Fuel Qualification

The aviation industry agrees that alternative fuels should “drop-in” to commercial engines, pipelines, fuel farms, and all other distribution and storage channels, thus requiring no new, modified, or segregated equipment or infrastructure. As a result, the sector has developed rigorous testing requirements to compare the properties of new, alternative jet fuels to petroleum-derived jet fuel to determine whether a fuel can be considered “drop-in.” This process and the development and management of specifications for alternative aviation fuels, are accomplished in the United States by ASTM International’s Committee D02.J0.06 (Emerging Turbine Fuels).

CAAFI’s Role

CAAFI’s members are engaged in two ways to assist potential producers with understanding and navigating their way through eventual industry fuel qualification.

  1. The CAAFI Certification and Qualification (CQ) Team helps to facilitate promising alternative jet fuels through the industry evaluation process towards the goal of specification issuance by ASTM International and other recognized certifying bodies. CAAFI’s CQ Team facilitates the creation of task forces to: collect appropriate data, write research reports, and obtain reviews from original equipment manufacturers (OEMs) throughout the ASTM process. A variety of CAAFI stakeholders, including government agencies, fuel producers, aircraft and engine manufacturers, and airlines participate on the CQ Team.
  2. The CAAFI Research and Development (R&D) Team can assist early stage technology developers or potential producers, prior to CQ and ASTM engagement:
    • In helping them understand their pending aviation engagement;
    • Identifying key technology needs and highlighting such in white papers targeted to various agencies and research institutions;
    • With Fuel Prescreening testing and analysis efforts designed to allow for process tweaks that might streamline their eventual qualification efforts.

D4054 Fuel Approval Process

Below are suggested steps to facilitate the D4054 fuel approval process of getting your fuel approved for deployment and commercialization. For more information, please see the CAAFI “Path to Alternative Jet Fuel Readiness” briefing document that outlines the process of fuel development, qualification and certification, and the role of CAAFI in facilitating the process in more detail.

  • Get to Know the Aviation Community
    To establish your company as an AJF provider, it is beneficial to develop relationships and engage the aviation community to share what you are working on and explain its potential for meeting aviation needs. Becoming a member of CAAFI is a great way to do this.
  • Establish Your Product as a Viable Aviation Fuel
    A new fuel producer must demonstrate the viability of their fuel for aviation (i.e., fuel performance, fitness for purpose and environmental benefits). Lack of due diligence or basic progress in these areas can entirely halt your fuel’s acceptance.
  • Conduct Technical/Performance Evaluation
    ASTM D4054 defines the requirements for technical evaluation of aviation fuels. To establish your fuel as a viable aviation jet fuel, you must develop data in accordance with D4054 for review by aviation fuel community stakeholders.
  • Conduct Environmental Evaluation
    You should be continually looking for ways to improve the environmental performance of your fuel production process and feedstock. Aviation fuel purchasers will be looking for a greenhouse gas emissions (GHG) Life Cycle Analysis (LCA) indicating that your fuel produces lower life cycle GHG emissions than conventional petroleum fuel. Your GHG LCA should be performed according to an internationally accepted methodology.
  • Engage with the Aviation Industry regarding Commercial Progress and Fuel Availability for Testing
    ASTM International Committee D.02, Petroleum and Lubricants, Subcommittee J, is responsible for the evaluation and approval of new aviation fuels. Prospective alternative fuel producers will need to participate in this committee and engage the other committee members in the evaluation and approval process. The approval process is detailed below.

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D4054 Qualification Process Overview

  1. Commercial aircraft manufacturers certify that their aircraft will achieve mandated performance and operability aspects when they operate with fuel meeting certain criteria defined in an internationally recognized specification. If an operator uses fuel that meets this specification, then the aircraft operate as expected. The most commonly used specification of conventional aviation turbine fuel is ASTM D1655 (Standard Specification for Aviation Turbine Fuels), while other equivalent standards may exist (DEF STAN 91-091). ASTM D1655 allows for alternative fuels that demonstrate their equivalence to conventional jet fuel, and are listed in ASTM D7566, to be redesignated as D1655 fuel.
  2. New AJF must go through ASTM’s D4054 Evaluation Process to determine if it is equivalent (either neat or as a blend) to conventional jet fuel.
  3. If the fuel is determined to be equivalent, an Annex with the new AJF (including any required blending level) is added to the D7566 Drop-In Fuel Specification.
  4. Since the D7566 Drop-In Fuels Specification meets the ASTM Conventional Fuel Specification, the new SAF is approved for use in all existing commercial aircraft.

Please refer to the following flowchart.

