Near-Nozzle Instabilities in Gasoline Direct Injection Sprays

Nozzle flow of multi-hole GDi injectors can lead to undesirable and uncontrolled spray instabilities. In this study, two different injectors were utilised in order to observe the near-nozzle spray using high magnification optics and a high speed camera; a symmetrical multi-hole injector and an asymmetric, stepped nozzle injector. It was found that the symmetric injector exhibited a number of different spray instabilities, including flapping of the spray cone from an individual nozzle, flapping across all nozzles and rapid flapping along a single spray axis. The typical time scale of the phenomena was in the order of a hundredth of a millisecond. On the other hand, the stepped nozzle injector was found to exhibit fewer spray structures associated with spray instability. The results also suggest the nozzle step plays an important role in the primary breakup of the spray and that most of this breakup occurs before the exit of the step