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Technology challenges. There are two approaches to using JP fuels in UA designed for lightweight gasoline engines; converting an existing gasoline engine to operate satisfactorily on JP fuels, or developing a true diesel engine light enough to be substituted for an existing gasoline engine. Depending on the approach chosen there are different technology challenges associated with each:
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Conversion – This approach will yield an engine of similar efficiency to the current gasoline engines (no improvement in BSFC) but will be close in power to weight and minimize integration efforts. Challenges include designing a combustion system that effectively burns JP fuels without using a diesel cycle, and obtaining acceptable engine reliability while using JP fuels.
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Light-weight Diesel – This approach will yield an engine of much greater efficiency than current gasoline engines but a significant technology challenge will be weight reduction in order to even approach that of current gasoline UA engines while maintaining reliability.
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Advancements in materials are needed to allow development of diesel engines to approach the power to weight ratios of gasoline engines. The high cylinder pressures associated with the diesel cycle will require advanced materials not presently found in reciprocating engines. Concurrently, dynamic components such as crankshafts, connecting rods and bearings also need improved weight to strength/wear for suitable use in aviation engines.
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Weight reductions in the area of diesel fuel systems and ancillary components will also be required. This includes the fuel injection system, turbochargers, intercoolers, scavenge pumps, cooling systems. Increasing efficiency requires advanced fuel system components such as lightweight high-pressure pumps/fuel injectors and advanced fuel control techniques such as rate shaping. These systems are required for diesel cycle engines operating on JP fuels.
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Shortcomings of Current Approaches. The ongoing development of the OPOC engine shows significant promise for meeting the need for a low cost heavy fuel engine. Other proposed solutions, such as low pressure diesels and modified two cycle gas engines have been without merit to date. To ensure the provision of reliable, efficient, lightweight JP burning engines for aviation use, additional in depth technology programs must be pursued. The resulting influence on UA designs (and their inherent capability) of the different design approaches is depicted in Figure D-3. Without an in-depth
APPENDIX D – TECHNOLOGIES
Page D-4
technology program the best that can be hoped for are mediocre solutions that meet some of our
requirements, but fall significantly short in providing the true solution needed.
Propulsion – Electric and Alternative Technologies
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