The REFINE project focuses on the experimental investigation and numerical simulation of real-fluid injection and mixing processes under sub-, trans- and super-critical conditions. The domain of interest of the present proposal concerns the propulsion with application to the automotive and aerospace science and technology where supercritical fluids may be considered as propellants. Indeed, the need for higher efficiency and lower emission levels leads to increase pressure and temperature levels, i.e. to reach supercritical properties of fluids. The objective of REFINE is to build a simple well-controlled test-bench able to study a fluid injection under sub-, trans- and super-critical conditions and to associate experimental and numerical diagnostics to deliver the finest information. An ethane injection occurs in a 5-liter high-pressure experimental test-bench. The X-ray diagnostics setting-up will be the project keystone, as it allows for delivering a non-polluted density measurement. Indeed, such diagnostics are not disrupted by the index gradient observed in corrugated flows, contrary to laser techniques. Colored background oriented Schlieren visualization is used for backup as well as a more classical shadowgraphy technique. Numerical simulations will be realized in parallel to consolidate physics understanding and for model validation.