This thesis applies simultaneous laser diagnostics to steady, rotationally symmetric, laminar jets of fluoroketone injected into a high-pressure and high-temperature vessel with the goal to unambiguously identify interface transitions under trans-critical conditions, for the first time. The chamber was filled with nitrogen and the ambient thermodynamic conditions were varied from subcritical, to transcritical, to supercritical levels, relative to both the pure injectant and the binary mixture that ultimately developed in the chamber following injection. The laminar jet presents a clear interface that can be studied optically and its evolution was monitored under different test cases. Vapour-liquid equilibrium calculations for the binary mixture helped establish conditions that would identify the mixture as supercritical. This was necessary owing to the effect that mixing has on the critical properties of the mixture (relative to its constituents) and to design the test cases.
Consistent with previous reports, it was found that the addition of nitrogen resulted in a rapid increase of the critical pressure of the mixture. The calculated phase envelopes reported here demonstrate the highly non-linear nature of mixing effects for the given binary mixture. Two main laser diagnostic techniques were employed: 1) Planar Laser Induced Fluorescence (PLIF) and 2) Planar Elastic Light Scattering (PELS). The former was used to obtain images of the mixture spatial distribution and the latter to monitor the strength of the interface. The diagnostics were applied simultaneously, thus allowing the comparison of interface strength and flow morphology at the same physical location and point in time. Using the average flow velocity at the nozzle, based on the known mass flowrate, and data from the elastic scattering signal, temporal estimates of the fluid interface destruction were calculated. Imaging results have shown that under all test cases a jet could be seen via PLIF, but a PELS signal was not always recorded. By knowing when a fluid interface was present or not, the PLIF images could be analysed in light of such information. Further, with the use of thermocouples 2-D temperature maps were obtained in the plane of injection. The temperature results presented further information about the heat transfer process of transcritical, laminar jets and, depending on the adopted definition of a supercritical fluid, indicated regions where the fluid was more likely to be supercritical. Cooling of the jet under the most demanding test case considered may have been an observation of pseudo-boiling effects (and their significance) due to injection near the Widom line. Investigation of intermittent, interface scattering observed even under supercritical cases revealed that the reflectivity of the fluid interface could potentially persist even beyond significant broadening of the interface. This meant that a decay of the interface scattering signal to zero would not necessarily coincide with the destruction of the interface, and some scattering could still be observed in supercritical cases where no interface is considered to be present. Magnified PLIF experiments were also done to obtain higher-fidelity images and density maps. These provided more information on fluid flow features and mixture distribution
