Large-eddy simulations of transcritical mixing of conventional and sustainable aviation fuels

Drop-in sustainable aviation fuels (SAFs), in conjunction with gas turbines featuring increased overall pressure ratios, are central to the decarbonization of the aviation sector in the short to medium term. However, the impact of SAF thermophysical properties on mixing processes under transcritical conditions, supported by the development of suitable numerical methodologies to represent multi-component aviation fuels, remains underinvestigated. In this study, a diffuse-interface large-eddy simulation framework, incorporating real-fluid thermodynamics based on the Peng–Robinson equation of state together with multi-component transport, is employed to analyze a single-round injector operating at 60 bar and 900 K ambient temperature. Three aviation fuels, represented by ad hoc physicochemical surrogate mixtures, are considered: a conventional petroleum-derived jet fuel (Jet A-2), an alcohol-to-jet sustainable aviation fuel (C-1 AtJ), and a 50% volumetric blend of the two, each injected at 322 K. Although the flow fields are broadly similar across all investigated fuels, statistical analyses reveal that compositional differences in the multi-component surrogates significantly alter their thermophysical properties, thereby governing the mixing dynamics under transcritical conditions. Quantitatively, Jet A-2 exhibits an approximately 27% shorter potential core and 10% wider mixing layers relative to C-1 AtJ. Furthermore, it shows temperatures 30–50 K higher in the transitional zone, while the 50% volumetric blend consistently displays intermediate behavior. These results demonstrate that the thermophysical response in the pseudo-boiling regime, particularly the fuel-specific heat capacity, governs transcritical injection and mixing in aeronautical fuel injectors.