Supercritical jets characteristics in different gas environments

To improve the thermal efficiency of engines, the temperature and pressure in the combustion chamber are raised close to the critical point of fuels, altering the mixing regime of jets. However, the mixing regime transition is not only affected by the critical point of fuels but also affected by the physical properties of ambient gases, which need to be further investigated. To investigate the mixing regime transition of jets with different fuels and ambient gases, this study used high-speed microscopic imaging to capture liquid propane jets in helium, nitrogen, and carbon dioxide. Liquid R134a was compared to propane to evaluate the effect of the fuel density. Results show that the morphological mixing regime of jets is dominated by the density of the ambient gas. Besides, the divergence angle of mixing regions in different ambient gases tends to exhibit the same profiles under supercritical chamber temperature, indicating that the divergence angle of mixing regions can be a key parameter to indicate the mixing regime transition. Furthermore, the nonlinear relationship between the divergence angle of jets and the density ratio of gas and fuel in high-temperature conditions is caused by the mixing regime transition of jets. These findings emphasize the influence of physical properties of ambient gases on mixing regimes and provide a more in-depth understanding of the transcritical mixing behavior.