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Traditionally, electric generators, driven by an aircraft's main propulsion engines or by a gas turbine Auxiliary Power Unit (APU,) have supplied the electrical needs of commercial aircraft. In flight, the marginal efficiency of electric power generated by the main engines and their generators is at most 30 -40%. While on the ground with the engines shut off, the average fuel efficiency of the turbine powered APU is typically less than 20% and also has undesirable noise and gaseous emissions. As environmental concerns mount, aircraft manufacturers and others are challenged to reduce fuel consumption while simultaneously reducing emissions. Hence, there is very strong interest in developing fuel cells for aerospace applications.This paper reports on the study results of using Solid Oxide Fuel Cells (SOFC) in combination with a Gas Turbine (GT) as a hybrid APU system for a commercial aircraft. The purpose of this feasibility study is to investigate the potential use of fuel cell based APUs for onboard power generation in future "more electric" commercial aircraft. In this paper, the modeling of the major components of the SOFC-GT power generation system, summary of the findings, challenges, and final recommendations are presented.

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A test unit has been developed by Rolls-Royce for the U.S. Navy to use in evaluating fuel thermal deposition typically found in various aircraft engine components. Although the current Jet Fuel Thermal Oxidation Tester (JFTOT) provides a qualitative thermal stability evaluation, it may not be able to predict in-service problems. Conditioning and testing of the fuel under realistic conditions is crucial if one is to predict deposit formations accurately. Engine fuel deposit evaluations and evidence from unpublished Rolls-Royce laboratory rig tests were used to help design a test unit that would address fuel stability problems in current or future aircraft. The Aviation Fuel Thermal Stability (AFTS) test unit embodies test modules that were selected with extensive fuel systems experience to enable the evaluation of thermal deposition in various fuel components using properly conditioned fuel. The test modules are controlled and results are recorded by a computer. This paper includes a review of the AFTS test unit design and preliminary test results thereof.