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Unformatted text preview: Alternate Fuels for use in Commercial Aircraft David L. Daggett 1 Boeing Commercial Airplane, Seattle, WA, 98124 Robert C. Hendricks NASA Glenn Research Center, Cleveland, OH, 44135 Rainer Walther MTU Aero Engines GmbH, Munich, Germany Edwin Corporan Air Force Research Laboratory, Dayton, OH 1 Copyright © 2007 by The Boeing Company. All rights reserved Abstract The engine and commercial aircraft research and development communities have been investigating the practicality of using alternative fuels in near, mid, and far-term aircraft. Presently, it appears that an approach of using a “drop in” jet fuel replacement, which may consist of a kerosene and synthetic fuel blend, will be possible for use in existing and near term aircraft. Future mid-term aircraft may use a bio-jet and synthetic fuel blend in ultra-efficient airplane designs. Future, long-term engines and aircraft in the 50-plus year horizon, may be specifically designed to use a low or zero-carbon fuel. Synthetic jet fuels are manufactured, using a Fischer-Tropsch process, from coal, natural gas or other hydrocarbon feedstocks. These fuels are very similar in performance to conventional jet fuel, but have almost zero sulfur and aromatics. This may result in lower particulate exhaust emissions. In addition, synthetic fuels exhibit excellent low-temperature properties, maintaining a low viscosity at lower ambient temperatures. Thermal stability properties are also improved, resulting in less fuel system deposits. As synthetic fuels have very good performance, and have already been in use for many years in Johannesburg airport (Sasol fuel) it will be easy to supplement current jet fuel supplies with synthetic derived fuel. If the additional CO 2 that is produced during the manufacturing process can be captured and permanently sequestered, synthetic fuel could be a good near-term supplement. For a possible mid-term solution (i.e., 10-50 years from now) it is envisioned that alternate fuels will make up a much larger percentage of jet fuels. These fuels may also involve the blending of bio-fuels with the synthetic fuel. The major challenges of using pure bio- fuels in a commercial aircraft are its propensity to freeze at normal operating cruising temperatures, its poorer high temperature thermal stability characteristics in the engine, and its storage stability over time. For these reasons, bio-jet fuels need to be developed that address these issues and so will be especially tailored for jet aircraft. Another drawback is that, because of limited excess farmland, present bio-fuels are not capable of supplying a large percentage of fuel without displacing food production. However, higher yielding future feedstocks, such as algae, may dramatically improve supply capability. The advantages of using bio-fuels would be its environmentally balanced CO 2 impact, its capability to become a sustainable fuel, and it may result in lower engine emissions. If the performance and resulting cost liabilities can be...
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- Spring '11