SUMMARY

Direct injection studies of liquid jets in supersonic crossflows are critical for understanding combustion in scramjet engines. Exploring these fluid dynamic interactions is not only an important step towards characterizing fundamental liquid breakup properties and key for improving engine design and increasing efficiency. Current engine designs lack precise injector optimization and, thus, are delivering inefficient fuel sprays.

To remedy this, previous studies in the literature have examined how supersonic crossflows affect gaseous and liquid jet breakup characteristics using backlit imaging or schlieren techniques, but our objective of this work is to study jet instabilities and droplet breakup characteristics
using the novel digital in-line holography technique. Experiments are conducted with a heated Mach 1.71 crossflow and a transitional regime liquid jet (slenderness ratio L/D of 19) with a diameter of 0.5 mm. High-speed and high-resolution digital in-line holography and schlieren methods are utilized to spatially resolve the jet breakup characteristics near the injection point. Results of these experiments show that the jet’s front-edge instability
wavelength spacing peak ranges from 68.3 to 104.5 microns, decreasing as the injected pressure increases from 100 to 500 psi.

These results signify that there exists an inverse
relationship between these inherent instabilities and injected pressure. Both windward and leeward droplet breakup parameters are also analyzed to determine trends in the cross-streamwise direction . All findings work in tandem to help improve mathematical models, optimize injector geometry, and refine scramjet engine designs.