Versa SOFC in undersea vehicle test-bed S olid oxide fuel cell developer Versa Power Systems reports that its technology has been successfully used in an experimental test-bed, which is representative of a propulsion system for stealth surveillance vehicles under development by the US Navy.
An SOFC stack was evaluated under conditions that simulate the expected demands on an unmanned undersea vehicle (UUV). The design goals for the vehicle are for it to operate autonomously, undetected, and conduct surveillance over lengthy periods.
In tests carried out by the Naval Undersea Warfare Center (NUWC) in Newport, Rhode Island the SOFC stack from Versa Power was integrated with a compact fuel processor fabricated by InnovaTek. The combined propulsion system is designed to fit within the tight confines of a UUV and offer more available energy than rechargeable batteries. According to Versa Power, the in-flow of specially formulated fuel and the high system efficiency will allow a UUV that is only 53 cm (21 inches) in diameter and approximately 6 m (20 ft) long to run continuously for 30-60 h, depending on the power demand.
'Long endurance is made possible by the SOFC's high electrical efficiency and small package size,' explains Dr Alan Burke, co-leader of the NUWC project. 'Even with the need to store on-board fuel and an oxygen source, the fuel cell system has the potential to store considerable energy compared with other propulsion systems.'
The test at NUWC simulated the fuel flow that an operational UUV would use to feed its SOFC, recycling unspent fuel back into the system to capture all the available energy. Under these conditions, the electrical efficiency of Versa Power's fuel cell stack was 70% for the duration of the test run. Overall system efficiency in operation would be expected to be somewhat lower -the difference stemming from energy consumption that is devoted to the propulsion device's parasitic power losses.
'Compared with traditional combustion engines, which generally achieve a maximum of 30% efficiency in operation, this system demonstrated a highly efficient means to use diesel-type fuels for power generation,' adds Burke.
UUV designers anticipate that fuel cells will be able to provide power for the vehicle's electric motor -for low-speed, silent propulsion -and also to run the guidance and control systems, sensors and transmitters.