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Wired wrote:

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Brad Pitt, Cameron Diaz and all the other celebrities driving Hydrogen 7 sedans can take heart because BMW still has their backs. The German automaker isn't giving up on hydrogen and says its latest hydrogen combustion engine matches the efficiency of the best turbodiesels.

What remains in question is whether hydrogen will arrive on scene fast enough to be of any good.

Hydrogen remains a long way from viability for several reasons, not the least of which is the relative lack of a distribution infrastructure. Some suggest it won't have any significant impact for 40 years or more. The major automakers have developed hydrogen fuel cell vehicles, but they've said little about them in recent months and shifted their attention to hybrids and battery electric vehicles.

But BMW, with Honda and its FCX Clarity fuel cell car, remains an industry leader in developing hydrogen technology and believes there is a place for it.

"In light of the limited availability of fossil fuels and the rising environmental impact from harmful emissions, we are convinced that the H2 combustion engine will assume an important position in the product portfolio of future alternative drive concepts," Dr. Raymond Freymann, managing director of BMW Research and Technology, said in a statement. "It will crucially contribute to safeguarding our individual mobility at the high level the customer expects."

The company's emphasis has been not on fuel cells but on internal combustion engines that burn liquefied hydrogen. BMW says its latest engine, developed with Hoerbiger, Graz University of Technology and HyCentA, develops record efficiency on the test bench.

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The engine is shown above, buried beneath all the test equipment. The cylinder head geometry is similar to that of a diesel engine, and progressive H2 high-pressure direct injection sends hydrogen into the combustion chamber at up to 4,500 PSI. The result is an efficiency level of up to 42 percent, which BMW claims is on par with the best turbodiesels. This means one of the biggest bugaboos of H2 — the fact you have to burn so much of it — has been overcome, at least in the laboratory. BMW believes it can achieve even greater efficiency through waste heat utilization.

BMW is pushing H2 technology in the Hydrogen 7, which so far has been driven mostly by celebrities (although Wired got behind the wheel of one a few years ago). Brad Pitt, Edward Norton and Cameron Diaz were among the early adopters, and Hilary Swank got one earlier this month.

The Hydrogen 7 can run on gasoline or liquefied hydrogen. Run it on hydrogen and the only thing coming out of your tailpipe is water vapor. A hydrogen-only model called the Hydrogen 7 Mono-Fuel is even cleaner; BMW claims the engine actually consumes pollution in the ambient air coming through the combustion chamber, so the air coming out of the tailpipe is cleaner than the air going through the grille.