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As fuel injection systems advance towards higher injection pressures and the combustor environment increases in both temperature and pressure in the pursuit of improved emissions and efficiency, advanced combustion strategies are required. Injecting fuel as a supercritical fluid has the potential to improve fuel/air mixing and eliminate steps in the spray vaporization process. Experiments are carried out on a heated fuel injector in an open-air test cell using Mie scattering, Schlieren imaging, and long-distance microscopy to investigate changes in spray characteristics with varying temperature and pressure. Spray angle, spray penetration length, and vapor-liquid ratio data are collected and evaluated. Near-nozzle imaging shows distinct changes in spray morphology during the initial microseconds of spray formation. Sprays injected under conditions further into the supercritical regime exhibit increased spray angle and vapor-to-liquid ratio. Spray penetration is found to decrease with increasing temperature. A jump in vapor-to-liquid ratio is observed in the vicinity of 568 K, indicating a transition in spray behaviour trending towards more rapid fuel/air mixing across the transcritical region. Changes in the micro-scale structure of the spray during the initial microseconds of spray formation exhibit this same narrow transition region. A significantly greater fraction of the spray plume is observed to be in a vapor or vapor-like state at a given time after injection initiation as the injection conditions are advanced into the supercritical state. These findings indicate that injection fuel as a supercritical fluid has the potential to improve the mixing of a fuel/air charge, and thus, improve combustion quality.