Jet A Alternatives

David Esler

This December, if the planets align properly and the members of the ASTM International concur, it will become legal to operate a business jet on a blend of conventional Jet-A and low-emissions biofuels refined from weeds, soybeans, tallow or algae.

After years of research and testing by engine and airframe OEMs, the airlines and armed forces, government laboratories and universities, and the refining and chemical industries, ASTM is expected to approve a biofuel specification as an amendment to the existing D7566 standard, titled "Aviation Turbine Fuel Containing Synthesized Hydrocarbons," which already covers synthetic fuels, or "syngas," refined using the Fischer-Tropsch gasification process from coal and natural gas feedstocks. It is noteworthy from safety and performance standpoints that the prime requirement for both ASTM and FAA approval of a jet fuel intended to substitute for petroleum-derived Jet-A and its military equivalents is that it qualify as a so-called "drop-in" alternative. This means that it will perform exactly as the fuel it stands in for, or to use the anthropomorphic analogy, that "neither the aircraft nor the engines will know the difference."

Two factors are driving the move toward alternative fuels in all modes of internal-combustion-powered transportation and electric power generation: fuels security and the need to address climate change by mitigating the proliferation of greenhouse gases (GHGs), principally carbon dioxide (CO2). The former — ensuring an uninterrupted supply of fuels for defense purposes — is of particular interest to the U.S. military establishment, especially considering the volatility of Middle Eastern politics, given that the majority of petroleum used by the West is imported from the region. Then, too, crude oil is a nonrenewable resource being consumed by all the world's nations — and especially the developed ones — at an unprecedented rate, and ultimately, suitable substitute sources of energy must be found and exploited. Thus, sustainability is essential if quality of life, the West's technologically driven lifestyle (including the mobility facilitated by air transportation) and the undeveloped world's climb to prosperity are to be maintained.

Getting Easier to Be Green — But at a Price

This report updates "Alternative Fuels for Jet Engines," an in-depth examination of substitute, or "green," fuels published by BCA in September 2007, page 82. BCA was curious to know what progress had been made in the ensuing three years in developing processes for refining sustainable and low-carbon-emissions fuels, establishing production and distribution infrastructure, certification status for use as drop-in alternatives and ultimate availability. And we learned that, indeed, alternative fuels development has made significant strides forward. In fact, the effort has reached a juncture where the technology is ready to be exploited.

Alan Epstein, Ph.D., vice president, technology and environment, at Pratt & Whitney Engines in Hartford, Conn., observed that "It may be easier now to 'go green' — but it isn't getting any cheaper. It's no longer technology that is the issue, it's money. In a year, the aviation industry will have completed what is needed to enable your readers to use biofuels in their airplanes. The question is, who is going to be making them? We are certifying the fuels to encourage people to invest in their manufacture. We realize that the sustainable future of aviation depends on the availability of biofuels."

The class of biofuels being considered by ASTM and the FAA for approval for use in jet engines this year is called bio-SPKs, for "synthetic paraffinic kerosenes." "In other words," another Epstein — this one, Mike Epstein, leader of alternative fuels at General Electric Aviation in Cincinnati (and no relation to P&W's Epstein) — said, "they are paraffins [i.e., wax]. We are focused on 50/50 blends with Jet-A, which, not surprisingly, already contains a great deal of paraffinic kerosene, so the chemistry is similar." Derived from plant oils, or triglycerides, the bio-SPKs thus hold the potential to be sustainable under the right cultivation circumstances. Therefore, selection of appropriate feedstocks from which to extract sustainable plant oils is critical, or as Epstein put it, "[N]o cutting down rainforests to make your bio oil or imposing on food production."

Bio-SPK developers have changed the proportion of paraffins in jet fuel, while meeting the current ASTM specification, "which is important," Epstein continued. "These blends meet that standard, which is mandatory for a drop-in fuel. We at G.E. and our competitors and the airframe OEMs will require no changes to either hardware or software [to burn these fuels], no new injectors, combustors or ground support equipment, because these fuels meet the current spec. They create mean shifts, so you are at the edge of the specification in a few areas, notable density. They are slightly less dense than petroleum but within the spec."

Graham Ellis, business manager for chemicals at UOP, a Honeywell subsidiary once known as United Oil Products and based in Chicago, elaborated on bio-SPKs by way of providing a chronology of their development. (Founded in 1914, UOP develops catalysts and refining processes, the latter which it leases to refiners.) "Three years ago, after we had completed an eco-fining process for making green diesel, DARPA [the Pentagon's Defense Applied Research Projects Agency] approached us to make a [military] JP8 biofuel. From that we developed a trademarked refining process that wound up as Honeywell Green Jet Fuel. Over the last three years it has also come to be referred to as SPK and HRJ [hydro processed renewable jet], although it's all exactly the same product. SPK is a generic term and HRJ is a military acronym, as used for HRJ5 or HRJ8."

(For the sake of clarity, JP8 and JP5 are current specifications for fuel used, respectively, by the U.S. Air Force and U.S. Navy. JP5 is formulated for, among other conditions, long-term storage aboard ships.)

"The bio-SPK is the one that is going through the ASTM certification process," Ellis continued, "the vehicle for which is ASTM D7566. The way we are looking at certifying for commercial use is as an annex to D7566. The concept is that the chemical composition is so similar to the Fischer-Tropsch fuel covered by D7566 that HRJ can be a subset of that specification. If the ASTM vote passes, then this fuel will be an up-to-50 percent blending component [with conventional petroleum-derived Jet-A] requiring no modifications to jet engines."

READ MORE: AviationWeek