Defense Technology International - September 2007 - (Page 24) DISPATCHES GLOBAL ENGINE TESTS U.S. Army diesel-electric hybrid motors get a reality check DAVID AXE•DETROIT espite concerns about the Future Combat Systems program, the U.S. Army plans large-scale tests of hybrid diesel-electric engines for FCS vehicles. The tests, which were slated to begin last month, are an important step in assembling data that will aid in developing durable hybrid vehicles. Engineers at the Army’s Tank-Automotive Research, Development and Engineering Center (Tardec) in Warren, Mich., say hybrids have an important place in the D a hybrid motor needs to work to haul a given weight under given conditions. And without that information, no one can predict how fuel-efficient a hybrid vehicle will be. The current testing program, Khalil says, includes “learning real-world mileage and fuel-economy ranges for different duty cycles.” Manufacturers of commercial hybrid automobiles tout the vehicles’ fuel efficiency over traditional cars, but Khalil says he suspects the generation of military hybrids just entering testing won’t always offer greatly Engine generators like this will provide power for FCS Manned Ground Vehicles and their hybrid-electric drives. service’s future, though the transition from diesel and gas engines won’t be easy. Hybrids require much better batteries and a more sophisticated understanding of how vehicles use power in different scenarios. “FCS represents the first major attempt at fielding a combat hybrid-electric system,” says Gus Khalil, a Tardec engineer who has worked on a number of demonstrator hybrid vehicles in the last decade. But those were all highly experimental efforts, and as a result “there hasn’t been a real test procedure” developed for hybrids. The lack of rigorous testing means a dearth of data for mapping hybrids’ “duty cycles” over particular “mission profiles.” In other words, nobody really knows how hard 24 improved mileage. “The military environment is totally different for fuel economy,” he says. “In some cases, vehicles now have better fuel economy [than hybrids].” But military hybrids aren’t intended only to save fuel. They are also capable of exporting usable electrical power to command stations, radars, medical equipment and other systems, says Satyanarayana Kodali, FCS mobility program manager. “FCS reduces generator logistics to almost nothing,” he says. Hybrids can also use their batteries at the same time as their diesel engines for short, high-speed “sprints.” Or they can run entirely on battery power—“silent mobility,” Khalil calls it. “We have driven a vehicle for 20 mi., silent, on battery power.” While totally silent, a hybrid’s endurance is limited by the capacity of its batteries. And that represents a major hurdle for Tardec. “If there is a component or technology that is a challenge, it is the batteries. We deal with tight spaces and have to operate all over the world.” Current battery designs are too bulky for space-constrained military vehicle designs and too delicate to stand up to extreme cold and intense heat. New chemistries are a potential solution, says Sonya Gargies, one of Tardec’s battery experts. Most batteries use lead acid or lithium; future batteries might pack more powerful silicon-carbide or lithiumion cells. “Lithium ion has the best energy density but has problems with safety and reliability,” Gargies says. Alternative chemistries are also more expensive. Silent mobility is scaleable, says Jennifer Hitchcock, a Tardec engineer specializing in hybrids. “We can dim the lights, put the computers on standby—things to conserve power,” she says, explaining that current military vehicles are mostly “all-on” or “alloff ” as far as the electronics are concerned. The ability to manipulate electrical power requires power-management systems that are far nimbler than anything in use today. “We embarked last year on a full effort to get our arms around this power-management issue,” Hitchcock reports. “It’s about developing the controls, the algorithms, the sensors—the enabling technologies.” As it stands, the military is mostly going it alone in developing tough hybrids. The commercial sector seems content for now to dabble in lightweight hybrids that only marginally advance the state of the art. Tardec is counting on that changing: Serious investment in advanced hybrids by automakers should help solve some of Tardec’s problems. “I think in five years you’re going to see a revolution in the car industry,” Khalil says, citing rising gas prices as a major factor. “People are going to start looking at alternative transportation, and hybrids are one of them. Things that are common between the military and [commercial] industry are going to get better. Today, 1 kw. of lithium-ion battery power costs $3,500—that’s a hundred times more expensive than lead acid. There is going to be demand and competition that will bring that price way down.” But while Tardec is optimistic about cooperation between the Army and automakers on future hybrids, existing military vehicle designs are unlikely to benefit. Retrofitting Humvees, M1 Abrams tanks and M2 Bradley fighting vehicles just isn’t costeffective, Hitchcock says. I Read Axe’s posts on DTI’s weblog, Ares, updated daily: aresblog.net U.S. ARMY DEFENSE TECHNOLOGY INTERNATIONAL SEPTEMBER 2007 http://aresblog.net
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