N252-104 TITLE: Compact Rotary Engine Materials, Coatings, and Architectures for Robust and Reliable Operation in a Marine Environment

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Sustainment

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop advanced materials, coatings, and/or material-architectures, supported by experiment, modeling and simulation, to improve the efficiency, durability, and performance of rotary engines that operate in a marine environment.

DESCRIPTION: The U.S. Navy and Marine Corps has a growing interest in compact and efficient propulsion and power solutions, particularly for applications that demand high power density, operational reliability, and fuel flexibility. Rotary engines, with their favorable power-to-weight ratios and simplified mechanical designs, are well suited for Unmanned Aircraft Systems (UAS) and other compact vehicles that need versatile and durable power sources. Conventional rotary engines often suffer from limitations in durability and efficiency when exposed to the marine environment’s high humidity and salt concentrations. Sand and dust, commonly encountered along coasts and in the desert, can also be problematic for these engines. Recent innovations, such as the "inside-out" Wankel and rotary vane designs, have introduced new cooling and sealing concepts that could be beneficial for Naval applications, but many challenges still need to be addressed.

Current Challenges

These challenges stem primarily from the high humidity, salt exposure, and abrasive particulates. Key issues include:

• Corrosion: Saltwater and high humidity accelerate corrosion on metallic engine components. Environmental, Galvanic, Crevice, and Pitting corrosion can deteriorate the structural integrity of critical engine components.
• Abrasive Wear: Sand, dust, and salt particles enter the engine through air intakes and cooling systems, causing abrasion on critical surfaces like apex seals, rotors, and housing walls. This wear diminishes efficiency, lowers power output, and shortens component lifetimes.
• Seal Degradation: Apex and side seals experience rapid wear in marine environments, leading to reduced compression and higher oil consumption.
• Heat Management: High humidity and salt exposure can impair heat dissipation. Poor heat transfer can result in the warping of lightweight materials, such as aluminum alloys, and accelerate material fatigue.
• Lubrication Breakdown: Exposure to moisture and salt can emulsify lubricants, reducing their effectiveness. Rotary engines that rely on oil for sealing face additional maintenance and leakage concerns caused by oil degradation.
• Coating Wear: Protective coatings that defend against corrosion and wear can deteriorate more rapidly in a marine environment, reducing their effectiveness.
• Limited Understanding and Modeling Capability: Poor understanding of degradation mechanisms complicates material, coating, and design choices while increasing modeling uncertainty. Derived fatigue and life performance estimates may be inaccurate, negatively impacting reliability, readiness, and capability.

Ultimately, this SBIR topic aims to advance the state of rotary engine materials and tribology, enabling reliable use on Navy and Marine Corps UAS. Proposers should demonstrate a strong understanding of Navy/Marine Corps unique material/tribology challenges and present a viable approach to solving them. Please note that, due to time and budgetary constraints, the authors are less interested in developing completely new engine designs. Priority will be given to efforts that leverage existing engines to demonstrate proposed technology benefits.

PHASE I: Evaluate the technical challenges and feasibility of the proposed material/coating/design solution to enhance the reliability and performance of rotary engines in marine environments.

• Technical Challenges Assessment: Conduct a detailed analysis of the material and tribological challenges associated with operating the target Rotary Engine in a marine environment. Consider specific issues associated with corrosion, wear, and thermal management.
• Solution Feasibility Assessment: Identify and assess material, coating, and architectural modifications that could address the identified challenges. Consider the practicality, cost-effectiveness, and compatibility of the proposed solution(s) with the target rotary engine application.
• Initial Risk Assessments: Identify and document any technical and programmatic risks associated with the proposed solution. Develop a risk mitigation plan that outlines specific mitigation strategies that will be used to address those risks.
• Modeling and Simulation: Use modeling and simulation tools to predict the performance and durability of selected materials, coatings, and design changes under relevant Naval conditions and to quantify how the proposed solution will mitigate issues without the need for extensive physical testing in Phase I.
• Proof of Concept Testing: Conduct proof of concept tests on a small scale to demonstrate the potential effectiveness of the proposed solution. (Note: This step may involve testing of individual components or material coupons to validate initial assumptions.)
• Cost and Schedule Estimation: Develop a detailed cost and schedule estimate for a potential Phase II effort. Include anticipated development, testing, and validation activities needed to mature the technology.

Deliver a final report summarizing the findings, assessing the feasibility of the proposed solutions, identifying technical and cost risks, and recommending next steps for development in Phase II.

