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Fuel Testing and Qualification

CAAFI’s Role

The 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 or modified equipment or infrastructure. The aviation 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 on emerging turbine fuels. CAAFI’s Certification and Qualification (CQ) Team helps to move 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.

Fuel Approval Process

Below are suggested steps to facilitate the 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.
  • Obtain ASTM Certification
    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.

Qualification Process Overview

  1. Commercial aircraft are certified to operate on specified fuel. All fuel used in commercial aircraft must meet the ASTM Conventional Jet Fuel Specification.
  2. To get added to the D7566 Specification, 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 SAJF 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
    • ASTM Subcommittee establishes a Task Force for the new SAJF. This Task Force is typically led by a group of companies with similar pathways who want to pursue certification.
    • 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 SAJF 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, the Tier 3 (Component/Rig Testing) and Tier 4 (Engine Auxiliary Power Unit Testing).
    • 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’ approval and initial balloting occurs at the subcommittee level.
    • ASTM allows a period for comments and review.
    • 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.
    • 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.

Approved Fuels

With assistance from the CAAFI Certification and Qualification Team, the following drop-in alternative jet fuels are certified for commercial use (listed in chronological order of approval). These approved fuels represent four different processes associated with various feedstock types.

  • Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK)
    • Year of Certification: 2009
    • Blend Level: Up to a 50%
    • Feedstock(s): Biomass such as municipal solid waste (MSW), agricultural and forest wastes, and wood and energy crops and non-renewable feedstocks such as coal and natural gas
    • Process/Product Description: The Fischer-Tropsch (FT) Synthesis Process is a catalyzed chemical reaction in which synthesis gas, a mixture of carbon monoxide and hydrogen, is converted into liquid hydrocarbons of various forms via the use of a reactor with cobalt or iron catalyst. The feedstock is gasified at high temperatures (1200 to 1600 degrees Celsius) into carbon monoxide and hydrogen primarily (synthesis gas or syngas), and is then converted to long carbon chain waxes through the FT Synthesis Process. The wax is then cracked and isomerized to produce drop-in liquid fuels essentially identical to the paraffins in petroleum-based jet fuel, but does not include aromatic compounds.
  • Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene (HEFA-SPK)
    • Year of Certification: 2011
    • Blend Level: up to a 50% blend
    • Feedstock(s): 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.
  • Hydroprocessed Fermented Sugars to Synthetic Isoparaffins (HFS-SIP)
    • Year of Certification: 2014
    • Blend Level: Up to a 10%
    • 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.
  • Fischer-Tropsch Synthetic Paraffinic Kerosene with Aromatics (FT-SPK/A)
    • Year of Certification: 2015
    • Blend Level: Up to 50%
    • Feedstock(s): Biomass such as MSW, agricultural and forest wastes, and wood and energy crops and non-renewable feedstocks such as coal and natural gas
    • 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.
  • Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK)
    • Year of Certification: 2016
    • Blend Level: Up to 30%
    • Feedstock(s): Starches, sugars, cellulosic biomass
    • Process/Product Description: Dehydration of an alcohol feedstock followed by oligomerization and hydrogenation to yield a hydrocarbon jet fuel. The alcohol feedstock is currently limited to isobutanol, but the incorporation of ethanol feedstocks is currently under evaluation.

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 Review & Ballot Alcohol-to-Jet Synthetic Paraffinic Kerosene (ATJ-SPK) Ethanol LanzaTech
Phase 2 Testing Hydro-deoxygenation Synthetic Kerosene (HDO-SK) Sugars and cellulosics Virent (inactive)
Catalytic Hydrothermolysis Synthetic Kerosene (CH-SK) Renewable FOG ARA
Phase 1 OEM Review High Freeze Point Hydroprocessed Esters and Fatty Acids Synthetic Kerosene (HFP HEFA-SK) Renewable FOG Boeing
Alcohol-to-Jet Synthetic Paraffinic Kerosene (ATJ-SPK) Ethanol LanzaTech
Phase 1 Research Report Hydro-deoxygenation Synthetic Aromatic Kerosene (HDO-SAK) Sugars and cellulosics Virent
Phase 1 Testing Alcohol-to-Jet Synthetic Kerosene with Aromatics (ATJ-SKA) Sugars and lignocellulosics Byogy, Swedish Biofuels

Pre-Qualification Process Fuels

CAAFI is aware of a significant number of pathways that are currently being pursued by multiple entities, but have yet to enter into the ASTM Certification 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.

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 SAJF 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 SAJF 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 SAJFs. 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.

Generic Annex

The U.S. Air Force funded an initiative to develop a generic annex for incorporation into the ASTM D7566 alternative jet fuel specification. The generic annex concept is intended to remove any restrictions on feedstock or conversion process, but limit the blend percentage to 10 percent and require the blend stock to meet more stringent specification criteria. The generic annex will allow new producers to immediately produce and sell their fuel without the need to conduct the ASTM D4054 evaluation of the new pathway. Work is currently underway to define advanced compositional test methods and other criteria and procedures necessary to ensure consistent quality and performance of SAJFs produced to the generic annex.

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

Other Testing Work

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