large production may be as simple as heat...
I was watching "Destroyied in seconds" last night (mainly because there was nothing else on worth watching), and a Magnesium fire was burning really well when the fire trucks got there and they put their water cannon on it and and the resulting explosion was Horrindious!.... it turns out that putting water on a magnesium fire brakes the water down into its individual molicules because of the intense heat , over 4,000 degrees.... the resulting cloud of Hydroxy gas exploded causing a bunch of damage.
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.... if a person could vaporise WATER that well it would be easy to produce any amount of hydroxy gas you desire....but the problem becomes one of produceing the heat needed once again....
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I doubt an exhaust pipe is hot enough but it may be 800 to 1200 degrees is the exhaust temp on most cars
more that enough to vaporise water for a short time... but you can't sustain that tempiture for long... it doesn't take long at all to make the exhaust pipe change tempiture to below the vaporizeing point of water... but perhaps a Brass incert between the exhaust headder and the exhaust pipe with a water pipe in it would produce enough hydroxy gas to run the engine.... say a 1/4" donut
of water in the brass incert.... surely it would stay hot enough to keep water vaporized...
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this is allot like my gasoline vaporization things , but water unlike gasoline won't return to its liquid form once it is broken down completely.... at least i don't think it will! steam will
but Hydroxy gas won't ...so the heat must have to be quite intense!
...more than likely this idea would just recondense on its way through the intake manifold and you'ed have nothing but water or steam to try to burn....
...what we need is 4000 degree heat on a tube and pump water through it....
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perhaps a coal fired furnace ? like a forge, hot enough to melt steel, but use it to make Hydroxy gas ?.... the amount of gas you could get off of it would be far more than you need to run even the biggest engines....
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so whats wrong with this idea guys

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Bob.....