Glenn Reynolds seems to have been in a motorhead mood yesterday. First, he links to this Autoblog post, about the new prototype Mazda hydrogen/gasoline RX-8, then to this this Jay Leno article in Popular Mechanics. The Leno article, coincidentally, features a pic of Jay with the lovely original Mazda Cosmo.
But I believe Autoblog’s Chris Paukert is a bit misleading, when he says the RX-8s are “street legal.” I don’t know about the specifics of Japanese law. But here in California, factory prototypes (to say nothing of alternative fuel vehicles) enjoy legal loopholes that don’t apply to the cars they might sell to rank-and-file drivers. So Glenn, you might have a VERY long wait for your test drive. That is, unless you can exploit your “celebrity” status. 
But BMW is still way ahead of Mazda in hydrogen combustion technology. The reader should note here that, in either case, these are quite different than the hydrogen fuel cell vehicles, as, rather than electric motors (and the fuel cell, of course), they use a more-or-less conventional internal combustion engine.
Some commenters on the Autoblog post lumped the Mazda in with the likes of the Toyota Prius, calling it a “hybrid”; when the term is used in that context, it is a misnomer. But “hybrid” can be applied to a lot of different technologies, and it can be quite confusing to the layperson. The Prius is an electric/internal combustion motive system hybrid. The Mazda is a hydrogen/gasoline fuel system hybrid.
I find it difficult to get too very excited about any of this. Popular hybrids, such as the Prius, do deliver better mileage than their conventional counterparts, but not that great. This is particularly true if one adopts a more intelligent urban driving style than the constant accelerate/brake cycle common to most Americans. And, as for hydrogen, any way you get it requires so much more energy than gasoline, or any other fossil fuel, that it simply is not economical. As well, when deriving hydrogen from the hydrocarbons in fossil fuels (the more economical alternative, as compared to electrolysis of water), the point of airborne emissions is simply moved from the automobile itself to the chemical plant, which, in the case of the Honda Home Energy Station (which reforms natural gas), is in the same chunk of atmosphere as the automobile it fuels.
Of course, hydrogen vehicle fuel, derived by simple, Very High Temperature, or perhaps even plasma-phase electrolysis (PDF), using clean and abundant nuclear power, is the natural end point of it all – once all the fossil fuel is gone (and we realize the actual environmental impact of biofuels). But, for the moment, the Earth’s proven reserves of petroleum keep going up and up. And, while it’s far more expensive to extract and refine bituminous sand and shale oil than light sweet crude, the total well-to-wheel cost is still far below that of hydrogen.
Than there is the matter of complexity, and that’s where Jay comes in. In his PopMech article, he laments the fact that owner’s manuals never say anything about basic and emergency maintenance anymore. Well, while I can’t help a bit of nostalgia for “the good ol’ days” myself, we all must realize that we can never go home again. Cars are becoming more complex, and hybrid technology, ANY hybrid technology, promises only to accelerate that trend.
This brings us back to BMW. The hybrid systems in cars available to us today achieve most of their economy by recapturing the kinetic energy of the moving vehicle during deceleration. As such, there is nothing to be gained in steady cruising. In an earlier post, I made the mistake of stating that contemporary gasoline internal combustion engines were over 98% efficient, without stating that I was writing merely of the combustion of the gasoline itself, and was corrected by at least one reader. About two-thirds of that energy is lost to waste heat, about evenly split between the exhaust (part of which can be recovered by a turbocharger), and the cooling system. To recover more of that waste energy, BMW has developed a steam hybrid system:
The TurboSteamer has two separate components: a high-temperature loop [red] heated by the exhaust system and a low-temperature loop [blue] heated by engine coolant. The circuits follow different paths but feed power into the same place. In the high-temperature loop, an electric pump circulates distilled water. First stop: a steam generator that vaporizes the water. A superheater further heats the steam to above 1,000?F. From there, steam spins a piston-driven expander, which powers a belt drive that helps turn the crankshaft. Then, the steam hits a condenser, which cools it back down to a liquid state.
The low-temperature loop—which assists the high-temperature loop—works similarly but uses ethanol because it turns into steam at just 173?. Its pump drives the ethanol through a steam generator heated by engine coolant (the ethanol actually helps cool the engine) and then into a second steam generator that it shares with the primary circuit. Steam exits at about 300? and flows into its own expander, which adds power via a belt drive to that of the high-temperature expander. On exiting, the ethanol flows through the car’s radiator, which cools it back down to liquid.
Wow, three different systems, and none of it user serviceable. Jay must be delighted. 
