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The mixing characteristics of an active coaxial injector in crossflow configurations are explored in this paper. A miniature rectangular CD nozzle generates crossflow for the injector for subsonic and supersonic test conditions. The flowfield of the active injection system consists of an actuation air jet at the inner core of the coaxial nozzle (1mm ID) that provides large mean and fluctuating velocity profiles in the shear layers of a fluid stream injected surrounding the core through an annular nozzle with ID=1.5 mm and OD=1.96 mm. The baseline flowfield of the annular stream in various crossflow conditions was studied first without actuation. The injector's active and passive actuation modes of operation are then evaluated and compared across multiple crossflow conditions with the baseline data. In the active mode, the annular stream is actuated by a pulsed jet operating at 17 kHz. In steady mode, the actuation jet is a steady coaxial underexpanded jet. Measurements using planar laser-induced fluorescence (PLIF) indicate that the active coaxial injection approach using high-frequency pulsed jets at the core significantly improves mixing of the acetone-seeded annular stream in supersonic crossflow conditions compared to the steady and baseline test cases. Data suggests that such a system has the potential to be evaluated further for real-life flow mixing and control applications, such as supersonic and hypersonic combustors.