Imaging and Vibro-Acoustic Diagnostic Techniques Comparison for a GDI Fuel Injector

This work presents the results of an experimental investigation on a GDI injector, in order to analyze fuel injection process and atomization phenomenon, correlating imaging and vibro-acoustic diagnostic techniques. A single-hole, axially-disposed, 0.200 mm diameter GDI injector was used to spray commercial gasoline in a test chamber at room temperature and atmospheric backpressure. The explored injection pressures were ranged from 5.0 to 20.0 MPa. Cycle-resolved acquisitions of the spray evolution were acquired by a high-speed camera. Simultaneously, the vibro-acoustic response of the injector was evaluated. More in detail, noise data acquired by a microphone sensor were analyzed for characterizing the acoustic emission of the injection, while a spherical loudspeaker was used to excite the spray injection at a proper distance detecting possible fuel spray resonance phenomena. In order to monitor vibration throughout the injection event, the injector was also equipped with an accelerometer sensor, adhesively mounted on the holder. Tests in both dry and fuel injection conditions allowed to distinguish the pure mechanical operation of the injector related to the needle opening and closing, and the effects due to the interaction of the internal fuel flow with the mechanical components. The recorded data were then processed using digital Fourier transform and wavelet analyses, capturing essential information related to the spectral and temporal characteristics of the injection event. In the paper, the outcomes obtained by the two different techniques are jointly analyzed and discussed, highlighting the potentiality of the vibro-acoustic approach in correctly monitoring the fuel injection process, since it is able to provide insightful details in accordance with the imaging technique.