As oil prices remain above the $60 per barrel mark, operators, oil companies and government regulators are showing ever more interest in alternative jet fuels. At a March 8 speech at the U.S. Air Force Energy Forum, FAA Administrator Marion Blakey echoed President Bush’s State of the Union desire “to wean America off the IV drip of foreign oil.” The aviation industry uses more than 200 million gallons of jet fuel per day, according to Chevron Global Aviation.
Blakey outlined FAA efforts to explore alternative fuels, including two studies that cost nearly $1 million. One is examining feasibility, costs, barriers and technical issues; the other looks at potential environmental benefits. Both are due for completion by September, Blakey said.
One large-scale industry effort is called the Commercial Aviation Alternative Fuels Initiative (CAAFI). Formed by airlines, manufacturers and representatives from the Energy and Defense departments, the project is the result of an alternative fuels workshop Boeing convened last May. CAAFI held its first meeting, with 80 participants, last October, one result of which was the articulation of the CAAFI mission: “Commercial aviation sponsors and stakeholders to work together with DoD/DOE to pursue alternative fuels for the purpose of:
• securing a stable fuel supply
• furthering research and analysis
• quantifying the ability to reduce environmental impacts
• improving aircraft operations
According to Richard Altman, CAAFI’s executive director, the U.S. Air Force is particularly interested in alternative fuels because an unstable fuel supply creates a major security issue.
One of the group’s primary goals is to get the fuel suppliers involved in the CAAFI initiative because their infrastructure will distribute any successful alternative jet fuel.
There are three types of alternative jet fuel: jet-A substitutes, bio-derived and cryogenic. South African Airways is flying with a jet-A substitute made from coal gasification by South African fuel company Sasol. According to CAAFI, Sasol’s fully synthetic jet fuel has completed testing to ASTM protocols and also actual turbine engine endurance, fuel atomizer cold spray, ignition and emissions tests.
Meanwhile, Sasol already provides what is likely the most promising interim jet fuel replacement, a 50/50 blend of synthetic coal-gasification-derived fuel and ordinary jet fuel. This fuel, in regular use in South Africa, was approved for aviation use in 1999, according to an alternative fuels report by Chevron Global Aviation.
More Costly Alternatives
Bio-derived and cryogenic fuels are also undergoing examination, but these have significant drawbacks that will require major airframe and engine changes and in some cases entirely new aircraft designs. According to the Chevron report, ethanol and biodiesel are the primary bio-derived fuels that could be an alternative to hydrocarbon jet fuel. Ethanol, which is produced from the fermentation of sugar cane or corn but could eventually be made from any cellulosic plant material, has significant drawbacks and likely won’t be used for turbine engines. At 35 percent by weight, its oxygen content is high, which means that its energy content is low. Unlike jet fuel, ethanol can mix easily with water, and it is also a strong solvent that could affect fuel system materials. Its higher heat of vaporization could affect atomization and vaporization properties in the combustor.
According to Chevron, “Use of 100-percent ethanol as an aviation fuel would require a storage and distribution system separate from that for conventional jet fuel. Blends of ethanol with conventional jet fuel also pose problems because of the significantly different physical and chemical properties of ethanol and jet fuel.”
Biodiesel presents a problem for aircraft turbine engine use, mainly because it freezes sooner than jet fuel. Biodiesel freezes near 0 degrees C. Jet fuel’s freezing point is -40 degrees C, so biodiesel would not be suitable for high altitudes, where it would solidify unless constantly heated. Made from vegetable oils or animals fats, bio-diesel has less energy content than jet fuel and could promote biological growth during storage. Other problems include possible water-separation issues and potential atomization/vaporization difficulties in combustion chambers.
Cryogenic fuels are substances such as hydrogen or methane that are gaseous at normal temperatures and stored in a liquid state at a temperature below their boiling point.
Both hydrogen and methane have high energy content but low density, according to Chevron, which means that a user would need to carry much more fuel. Another drawback is that use of this fuel would necessitate an entirely new distribution infrastructure and new engines and airframes.
The cryogenic fuel also has a heavy environmental footprint. Hydrogen is currently made by reforming methane from natural gas into hydrogen, which produces hydrogen carbon dioxide. The latter, of course, is a greenhouse gas. “Before hydrogen can displace fossil fuels as a major source of energy,” the Chevron report noted, “an efficient and economical process will be needed to generate hydrogen from water and other renewable resources such as solar or biomass. Cryogenic fuels might be used in commercial aviation, but not for several decades.”
It appears as though the Sasol-type 50/50 blend of jet fuel and synthetic fuel offers promise for reducing dependence on oil in the short term. Meanwhile, CAAFI continues its work. The group is seeking participation from general aviation interests. Altman, the main contact for CAAFI, can be reached at (860) 721-8634 or e-mail email@example.com.
Alternative fuels, said Blakey, are “no longer the domain of the tree-hugger set. This is serious business, and the FAA is determined to work with our partners to find an alternative that strikes the balance between energy security and aviation’s environmental performance.”