Hurm.. I've seen all these "water cells" and stuff. there are commercially produced hydrogen/browns gas producers. They claim massive fuel economy benefits.. but look like they were made of sandwich boxes. Working in alternative fuel research, I keep tabs on these technologies. In my opinion, such a device would produce only a small amount of hydrogen. You may see a VERY small change but it won't be a lot. The most believable website detailing such a product reckoned on a couple of litres of water lasting approx. 400 miles and giving ~10-15% extra mpg. This however was tested on quite inneficient (low compression) engines. The claims given by most places seem.. well, for want of a better word, bull****. I remember back in the late 90s a device called a TurboZet was marketed as giving 40% improvements across the board, power, mpg the lot. It was a little fan that fitted into the intake pipes. It was found to restrict airflow and therefore damage power output and mpg. Having said that, my uncle has a device called a Hiclone which is a little metal contraption that fits in the intake hose. He SWEARS it makes a difference, and i can see it would help atomisation somewhat via turbulence.. but.. yeah...
Anything that claims any power increase must do one simple thing. it MUST somehow increase the oxygen your engine gets, so it can burn more fuel. And a 10 percent increase needs around the same amount of extra air or fuel. If it doesn't do that it cannot work.
Bac on topic, this to me is more interesting with reference to diesel engines being run on vegetable oil and its derivatives. both clean veg oil and waste veg oil (SVO/WVO respectively) do not quite combust as well as diesel, particularly in direct injection engines. adding an amount of hydrogen could help combustion. Even so it would only be a very small benefit, found mostly in reliability by stopping the piston rings getting gunked up by unburnt vege oil. you may see a VERY slight power increase, but no fuel economy increase unless the engine was a very modern one with sensors and on-the-fly (learning) mapping. Even in that case, you're looking at a very small change, if any at all.
It's interesting to me, as i'm running my puke-goat partner 1.9D (XUD) van on 100% WVO. It starts on biodiesel, then once hot, switches to WVO. The pukey, being an indirect injection engine, does not suffer from gunking due to unburnt fuel, and i've found the oil does not polymerise (get diluted by wvo) within a normal service interval. This is not the case for most direct injection engines. I've yet to test it, but when my Series3 is completed, with it's Perkins Prima 2.0TDi engine, i'll be attempting to run it on WVO, in varying percentages with the end aim of getting it to run on 100% WVO. From the information I have gathered, these engines need servicing slightly more often when run on 100% veg, and **can** gunk up a little. a tiny bit of hydrogen/browns gas could help this.
I encourage all research into alternative fuels, so keep it up mate.
By the way, i might be mistaken on this, but some memory lost deep within the fog of time tells me that in WW2, the japanese developed a way of powering their planes derived from vegetable matter. Experience tells me this was probably wood alcohol gained from the fermentation process.