to control the valve opening and the flow rate. Though the disk-type injectors provide several advantages over the pintle-type injectors, some disk injector drips and produces undesired large droplets after several minutes of operation. High-speed photography shows that the injector dripping problem could be a result of slow droplets coming out of the injector at the end of the injection cycle. Namely, a second slow spray is generated. Purpose of this work is to employ the Computational Fluid Dynamics (CFD) techniques to identify the causes of the slow droplets and to improve the injector design. The CFD analysis thus focuses only on the closing stage of the injection cycle. The computational domain in the valve decreases with the time; the transient grid sizes and locations are determined by a constant valve closing velocity.

During the fuel injection process, the flow is mainly metered by the smallest flow area inside the injector. There are two possible locations for the smallest flow areas: at the nozzle and at the valve. In the initial and final stages as the needle is only slightly lifted, the valve area is the metering area. In the fully open stage, the nozzle area is usually smaller than the valve area. However, if the valve area is not much larger than the nozzle, some of the flow may be metered at the valve. This is generally true for injectors with larger nozzles. Objective of this work is to find out how the needle lift affects the static flow, so as to ensure proper control of the needle lift and thus the injector metering process. Three injectors with three different nozzle sizes were studied through CFD analysis. The computational domains cover from the valve to the injector exit for needle lifts of 30-80 μm.