Experimental Assessment of a Novel Instrument for the Injection Rate Measurement of Port Fuel Injectors in realistic operating conditions

Paper #:
  • 2017-01-0830

  • 2017-03-28
In the current automotive scenario, even if Direct Gasoline Injection technology is quickly spreading in several markets due to its higher potential for the fulfillment of stringent CO2 emission regulations, the more conventional Port Fuel Injection (PFI) technology is still being developed for those applications for which the reduced vehicle mass and/or less rigorous fuel conversion efficiency targets are to be achieved. The injector operation accuracy and repeatability are crucial for indirect injected, spark ignited engines, raising the need for an accurate shot-to-shot measurement of the global injected volume in realistic operating conditions in terms of upstream and downstream pressure levels and actuation frequency. Further, even if the injection rate time profile is commonly considered not-crucial for PFI engines, the detection of the actual discharge time-history could significantly assist in the development and fault-analysis of PFI injectors, e.g. identifying dispersions in the opening/closing transients or bouncing phenomena. Unfortunately, the actual operation of PFI injectors can be hardly determined by the commercially available Injection Analyzers which are normally designed in order to capture the injection rate profile and/or the shot-to-shot injected quantity for Diesel and GDI injectors. The main limitations in using conventional Injection analyzers with PFI injectors are related to their need of applying a significant counter-pressure downstream the injector, typically in the range 5 to 10 bar, which implies a significant modification of the PFI injector operation with respect to standard conditions; further, in the closed-vessel type instruments, the fuel injection process implies a significant vessel pressure rise which tends to reduce the injection rate during the discharge process. Finally, as for GDI and Diesel injectors, the use of conventional Injection Analyzers to measure the injection rate prevents any contemporary analysis of the resulting spray in terms of imaging or drop sizing/velocimetry. In the present paper, a novel Injection Analyzer specifically developed for low pressure injectors is assessed in comparison with a conventional Zeuch’s Method-based Analyzer. The proposed instrument is based on the detection of the pressure time-history in a closed vessel acting as isolated fuel rail during the injection process. The PFI injects in an ambient pressure vessel, preserving its standard upstream/downstream operating conditions and allowing the application of diagnostics for the resulting spray analysis, while the upstream vessel is designed in order to minimize the pressure fall during the injection. At the end of the injection process, a synchronized, fast acting valve is used restore the target rail/vessel pressure for the next injection process . By the proposed instrument, the shot-to-shot injected quantity and injection rate time-profile detection can be determined.
Also in:
  • SAE International Journal of Fuels and Lubricants - V126-4
  • SAE International Journal of Fuels and Lubricants - V126-4EJ
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