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Durable Pre-cooling Heat Exchangers for High Mach Flight



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 section 5.4.c.(8) of the solicitation and within the AF Component-specific instructions. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. Please direct questions to the AF SBIR/STTR Contracting Officer, Ms. Gail Nyikon,

OBJECTIVE: Enable turbomachinery operation in excess of Mach 4 by pre-cooling the incoming air. Utilize modern materials, manufacturing, and design processes to design a durable pre-cooling heat exchanger.

DESCRIPTION: Throughout the past 50 years, there have been multiple efforts to develop a single air-breathing engine that is capable of thrust from takeoff up to Mach 4 speeds and faster. A major challenge in developing this capability is the hot air that is ingested at high Mach speeds. There have been attempts dating back to the 1960s to solve this problem by using a pre-cooler heat exchanger in front of the air compressor face to reduce the temperature of the incoming air. It is expected that high Mach flight will be growing in importance for the Air Force to execute its five core missions and that precooled propulsion could be an enabler for new platform capabilities. The objective of this topic is to mature the technology for a lightweight and compact pre-cooler heat exchanger for high Mach propulsion that uses turbomachinery.

No pre-cooling heat exchanger has ever been flown. The biggest difficulty is getting the heat exchanger light weight and compact enough to be practical for flight. In many industries, modern manufacturing has allowed for lighter weight components and unique geometries to be built. This topic will leverage modern manufacturing techniques (e.g., additive manufacturing, friction stir welding, C&C milling, etc.) to develop a pre-cooler heat exchanger that is practical to be used in a propulsion system on a high Mach flight system. At the end of the Phase II, it is expected to fabricate a scaled prototype of the heat exchanger and conduct initial evaluation testing. Throughout this topic, it is important to address thermal integration for the necessary systems involving the heat exchanger.

Important attributes of pre-cooler heat exchangers (of roughly equal importance) that need to be addressed include durability, affordability, ability to integrate with propulsion and flight systems, scalability, manufacturability, impact on ground operations, material and manufacturing maturity, amount of pressure drop across the heat exchanger, and maintainability. The pre-cooler should be able to cool incoming freestream air to about 500 degrees F or cooler for flight conditions at altitudes above 55,000 feet. It is also expected the heat exchanger to be developed will have a specific power of at least 15kW/lbm.

Both Phase I and Phase II will consist of an appropriate level of design and systems engineering efforts to understand what it will take to fully develop the proposed solution. These efforts should address all issues but focus on the demonstrations that will be performed in Phase II. Modeling of the heat exchanger’s performance and its integration is needed throughout both phases to understand its potential. Recommend developing one or more reference vehicle platform designs for one or more Air Force core missions to show how the heat exchanger could enable that capability.

A letter of endorsement from a Versatile Affordable Advanced Turbine Engines (VAATE) participant is highly encouraged.

Commercialization of the pre-cooler heat exchanger involves integration of the pre-cooler into high-speed propulsion systems for DoD and/or commercial needs such as point to point cargo and access to space. Commercialization of the heat exchanger can also be used for propulsion thermal management and terrestrial applications.

Remote access to the DoD Supercomputing Resource Center (DSRC) to cleared personnel will be made available if needed.

PHASE I: Conduct initial design of the pre-cooler heat exchanger with an emphasis on its integration and manufacturing. Based on higher level platform requirements, derive requirements for the heat exchanger components that have early verification and validation. Develop plans for the Phase II fabrication and testing.

PHASE II: Fabricate a scaled prototype of the heat exchanger utilizing the proposed manufacturing approach. Conduct testing in a relevant laboratory environment. Develop and validate performance and lifting models based on the testing. Utilize this information to increase the understanding of how the heat exchanger integrates into a platform or platforms.

PHASE III DUAL USE APPLICATIONS: Phase III will focus on maturing the heat exchanger and beginning to integrate it into a full propulsion system and a vehicle platform. Additional Phase III activities can consist of applying the heat exchanger and its manufacturing to other defense and commercial domains.


    • Murthy, S.N.B., "Developments In High-Speed Vehicle Propulsion Systems," AIAA, 1996.


    • Balepin, V.,, "Combined propulsion for SSTO rocket - From conceptual study to demonstrator of deep cooled turbojet," AIAA 96-4497.


    • Taguchi, H.,, "Performance Evaluation of Hypersonic Pre-Cooled Turbojet Engine," 20th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, AIAA 2015-3593.


    • Ahren, J.E., "Thermal management of air-breathing propulsion systems," 30th Aerospace Sciences Meeting and Exhibit, AIAA 92-0514, 1992.


  • Murray, J.J.,, "An Experimental Precooler for Airbreathing Rocket Engines," 48th International Astronautical Federation Congress Melbourne, Australia 1998, IAF-98-S.5.02.

KEYWORDS: high mach, precooling, precooler, heat exchanger, thermal, materials, manufacturing, design, propulsion, hypersonic

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