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Advanced Sealing Concepts for Small Heavy-fuel, Remotely Piloted Aircraft Propulsion Systems


OBJECTIVE: Develop sealing technologies for heavy fuel engines for Remotely Piloted Aircraft (RPA). The technology should address sealing in engine classes of reciprocating and rotary engines for improved durability. DESCRIPTION: Shortfalls with existing RPA systems include durability issues associated with engine seals. Two key RPA systems in the DoD inventory are the USAF's Predator and US Army's Shadow-200. Both of these systems have seal/wear issues. In the reciprocating engine - it's the piston - cylinder interface, and in the rotary engine it's the rotor - housing interface. Sealing systems which have high wear resistance, light weight, and have high thermal stability are sought. Future, advanced engines for small RPA"s are expected to make use of new materials, such as: ceramics, advanced metallics, composites, and other lightweight materials. This will require the development of new sealing technologies that are compatible with the materials used in these advanced engines. Such efforts are in the initial stages of development, exemplified by a program to replace the metallic rotor in a rotary (Wankel) engine, with a silicon nitride rotor. Other engine developments such as the Nutating engine and Migrating Combustion Chamber (MCC) are under development and are developing new lightweight materials to optimize the combustion systems in these engines. Considerations are to examine an array of tribologic factors, such as surface hardness, surface coating, and self-lubrication. Improvements are sought to address the wear/durability issues; specifically for the apex seal/rotor/housing of the rotary engine, piston/ring/cylinder for reciprocating engines, and other sealing technologies for innovative engines. Furthermore, these wear/durability issues must address engines running on heavy fuel (JP-8 and/or diesel fuel) and have such characteristics to increase the time between overhauls. PHASE I: Determine common combustion seal material issues between piston ring/cylinder interface for reciprocating engines, apex seal/trochoid housing for rotary engines, and other sealing technologies for innovative engines. Items to be identified include: relative speed between sealing surfaces, loading, estimate of friction coefficients and lubrication. Develop concepts and material combinations to address these issues. Activities included in this phase consist of analytical modeling and small scale coupon testing to show proof of concept. PHASE II: The Phase II effort would consist of selecting material combinations from those identified in Phase I and conducting controlled bench tests to evaluate the combinations for each different engine applications in terms of: relative surface speed, loading between seal face and housing/cylinder, level of lubrication, and temperature at the sealing surface. These material and sealing designs are to be demonstrated in representative UAV engines. PHASE III DUAL USE APPLICATIONS: Military Application: Advanced sealing concepts for small, heavy fuel engines are applicable to the Air Force, Navy, and Army forces. Each service of the DoD operates RPAs that are powered with small engines. Incorporating advanced sealing concepts into RPAs such as the USAF"s Predator-Rotax 914 engine and the US Army"s Shadow-200 has the potential to increase engine efficiencies, reliability, and durability. Commercial Application: This technology has additional transition opportunities in the commercial sector for small engines, ground vehicles and equipment, and lightweight power generation. Incorporating advanced sealing technologies into commercial engines has the capability for companies to change material interfaces to increase engine efficiencies. Furthermore, this technology is applicable to hybrid applications.
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