Finding the right mix of conventional and sustainable aviation fuels

For the aviation sector to achieve net-zero carbon emissions, about 65% of its fuel consumption must be sourced from sustainable aviation fuels (SAFs); currently, they make up less than 1%. One key challenge for scaling up is a lack of understanding of how SAFs behave under transcritical thermodynamic conditions, including the extreme pressures that occur during takeoff and climb, where the underlying physics are fundamentally different.

To help fill this gap, Molinari et al. simulated and compared the mixing dynamics and thermal evolution of conventional aviation fuel, a synthetic fuel, and an equal volume mix of the two within transcritical conditions.

The researchers found a fuel’s mixing behavior is primarily a result of its isobaric specific heat capacity. Due to its higher thermal inertia, the SAF they tested — Jet C-1 POSF-11498 (C-1 AtJ), an alcohol-to-jet synthetic fuel — mixes more slowly than traditional fuel. As a result, its liquid core remains intact for longer, and its mixing layers are narrower.

As expected, the blended fuel fell between the two pure fuels; however, its thermal response was closer to that of C-1 AtJ. Finding the right ratio will be critical for achieving the more widespread adoption of SAFs.

“Bio-based SAFs like C-1 AtJ are produced from feedstocks such as biomass-derived alcohols, which significantly reduces their lifecycle greenhouse gas emissions. Their chemical composition also means substantially less soot and particulate matter at the point of emission,” said author Marco Maria Molinari. “However, that same composition gives them a higher thermal inertia, and if the slower mixing carries over to reacting conditions, it could partially offset those benefits by reducing combustion efficiency and requiring higher fuel flow rates to deliver the same thrust.”

The group hopes this work will help inform combustor design for enhanced SAF compatibility and facilitate certification procedures that can help extend SAF utilization.

Source: “Large-eddy simulations of transcritical mixing of conventional and sustainable aviation fuels,” by Marco Maria Molinari, Davide Cavalieri, Leandro Lucchese, Jacopo Liberatori, Mauro Valorani, and Pietro Paolo Ciottoli, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0320355 .