Review of Autonomous Undersea Vehicle (AUV) Developments 
applications using methanol as fuel and where power density is an issue. For shipboard use, a diesel fuel 
reformer and desulfurizer would be required, and, although power density is an issue, it must be weighed 
against impact on acquisition cost--the further removed from commercial practice, the more expensive it will 
become. Existing Navy exploratory development efforts are focused on the fuel-processing issues of 
reforming and desulfurization with a 10-kW fuel cell demonstration planned. DARPA is supporting 
development of fuel cells that operate on logistic fuels (JP8 or DF2). " 
Table 1. Available Fuel Cell Systems 
Type Electrolyte Operating Efficiency lb/kw ft3/kw 
Fo SE a Se a a ee en HY 111) © ea Sh) cree eer ee en ee ee 
Phosphoric acid Phosphoric acid 350 to 450 38 to 40 30 to 46 0.93 to 
(liquid) 5 
Molten carbonate Carbonate salts 1.7: 2.00 to 420: to: 55 40 to 60 0.98 to 
(liquid) 1,400 ell 
Solid oxide Zirconium oxide 1,700 ‘to. 45 to 60 20 to 30 O.6to 
(tubular) (solid) 1,900 1.2 
Solid oxide Zirconium oxide 1.700 to 4'5 to 60 BS to. 13:25) J0\x3: to 
(planar) (solid) 1, 9:00 0.81 
Proton exchange Sulfonated 180 ito 250 39 to 42 6 to 11.9 0:29) “to 
membrane polymer (solid) 0.3 
SOURCE: Adapted from the Advanced Surface Machinery Programs Office, 1996, A Strategy Paper on Power for U.S. Navy 
Surface Ships, draft, Naval Sea Systems Command, Arlington, VA., Table A-1, p. A-7, April 8. 
Included in this repor’ NAVMETOCCOM commissioned a review of powering UUVs using 
Proton Exchange Membrane fuel cells. Several 5-kW systems were studied for integration. 
Direct-Feed Hydrogen systems were found to require excessive compressed pressure gas for 
extended missions. Reformed-Diesel systems expected to be available in the next two years 
are not feasible. Small modifications to the reformed-Diesel technology, when coupled with the 
A&T proprietary O2-generator/CO2/S-absorber, will perform at power densities approaching 500 
w-hrs/kg. Two methanol-fueled systems were studied. The Reformed-Methanol technology is 
available today and will produce power at the 500 w-hr/kg standard. Direct-Methanol is 
mechanically much simpler and is the best solution for the UUV application. A 1-kW system is 
under development at the Jet Propulsion Laboratory. Five kW systems are expected in the next 
two to three years with appropriate development. 
The key to using fuel cell technology in a UUV powered by a hydrocarbon fuel is the production 
of the oxidant and the management of carbon dioxide. A&T has developed a proprietary system 
that accomplishes these goals without using large parasitic electrical loads. This important 
technology can be used for fuel cells or any hydrocarbon fuel. The same need exists for 
turbines and small internal combustion engines. 
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