All Engines Used Alternative Jet Fuel Blends

The Air Force's ongoing alternative fuels certification efforts took another step forward late last month when a C-17 Globemaster III from Edwards Air Force Base, CA flew on all engines using jet fuel blended with a combination of traditional petroleum-based fuel, or JP-8, biofuel derived in part from animal fat, and synthetic fuel derived from coal.

The 418th Flight Test Squadron here conducted the flight tests August 23rd to 27th. The flight was a first for any Department of Defense aircraft where a 50 percent mix of JP-8 was blended with 25 percent renewable biofuel and 25 percent fuel derived from the Fischer-Tropsch process, which is essentially liquified coal or natural gas. It was also the first time an aircraft from Edwards Air Force Base had used fuel derived from beef tallow, which is essentially waste animal fat.

"The C-17 fleet is the biggest Air Force consumer of jet fuel annually," said Lt. Gen. Mark D. Shackelford the military deputy to the assistant secretary of the Air Force for acquisition. "This is a big step forward in achieving the Air Force's energy goal of increasing the available supply of fuel by acquiring half of the Air Force's domestic jet fuel requirement from domestically derived, environmentally friendly alternative sources by 2016."

For several years, the Air Force been looking at alternate sources of fuel to support their operations, said James Holther, a 418th FLTS project engineer for biofuel testing. "The first thing the Air Force did was look at Fischer-Tropsch fuels that use natural gas or coal as the feedstock, and this is just a continuation of that ongoing effort. The fuel we're testing this time around is a biofuel manufactured with biomass as the feedstock," he said.

The hydro-treated renewable jet fuel, or HRJ, used by the C-17 contains biomass that can be made from either animal fats or plant extracts such as camelina, a weed-like plant not used for food. The HRJ is blended with regular JP-8 jet fuel for the testing to gather data to support Air Force transport aircraft certification on alternative fuels from various feedstocks.

The Air Force Fuels Certification Office at Wright-Patterson Air Force Base, Ohio, has certified over 85% of all Air Force aircraft to use Fischer-Tropsch derived fuels, and is now focusing efforts on certifying aircraft to fly on HRJ biofuel blends. "When the certification effort is completed, it won't matter what feed stock or process was used to make the fuel, we will simply call it JP-8,'" said Jeff Braun, the director of the Air Force Fuel Certification Office.

Braun said his office is responsible for testing and managing certification of "drop-in" alternative fuel blends that will require absolutely no modification to aircraft or ground equipment. It also would necessarily provide the desired performance and burn as clean or cleaner than current JP-8, as demonstrated during the ground engine emission evaluation conducted as part of the C-17 test program. "We want maintainers, aircrews and fuels handlers to be able to say they can perceive absolutely no difference between traditional JP-8 and the alternative blends," he said.

The testing process featured the C-17 flying with different combinations of HRJ and JP-8. The testing required the C-17 to perform several maneuvers at different altitudes such as decelerating and then accelerating, to see how the plane responds with the HRJ mixed in, Holther added.

The 418th FLTS took precautionary measures to build up to the final test day. "On Monday we had JP-8 in three engines, and one engine had a blend of 50-50 biofuel and the JP-8," Holther said. "It's part of a safety build-up. We'll build up to putting the fuel in all four engines by verifying the performance differences are insignificant between the blended fuel engine and the regular fuel engines." On August 24th, the test team expanded the evaluation by utilizing the HRJ blended fuel in all four engines, flying the aircraft on 50 percent biofuel. A successful test is signified when the C-17 performs with little or no difference between the blended fuel and JP-8. The flight testing culminated August 27th with the C-17 using a blend of HRJ: JP-8 and a Fischer-Tropsch fuel mixture: 50 percent JP-8, 25 percent HRJ and 25 percent Fischer-Tropsch.

The potential use of alternative fuels could provide the Air Force with more options and greater flexibility in the future. "This is an opportunity for us to investigate the possible use of clean, renewable fuel sources," said Lt. Col. Clifton Janney, the 418th FLTS commander. "If successful, it can broaden the spectrum of fuels that we can use Air Force-wide."

Successful testing of the HRJ with the C-17 will be used by the AFCO office to support certification of the biofuel in military and commercial transport aircraft, Holther said. "This test we are doing with the C-17 and biofuel is considered a 'pathfinder' effort, which means similar aircraft, like the C-5 (Galaxy), might be qualified to use this fuel based on the test results we get with the C-17."

Braun said lessons learned from certifying individual airframes on Fischer-Tropsch fuels has been applied to the HRJ alternative fuel certification process, which will enable accelerated certification using pathfinder aircraft, then certifying other systems by similarity. The F-22 Raptor is the planned pathfinder for certifying the fighter fleet and the RQ-4 Global Hawk is being explored for platforms which operate at high-altitude.

FMI: www.usaf.mil