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Advanced Material/Sealing Concepts for Small Heavy-Fuel, Remotely Piloted Aircraft (RPA’s) Propulsion Systems

Description:

OBJECTIVE: Develop advanced 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 and performance. Seals for the piston engine are the ring/cylinder pair and for the rotary are the apex seal/housing pair. Improvements in materials pairs which exhibit less wear and new seals design to promote less leakage and longer life are sought. 

DESCRIPTION: Future, advanced engines for small RPA’s are expected to make use of new materials and coatings, such as: ceramics, advanced metallics, composite, superlubrious coatings and other light weight materials. New designs along with the advanced materials are needed to improve engine durability and performance; such as material coatings that offer increased wear resistance for sliding contact; materials with low coefficient of thermal expansion to eliminate piston rings; and materials with high insulating capability to raise thermal efficiency will require advanced sealing concepts. Considerations are to examine an array of tribologic factors; such as surface hardness, roughness, surface coating, and self lubrication. Improvements are sought for seal concepts to address the wear/durability issues; specifically for: the apex seal/rotor/housing of the rotary engine, and piston/ring/cylinder for reciprocation engines, thru advanced materials/designs. Present day state-of-the-art materials for seals are cast iron on chrome/nickel plating; hence improvements are sought to improve this baseline. 

PHASE I: Conduct an assessment of candidate designs/materials to improve combustion chamber sealing of small RPA engines. This includes small scale wear testing of material pairs, analysis of "ring-less" piston designs, and insulating materials for improved performance. Additional items to consider are improvements to the existing seal design i.e.,. integrated seal/spring, elimination of cylinder wall distortion, effects of surface finish, impregnated materials for improved lubricity, and advanced coatings with self healing properties (dry film lubricants). 

PHASE II: The Phase II effort would consist of selecting the best design and material/coating combinations from those identified in Phase I and conducting engine tests to evaluate the ability of selected design/material combinations to operate under engine test conditions. This include improved material pairs, tighter tolerance thru low coefficient of thermal expansion materials, and the effects of insulating materials on thermal efficiency. 

PHASE III: Advanced sealing concepts for small, heavy fuel engines is applicable to the Air Force, Navy, and Army forces. Each service of the DoD operates RPA’s that are powered with small engines. It is currently a DoD directive to transition to a single battlespace fuel, which would inherently be a heavy fuel such as JP-8. Incorporating advanced sealing concepts into RPAs has the potential to increase engine efficiencies, reliability, durability, and to achieve current DoD objectives. Advanced engine sealing thru new materials/designs are applicable to all small size commercial engines for portable power generation, recreational vehicles and light industrial applications. Hence better sealing with provide higher efficiency and lower fuel consumption. 

REFERENCES: 

1: "New Materials Approaches to Tribology: Theory and Applications", Larry E. Pope, Larry L. Fehrenbacher, and Ward O. Winer. Cambridge University Press, 2012

2:  "A Critical Analysis of the Rotary Engine Sealing Problem", H.F. Prasse, H.E. McCormick, and R.D. Anderson, SAE 730118, 1973.

3:  "Ceramic Materials and Components for Engines", edited by Jürgen G. Heinrich and Fritz Aldinger, Wiley 2001, ISBN

4:  3-527-30416-9.

KEYWORDS: Piston Ring, Tribology, Apex Seal, Heavy-fuel, Ceramic Seals 

CONTACT(S): 

Gregory Minkiewicz 

(937) 255-1878 

gregory.minkiewicz@us.af.mil 

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