“Ultimate Driving Machine” Comes To Caltech

A sleek, silver-blue Bimmer joined the Caltech motor pool March 26. It was evident from the paint job that it’s a hydrogen-powered car, but the car doesn’t run on a fuel cell, like the Honda Clarity and its kin. Instead of converting H2O2 to water and electricity, with a set of electric motors to drive the wheels, this BMW Series 7 sedan has the same 12-cylinder engine as the $80,000 + street version.

At the flip of a switch on the steering wheel, the engine reconfigures itself – adjusting the mixture ratio, ignition timing, valve delays, and so on – to burn hydrogen instead of gasoline. As with a fuel-cell car, the emissions out the tailpipe are essentially water vapor.

A heavily insulated tank in the trunk holds seven kilograms of cryogenic rocket fuel, giving the Hydrogen 7 a gasoline-free range of about 150 miles. Although a frosty 23 Kelvin, the pressure in the tank is only 35 pounds per square inch, allowing it to be very light. By contrast, the fuel-cell-powered Clarity’s hydrogen gas is stored at 5,000 psi at room temperature, requiring a much heavier tank that only holds 4.1 kilograms of fuel.

In a clever piece of engineering, the BMW’s hydrogen tank keeps itself cold by slowly bleeding off, the way a can of “liquid air” turns cold in your hand as you blow the dust off your computer components. But it would still be safe to sneak out to the garage for a smoke, as a catalytic converter in the vent line turns the hydrogen into water vapor. And the fuel loss is very gradual – it would take about a month for the tank to empty if the car is not driven.

“We began working on H&sub2 internal-combustion engines in 1978–79,” said James Ryan, program director for BMW CleanEnergy. “But only now, in the ninth generation, have they matured to where we can place them in the hands of consumers.” The vehicle is market-ready, but don’t get in line for one just yet-only 100 of them were built, and only 20 of those went to North America.

“It’s a chicken-and-egg problem,” said Ryan. “You can’t sell the cars unless you have a network of refueling stations, but nobody’s going to build those stations until there are a lot of these cars on the road.”

At the moment, there’s only one liquid-hydrogen station – at BMW’s engineering center in Oxnard – with a second one to be opened soon at the Van Nuys airport. Of course, a fueling station is only as green as the electricity used to liquefy the hydrogen, but that’s beyond the scope of these prototypes.

That’s where Caltech comes in – Irvine Professor of Environmental Science Michael Hoffman, who engineered the deal, is developing solar-powered electrochemical systems to make hydrogen from water while at the same time breaking down such water pollutants as 2, 4, 6-trichlorophenol, a carcinogen formerly widely used as a pesticide.