The current ASTM D4054 Evaluation Process for getting a fuel approved for commercial use includes the following three phases (also see figure below):

  • Phase 1. Initial Screening
    • Based on a request from the producer or technology developer, the ASTM Subcommittee approves the establishment of a Task Force for the new AJF. This Task Force is typically led by the producer/developer, but could also be a group of companies with similar pathways who want to pursue qualification. The intent for the task force is to oversee all of the work leading to qualification, but also to enable input and assistance from other members who have knowledge and experience that might help expedite the effort.
    • Data and research are acquired through Tier 1 (Specification Properties) and Tier 2 (Fit-for-Purpose Properties) testing.
    • Testing results are compiled into a Phase 1 Research Report and submitted to participating Original Equipment Manufacturers (OEMs) for review. OEM review is necessary to determine if the proposed SAF is fit for purpose for use on aircraft and engines, and to identify the Phase 2 testing requirements.
    • OEMs review the report and approve the fuel to move on to Tier 3 and Tier 4 testing in Phase 2 with specific testing requirements.
  • Phase 2. Follow-on Testing
    • In Phase 2, data and research are compiled from defined Tier 3 (Component/Rig Testing) and Tier 4 (Engine and Auxiliary Power Unit Testing) testing requirements.
    • Testing results are compiled into a Phase 2 Research Report and submitted to OEMs for review and approval.
    • Similar to Phase 1, OEM review is necessary to determine if the proposed AJF is fit for purpose for use on aircraft and engines.
  • Phase 3. Balloting and Approval
    • Once approved for Phase 3, the U.S. Federal Aviation Administration (FAA) reviews the OEMs’ approvals and specification language, and concurs that initial balloting should be initiated at the subcommittee level.
    • ASTM allows a period for comments and review. All members of the D02.J subcommittee have an equal opportunity to comment or vote for acceptance or rejection.
    • Comments are addressed to mitigate concerns (additional data generation/research conducted if required). These may be discussed and voted on at the semiannual ASTM meeting.
    • Final balloting at the committee level occurs when all subcommittee level comments are addressed. All members of the full D02 committee have an equal opportunity to comment or vote for acceptance or rejection.
    • Ballots are considered passed with a unanimous affirmative vote, or when negative votes are withdrawn or overruled by the committee or subcommittee members.
    • Upon passage of the ballot, ASTM adds the new fuel to the D7566 standard as a new annex.

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Approved Fuels

The following drop-in alternative jet fuels went through the D4054 process and are qualified for commercial use (presented in chronological order of approval, as listed in the Annexes of D7566). These approved fuels represent multiple conversion processes associated with various feedstock types.

