Evaluation of a 3-Way Direct Needle Control Unit Injector on Hydraulic Test Bench and V8 Engine

Direct needle control (DNC) has been the enabling technology for diesel fuel injection systems in recent years. It allows for pressurized fuel to be delivered in a concise, controllable manner. Most common rail systems (CRS) utilize 2-way valve principles, which tend to be inefficient and slow relative to 3-way, but robust in implementation. Integration of a DNC valve into a unit injector application has proven to be a challenge to the diesel industry, and most unit injectors have accomplished this using a 2-way valve with flow controlling orifices. 3-way digital spool valves are currently being used in production on hydraulically intensified unit injector applications as a hydraulic intensifier valve for fuel pressurization. 3-way non-latching (NL), single coil spring return (SCSR) DNC valves offer performance advantages over 2-way SCSR DNC valves in the areas of hydraulic efficiency and actuation speed. Due to these advantages, the 3-way digital spool valve is an excellent valve candidate for integration into a unit injector as a DNC valve. The DNC valve described in this paper utilized numerical modeling to determine the best design configuration required for the application, predict injection performance and validate the DNC design. DNC prototype injectors were produced and tested against the application specification on hydraulic test benches. DNC injector performance evaluations were tested for rate of injection (ROI), close coupling of events, start and end of injection events (SOI and EOI), precise quantities delivered and variability, and overall injection spray characteristics. After completion of injector validation on test benches, dynamometer engine testing began to evaluate the DNC injection system versus the baseline fuel system. Engine and emission results indicate that integrating a 3-way SCSR digital spool valve, for DNC, into an existing hydraulically intensified unit injector has the potential for greatly improving the engine performance and emissions.