Achieving an adequate knowledge of the fuel injector dynamic operation is an important step in the global effort of improving direct injection gasoline engine efficiency while limiting pollutant emissions. In this frame, needle displacement measurement is an important add-on to evaluate the injector actual performances and can be very useful for developing predictive numerical models to support both the component and engine development. In this study the dynamic behavior of a GDI injector was investigated by the simultaneous measurement of injector needle lift and of the resulting injection rate. With this methodology, the needle displacement is measured by laser Doppler vibrometry, while the injector is tested by an injection analyzer based on the Zeuch method. The vibrometer laser beam points on the needle back surface, passing through a quartz window allowing the fuel pressurization and the normal injector operation. The analysis of the simultaneously acquired needle displacement, injection rate, fuel inlet pressure and current time-history profiles allows a complete insight in the injector dynamic operation. The pressure effect on the needle dynamics was assessed with a detailed analysis of the opening and closing transients; further, multiple actuation strategies were analyzed focusing on the influence of dwell time on the injector dynamics evidencing how the resulting injection rate profile is affected by the needle inertia and by the pressure wave propagation along the fuel line.
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