  • Annex A1: Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK)
    • Year of Certification: 2009
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 50% maximum level.
    • Feedstock(s): Synthesis gas (or syngas, a mixture of CO and H2). Syngas is typically produced from the gasification of biomass such as municipal solid waste (MSW), agricultural and forest wastes, and wood and energy crops, as well as non-renewable feedstocks such as coal and natural gas. The feedstock is gasified at high temperatures (1200 to 1600 degrees Celsius), which deconstructs the feedstock into carbon monoxide, hydrogen, and CO2 primarily, as well as some ash. The gas mixture is separated and cleaned to produce pure syngas, and it is then converted to long carbon chain waxes through the FT Synthesis Process. Syngas, or its components, can also come from other industrial processes.
    • Process/Product Description: The Fischer-Tropsch (FT) Synthesis Process is a catalyzed chemical reaction in which synthesis gas is converted into liquid hydrocarbons of various forms via the use of a reactor with cobalt or iron catalyst. The wax is then cracked and isomerized to produce drop-in liquid fuels essentially identical to the paraffins in petroleum-based jet fuel, but the FT process does not typically produce the cyclo-paraffins and aromatic compounds typically found in petroleum-based jet fuel.
  • Annex A2: Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene (HEFA-SPK)
    • Year of Certification: 2011
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 50% maximum level.
    • Feedstock(s): Specifically, fatty acids and fatty acid esters, or more generally various lipids that come from plant and animal fats, oils, and greases (FOGs).
    • Process/Product Description: Natural oils are converted from lipids to hydrocarbons by treating the oil with hydrogen to remove oxygen and other less desirable molecules. The hydrocarbons are cracked and isomerized, creating a synthetic jet fuel blending component comprised of paraffins.
  • Annex A3: Hydroprocessed Fermented Sugars to Synthetic Isoparaffins (HFS-SIP)
    • Year of Certification: 2014
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 10% maximum level
    • Feedstock(s): Sugars
    • Process/Product Description: The process uses modified yeasts to ferment sugars into a hydrocarbon molecule. This produces a C15 hydrocarbon molecule called farnesene, which after hydroprocessing to farnesane, can be used as a blendstock in jet fuel.
  • Annex A4: Fischer-Tropsch Synthetic Paraffinic Kerosene with Aromatics (FT-SPK/A)
    • Year of Certification: 2015
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 50% maximum level.
    • Feedstock(s): Same as Annex A1.
    • Process/Product Description: Uses the FT Synthesis Process plus the alkylation of light aromatics (primarily benzene) to create a hydrocarbon blend that includes aromatic compounds that are required to ensure elastomer seal swell in aircraft components to prevent fuel leaks. FT-SPK/A introduces the migration toward fuels that offer a full spectrum of molecules found in petroleum-based jet fuel, rather than just paraffins.
  • Annex A5: Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK)
    • Year of Certification: 2016
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 50% maximum level.
    • Feedstock(s): This annex is intended to eventually cover the use of any 2 to 5 carbon alcohols, but at present, it only allows the individual use of ethanol and isobutanol. The alcohols can come from any source, but are usually derived from:
      • Fermentation of starches/sugars, which themselves can come from starch/sugar producing feedstocks (e.g. field corn, sweet sorghum, cane, sugar beets, tubers) or derived from cellulosic biomass (e.g. via hydrolysis from lignocellulose).
      • The biochemical conversion of other forms of hydrogen and carbon (e.g. via organisms that convert CO, H2 and CO2 to alcohol).
    • Process/Product Description: Dehydration of isobutanol or ethanol followed by oligomerization, hydrogenation and fractionation to yield a hydrocarbon jet fuel blending component.
  • Annex A6: Catalytic Hydrothermolysis Synthesized Kerosene (CH-SK, or CHJ)
    • Year of Certification: 2020
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 50% maximum level.
    • Feedstock(s): Specifically, fatty acids and fatty acid esters, or more generally various lipids that come from plant and animal fats, oils and greases (FOGs).
    • Process/Product Description: Hydroprocessed synthesized kerosene containing normal and iso-paraffins, cycloparaffins, and aromatics produced from hydrothermal conversion of fatty acid esters and free fatty acids along with any combination of hydrotreating, hydrocracking, or hydroisomerization, and other conventional refinery processes, but including fractionation as a final process step.
  • Annex A7: Hydroprocessed Hydrocarbons, Esters and Fatty Acids Synthetic Paraffinic Kerosene (HHC-SPK or HC-HEFA-SPK)
    • Year of Certification: 2020
    • Blending: Required to be blended with petroleum-based jet fuel, up to a 10% maximum level.
    • Feedstock(s): Specifically, bio-derived hydrocarbons, fatty acid esters, and free fatty acids. Recognized sources of bio-derived hydrocarbons at present only include the tri-terpenes produced by the Botryococcus braunii species of algae.
    • Process/Product Description: Bio-derived hydrocarbons and lipids are converted to hydrocarbons by treating the feedstock with hydrogen to remove oxygen and other less desirable molecules. The hydrocarbons are cracked and isomerized, creating a synthetic jet fuel blending component comprised of paraffins.

The Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants, as well as their D02.J0 Sub-committee on Aviation Fuels, have also approved the co-processing of renewable content with crude oil-derived middle distillates in petroleum refineries. This includes:

  • Lipids (plant oils and animal fats)
  • Fischer Tropsch Biocrude (unrefined hydrocarbon content coming from an FT reactor)

The co-processing provisions have been added to Annex A1 of ASTM D1655, Standard Specification for Aviation Turbine Fuels. The Annex includes co-processing of up to 5% by volume of these components as feedstocks in petroleum refinery processes.

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Current Fuels in the D4054 Qualification Process

The table below shows the pathways actively pursuing certification at various stages in the process.

ASTM Progress Pathway Feedstock Task Force Lead
ASTM Balloting
Phase 2 OEM Review
Phase 2 Testing Hydro-deoxygenation Synthetic Kerosene (HDO-SK) Sugars and cellulosics Virent (inactive)
Hydro-deoxygenation Synthetic Aromatic Kerosene (HDO-SAK) Sugars and cellulosics Virent
Phase 1 OEM Review High Freeze Point Hydroprocessed Esters and Fatty Acids Synthetic Kerosene (HFP HEFA-SK) Renewable FOG Boeing
Integrated Hydropyrolysis and Hydroconversion (IH2) Lignocellulosics Shell
Phase 1 Research Report
Phase 1 Testing Alcohol-to-Jet Synthetic Kerosene with Aromatics (ATJ-SKA) Sugars and lignocellulosics Swedish Biofuels, Byogy
Alcohol-to-Jet (ATJ) Sugars Global Bioenergies

Pre-Qualification Process Fuels

CAAFI is aware of a significant number of additional prospective pathways that are currently being pursued by multiple entities, but have yet to enter to the ASTM Qualification Process. These approaches have the potential to convert the carbon or hydrocarbon content of various feedstocks using biological (fermentation or microbial conversion) or thermochemical (pyrolysis, hydrothermal liquefaction, catalytic conversion, etc.) processes into the chemical components of jet fuel.

