Quantifying isomeric effects: A key factor in aviation fuel assessment and design

Isomeric structural differences can profoundly influence hydrocarbon properties of importance to aviation turbine fuels. This is particularly true for alternative fuels that often contain fewer components than conventional fuels, making isomeric differences more impactful. The inability of standard analytical methods to distinguish isomers within a hydrocarbon family poses a significant challenge for the assessment and formulation of jet fuels. Such missing information leads to considerable uncertainties in model predictions used for fuel assessment, or aircraft and jet engine design. This work explores the influence of isomers on critical fuel properties using quantitative metrics from the chemical family, size, topology, and, particularly, branching. Isomeric property ranges within a given hydrocarbon class are deduced from a database study. The extent of these intrahydrocarbon group property ranges is related to the change conferred via shifting to adjacent carbon numbers and dissimilar hydrocarbon families. This approach shows that isomeric information is as critical, if not more, for properties such as viscosity and freeze point, as carbon number and hydrocarbon class. This perspective significantly changes from the historical focus on carbon numbers and group-type analysis procedures. The correlations identified in this study can serve as a foundation for improving chemometrics. This, in turn, can enhance the accuracy of model-based property prediction and facilitate the design of new sustainable aviation fuels at a component level.