Experimental Investigation of Superheated Liquid Injection in Quiescent and Supersonic Crossflow

This research delves into liquid fuel injection in scramjet combustors, with a focus on the effects of injector length-to-diameter (L/D) ratios and temperatures, spanning from ambient to superheated states. Efficient atomization within the short residence times of liquid-fueled supersonic combustors is crucial for maximizing combustion efficiency. Initial investigations in a quiescent environment aimed to isolate the impact of injector geometry and temperature, utilizing quantitative analysis and diffused backlit illumination to demonstrate that heating fuel beyond its boiling point significantly enhances atomization and dispersion. A notable finding is that higher L/D ratios led to a quicker initiation of flash boiling. Subsequent analyses under supersonic crossflow, using two-dimensional planar laser-induced fluorescence, support these observations. The study further employs spray structure and spatiotemporal characteristic analyses, coefficient of variation, and proper orthogonal decomposition, revealing enhanced flashing atomization at higher L/D ratios. This underscores the critical role of injector design and temperature in optimizing fuel atomization in scramjet engines, highlighting the nuanced interplay between physical injector characteristics and thermal properties in achieving efficient combustion.