Scientists at Sandia National Laboratories and Los Alamos National Laboratory have recently published research data demonstrating how cycloalkanes, when used in jet fuel, may reduce condensation trail formation and soot emissions as compared to current fuels. The team detailed its findings in an open-access paper published in Frontiers in Energy Research.

Minimizing aromatics in aviation fuel is desirable because of the high propensity of aromatics to produce soot during combustion. Because aromatics cause O-rings to swell, they are important for maintaining engine seals, and must be present in at least 8 vol% under ASTM-D7566.

Recently, cycloalkanes have been shown to exhibit some o-ring swelling behavior, possibly making them an attractive substitute to decrease the aromatic content of aviation fuel. Cycloalkanes must meet specifications for a number of other physical properties to be compatible with jet fuel, and these properties can vary greatly with the cycloalkane chemical structure, making their selection difficult.

Building a database of structure-property relationships (SPR) for cycloalkanes greatly facilitates their furthered inclusion into aviation fuels. The work presented in this paper develops SPRs by building a data set that includes physical properties important to the aviation industry. The physical properties considered are energy density, specific energy, melting point, density, flashpoint, the Hansen solubility parameter, and the yield sooting index (YSI).

—Landera et al.

One of the team’s key objectives has been to minimize the aromatic content of aviation fuel and replace it with cycloalkanes.

Aromatics are substances derived from refining crude oil and are used as a source of octane, which increases the engine’s power and fuel efficiency. Aromatics have traditionally been beneficial in fuel because they cause the O-rings in the engine to swell, an important function in maintaining engine seals and preventing fuel leaks.

However, aromatics are problematic because they produce soot during combustion, which, like carbon dioxide, has a greenhouse effect and contributes to the heating of Earth’s climate system, Sandia chemist Alexander Landera said.

Ideally, we would wish to remove all aromatics from fuel. But if we can even replace a large portion of the aromatics with cycloalkanes, we find they make good candidates as far as their ability to cause O-ring swelling and their strong fuel properties.

—Alexander Landera

Cycloalkanes can also be produced from feedstock or renewable biological material, Landera added, potentially making their production more carbon sustainable.

The research data examines physical properties of cycloalkanes that would influence the aircraft’s operability, performance and safety. Landera hopes that by building a database of these properties, their research will help clear the way for cycloalkane’s inclusion in future aviation fuels.

We’ve looked at various families of cycloalkanes to identify which ones have the strongest fuel properties, and which have higher energy content.

—Alexander Landera

Sandia is engaged in work to decrease the cost, increase the sustainability and expand the production and use of sustainable aviation fuels.

Resources

• Landera A, Bambha RP, Hao N, Desai SP, Moore CM, Sutton AD and George A (2022) “Building Structure-Property Relationships of Cycloalkanes in Support of Their Use in Sustainable Aviation Fuels.” Front. Energy Res. 9:771697. doi: 10.3389/fenrg.2021.771697