Injection Rate Measurement of GDI Systems Operating Against Sub-Atmospheric and Pressurized Downstream Condition

Paper #:
  • 2017-24-0110

  • 2017-09-04
In the current automotive scenario, Direct Gasoline Injection technology is quickly spreading in several markets due to its higher potential for the fulfillment of stringent CO2 emission regulations. The stringent efficiency targets achievement is enabled by engine downsizing and by stratified-charge combustion strategy implementation; both these technologies are based on direct injection technology. Consequently, the fuel injector represents one of the key components for present and next SI engines. Along with appropriate spray characteristics in terms of sizing and jets shape and penetration in the combustion chamber, an accurate instantaneous injection rate control is required particularly to actuate complex multi-event injector actuation strategies. The injection rate measurement is hence one of the most important measurement capabilities required for the injection system development and for its application to a specific engine in order to obtain the required accuracy and repeatability targets for injected mass and fuel flow rate. Further, the injection rate measurement capabilities should ideally be provided in the actual upstream-downstream pressure conditions. Unfortunately, this basic task is hardly accomplished by commercially available Injection Analyzers which are affected by the need of applying a significant counter-pressure downstream the injector, typically in the range 5 to 10 bar, which implies a significant modification of GDI injectors operation with respect to part of their operation range. Finally 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 –named dINJ - specifically developed to remove need for a high downstream counter pressure boundary condition is assessed for GDIs in comparison with a conventional Zeuch’s Method-based Analyzer. In previous papers, the dINJ efficacy for low pressure injection systems injection rate analysis was demonstrated. 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 GDI can inject in atmosphere or in a closed vessel where the desired pressure level is maintained, obtaining the prescribed upstream/downstream operating conditions and allowing the application of diagnostics for the resulting spray analysis. 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 for GDI injectors.
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