Modeling fuel effects on high-pressure transcritical mixing of Sustainable Aviation Fuels.

Drop-in Sustainable Aviation Fuels (SAFs), coupled with the development of ultra-high overall pressure ratio jet engines, constitute a promising strategy to achieve carbon neutrality in aviation by mid-century. While extensive research has investigated the effects of pressure and temperature on transcritical fuel injection, significant uncertainties remain regarding the impact that surrogate fuel composition has on numerical modeling. In this regard, the present study, we present an analysis based on Large Eddy Simulations (LES), including real-fluid thermodynamic and transport modeling, to characterise the high-pressure injection of SAFs. We focus on the Alcohol-To-Jet (AtJ) fuel POSF-11498, classified as a Category C fuel by the National Jet Fuels Combustion Program (NJFCP). We assess how different approaches to fuel modeling impact the turbulent transcritical mixing dynamics by comparing surrogate representations of varying fidelity. We show that a two-component surrogate capturing the key $C_{12}$ and $C_{16}$ branched paraffins closely matches the results of the seven-component surrogate while significantly reducing computational cost. In contrast, a single-component model misses critical non‑ideal effects. This binary surrogate, therefore, provides an efficient, high‑fidelity choice for LES of transcritical SAF injection.