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Streamlining ASTM D4054 Qualification Process

There are several efforts underway to develop a more streamlined qualification process to increase process efficiency and decrease the amount of time and capital required to achieve certification. The fuel testing and evaluation goals of the Federal Alternative Jet Fuels Research and Development Strategy focus on facilitating the approval of additional SAF pathways by enabling the efficient evaluation of fuel-engine performance and safety through advancement of certification and qualification processes and collection and analysis of data.

D4054 Clearinghouse Concept

FAA’s Aviation Sustainability Center (ASCENT), or Center of Excellence for Alternative Jet Fuels & Environment, funded the establishment of the D4054 Clearinghouse. The Clearinghouse is intended to provide a “one-stop-shop” for management of the testing and data review program for candidate SAF fuels. The University of Dayton Research Institute (UDRI) is the project leader for this activity. UDRI is initially funded under ASCENT to support Phase 1 (Tier 1 and 2) testing and Phase 1 research report review of candidate SAFs. Support of Phase 2 (Tier 3 and 4) testing and final research report reviews will be contingent on the identification of other sources of funding or in-kind support. For example, National Research Council Canada proposed to support some Tier 3 and 4 Testing and the U.S. military is expected to conduct a portion of the testing. Contact info@caafi.org to connect with the D4054 Clearinghouse Team.

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D4054 Fast Track

A Fast Track provision has been incorporated as Annex A4 in ASTM D4054. The Fast Track provision permits a limited test protocol of only Tier 1 and other limited testing based on acceptable hydrocarbon bulk composition and trace material analyses. This abbreviated testing results in a new D7566 Annex for each new production concept, but is intended to avoid the need to conduct costly Tier 2, 3 and 4 testing, provided there are certain disclosures of process and management of change by producers. The blend percentage for each concept that goes through the D4054 Fast Track is limited to 10 percent and requires the blendstock to meet stringent specification criteria.

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The National Jet Fuels Combustion Program (NJFCP)

Funded by FAA through ASCENT, as well as NASA, Air Force Research Lab and others, the NJFCP is focused on developing an experimental and analytical capability to facilitate OEM evaluation of physical and chemical properties of fuels on engine operability and to streamline ASTM fuels approval process. The project includes six components:

  • Chemical kinetics combustion experiments
  • Kinetics modeling
  • Advanced combustion tests
  • Combustion modeling
  • Atomization tests and modeling
  • Referee swirl-stabilized combustor evaluation/support

The overall goal is to relate fuel properties to combustion performance to better predict the performance of novel fuels and thereby streamline fuel ASTM approval.

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Alternative Jet Fuel Prescreening

The CAAFI R&D team, in collaboration with the University of Dayton Research Institute, has introduced the Prescreening Guidance for Alternative Jet Fuels document developed from the National Jet Fuels Combustion Program (NJFCP). These are intended to be early-stage, low volume, low cost, and rapid prescreening techniques outside the formal ASTM D4054 approval and evaluation process, especially those that relate to the assessment of jet engine combustor operability, which are among the most expensive testing requirements of the evaluation process. These prescreening methods can provide early-stage confidence to fuel developers on whether AJF formulations might encounter downstream challenges with the completion of the ASTM D4054 evaluation process. These methods do not replace the ASTM D4054 evaluation process and its requirements. However, results from prescreening should provide an early assessment of whether serious combustion issues could be encountered in the formal approval process. This could help AJF developers make early decisions on AJF composition or production processes that could help facilitate later approval, either for Fast-Track or Standard approvals (see ASTM D4054 Standard Practice).

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Other Testing Work

There are numerous ongoing efforts to improve the qualification process. The results of these efforts will be posted here when available.

Alternative Jet Fuels Test Database (AJFTD)

Sponsored by the FAA under ASCENT (the Aviation Sustainability Center), the University of Illinois has developed an Alternative Jet Fuels Test Database (AJFTD), a technical library of alternative jet fuel reports and data. The database is in its first iteration, but as database development continues, all the data will be in a non-relational flexible format and will include analysis tools. Users can upload a fuel and see where it stands in comparison with the fuels already in the database. The database will also incorporate a linkage with the JETSCREEN database in Europe.

Access to the site is by invitation only, but prospective fuel producers may contact the University of Illinois to request access.

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Existing Standards and Approvals

Alternative Jet Fuel (AJF) Readiness Tools

Streamlining the ASTM Process

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Other R&D and Strategy Resources

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CAAFI Contacts

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