Smart Exhaust Waste Heat Recovery Unit (SEWHRU)

Navy STTR 24.A - Topic N24A-T009
NAVSEA - Naval Sea Systems Command
Pre-release 11/29/23   Opens to accept proposals 1/03/24   Now Closes 2/21/24 12:00pm ET

N24A-T009 TITLE: Smart Exhaust Waste Heat Recovery Unit (SEWHRU)


OBJECTIVE: Develop and demonstrate a self-cleaning Smart Exhaust Waste Heat Recovery Unit (SEWHRU) for internal combustion engines flue gas ranging in temperature from 500 to 1200 °F, for use in electric generation and/or heating and cooling processes.

DESCRIPTION: A typical diesel engine attains approximately 42% brake thermal efficiency, with approximately 28% of fuel energy dissipated to the environment through engine exhaust flue gas as waste heat. Effective recovery and conversion of the waste heat into useful work would increase the diesel engine’s thermal efficiency, resulting in a reduction in the engine’s fuel consumption for equivalent work. This STTR topic seeks a SEWHRU to capture and transfer at least 50% of the heat from the exhaust flue gas to an intermediate working fluid, and on to the components that will convert the heat into useful work.

WHRUs for legacy internal combustion engines exist commercially as an afterthought for prime movers. The WHRUs are dependent on the prime mover, with a WHRU that consists of a Heat Exchanger (HX) placed directly into the flue gas pathway and expected to work effectively without interfering with the operation of the prime mover. Some WHRUs designs incorporate dampers and a bypass system that redirects the flue gas around the HX; however, the legacy systems do not provide the following features that would be beneficial to the life, efficiency, reliability, and maintainability of the HX:

• Controlled flow rate of the flue gas through the HX

• Controlled flow rate of the working fluid through the HX

• Flue gas treatment for reducing particulate matter and other contaminants

• Even distribution of the flue gas through the HX

• Protective mechanism or process to protect the HX from over heating

• Control mechanism or process that prevents condensation within the HX

• Forced air system to counteract pressure losses

• Modular design to ensure maintainability

The legacy WHRUs that utilize conventional processes to recover waste heat from flue gas are plagued with multiple problems as follows:

• Thermo-mechanical stress due to transient flue gas temperature profiles

• Resonance within the heat exchanger when flow of the secondary fluid is secured

• Maintenance due to fouling and corrosion

• Secondary fluid thermal and pressure constraints, decomposition limits of fluid

• Unrestricted prime mover or plant operations

• Effect on efficiency or power output due to exhaust stack backpressure

A self-cleaning SEWHRU design is needed by the Navy with systems and processes incorporated and synchronized with the prime mover and the waste heat recovery system’s operation sequences in order for the WHRU to work effectively.

The WHRU shall transfer heat from the diesel engine’s flue gas to a working fluid with an inlet temperature range between 60 and 190 °F. Pressure drops across hot flue gas side of the WHRU shall not exceed 4 inches of water and/or interfere with the prime mover’s efficiency. The heat recovery unit design shall be capable of withstanding thermal shock effects when a working fluid at 60 °F enters a 1200 °F heat exchanger. The WHRU shall possess a self-cleaning function that mitigates fouling and corrosion effect from combustion byproducts and operates with minimal operator intervention. Weight and volume of the WHRU shall be comparable or less than the prime mover’s weight and size to power ratio. The WHRU shall be utilized in place of a silencer and shall be comparable to or better than the existing silencer in attenuating engine exhaust noise. The WHRU shall be scalable to 4000 Brake Horse-Power (BHP) marine diesel engines.

PHASE I: Develop a concept for a self-cleaning SEWHRU that meets the needs of the Navy as defined in the Description. Evaluate the unit’s economic, technical, and manufacturing feasibility and quantify the SEWHRUs efficiency and operating parameters. Demonstrate the design and manufacturing concepts through modeling, analysis, and bench top experimentation where appropriate. Document the ability and impact of scaling engine size. Include in the Phase I final report the technical and economic feasibility of the proposed solution. The Phase I Option, if exercised, should include an initial detailed design and specifications to build a prototype with the Phase II effort.

PHASE II: Develop, fabricate, deliver, and test a prototype of a WHRU at an appropriate scale that captures at least 50% of the heat in the flue gas of a demonstration engine. Demonstrate the ability to withstand the flue gas temperature cycles. Validate analytic models developed in Phase I and evaluate scalability of design up to 4000 BHP. Perform testing activities that include demonstration and characterization of key parameters and objectives at the proposer’s facility or other suitable testing facility identified by the offeror. Design the full-scale waste heat recovery unit for a rated diesel engine that fits in place of the existing exhaust stack silencer and integrate the unit with the rated diesel engine. Test the unit to demonstrate the ability to meet the design characteristics. Provide an updated economic and manufacturability study with updated designs that result from developments during prototype testing. Test the waste heat recovery unit in a relevant environment and ensure that the system meets the unique requirements for deployment on a U.S. Naval vessel such as shock and vibration. Analyze the ability to complete more than one prototype with the Phase II funding.

PHASE III DUAL USE APPLICATIONS: Assist the Navy in transitioning the technology to Navy use. Develop a transition strategy through research, analysis, and identification to establish production-level manufacturing capabilities and facilities that will produce and fully qualify a SEWHRU. Based on the results of the cost-benefit analysis, provide an economic and manufacturability study with updated designs that result from developments during prototype testing, DDG(X) may assess potential for design insertion for potential forward fit/back fit application.

This technology has commercial application in the internal and external combustion engine industry, electric power generation industry, and other manufacturing or production process that rejects low grade waste heat into the environment. This technology will enable lowered operation and production costs, reducing effects on the environment.


  1. HeatMatrix Group BV. "Corrosive flue gas is no longer a show-stopper for heat recovery." Polymer or Stainless Economiser-ECO. November 29, 2021.
  2. U.S. Department of Energy. "Chapter 6: Innovating Clean Energy Technologies in Advanced Manufacturing: Technology Assessments." Quadrennial Technology Review 2015, Chapter 6. November 29, 2021.

KEYWORDS: Heat Exchanger; Waste Heat Recovery Unit; Internal Combustion Engines; Diesel Engines; Thermal Recovery; Prime Mover


The Navy Topic above is an "unofficial" copy from the Navy Topics in the DoD 24.A STTR BAA. Please see the official DoD Topic website at for any updates.

The DoD issued its Navy 24.A STTR Topics pre-release on November 28, 2023 which opens to receive proposals on January 3, 2024, and now closes February 21, (12:00pm ET).

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