Fill `Er Up With Hydrogen, Please

As your Mercedes 230E glides along, its computer signals that fuel is low. So you find a station with those newfangled gas pumps as big as a truck. It takes such a contraption to fill `er up with hydrogen--a fuel made from water whose byproduct from combustion is mostly water, too.

German auto makers have pursued this dream for two decades--and it will be years, if ever, before hydrogen-burners come to market. But the Mideast war is piquing interest in alternative fuels. And new clean-air laws make hydrogen seem less far out than it once did. Starting in 1998, California will insist that auto makers phase in some cars with zero emissions. Most favor electric cars for this, but hydrogen would do, too: Burning it mainly creates steam, most of which condenses and trickles out the tail pipe with only a few nitrous oxides left over. In fact, Japan's Mazda Motor Corp. hopes to sell a few hydrogen cars in California within 10 years.

WASTED ENERGY. There is one huge obstacle to overcome first. "The main problem," says Wolfgang Reitzle, BMW's research and development chief, "is how to produce and distribute hydrogen." This is more than a matter of new gas stations. Hydrogen is made by electrolysis: An electric current passes through electrodes immersed in water, splitting water molecules into hydrogen and oxygen atoms. This requires huge amounts of electricity, which if generated with oil or coal defeats the purpose of a hydrogen engine: It would be more efficient to turn oil into gasoline. That leaves nuclear-generated electricity or, better yet, renewable solar, wind, or hydroelectric power. The problem is, few countries have surplus hydropower. Environmentalists, who are politically potent in Europe, just hate nuclear power. And solar panels are still too costly and inefficient.

Putting the fuel source aside, however, motoring on hydrogen is clearly feasible. Mercedes-Benz has clocked 500,000 total miles on prototypes, including a three-year-plus road test in Berlin of five cars and five vans. In Munich, meanwhile, BMW is running two 735i models on liquid hydrogen. By 1997, Mercedes' hydrogen-powered buses could be plying the streets of Hamburg. Mazda plans to unveil its hydrogen prototype this fall.

So far, all three are using gasoline engines that have been modified for hydrogen--though not yet optimized. The BMW's 3.8-liter engine turns out 150 to 170 horsepower, instead of 208 in a gasoline version. And a 790-pound fuel tank in the Mercedes' trunk gives that car a heavier feel. Still, with more weight in the back, the car can be thrown into corners with more abandon, a plus when driving fast. And the Mercedes still tops out at 106 mph and hits 63 mph in 18 seconds, vs. 125 mph and 9.9 seconds in the gasoline model. Tadahiko Takiguchi, Mazda's technology manager, believes that his company's rotary engine may have more oomph than that, although the Germans don't agree.

FROSTBITE. But the key question is how the fuel should be stored. Mercedes has opted for gaseous hydrogen that bonds in the fuel tank with powdered metals, mainly titanium, vanadium, and manganese, at a pressure of 725 pounds per square inch (psi). This creates hydrides, which turn to powder again as the hydrogen burns. Mazda plans a tank that stores hydrogen in metal alloy balls, though that's all it will say. BMW uses liquid hydrogen stored at

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