Building Structure-Property Relationships of Cycloalkanes in Support of Their Use in Sustainable Aviation Fuels

Abstract

In 2018 13.7 EJ of fuel were consumed by the global commercial aviation industry. Worldwide, demand will increase into the foreseeable future. Developing Sustainable Aviation Fuels (SAFs), with decreased CO2 and soot emissions, will be pivotal to the on-going mitigation efforts against global warming. 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). Further, our data set includes cycloalkanes drawn from the following structural groups: fused cycloalkanes, n-alkylcycloalkanes, branched cycloalkanes, multiple substituted cycloalkanes, and cycloalkanes with different ring sizes. In addition, a select number of cycloalkanes are blended into Jet-A fuel (POSF-10325) at 10 and 30 wt%. Comparison of neat and blended physical properties are presented. One major finding is that ring expanded systems, those with more than six carbons, have excellent potential for inclusion in SAFs. Our data also indicate that polysubstituted cycloalkanes have higher YSI values.

Densities, Viscosities, and Speeds of Sound of n-Tetradecane and n-Alkylcyclohexane Binary Mixtures within the Temperature Range (288.15–333.15) K

“…Recently, Landera et al sought to gain information on cycloalkane behavior for use with sustainable aviation fuels. 30 Part of the screening process used to select surrogate components involves examining the physical properties that are important for engine systems, including density and viscosity. The density and viscosity influence the formation of droplets in the combustion chamber, and bulk modulus, which depends on speed of sound and density, affects the start of injection.…”

“…Cycloalkanes and linear alkanes are two of the main groups that can make up a significant portion of liquid fossil fuels (e.g., ∼20 to 47% for Jet A) and sustainable fuels (e.g., 60% for sustainable aviation fuel). − Representatives from these classes of compounds are often included in formulations of simple mixture systems (surrogate mixtures) to model the real fuel that can contain hundreds of compounds. ,,,,− Dooley et al found that the reactivity of a surrogate mixture containing a cycloalkane better matched the real fuel reactivity than did a surrogate without cycloalkanes. Recently, Landera et al sought to gain information on cycloalkane behavior for use with sustainable aviation fuels . Part of the screening process used to select surrogate components involves examining the physical properties that are important for engine systems, including density and viscosity.…”

Sustainable Aviation Fuels for Clean Skies: Exploring the Potential and Perspectives of Strained Hydrocarbons

“…For example, Jet-A (POSF-10325) fuel typically contains an average of 32 wt % total cycloalkanes including both mono- and bicyclic alkanes . When 10 or 30 wt % of cycloalkanes is added to Jet-A, the cycloalkane content in the standard fuel increases from 32 wt % to 40 or 52 wt %, respectively . There is an urgent need to understand the changes in the physical and chemical properties of the fuel based on varied percentages of different blended components of SAFs to explore how energy is stored within the structures of the cycloalkanes, to establish the structure–property relationship, and ultimately to rationally design new cycloalkanes for SAFs.…”

Insights into Constraining Rate Coefficients in Fuel Oxidation Mechanisms Using Genetic Algorithm Optimization

“…Incomplete combustion of cycloalkanes at high temperatures can also potentially lead to production of polycyclic aromatic hydrocarbons and soot particles. 13,14 At low temperatures, cycloalkanes tend to be less reactive than the corresponding linear alkanes because of conformational strain imposed by the ring. 14,15 Cyclohexane is a typical cycloalkane that exhibits the common characteristics of a cyclic hydrocarbon and can serve as a general model for understanding cycloalkane reactivity.…”

“…Cyclic hydrocarbons can make up a large fraction (15–40%) of traditional transportation fuels − and their content can be up to 100% in unconventional fuels, including coal-based synthetic, shale-derived, and biomass fuels. A recent study suggests that cycloalkanes can be useful in developing sustainable aviation fuels by reducing the need for aromatic additives, which have high soot formation propensity during combustion. Incomplete combustion of cycloalkanes at high temperatures can also potentially lead to production of polycyclic aromatic hydrocarbons and soot particles. , At low temperatures, cycloalkanes tend to be less reactive than the corresponding linear alkanes because of conformational strain imposed by the ring. , …”