Influence of blending cycloalkanes on the energy content, density, and viscosity of Jet-A

Abstract

This work focuses on the influence of addingvarious cyclohexanes on the volumetric and gravimetric energy content, density, and kinematic viscosity of Jet A. Mixtures of Jet-A and alkylcyclohexanes with varying alkyl-chain lengths, degrees of branching, and number of rings at 5, 10, 15, 30, and 60 % wt./wt. were examined. Among the alkylcyclohexanes under study, addition of the compounds with the longest alkyl chains, i.e., n-hexylcyclohexane and n-heptylcyclohexane, were identified as compounds with the potential to increase both the specific and energy density of the mixtures. Contrasting results obtained for 1,2,3-trimethylcyclohexane (decreasing specific energy and increasing density) and 1,3,5-trimethylcyclohexane (decreasing energy density and kinematic viscosity) revealed the importance of the relative position of the substituents in cycloalkanes. More sterically hindered isomers and less symmetrical structures were associated to higher density and kinematic viscosity values. C9-cycloalkanes were identified as potential molecules to decrease the kinematic viscosity of blending mixtures. Branched structures in C12-cycloalkanes, such as 1,3-diisopropylcyclohexane and 1,4-diisopropylcyclohexane, were found to decrease gravimetric energy. However, additions higher than 15 % wt./wt. of branched cycloalkanes were also associated with increments of the volumetric energy content to values similar when linear alkyl-chain cycloalkanes of the same carbon number were added into the mixture. Decalin withcis-stereochemistry exhibited greater energy density, density, and kinematic viscosity thantrans-stereochemistry. JP-10 additions provided slightly higher energy densities but lower specific energies thancis-decalin. At low mass additions (<10 % wt./wt.), tricyclic compounds, such as tetradecahydroanthracene and adamantane, caused the largest increases in the energy density and density of the mixtures. Tetradecahydroanthracene increased the specific energy by +0.26 % and the volumetric energy by +1.40 % when added at 5 and 10 % wt./wt., respectively. However, larger mass additions (>10 % wt./wt.) of adamantane into Jet-A are not possible due to solubility conditions. Additions of JP-10 (28 % wt./wt.), cis-decalin (40 % wt./wt.), or trans-decalin (50 % wt./wt.) into Jet-A are proposed to maximize energy content (∼+3.5 %) while meeting density and kinematic viscosity requirements. These results broaden the understanding of cycloalkanes as potential key compoundsof sustainable aviation fuels withhigher energy content and minimal environmental impact.