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Hydrogen Powers Up the Small Engine Market

In a new development that could make fuel cells practical for small machines such as lawnmowers and chainsaws, researchers at Princeton University have developed a new mechanism to efficiently control hydrogen fuel cell power. The secret of their success is a system in which the fuel input itself changes the size of the reaction chamber, and therefore the amount of power produced.

Jay Benziger, a professor of Chemical Engineering at Princeton University, developed the new technique with former student Claire Woo — a recipient of a National Science Foundation Research Experiences for Undergraduates award and now a doctoral candidate at the University of California, Berkeley. The new process controls the hydrogen feed to match the required power output, just as one controls the feed of gasoline into an internal combustion engine. The system functions as a closed system that uses the waste water to regulate the size of the reaction chamber, the site where the gasses combine to form water, heat and electricity. Many standard fuel cell designs use electronics to control power output, but such designs require complex systems to manage humidity and fuel recovery and recycling systems to achieve acceptable efficiency. Because the new design is closed, 100 percent of the fuel is used and there is no need for a costly fuel recycling system. “The fuel cell functionally operates as a dead-end design where no gas flows out of the cell and water is permitted to flow in and out of the gas flow channel. The variable water level in the flow channel regulates the internal resistance of the fuel cell. The hydrogen and oxygen (or air) feeds are set directly to stoichiometrically match the current, which then control the water level internal to the fuel cell. Standard PID feedback control of the reactant feeds has been incorporated to speed up the system response to changes in load,” stated the researchers in the Chemical Engineering Science article abstract. The researchers believe the first applications for their technology will be in smaller engines. Fuel cells, which use hydrogen to make electricity with only water and heat as byproducts, are currently inefficient on such scales due to the need for fuel recycling and excess hydrogen in standard designs. “The system is ideal for small internal combustion engines that lack emissions controls and are highly polluting,” said Benziger. “There is also no need for an extensive hydrogen distribution system for these small motors; the hydrogen could be supplied in returnable tanks such as the propane tanks used for gas grills.” Though the potential for fuel cell-powered vehicles is widely recognized much work remains to be done before they become commercially available. However, Benziger and Woo’s breakthrough adds to the understanding of water management in fuel cells — one of the major obstacles to large-scale deployment of the technology in automobiles. Benziger’s next goal is to connect several of the new fuel cells together to increase power, a system that could potentially compete with cells now being tested in the automotive industry. The team’s findings were recently published in the February 2007 issue of Chemical Engineering Science.