An experimental and numerical analysis of pressure pulsation effects of a Gasoline Direct Injection system

• A complete Wet-System hydraulic bench for Gasoline Injection Systems was setup.
• The actual GDI injector hydraulic behavior when operating in an engine-like system layout was assessed.
• The possible influence of the injection system layout on the rail pressure pulsation and injector operation was investigated.
• A 1D numerical code modeling the entire injection system was tuned and applied to further complete the analysis.
• The injector hydraulic behavior with advanced injection strategies (reduced dwell time) was investigated.

Downsized, turbocharged GDI engines are considered as the most effective system architecture car makers can implement to meet stricter CO2 production and pollutant emissions regulations. Moreover, the GDI engine is accounted to be the ideal thermal part of hybrid powertrains which will play a more and more significant role to meet future CO2 and emissions standards. Hence in the last years significant research efforts are being applied to the development of GDI technology in order to optimize its performance in terms of specific fuel consumption and emission control capabilities.These engines require an extremely reliable high pressure fuel injection system to allow advanced combustion strategies and to improve the fuel atomization process and the air–fuel mixing. Nevertheless, in these installations intense fuel pressure fluctuations may occur due to continuous pumping and injection events, possibly causing low precision in the fuel metering from cylinder to cylinder and relatively poor spray quality. For this reason the injection system design must be supported by accurate computational models able to predict the actual injector flow and the whole fuel system behavior.This paper describes a combined 1-D numerical and experimental analysis of a complete GDI injection system with a particular focus on the waves propagation phenomena and their dependence on the system geometry, such as high pressure pipe length and internal diameter, rail inlet position, flow-restrictor diameter.The numerical code was validated through the comparison of the predicted results with experimental data, mainly pressure and instantaneous injected flow rate measured by a hydraulic test bench (named Wet-System) developed at SprayLab – University of Perugia, which consists of the high pressure pump, the pipes, the fuel rail and injectors so to simulate the complete injection system operation. The injection-system mathematical model was then used to predict the system dynamic response in operating conditions beyond the test bench limits, paying specific attention to the flow-restrictor effect. Finally, the model capability in accurately predicting the waves dynamics effects on the injected fuel flow rate and mass was assessed for multi-injection strategies, when the dwell time between consecutive injections is varied.