Setting aside the web sites selling plans for such systems, it turns out that H2 on-board generation is in fact energy efficient. The increased engine power and fuel efficiency is not gained from burning the H2 instead of gasoline. Adding H2 to the fuel-air mixture increases the flame temperature, enables a higher compression ratio and, most significantly, enables the engine to run with greater efficiency on a much leaner fuel-air mixture. All these things combine to improve fuel economy quite a bit.

But only in engines designed for H2 injection. Retrofitting a car with an H2 system gives some benefit, but not a lot, and one auto forum member who tried it pretty much concluded its maintenance and aggravation were more trouble than they were worth.

Note that there is no violation of the laws of thermodynamics here. The improved efficiency does not come from burning the H2, but from H2's catalytic effect on the gasoline's combustion. The energy gained from burning the H2 is less than the energy it took to electrolyze or reform it, but the energy gained from improved gasoline efficiency is more than the energy required to make the H2. And the net energy gotten from the gasoline is still less than the energy it took nature to make the oil to begin with.

Now, on to plasma-drive cars.

Whilst surfing around the Internet getting some links for Avoiding gas-mileage ripoffs, I came upon a site offering for sale a Pre-Ignition Catalytic Converter.

Using a magnetic and electrical reaction to break down the fuel molecules into their elemental state, the PICC creates a plasma, which burns super efficiently and cleanly!

Italics original. The site claims its system can improve gas-engine efficiency by up to nine times. Their test car, they claim, improved from 22 mpg to almost 200 mpg.

I actually laughed aloud when I read that. Yet as it turns out, gas-plasma engines may be a near-term reality after all. That from no less authority than the Los Alamos National Laboratory, which says that Plasma combustion technology could dramatically improve fuel efficiency.

The technology, a plasma combustion technique that applies electrical voltage to the gaseous-phase fuel stream prior to combustion-turning the fuel into a plasma-has already produced excellent results with propane. ...

Kerosene, propane, gasoline and diesel fuel are all hydrocarbons, all made up of the same basic chemical constituents but separated by the size of their individual molecules. The more efficient fuels, and therefore more highly refined and expensive kerosene and propane, consist of fairly small chains of carbon and hydrogen atoms, whereas the less efficient and cheaper fuels, gasoline and diesel, are made of long chains of molecules. According to Coates, when electrodes attached at the spray nozzle of a fuel injector apply enough voltage to the fuel, energetic plasma electrons from voltage-induced breakdown of the fuel cause reactive species to be created, changing the basic chemical composition as the fuel becomes a plasma

"You put into an engine the equivalent of a 'process plant' or fuel refinery," said Coates. "The plasma unit basically acts like a 'cracker' in a refinery, cutting the long chains of hydrocarbons into bite-size parts -- the smaller the parts the better the burn -- taking cheap fuels and making them combust like expensive ones."

The three researchers also believe they can construct a device that is relatively simple, cheap and easy to retrofit to existing fuel injection systems.

The Lab makes no claim of how much efficiency will be gained using its system, but it would seem to be a very large amount.

But wait, there's more!

Massachusetts Institute of Technology is also working on plasma system for cars. Their tack is a little different. Instead of making the fuel itself into plasma for combustion, they use a plasma unit to reform gasoline into H2, which is mixed with the air-fuel mixture as I described above:

(Click image for larger view)

MIT claims that their system can make a significant impact on petroleum use by 2025 while fuel-cell vehicles, they say, won't do so until 2050.

Of the two approaches, the Los Alamos system seems to me to offer the most promise because it can be retrofitted to existing engines and because it does not involve injecting H2 into the combustion chamber. It's not that the latter doesn't work, it's that doing so (as a retrofit) runs the risk of hydrogen embrittlement of engine parts and rust of interior engine parts since the product of H2 combustion is water.