|MadSci Network: Engineering|
Greetings: Your questions address some of the key issues facing fuel cell designers and the questions will not be settled until a great deal of testing in an operational environment is conducted. It is claimed that the major emissions from a gasoline powered fuel cell are carbon monoxide (CO) and carbon dioxide (CO^2). How much improvement will fuel cells offer relative to internal combustion engines has been studied on a small scale in laboratories with some promising results ; however, much testing will be required in the future. The following quotations present two different views on gasoline powered fuel cells. From the New York Times (URL http://www.abe.msstate.edu/classes/abe4312/sustain/sci-gasoline.html) "The A.D. Little innovation, which was tested earlier this month, mixes oxygen with the gasoline fumes, breaking up the complex hydrocarbon molecules into H2 and carbon monoxide, which is a pollutant. If carbon monoxide exceeds about 40 parts per million, it will poison the fuel cell. To prevent such damage the new system includes a device built at the Los Alamos National Laboratory, a nuclear weapons laboratory, that accepts the gas and adds a second oxygen atom to the carbon monoxide, producing carbon dioxide. Engineers were able to accomplish that difficult step without adding oxygen to the H2, a step that would rob the fuel cell of its fuel. Then the gas, almost pure H2, goes to a fuel cell, an older technology that has been gradually improved in the last few years. The hydrogen atoms, which consist of one proton and one electron, flow down one side of a permeable membrane. On the other side is oxygen from air. The hydrogen's proton wants to join with the oxygen, to create H2O, or water, and is drawn through the membrane, but the electron is left behind. With the positively charged proton on one side and the negatively charged electron on the other, the membrane creates an electrical difference that becomes a current. " ---------- "In 16 hours of tests earlier this month at a Little laboratory in Cambridge, Mass., a processor ran smoothly on gasoline and ethanol, officials said. It produced enough hydrogen for 50 kilowatts, big enough to run a medium-size car. Ethanol can be produced from corn, and the Energy Department hopes it will eventually be the main fuel for such cells. Gasoline might therefore be a transitional step to ethanol, which is completely renewable. The system delivers 84 percent of the energy in a gallon of gasoline to the fuel cell, said Jeffrey M. Bently, a vice president of Little, and the fuel cell turns most of that energy into electricity. In contrast, an internal combustion engine loses more than 80 percent of the energy in a gallon, either as heat out the tail pipe or friction in the drive train. " --------- "In this version, a team of researchers at Arthur D. Little Co., a Boston- based energy consulting firm, came up with a fuel cell that produces energy by combining oxygen and hydrogen from gasoline. The company said Tuesday it would work with major automakers to develop the system in an electric car, cutting auto emissions by 95 percent while doubling fuel efficiency. Officials estimated commercial production as early as 2005. Some remaining challenges include reducing the cost, getting the system smaller to fit under a car's hood and developing more power than the laboratory model, company officials said. A spokesman for Chrysler Corp., which has worked with the research team, said costs would have to be cut drastically for the engine to compete with current cars. Even mass produced, the technology would cost $30,000 per car now compared with $3,000 for conventional cars. But, said Chrysler spokesman Tony Cervone, the automaker anticipates having a prototype car using the technology in less than two years and expects to cut costs enough to have commercial production before 2010. The chemical reaction between oxygen and hydrogen produces energy and leaves only water. The extraction of hydrogen from gasoline leaves carbon dioxide, but because of increased efficiency carbon emissions would be cut by 50 to 70 percent from conventionally powered cars. The fuel cell could produce cars that get up to 80 miles per gallon while cutting air pollution by 95 percent,the researchers said. --------- What the gasoline fuel cell doesn't do (URL: http://www.primenet.com/~evchdlr/fuel_cell.html). "It doesn't do much for the greenhouse effect. The end product of gasoline combusion is CO2, whether you burn the fuel in an engine, or chemically oxidize it to release hydrogen in a reformulator (the hydrogen is then fed to the fuel-cell directly or tanked for later use). Combustion, by definition, uses up oxygen and releases CO2. What improvements in CO2 emissions comes about as a result of using an electric drivetrain. Don't think about sitting in a closed garage with a running fuel-cell car with a gasoline reformulator on- board. You may not die from the hydrocarbons or NOX, but you will still suffocate. Fuel-cells are best used in a complete hydrogen energy cycle, which uses renewable solar or thermal energy sources to generate hydrogen from water without releasing CO2. Stored hydrogen then is used to drive hydrogen fuel- cell EVs, which emit only water vapor. If we are going to use feul-cells. let's use the hudrogen ones. Even methanol isn't so bad, since it can be produced from corn." -------------- The process for electrically converting water (H2O) into hydrogen (H2) and oxygen (O2) gas has been studied for many years. One of the most promising techniques was by using a photovoltaic membrane process similar to solar cells; however, to date all of these processes have been very inefficient requiring far more energy input than fuel output. Also, the major costs for all forms of energy for use in transportation are for the fuel delivery system. Gasoline powered fuel cells will use a multi - billion dollar system that is already in place. The cost and environmental effects for creating a new fuel delivery system must be balanced with the environmental impact of the vehicle emissions. Best regards, Your Mad Scientist Adrian Popa
Try the links in the MadSci Library for more information on Engineering.