Carbon capture and storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO₂ to supercritical conditions. To reduce the power requirements, supercritical carbon dioxide compressors must operate near saturation where phase change effects are important. Nonequilibrium condensation can occur at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on metastable fluid properties. In this paper, we assess the behavior and nucleation characteristics of high-pressure subcooled CO2 during the expansion in a de Laval nozzle. The assessment is conducted with numerical calculations and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41-82 bar. The state of the metastable fluid is characterized through pressure and density measurements, with the latter obtained in a first-of-its-kind laser interferometry setup. The inlet conditions of the nozzle are moved close to the critical point to allow for reduced margins to condensation. The analysis suggests that direct extrapolation using the Span and Wagner equation of state (S-W EOS) model yields results within 2% of the experimental data. The results are applied to define inlet conditions for a supercritical carbon dioxide compressor. Full-scale compressor experiments demonstrate that the reduced inlet temperature can decrease the shaft power input by 16%.

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This paper presents a numeric al framework for characterizing fuel injection in modern combustors. The approach utilizes scaling analysis to describe the dro plet evaporation in non - dimensional and fluid - independent terms. The results of the model are validated against published experimental data of isolated droplets evaporating at subcritical and near - critical conditions. The model is incorporated in a spray c alculation framework and extended to the supercritical regime to assess the impact of different fluid - properties and evaporation models on temperature and fuel vapor distributions. The results suggest that in a non - convective environment the transient and quasi - steady evaporation rates vary exponentially with Lewis number. Furthermore, the results show fluid - independent behavior of the droplet evaporation, indicating that a single - component fluid can potentially be used as a modeling surrogate for jet fuel . The first - principles analysis demonstrates that classical evaporation models overestimate transient evaporation and underestimate quasi - steady evaporation, with discrepancies up to 70% at supercritica l conditions. This is due to limitations in fuel - prope rty description and the lack of non - isothermal droplet characterization at near - critical conditions. The temperature profiles are typically under - predicted and fuel vapor concentrations are over - predicted in standard spray calculations with subcritical eva poration models. As such the proposed framework breaks new ground in modeling of supercritical fuel injection. The improved quality in the predicted fuel concentration and temperature distribution can enable more accurate assessment of flame position, impr oving the estimation of combustion stability margins and NOx emissions. The model can be incorporated in commercial codes to guide the design of combustors operating at supercritical conditions. @en