As the military and commercial aviation community certify the 50/50 blends of petroleum-derived and synthetic jet fuels for everyday use, decades of experience with the petroleum-derived specifications provide a foundation upon which to base performance expectations. However, for blends with higher synthetic content, potentially approaching 100%, the empirical foundation of current specifications no longer applies. Consequently, identifying the relationships between composition and specific properties relating to the full spectrum of fit for purpose specifications grows in importance. For example, the role played by alkyl aromatic compounds in ensuring seal swell is well-documented.

Conventional petroleum-derived fuel is composed of thousands of individual components that vary considerably in proportion from one lot of fuel to another. Therefore, separating such a mixture into its constituent parts is simply not a viable approach to developing a new specification. Furthermore, petroleum-derived fuels may contain constituent classes, such as aromatics and molecules containing saturated rings, not contained by every synthetic fuel composition. As a path forward, an approach where specific classes of constituents can be prepared and the functional performance of these individual classes better understood appears to be preferable.

—Robota and Alger

The objective of the work described in the paper was to produce a distribution of C₁₄ alkane isomers that also meet the −47 °C freezing point specification of JP-8.

The group’s goal is not to invent commercial fuels or ways of making them, according to Robota, but rather to develop fuel samples with certain properties the Air Force can use to broaden its understanding of the composition of alternative fuels and how different compositions influence their practical in-use properties.

My goals are to supply the Air Force with ready-to-test fuel compositions developed in our lab that are unlike commercial fuels; understand the chemistry and chemical engineering issues related to production of these fuels; and be able to provide further assistance as the Air Force tests the samples.

—Heinz Robota

In addition to making research fuels, Robota’s group is working with the Air Force to further advance alternative fuels by working with commercial partners to make testable quantities of fuel using the Air Force Research Laboratory’s Assured Aerospace Fuels Research Facility Sample Preparation Unit.

Robota’s group is currently in the middle of such an undertaking with a commercial partner, converting 1,750 gallons of a renewable crude to roughly 500 gallons of what is expected to be a true renewable fuel. When completed, the fuel will be delivered to a major engine manufacturer for testing on a full-scale engine stand.

After initial rounds of engine testing, further tests will examine burn rate, emissions, how the fuel interacts with engine parts and how the fuel performs at high altitudes.

Resources

• Heinz J. Robota and Jhoanna C. Alger (2012) Preparation of a Research Jet Fuel Composition Comprised of Nearly Exclusively Methyl-Branched Tetradecane Isomers Having a Freezing Point below −47 °C. Ind. Eng. Chem. Res., 51 (31), pp 10313–10319 doi: 10.1021/ie301041c