Coal-Derived Jet Fuels Less Likely to Form Engine Deposits at High Speeds
SAN FRANCISCO, March 29 — To allow jet planes to fly faster safely, scientists are looking to coal, rather than petroleum, as a source of fuel. Coal-derived fuel is less likely to form engine-clogging coke deposits in jet engines at higher speeds and temperatures, according to research being done at Pennsylvania State University.
The research, which is funded by the United States Air Force, was reported here today at the 219th national meeting of the American Chemical Society, the world’s largest scientific society. The weeklong meeting is expected to attract about 20,000 scientists from around the world.
Fuel now used in commercial jet aircraft comes from petroleum and is typically exposed to operating temperatures below 600 F (300 C). As speeds increase, temperatures are expected to reach up to 900 F (482 C) and higher, says John Andrésen, Ph.D., of the Energy Institute at Penn State, where the research is being done.
“Jet fuels presently used have been shown to form solid deposits that can plug the fuel system and ultimately lead to catastrophic malfunction of the jet aircraft,” says Andrésen. Coal-derived liquid jet fuels can withstand temperatures up to about 500 C for several minutes, he adds.
The reason for the superior performance of the coal-derived fuel is its ring-shaped hydrocarbon (alkane) makeup. Coal is rich in cycloalkanes, which are more thermally stable than the straight-line linear alkanes found in petroleum. Linear alkanes “are highly susceptible to thermal degradation at temperatures above 400 C, resulting in solid particle formation (coke),” says Andrésen.
Underway since 1991, the research project so far has been confined to laboratory measurement and analysis of how petroleum-derived and coal-derived jet fuels behave at different temperatures. The next step is laboratory testing of the fuels in actual engines. This phase is expected to take about five years, Andrésen estimates.
Although jet speed can be increased using current petroleum-derived fuels, how long you safely operate at higher speeds is the crux of the matter, Andrésen points out. Using coal-derived jet fuels, “you can operate at a high max speed for a longer time without running into any problems with solid particle formation,” he says.
Speed isn’t the only benefit of using coal as the source for jet fuels. Coal is much more plentiful in the United States than oil, which could reduce reliance on imports. Bituminous coal, the most abundant type of coal in the United States, is being used in the research project.
While more processing is needed to produce jet fuel from coal than from petroleum, it is still economically viable and competitive, Andrésen believes.
The investigation into coal-derived jet fuels is part of a large Penn State research project on jet fuels being conducted at the school’s Energy Institute under the direction of Harold Schobert, Ph.D. Co-authors of the research report on jet fuel from coal are Chunshan Song, Ph.D., and undergraduate student James Strohm.
Dr. Andrésen is Associate Director and Research Associate, Applied Catalysis in Energy Laboratory, The Energy Institute, The Pennsylvania State University, University Park, Pa.
Dr. Chunshan Song is Associate Professor, Energy & Geo-Environmental Engineering, The Pennsylvania State University, University Park, Pa.
James Strohm is an undergraduate student studying science and engineering at The Pennsylvania State University, University Park, Pa.
Dr. Harold Schobert is Professor and Director of The Energy Institute, The Pennsylvania State University, University Park, Pa.
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