TECHNOLOGY AREAS: Ground/Sea Vehicles

ACQUISITION PROGRAM: PM Expeditionary Power Systems

OBJECTIVE: Develop a power dense heat recovery bottoming cycle for increasing portable generator efficiency.

DESCRIPTION: Battlefield power generation requirements continue to rise dramatically due to the increasing number of electronic systems being forward deployed. There is significant desire to minimize the size, weight, and fuel consumption of today�s generator sets. Small gas turbines and microturbines can provide large amounts of power in a small size and with a low cost per kilowatt. However, these engines require recuperators to maintain a competitive efficiency, which compromises power density and cost. Bottoming cycles have the potential to increase both fuel efficiency and power density over existing recuperated microturbines due to the increased power production without burning additional fuel.

The U.S. Navy and Marine Corps are interested in exploring the use of power dense bottoming cycles for microturbines in order to utilize the exhaust heat for producing additional power without consuming additional fuel, while maintaining similar power density of simple cycle engines and reducing cost per kilowatt. Candidate technologies include, but are not limited to, organic Rankine cycles, Stirling engines, and thermoelectric generators. The expected benefits of this technology are increased system efficiency, reduced lifecycle cost over diesel generators, and reduced thermal signature. Technologies should operate over a wide range of ambient temperatures. Electrical and hardware system integration, as well as dynamic response to varying load, should also be addressed.

PHASE I: Design and model a conceptual bottoming cycle which interfaces with a 30 kW recuperated microturbine engine and, has a target output of 10 kW of electrical power at full load. Target power density for the bottoming cycle portion is 50 Watts per Liter including radiators or other parts separate from the main engine. Proposals may assume a 260 �C exhaust and a 0.3 kg/sec exhaust flow rate for a simple cycle microturbine. Conduct a feasibility study and cost-benefit analysis to determine the incremental benefit over the current state of the art.

PHASE II: Build and test a full scale prototype device to establish a proof-of-concept, and demonstrate using actual or simulated gas turbine exhaust. Performance data shall be collected at ambient temperatures from 0 to 120 �F. Validate analytic models developed in Phase I.

PHASE III: Design and develop a market ready prototype using the knowledge gained during Phases I and II. Develop a commercialization strategy for dual use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The bottoming cycles developed under this topic could be used to increase the efficiency of portable generators in the private sector. These devices may also be compatible with other types of generators, including diesel engines, allowing similar improvements in efficiency. Due to the limited availability of bottoming cycle devices in the commercial market, sales to users without space and weight constraints are also expected.

REFERENCES:
1. C. Invernizzi, P. Iora, and P. Silva, "Bottoming micro-Rankine cycles for micro-gas turbines," Appl. Therm. Eng. 27, 100 (2007).

2. J.H. Lee and T.S. Kim, "Analysis of design and part load performance of micro gas turbine/organic Rankine cycle combined systems," J. Mech. Sci. and Tech. 20, 1502 (2006)

3. H. D. Marron, "Gas Turbine Waste Heat Recovery Propulsion for U. S. Navy Surface Combatants," Nav. Eng. J. 93, 65 (1981).

4. D. T. Rizy et al., "Integration of Distributed Energy Resources and Thermally-Activated Technologies," DistribuTech Conference, Miami Beach, FL (2002).

5. http://www.marcorsyscom.usmc.mil/sites/PMEPS/MEP.asp.

KEYWORDS: bottoming cycle; microturbine; energy recovery; energy efficiency

** TOPIC AUTHOR (TPOC) **

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