I'll admit that I'm fairly skeptical about that one.

Wired Magazine had an article about this about a month ago. Truckers (a couple dozen at least so far) who have been so fitted have saved around $700 a month. Probably the only operational difficulty is finding enough distilled water.

The main point is that while hydrogen does not have the energy density advantage that diesel has, it burns so much hotter that when combined with a regular diesel engnine, it helps burn diesel better than diesel alone. Thus it reduces particulate/smoggy emmmissions while improving power performance, fuel economy (+10%), and costs.

Mega-Double-plus!

This would have the effect of reducing tail pipe CO emission levels, converting it to CO2 of course. Because so many truckers are of the habit of leaving their engines running when at idle, the electrolysers could presumably crank out excess of H2 at during those intervals, iif the design includes compressed storage? Converselyl, when on the road, the alternator is always belted but we do not know whether it is always under load or if that load is variable. Key question is whether this system is using a designed-in excess load capacity from the alternator or if it is instead parasitizing the engine's total fuel efficiency? Not able to evaluate with the information given. Hence, some cycnicism seems justified.

"Because so many truckers are of the habit of leaving their engines running when at idle"

The obvious solution to that is:

http://www.treehugger.com/files/2005/10/truck_stop_elec.php

Good if the hydrogen thing works, though. There are so many H2 hoaxes out there that caution is required.

"hydrogen" as a brand is almost synonymous with green and high-tech, so con-men who want to sell useless gadgets often just have to mention it and invent a bunch of fake testimonials..

The problem with requiring distilled water is that distilling water takes a fair amount of energy, and distilled water doesn't electrolyze efficiently. Slightly acidic or slightly salted water is what works best, at least as far as lab experiments have shown; very pure water does not conduct electricity hardly at all, and without a good current, you don't get a good rate of electrolysis. If I were them, I'd just use a good filter and something to drip a few drops of a mild acid into each batch of water.

I suppose that they don't just dump the oxygen, do they? And if they're pumping that oxygen in with the air intake, basically they're electrolyzing water just to re-combust it. Unless this really boosts the heat and efficiency of combusting diesel by more than enough to offset the cost of electrolysis, I don't see why this would boost efficiency. (And if it works, I guess that's what it does.)

Using distilled water is pretty important to the longevity of the electrolyzer. Many use stainless steel, which when exposed to solutions of salts and other minerals, can corrode the plates. Distilled water plus KOH or NaOH as an electrolyte is a common way to get good output, while keeping the materials from being eaten away.

Onboard hydrogen production has often been criticized for using more gas than that which can be saved by boosting efficiency, but with an efficient electrolyzer, people have witnessed otherwise. Running two electrodes straight from a car's battery creates a good heater and not much else. You see many of these types of systems for sell on ebay, often using stainless (or not) threaded rod and a lot of washers and nuts. Using the appropriate number of cells (around 7 for a 12v system) to bring up the efficiency has shown to provide an improvement on many vehicles.

I would think, for a home user, producing your own distilled water with a solar distiller could be a good route, but producing your own clean KOH (ashes maybe?) would be beyond most people's abilities.