Considerations for Using Existing Standards as Part of Alternative Fuels Approval and Deployment

by Melanie Thom (Baere Aerospace Consulting, Inc./Coordinating Research Council, Inc.) Adequacy of Testing Methods for Aviation Fuels and Additives -- The work presented here is a summary of an
effort performed for the Coordinating Research Council, Inc. (CRC) and reported under the document AV-23-15 “Adequacy of Existing Test Methods for Aviation Jet Fuel and Additive Property Evaluation”, July 2017, available from www.CRCAO.org.

The work entailed reviewing all of the standards and specifications referenced in ASTM D-1655 Standard Specification for Aviation Turbine Fuels, ASTM D7566, Standard Specification for Aviation Turbine Fuels Containing Synthesized Hydrocarbons, and ASTM D4054, Standard Practice for Qualification
and Approval of New Aviation Turbine Fuels and Fuel Additives to determine what, if any, impact a change in the fuel composition or in how the standard was used might have on the results.

The purpose of the study was to assess the continued adequacy of the referenced test standards for use with: fuels prepared in manners other than those used with traditional petroleum crude; D7566 blendstocks which may not be fluids meeting the traditional kerosene distillation profile; and additives. It was considered beyond the scope of the program to assess how potential issues and concerns were evaluated or addressed, and it was beyond the scope of the project to evaluate the constraints provided by the parent documents on the quantitative values.

The results indicated of the 348 individual documents reviewed, 140 documents were identified as being test methods. Of those 140 documents, 70 showed no indications of impact, 27 indicated reasons for more careful review, and 6 showed reasons for probable concern. An additional 10 documents were specifically used in relational analyses.

Because of the interrelationship of the fuel with the aircraft engines and fuel systems, changes in the aircraft hardware meant changes in the specific types of data and related fuel properties required by the designers in the fuel specification.

First encountered during the evaluations of the +100 thermal stability additive, and later with the introduction of alternative jet fuels, the assumptions on what was known about fuel needed to be reconsidered. The industry began to encounter the extent of the assumptions related to fuel properties and performance embodied in the requirements.

With research into alternatively derived and alternatively composed fuels, the standards were being employed to measure the properties and performances of fuels that might not be kerosene distillation range hydrocarbons. Test methods that had not been routinely performed were being resurrected. Data that had not been routinely considered were being collected and reviewed.

This raised the question, are these methods still adequate? Do they report data that are meaningful? Accurate? Precise? Useful? Applicable? To explore these questions, the Coordinating Research Council, Inc. (CRC) funded a review of the specifications and standards referenced by the aviation fuel community. The goal was to begin a conversation on the methods, not to conclude them.

First there is a concern that over time the requirements specified by the standard have been driven by needs that are based on the interaction of aircraft engines and fuel systems (hardware) with traditional petroleum-based kerosene boiling range fuels. Are the needs the same if the fuel is not a traditional jet fuel? The second concern is that analytical chemistry techniques have evolved over time and the
fundamental assumptions involved in developing the methods may or may not be appropriate for their use on alternative fuels. The third concern is if the properties required by the standards, that are devised to control the production of petroleum fuels, are suitable for controlling fuels derived from alternative production methods.

These concerns have raised questions regarding three potential data gaps; 1) that test methods and accuracy statements were developed specifically for petroleum derived kerosene range jet fuels and the validity of their use on alternatively produced and composed fuels is not known, 2) that the test methods have evolved or been superseded based on test parameter assumptions from the original test method performance with petroleum based kerosene jet fuels and those assumptions may not be valid for other types of fuels, and 3) there is an inference of fuel performance from an absolute data value that
may or may not correspond when the fuel is produced by alternative means. This third data gap may be because the performance only relates to an absolute value from a fuel with a specific formula, or because assumptions of data at a single test parameter are assumed to be a predictor of test performance across a range of parameters and when the fuel formula changes this assumption is not correct.

As fuel technology has evolved, the emerging situation is a state where the aircraft engine and airframe manufacturers using the fuel in their hardware do not necessarily know what is specifically needed from the fuel, only that the fuel needs to do what it has always done. Because it is not known which requirements are primary, relating to performance and which are secondary, like controlling refining, compliance to all the properties is required. These restrictions may constrain technology change. A fluid is required to give the same data on all the tests even if the result is non-applicable, non-valid or makes no sense. The first step in stretching into new technologies is to relearn what the data are capable of telling us and why it should be considered. READ MORE