Influence of Needle Lift on Gasoline Injector Static Flows

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. CFD results indicate that the flow rate of a larger nozzle injector is indeed more sensitive to the needle lift. The predicted flow rates of a smaller nozzle injector compare well with the test data. An equation for predicting injector static flows at various orifice sizes and needle lifts was also developed from statistical methods.