Structures and phase transition processes of supercritical methane/ethylene mixtures injected into a subcritical environment

The structure and phase transition of supercritical methane/ethylene mixtures injected into quiescent subcritical nitrogen were investigated in this study. Visualization of the near-field jets and flow structure inside the injector, as well as measurement of shock/jet structures, were performed using shadowgraph images. It was found that supercritical methane/ethylene jets injected away from the critical point undergo ideal-gas-like expansion and exhibit visible internal shock structures. Opaque jets with condensation occurring at the injection plane or even inside the injector were observed when the supercritical mixture was injected near the critical point. The pressure profile along the injector axis for the condensed jet indicates that a pressure rise inside the injector comes from the release of latent heat during homogeneous nucleation processes and is the primary factor in the production of a large jet expansion angle in the condensed jet. The fluid along streamlines passing through the Mach disk is less likely to condense, due to the short residence time within the nongaseous region and substantial increases in pressure and temperature downstream of the Mach disk.