TY - JOUR
T1 - Evaluation of physicochemical variability of sustainable aviation fuels
AU - Oldani, Anna L.
AU - Solecki, Alexandra E.
AU - Lee, Tonghun
N1 - The International Civil Aviation Organization (ICAO) defines Alternative Jet Fuels (AJF) as any fuel derived from an unconventional (non-petroleum based) feedstock (). In the past decade, significant strides have been made in developing newer, more optimal production pathways for these fuels. Sustainable Aviation Fuels (SAF) are a subset of AJF that have gained popularity in recent years in response to aggressive global goals in de-carbonizing the aviation industry (). SAF production pathways can be broadly categorized by processing method and include Fischer-Tropsch (FT), Hydroprocessed Esters and Fatty Acids (HEFA) [previously known as Hydrotreated Renewable Jet (HRJ)], Synthesized Iso-Paraffins (SIP), Synthetic Kerosene with Aromatics (SKA), Alcohol to Jet (ATJ), Catalytic Hydrothermolysis (CHJ), and Hydrocarbon Hydroprocessed Esters and Fatty Acids (HC-HEFA). In September 2021, the White House published a new Sustainable Aviation Fuel Grand Challenge, a plan outlining a multi-modal approach to increase annual SAF production to at least 3 billion gallons by 2030 (). The push to develop these fuels can be attributed to several key drivers, namely: economic incentives, energy security, and environmental considerations. With high price volatility in the global fuel market, fuel producers and customers want to secure predictable fuel sources independent of external suppliers, additionally supporting domestic skilled job growth. In recent years, jet fuel price volatility has skyrocketed, with fuel prices rising by more than 70% in 2021 alone (). The second key driver for SAF development, energy security, is reflected in US government mandates that set clear requirements for various military branches to secure alternative energy sources, with the Navy goal of 50% alternative energy for its fleet by 2020 (). The national government realizes the advantage in having secure domestic energy resources, not subject to international conflicts, which can cause supply disruptions and further challenges. Finally, some SAF have the potential to provide environmental benefits, namely in the reduction of fossil fuel usage and greenhouse gas/particulate emissions levels. As shown in a recent report, conventional jet fuel blending with HEFA in a 50:50 (by volume) blend reduces particulate emissions from aircraft at cruise conditions by greater than half and up to 70% (). Fuel producers seek to develop “drop-in” SAF that can be blended with conventional fuels and used in current engine architectures. This reduces switching costs of having to update engine systems, fuel lines, storage facilities, and delivery equipment while minimizing risks associated with keeping incompatible fuels and systems separate. Current SAF specifications set maximum blending limits to ensure compatibility in operating systems. Before obtaining blending approval, new SAF must undergo rigorous testing from property evaluation to rig and engine testing, which is cost and time intensive for producers, discouraging greater SAF development. The extensive fuel database maintained by the Air Force Research Laboratory (AFRL) provided much of the needed fuel property data utilized for this study and is available through the Alternative Jet Fuel Test Database (AJFTD) maintained at the University of Illinois at Urbana-Champaign ( altjetfuels.illinois.edu ). This is in collaboration with the National Jet Fuel Combustion Program and supported by the FAA Center of Excellence for Alternative Jet Fuels and Environment (ASCENT) research program, funded by the FAA, NASA, Department of Defense, Transport Canada, and the EPA. Much of the work in the SAF landscape concerns feedstock and fuel production, life cycle economic and environmental analyses, and end use emissions and noise studies. In safely and efficiently integrating SAF produced from broadly varied feedstocks, understanding the relations between fuel composition and combustion performance and fuel physical/chemical properties is of utmost concern and has lacked significant study. The following sections of this paper will address this area through a statistical analysis of the variability present in jet fuels for key fuel properties preceded by a discussion of the SAF certification process.
This work was funded by the US Federal Aviation Administration (FAA) Office of Environment and Energy as a part of ASCENT Project 33 under FAA Award Number: 13-C-AJFE-UI Amendment 33. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the FAA or other ASCENT sponsors. This research was performed while Anna Oldani held a National Science Foundation Graduate Research Fellowship.
PY - 2022/11/24
Y1 - 2022/11/24
N2 - This study outlines an effort to report on the physicochemical variability of Sustainable Aviation Fuels (SAF), leveraging data from the FAA Alternative Jet Fuels Test Database (AJFTD). The AJFTD, containing fuel sample records of conventional and sustainable aviation fuels to date, was developed by the PIs through the FAA Center of Excellence (ASCENT). With the development of SAF from various feedstocks and processing methods, new approval processes have been developed to accommodate the changing jet fuel landscape. To control for these differences, approval procedures were designed as each new fuel category came through the development pipeline. However, recent studies have suggested that rather than feedstock or processing method, chemical properties and fuel performance can be accurately judged by considering fuel composition characteristics such as carbon chain length, hydrocarbon class, and branching level. To quantify the variability present in recently approved jet fuels, this paper evaluates physicochemical property variability and provides relevant thermophysical property relations for conventional and alternative jet fuels with a discussion of efforts to streamline approval, reducing the time and cost of bringing new SAF to future markets. Findings from this study show that the variability in the composition and properties of SAF as compared to conventional fuels is small enough such that they still satisfy specification requirements outlined by the American Society for Testing and Materials (ASTM) D7566 standards for aviation fuels containing synthesized hydrocarbons.
AB - This study outlines an effort to report on the physicochemical variability of Sustainable Aviation Fuels (SAF), leveraging data from the FAA Alternative Jet Fuels Test Database (AJFTD). The AJFTD, containing fuel sample records of conventional and sustainable aviation fuels to date, was developed by the PIs through the FAA Center of Excellence (ASCENT). With the development of SAF from various feedstocks and processing methods, new approval processes have been developed to accommodate the changing jet fuel landscape. To control for these differences, approval procedures were designed as each new fuel category came through the development pipeline. However, recent studies have suggested that rather than feedstock or processing method, chemical properties and fuel performance can be accurately judged by considering fuel composition characteristics such as carbon chain length, hydrocarbon class, and branching level. To quantify the variability present in recently approved jet fuels, this paper evaluates physicochemical property variability and provides relevant thermophysical property relations for conventional and alternative jet fuels with a discussion of efforts to streamline approval, reducing the time and cost of bringing new SAF to future markets. Findings from this study show that the variability in the composition and properties of SAF as compared to conventional fuels is small enough such that they still satisfy specification requirements outlined by the American Society for Testing and Materials (ASTM) D7566 standards for aviation fuels containing synthesized hydrocarbons.
KW - AJFTD
KW - alternative jet fuel test database
KW - certification
KW - fuel properties
KW - fuel variability
KW - jet fuel
KW - physicochemical
KW - sustainable aviation fuel
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U2 - 10.3389/fenrg.2022.1052267
DO - 10.3389/fenrg.2022.1052267
M3 - Article
AN - SCOPUS:85143439398
SN - 2296-598X
VL - 10
JO - Frontiers in Energy Research
JF - Frontiers in Energy Research
M1 - 1052267
ER -