seen an read a few articles now on these hho kits have heard of several working models and even some on big rigs.....anyone know anything or have experience with any of these yet?

Wondering the same thing myself. Some farmers south of town are purchasing one. Within the next few weeks, I will be able to inspect the item as it is installed and see about how it impacts mileage.

http://www.saeenergy.com/products.htm

After a few emails though still haven't heard from them.

If you guys are talking about the electrolysis units that split water into oxygen and hydrogen, they're a scam. It's a matter of energy balance-you have to put more energy into the water to get hydrogen and oxygen out than you get back by recombining the two (i.e. combustion). The net difference in energy is mostly due to the inefficiency of the electrical generation it takes to power the unit, but also the heat generated during the electrolysis itself is a waste factor also.

The argument can be, and has been, made that by introducing the hydrogen/oxygen gases into the air stream you burn the diesel more efficiently. So the extra energy you get out of the diesel makes up for the losses incurred in the electrolysis of the water. I have yet to see any scientific data supporting that claim, however. I think at best it'd be a wash, if not still a net loss of energy. And, you're out the hundreds or thousands of dollars you spend on the unit.

This "green revolution" has been a boon to scam-artists so you have to really take everything you hear or read with several grains of salt...

If you guys are talking about the electrolysis units that split water into oxygen and hydrogen, they're a scam. It's a matter of energy balance-you have to put more energy into the water to get hydrogen and oxygen out than you get back by recombining the two (i.e. combustion). The net difference in energy is mostly due to the inefficiency of the electrical generation it takes to power the unit, but also the heat generated during the electrolysis itself is a waste factor also. Correct. In practice, electrolysis is only about 50% to 75% efficient, and even the theoretical maximum efficiency of the water electrolysis is between 80–94%,
refs.:
http://www.hyweb.de/Knowledge/w-i-energiew-eng3.html#3.4
http://www.bellona.org/filearchive/fil_Hydrogen_6-2002.pdf

with small-scale units (like someone might put under the hood of a vehicle) being on the lower end of that 50-75% range. So it could easily take up to twice the energy input vs. the energy contained in the hydrogen produced. But of course, it is doubtful that the hydrogen would burn any more efficiently in an internal combustion engine than the fuel it was designed to use, so...

The argument can be, and has been, made that by introducing the hydrogen/oxygen gases into the air stream you burn the diesel more efficiently. So the extra energy you get out of the diesel makes up for the losses incurred in the electrolysis of the water. I have yet to see any scientific data supporting that claim, however. I think at best it'd be a wash, if not still a net loss of energy.

...yes, it would be a net loser, because very little fuel - less than 2% - is unburned in a modern diesel or gasoline engine under normal operating conditions (even though they do convert most of that fuel into heat rather than mechanical energy). And the alternator used to generate the electricity for electrolysis is not 100% efficient either.

It would work something like this:

For each 1,000 watt-hours (1.34 Horsepower-hours) of mechanical energy produced by the engine, the ~80% efficient alternator could produce ~800 watt-hours of electrical energy, which could be converted into hydrogen and oxygen at ~60% efficiency, resulting in 480 watt-hours of energy in the hydrogen.

Such an arrangement is far too deep in the hole to ever provide any useful fuel efficiency benefit. If the electrical energy for electrolysis comes from an extra battery instead of the alternator, you'd then be better off converting it directly into mechanical energy with an electric motor, and what you'd then have would be a plug-in hybrid.

About the only thing that might theoretically happen with adding both the hydrogen and the oxygen is the oxygen might potentially be able to provide an effect similar to running a tiny bit more boost, but that would go toward increasing power, not fuel efficiency. But Hydrogen is far less dense than air, which would volumetrically offset the potential "supercharging effect" of displacing some air with pure oxygen. Of course, injecting a more oxygen-rich oxidizer than air is what a nitrous-oxide system does.

By the way, HHO (a.k.a.: "Brown's gas") generators became popular as a fuel source for certain brazing operations (like jewelry) because of the complete absence of soot, and the convenience for small-scale, low-volume operations, compared to conventional oxy-acetylene. More recently, larger scale Brown's gas generators have become economically viable for other commercial uses, like plumbing. They are legitimate devices in these applications, but not to improve automotive fuel economy.