TECHNOLOGY AREA(S): Air Platform
OBJECTIVE: Develop and demonstrate lightweight, durable, low cost recuperators for 5 Kilowatt turbo-generators to power DoD Group 2/small Group 3 unmanned aerial systems (UASs) for increased reliability and operational capability.
DESCRIPTION: Tactical requirements for unmanned aerial systems are exceeding current capabilities for performance (payload, range), reliability, maintainability, and supportability. Mission requirements such as increased power, extended endurance, low altitude maneuverability in urban environments without detection, and high reliability are becoming paramount. These combined requirements are currently not fully realized with conventional rotary, internal combustion, or turbine-based propulsion. Improved engine reliability is a critical need area. The electrical power requirement for advanced payloads is also increasing, which adds weight to the air vehicle. Turbine based propulsion systems offer good power to weight ratio over typical internal combustion engines, however, do not compete well in fuel efficiency in small size engines due to increased clearances and losses. The addition of recuperation can improve micro-turbine fuel consumption across the operational spectrum, such that it is competitive with internal combustion engines. This would allow small UASs to take advantage of the turbine engines inherent reliability and durability, while reducing the weight advantages somewhat. Additionally, the high frequency of the noise generated by turbine engines makes it inherently easier to meet detection requirements. Therefore, for a successful recuperated small turbo-generator (5 Kilowatts) to be developed for application to Group 2/small Group 3 UASs, it will be critical for the recuperator to be lightweight, have reasonable effectiveness for good fuel consumption characteristics, use low-cost and repeatable manufacturing techniques, and be durable/reliable so that overall engine performance, cost, and reliability/durability is achieved. The objective of this topic is to develop lightweight, low cost, and durable/reliable recuperators for small turbo-generators, which offer potential for high power to weight ratio and reliability, in order to meet current and anticipate future needs of Group 2/small Group 3 UASs. Program goals/metrics consist of greater than or equal to 75 percent effectiveness and less than or equal to 4 lbs weight for a recuperator designed to integrate with a 5-8 kilowatt turbo-generator. Advanced manufacturing techniques are encouraged to be explored, such as additive manufacturing; moreover, use of brazing, in the manufacturing process, is not of interest due to reliability and repeatability concerns. The resulting advanced recuperated propulsion system would need to be able to meet different operational requirements of a Group 2/small Group 3 UAS, which include full power takeoff capability, high part-power cruise fuel efficiency for improved endurance, and quiet operation capability. Additionally, commercialization of the advanced manufacturing techniques used in this effort will benefit industry officials with applications for high-efficiency recuperators and heat-exchangers where size and weight are critical design factors. Moreover, this effort will aid in reducing costs for advanced manufacturing techniques to further help commercial entities with a need advanced recuperator design applications.
PHASE I: Key components/geometry features of the proposed recuperator concepts should be studied by the company with design work, analysis, computational studies, and key idea tests to substantiate the ability to provide a lightweight, low cost, and durable/reliable recuperator that can be effectively integrated into a current or future 5-8 kilowatt turbo-generator system.
PHASE II: Phase II will fully develop and fabricate the recuperator, integrate it with a 5-8 kilowatt turbo-generator (that will operate on heavy-fuel (JP-8, diesel) and provide power to electrical payloads in additional to motor driven propulsors), and demonstrate the fully recuperated turbo-generator system in a ground test environment.
PHASE III: Phase III options would include further design enhancements, endurance/reliability testing of the recuperated micro-turbine engine, and potential integration into a representative UAS system and demonstration of the performance of the system with flight testing in a UAS mission environment.
McDonald, C.F., 1996, Heat Recovery Exchanger Technology for Very Small Gas Turbines, International Journal of Turbo and Jet Engines, 13, pp.239-261.
McDonald, C.F., 2000, Low Cost Recuperator Concept for Microturbine Applications, 2000, ASME paper 2000-GT-0167, Am. Soc. Mech. Engin., New York, NY.
Ward, M.E., 1995, Primary Surface Recuperator Durability and Applications, Turbomachinery Technology Seminar paper TTS006/395, Solar Turbines, Inc., San Diego, CA.
Oswald, J.I., Dawson, D.A., and Clawley, L.A., 1999, A New Durable Gas Turbine Recuperator, ASME paper 99-GT-369, Am. Soc. Mech. Engin., New York, NY.
KEYWORDS: Unmanned Aerial System, Recuperated Small Turbo-generator, Heavy Fuel Engine, Power To Weight Ratio, Fuel Efficiency, Low Noise, Low-cost Manufacturing