Abstract
In this study, an experiment method and apparatus are developed which allow exploration of partial-lift spray in a production gasoline direct injection (GDI) injector. For this injector, discretizing the needle’s stroke into a series of steady partial-lift tests seems a viable approach for quantifying transient behavior, where spray performance is often inferior from the perspective of emissions. However, performing such tests is not trivial due to manufacturing challenges and material limitations making it difficult to isolate any particular lift at pressure. To explore the applicability of fixed partial-lift tests, the following are performed: (1) An inward-opening multi-hole GDI injector is minimally modified with an apparatus to finely control needle lift by limiting the needle’s stroke with a fine micrometer head. (2) An experiment process is developed to associate the micrometer set-point with the imposed needle lift, compensating for pressure induced component flex. This flex is significant and of a similar magnitude to the needle’s stroke. (3) In-nozzle flow is simulated using computational fluid dynamics (CFD) within the AVL FIRE software to compare a stationary and moving needle. The comparison reveals a relative insignificance of needle velocity for the majority of the needle’s stroke (>5 μm). The nozzle hole flow rates and effective exit velocities are similar, suggesting fixed partial-lift spray well approximates the normally moving needle spray. This new experiment method can be used on current injectors to quantify spray performance during needle transients by discretizing the stroke into steps as small as 2 μm, exceeding the control in any current published literature.
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