PHASE II: Focus on the detailed design, optimization, fabrication, and testing of the materials, coatings, and/or design modifications identified in Phase I, including:

• Detailed Solution Design and Optimization: Develop and refine designs based on Phase I findings, optimizing materials, coatings, and structural modifications to meet marine environment requirements. Include advanced modeling and iterative simulations to ensure the proposed solution addresses challenges effectively and if necessary.
• Prototype Fabrication and Integration: Fabricate prototypes of the optimized components/assemblies for testing. Ensure that the prototypes integrate selected materials, coatings, and design improvements in a manner that closely replicates final application conditions for rotary engines in marine environments.
• Testing and Characterization: Conduct rigorous testing and characterization of the prototypes under simulated marine conditions, including exposure to saltwater, humidity, sand, and representative stress/thermal loads. Perform cyclic corrosion testing, inclusive of representative temperature variations, to demonstrate solution durability under relevant operating conditions. Assess key performance metrics, such as corrosion resistance, wear rate, sealing integrity, and thermal stability, as appropriate. Testing should aim to validate the effectiveness of the solution and identify additional refinements needed to increase the durability/reliability of the proposed solution.
• Performance Evaluation and Optimization: Analyze test data to understand the performance of the proposed solution. Based on test results, optimize the design, materials, and/or coatings as needed to further enhance the durability while reducing maintenance requirements in a marine environment.
• Risk, Schedule, and Cost Updates: Reassess technical/programmatic risks and update the cost/schedule estimates based on testing outcomes and prototype performance.

Deliver a comprehensive report detailing the prototype performance, testing outcomes, solution optimizations, and updated risk/cost/schedule assessments. Recommendations for further development or scaling should also be included, along with any insights gained for potential Navy/Marine Corps/Commercial applications.

PHASE III DUAL USE APPLICATIONS: • Collaborate with Navy stakeholders, aircraft manufacturers, and/or engine original equipment manufacturers (OEMs) to further mature and integrate the technology into Navy/Marine Corps relevant platforms.

• Transition Plan Development: Develop a plan to transition the proposed technology to a relevant Navy/Marine Corps application.
• Further Technology Maturation: Further refine the technology solution in preparation for technology transition.
• Work closely with industry partners to redesign/optimize certain aspects of the technology to meet transition requirements as necessary and to understand military/commercial requirements and formulate a realistic plan to deploy the technology. Maturation efforts that increase the power density, reliability, and overall performance of rotary engines will further increase customer interest in the technology.
• Optimize the design for manufacturability and scale up production to meet customers’ needs.

The proposed rotary engine materials/tribology technology may be applicable across multiple industries (e.g., automative, commercial aviation, power generation).

REFERENCES:

1. Kchaou, M. "New Framework for studying High Temperature Tribology (HTT) Using a Coupling Between Experimental Design and Machine Learning." Finland. TRIBOLOGIA – Finnish Journal of Tribology 1-2, vol 41/2024, https://doi.org/10.30678/fjt.142331
2. Ezhilmaran, V., Vasa, N. J., Krishnan, S., and Vijayaraghavan, L. (September 21, 2020). "Femtosecond Pulsed Ti:Sapphire Laser-Assisted Surface Texturing on Piston Ring and Its Tribology Characterization." ASME. J. Tribol. April 2021; 143(4): 041801. https://doi.org/10.1115/1.4048385
3. Macknojia, A., Dockins, M., Ayyagari, A., Montoya, V., Rodriguez, J., Cairns, E., Murthy, N., Berkebile, S., Voevodin, A., Aouadi, S., and Berman, D. (February 3, 2025). "Tribological Evaluation of Coatings in Fuel Environments." ASME. J. Tribol. doi: https://doi.org/10.1115/1.4067814
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5. Johar, T. and Hsieh, C-F. "Design Challenges in Hydrogen-Fueled Rotary Engine—A Review." Energies, 16(2):607, 2023. https://doi.org/10.3390/en16020607
6. Stolarski, Tadeusz. "Tribology in Machine Design 1st Edition." Butterworth-Heinemann, December 16, 1999. ISBN: 9780750636230. https://shop.elsevier.com/books/tribology-in-machine-design/stolarski/978-0-08-051967-8
7. "Unmanned Systems Integrated Roadmap FY2013-2038 (Reference Number: 14-S-0553)." https://dod.defense.gov/Portals/1/Documents/pubs/DOD-USRM-2013.pdf
8. DellaCorte, C., Wood, J.C., (October 1994): High Temperature Solid Lubricant Materials for Heavy Duty and Advanced Heat Engines. DOE/NASA/50306-5 NASA TM-106570 https://ntrs.nasa.gov/search.jsp?R=19950006351
9. DellaCorte C. (June 2010): Nickel-Titanium Alloys: Corrosion "Proof" Alloy for Space Bearings, Components and Mechanism Applications. NASA/TM-2010-216334 https://ntrs.nasa.gov/search.jsp?R=20100025843

KEYWORDS: Rotary Engine; Hybrid Electric; High Temperature Materials; APEX Seals; Vane Seals; High Temperature Tribology; High Temperature Wear and Lubrication; High Temperature Ionic Lubrication; Advanced Ceramics; Additive Materials; Digital Engineering; ICME; Co

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