Time resolved characteristics of gaseous jet injected by a group-hole nozzle

In this study, we investigate the evolution of a transient gaseous helium jet issuing from a multi-hole fuel injector at pressure ratios of 2, 3, 4 and 5. High speed Schlieren was used to visualize the jet development process and a digital edge detection method applied to determine time resolved jet penetration and tip speed. Both near and far field regions of the jet were investigated. Measurement of jet tip axial penetration and speed revealed that jet formation is comprised of three stages: emergence of individual jets, merging individual jets into the final stage of a merged single jet and penetration of the single merged jet. Penetration of the jet tip was found to be more sensitive to nozzle pressure ratio while the jet spread showed sensitivity to the stage of the jet evolution. Little sensitivity in jet parameters was found for the jet emergence and merge stages where it is likely that nozzle-opening processes play an important role. Scaling of the jet parameters based on those typical of free jets revealed the single merged jet to be similar to that of a free jet, although the form of the scaling depends on the parameters used to define the nozzle diameter and jet speed.