Previously published efforts regarding the unsteady nature of a self-exciting air/water (AW) coaxial three-stream airblast injector considered first the effects of feed stream flow rate changes and then the effects of nozzle geometric permutations. Frequency domain analysis, automated video analysis, and spray profile assessments were used to draw conclusions about spray quality and character. The computational method was validated using an AW test stand (AWTS). Here, the focus of the work shifts to the use of slurry and a high-density gas (SH). Again, the effects of flow rate and nozzle geometry are considered. It was found that the nature of the SH flow changed dramatically in comparison with its AW counterpart. As a result, the video analysis technique had to be revamped, and therefore direct comparisons are limited. As with its AW counterpart, inner nozzle retraction and stream meeting angle proved to be the most influential geometry variables. A flushed nozzle showed a wider spray with a strongly trimodal character. Increasing the relative inner gas flow rate had a pronounced, but mixed, effect on the considered metrics. In general, the transient signatures of the pressure and video analysis metrics were similar enough to indicate that the unsteady driving mechanisms were consistent for each. Lastly, attempts to further stimulate the spray via modulating the inner gas proved futile for both sets of flowing materials for the measures considered.