Fuel cells start to look real
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Gasoline reforming
If fuel-cell cars were to extract hydrogen from gasoline onboard, the transition to the fuel-cell vehicle would be much simpler as the current infrastructure would need less drastic changes. But refining gas on the road is difficult - much harder than cracking methanol. The reformation reactions occur at 850-1000°C (1560-1830°F), making the devices slow to start and the chemistry "temperamental." While the process is routine in chemical plants and oil refineries, squeezing it under the hood is difficult. Another unsolved problem is finding ways to protect the fuel cell from the catalyst-poisoning sulfur in current grades of gasoline.
Despite its focus on methanol, XCELLSiS is also working with Shell Oil on gasoline-reforming technology, reported DaimlerChrysler's Mohrdieck (see sidebar). "It's a much more complicated technology that operates at higher temperatures, which means it requires different materials able to handle the high heat. Similarly, high operating temperatures are the primary reason we didn't pursue onboard solid oxide or molten carbonate fuel cells," he noted. "Gasoline reformation requires a catalytic shift reaction that runs through a series of catalytic beds in which precise temperatures are critical," according to Ford's Staley. "In addition, you get carbon monoxide out the end, which means death to fuel cells."
Despite the technology challenges, GM and ExxonMobil have recently announced the joint development of a promising gasoline fuel-processor technology. The automaker argues that while hydrogen will likely be the eventual fuel of the future, gasoline-processing technology will provide a critical transition in making fuel-cell cars and trucks practical. "GM is not particularly in favor of using methanol reformate," said McCormick. "If the end state fuel is hydrogen, why spend the time and money to put in a methanol infrastructure? Why not start with the existing gasoline infrastructure?" he asked. Added Greg Ruselowski, Director of Finance Planning and Infrastructure at GM Global Alternative Propulsion Center, "Methanol use comes down to a question of the ultimate economics, various issues concerning the natural gas supply, and continuing worries about methanol toxicity, not to mention that it only has half the energy value of gasoline."
"GM is moving aggressively on gasoline reforming," said McCormick. "Our goal is to build an 80% efficient fuel processor." Generation 1 is a proof-of-concept bench model built at a facility near Rochester, NY. "We wanted to understand the fundamentals first," he noted.
GM's second-generation gasoline reformer unit - which, at 760 mm (30 in) long, 460 mm (18 in) high, and 200 mm (8 in) deep, is about half the size of the previous system - uses a new robust catalyst technology. Engineers addressed a problem that had so far plagued them - how to prevent the catalyst from breaking down due to driving vibration. The catalyst is "supported" in a honeycomb-like device that holds it in place and prevents it from deteriorating. GM engineers have tested this system for more than 1000 h - about 20% of the time needed for automobile applications - with no reduction in performance. "Right now, we're integrating the new (catalytic) process with a 25-kW fuel-cell stack. After that, we'll continue to reduce the size and further cut the startup time, while keeping the efficiency up and driving the cost out," he explained. The new catalyst will also be used in a next-generation fuel processor system that will be installed in a Chevrolet S-10 pickup that GM plans to demonstrate in early 2002. "Our rate of progress in gasoline reforming is surprisingly good," he stated. "Stay tuned..."
In general, "fuel-reforming technology requires the clever integration of all the components into a compact, lightweight, efficient, low-cost system," said Mark Voss, Engineering Manager for Modine Manufacturing Co. in Racine, WI. Modine has an exclusive agreement with XCELLSiS to supply heat transfer-related parts of fuel-cell systems. "The key is to couple the various subsystems together, some of which generate heat and others that use heat, so that the available heat is moved to where it's needed. Right now, we're focusing on the optimal materials choice in terms of durability and low-cost."
"Fuel-cell engine technology is still progressing in big technological steps where many disciplines such as process engineering, chemistry, heat transfer, special manufacturing skills, and so forth have to be optimized in a novel approach," said Gunther Dietrich, Senior Vice President, Development, Engineering, & Manufacturing, for XCELLSiS. "Under the arrangement, Modine, using its knowledge in solving thermal-management problems, will work together with XCELLSiS and its partners to bring fuel-cell engines to the marketplace." The company also will make radiators and heat exchangers for XCELLSiS-powered fuel-cell vehicles.
Another major question regarding hydrocarbon-fuel reforming is whether the chemical processing should be done onboard the car or at the service station. The answer depends on whether there is an eventual breakthrough in hydrogen-storage technology. A typical stationary reformer can run at higher-efficiency (about 90%), steady-state conditions, whereas onboard units must operate in load-following mode, making them less efficient (80-85%). Onboard reforming, of course, involves various hurdles including packaging issues, extra weight, and complicated controls.
Several automotive industry observers characterize the oil companies' general position on automotive fuel choice as surprisingly open. Said one, "Like us, they're asking if the technology is real, while trying to prepare to satisfy whatever need emerges. The oil companies are spending a fair amount of resources on this issue, but it's a classic chicken-and-egg problem of which comes first: the fuel or the fuel-cell engine. In addition, different fuels are probably better suited to different parts of the world. Though the oil industry seems to be a big, lumbering, monolithic giant that does what it wants, recent divestitures now mean it's more a collection of a lot of little guys who have to follow the market just like everyone else. This makes the huge investments that are going to be needed much more difficult to accomplish."
