October 04, 2005

US Air Force working on stealthier UAV powered by an alternative energy source

10/3/2005 - U.S. AIR FORCE ACADEMY, Colo. (AFPN) -- Future Air Force leaders here are working to produce a stealthier unmanned aerial vehicle powered by an alternative energy source.

The research project into fuel cells and hydrogen storage materials started about 10 years ago as a collaboration between the academy, Ball Aerospace Corp in Boulder, Colo., and Hydrogen Components, Inc., in Littleton, Colo. The goal of the research is to find an alternative to batteries for personal electric power used in Department of Defense special operations.

The UAV research group here involves the work of 11 academic departments working on individual and collaborative projects. Ball Aerospace focuses on fuel cell development while academy faculty and cadets work with hydrogen components on the chemistry and hardware of the hydrogen generator.

The general idea of the chemical hydrogen generator is to store hydrogen that is

chemically combined with atoms from lithium and aluminum. The hydrogen is then released through chemical reactions that produce hydrogen fuel for a fuel cell. Hydrogen fuel is released at exact rates and amounts matching the electric power needed in a UAV.

"That's the tricky part," said Dr. John Wilkes, Chemistry Research Center director. "It works well, but we want to do better. We are now working to improve the performance of the hydrogen generator by a factor of three by improving the hydrogen yield and using storage materials with higher hydrogen content. Ultimately, we would like to develop a very light hydrogen generator/fuel cell combination that could be used to fly an electrically powered UAV."

Small UAVs using electric propulsion will be the major benefactor of hydrogen fuel cell technology. An electric motor has several advantages over the more common internal combustion engines or turbine engines.

Electric motors are quiet and produce less heat, making them stealthier, and they also start reliably and are extremely compact. But, the required batteries are still too heavy to power an electric UAV for very long.

However, a fuel cell that runs on hydrogen is less than half the weight of conventional batteries with equivalent capacity. Batteries are still relatively inexpensive and more available than other power sources.

"We have already met the first goal of a hydrogen source that produces 6 percent by weight hydrogen," Dr. Wilkes said. "That is, if the hydrogen storage system weighs 100 pounds, then you could get 6 pounds of hydrogen. That may not sound like a lot of hydrogen, but since it is the lightest of all elements, 6 pounds translates to over 30,000 liters of hydrogen. We have ideas to try that could triple that amount."

The chemical process that met the 6 percent goal produces only half of the energy that is potentially available. Cadets are currently doing experiments to solve that problem. The Cadets are attempting to apply nanoparticle technology to make every molecule of the stored hydrogen available. They are also working on catalysts to improve the speed at which hydrogen is produced during the chemical reaction so that more sources of hydrogen may be used.

"The U.S. Army has tested nine of our prototype hydrogen generators with 50-watt fuel cells, and they work," Dr. Wilkes said. "At this stage, the cost is high, the chemical compounds are rare and the storage system cannot be recharged easily. The big positive for our chemical system is that the hydrogen is not contained at thousands of pounds of pressure or at super-low temperatures. It is stable forever at normal temperatures and pressures, just waiting for you to turn on the fuel cell.

"Like many new technologies, the adoption of our hydrogen storage method depends on some further research on improved yield, a lot of engineering development and an investment in manufacturing technology," the doctor said. "It is a long road from basic research to a fielded system, and the journey along that road is usually 20 years or more."

In the future, hydrogen fuel cells could replace petroleum in cars, trucks and trains, and in stationary power such as municipal power plants. The world currently uses electric power at a rate of about 13 terawatts and most of that comes from energy stored as petroleum, coal or natural gas. A terawatt is 1 trillion watts of power.

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