Injection Rate Measurement of GDI Systems Operating against Sub-Atmospheric and Pressurized Downstream Conditions

In order to optimize gasoline direct injection combustion systems, a very accurate control of the fuel flow rate from the injector must be attained, along with appropriate spray characteristics in terms of drop sizing and jets global penetration/diffusion in the combustion chamber. Injection rate measurement is therefore one of the crucial tasks to be accomplished in order both to develop direct injection systems and to properly match them with a given combustion system. Noticeably, the hydraulic characteristics of GDI injectors should be determined according to a non-intrusive measuring approach. Unfortunately, the operation of all conventional injection analyzers requires the injection in a volume filled with liquid and the application of a significant counter-pressure downstream of the injector. This feature prevents any operation with low pressure injection systems such as PFIs. Also with GDI systems the need for a pressurized and liquid-filled volume or pipe downstream the injector can represent a significant limitation with respect to standard operating conditions, in which the injection takes place in a gaseous environment with counter-pressure ranging from sub-atmospheric to pressurized conditions. Further, the application of any diagnostics to the resulting spray is unfeasible. In the present paper an innovative Injection Analyzer called dINJ, which has been specifically developed to remove the 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 efficacy of the dINJ for the injection rate analysis of low pressure injection systems has been demonstrated. The proposed instrument is based on the detection of the pressure time-history in a closed vessel acting as an isolated fuel rail during the injection process. The GDI can inject in atmosphere or in a closed vessel where the gaseous environment is maintained at the desired pressure level. By this approach, the prescribed upstream/downstream operating conditions are obtained and the simultaneous application of diagnostics for the resulting spray analysis is allowed. Using the proposed instrument, the shot-to-shot injected quantity and injection rate time-profile detection can be determined for GDI injectors while operating against any pressure level.