NRL pushes research to draw power from the sea

Benthic fuel cells with ocean sensor

Benthic fuel cells surround an oceanographic sensor.

You can't do much of anything without power. And nowhere is power harder to come by than in the air and at sea.

Hence, the U.S. Naval Research Laboratory continues to pursue various avenues for generating and storing power for use in aircraft and sensors, in some cases drawing power from the sea itself.

In April, for example, NRL's Materials Science and Technology Division demonstrated a concept for recovering carbon dioxide and hydrogen from seawater that could be converted to hydrocarbon fuel. Liquid hydrocarbon, the byproduct of a NRL gas-to-liquid process, was used to power a scale model prop aircraft with an unmodified two-stroke internal combustion engine.

And then there is the "benthic microbial fuel cell," which could generate continuous electrical power at the bottom of the sea. These ocean-floor fuel cells convert microorganisms on the sea floor into fuel and oxidants to produce electricity. They can provide a low-cost, continuous power supply for oceanographic sensors, which currently use batter power that eventually runs. The fuel cells could keep them operating remotely for indefinite periods, NRL researchers claim.

They also claim that microbial fuel cell development could have major implications for Navy intelligence, surveillance and reconnaissance operations at sea and in littoral environments.

Previously, NRL engineers said they broke an endurance record for a small electric UAV. An electric fuel cell using liquid hydrogen in a cryogenic fuel storage tank kept an Ion Tiger UAV aloft for just over 48 hours. The previous record was 26 hours and two minutes.

Long endurance flights are possible using conventional fuels, but researchers are focusing on extending the range of much quieter electric fuel cells. Electric-powered UAVs would also have a smaller radar signature to reduce the chances of detection, NRL researchers noted.

"Liquid hydrogen coupled with fuel-cell technology has the potential to expand the utility of small unmanned systems by greatly increasing endurance while still affording all the benefits of electric propulsion," said NRL principal investigator Karen Swider-Lyons.

On the seawater-to-fuel project, , which uses NRL’s proprietary electrolytic cation exchange module (E-CEM), NRL researchers are focusing on seawater as feedstock for the gas-to-liquid fueling concept since the concentration of CO2 in the ocean is about 140 times greater than in the atmosphere.

"This is the first time technology of this nature has been demonstrated with the potential for transition, from the laboratory, to full-scale commercial implementation," NRL research chemist Heather Willauer said in a statement.

NRL projects that the cost of jet fuel produced using the technology could range between $3 and $6 per gallon. With sufficient funding, the lab predicts it approach could be "commercially viable" in seven to 10 years.

About the Author

George Leopold is a contributing editor for Defense Systems and author of Calculated Risk: The Supersonic Life and Times of Gus Grissom."Connect with him on Twitter at @gleopold1.

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