A rare recantation

A reader brought New Zealand company "Octafuel" to my attention. As I write this, the Octafuel Web site contains nothing but a press release admitting that "on-demand hydrogen generator technology" - which is either injecting a little electrolytically-generated hydrogen into your fuel-air mixture to allegedly greatly increase engine efficiency or, according to countless dodgy Web sites, a full-blown "Run Your Car On Water!" system - is indeed worthless.

What a surprise.

Octafuel do, however, stick to their previous statement that "there are a number of international studies supporting" the idea that these generators work.

It is my considered opinion that if you set your plausibility-of-evidence bar low enough to believe that trickling a little electrolytically-generated hydrogen into the fuel/air stream will have any significant effect on anything - here's a decent starting point for exploring what evidence there is - then you must also believe that people bouncing around on their bottoms are flying, that people who allegedly have psychokinetic powers that never manifest when someone's looking at them aren't just cheating, that stickers can improve battery performance, and that magnets make wine taste better.

Apparently Octafuel issued this press release shortly before one Eric Otoka was going to have this piece published in the Waitako Times, detailing the results of his month-long test of the system. Otoka concluded that the Octafuel device achieved "a maximum of only 4.8 per cent fuel savings", which suggests to me that the error margin of his testing technique was 5% or more.

Octafuel was "'absolutely' confident the product would save between 25 and 40 per cent", though, so this is still a pretty solid piece of evidence to the contrary. And Octafuel are now arranging a product recall with refunds for purchasers. This makes them about a million times more honest than the average fuel-saver outfit.

Octafuel are behaving so unexpectedly honourably because they are not an outright scam organisation like Firepower. They actually offer some fuel-saving devices that do not blatantly defy any laws of physics. (Or, at least, they've talked in the past about offering such devices. There's nothing on their Web site but the press release at the moment.)

Octafuel apparently have a bolt-on regenerative braking system for normal cars, for instance. I've no idea how their one is supposed to work, but I've seen others. One type basically clamps an electric motor over each rear wheel - it's conceptually similar to smaller systems to add electric assist to bicycles. The motors work as generators when you brake, charging a relatively small battery or capacitor bank, which gives you extra drive when you accelerate again. This is pretty much useless for highway driving - the extra weight and drag are likely to eat up what small fuel savings there are - but it can give a not inconsiderable economy improvement for stop-start city driving. It also makes your car look a bit like a prototype Spinner.

Octafuel have also talked about Peltier-device heat-recovery units, which turn waste exhaust heat into electricity to take load off the car's alternator. Less alternator load means less fuel burned - though not much less, if you're not running an impressive wattage of electrical gear in your car.

Modern cars are adding more and more high-powered electrical hardware, though, and there's room for more. A good enough exhaust-heat scavenger could, for instance, deliver enough power to make an electrically-powered automotive air conditioner a more economical choice than the current type, which is belt-driven from the engine. And just harvesting heat from the exhaust - rather than, say, making exhaust gases directly turn a turbine - won't affect the power or economy of the engine itself at all.

Major car manufacturers have been researching this for some years. It's possible that the miserable efficiency and not-so-great durability of Peltier electrothermal devices may make "Automotive Thermoelectric Generators" uneconomical, though. I'm delighted to say that this means it may turn out to be better to run a closed-cycle steam engine from exhaust heat!

7 Responses to “A rare recantation”

  1. robinsonb5 Says:

    Something I've wondered a few times, actually - you know those camping fridges that use a gas flame to run an adsorption cycle? Is that technology remotely scalable?
    Could that waste heat from the exhaust be used directly to run some form of air-con, or would the coolant volumes/pressures be prohibitive? I guess the efficiency would be lousy, but efficiency matters very little when you can use waste heat for free, and in so doing take the load off another part of the system.

  2. reyalp Says:

    AFAIK cooling your exhaust actually does impact performance somewhat, due to the effects of increasing the density. If you just add peltiers to the outside of your existing pipes, that wouldn't be an issue (in fact, it would probably retain even more heat), but you set things up to extract maximal heat, that could be a different story. Scavenging the heat from your oil, block or cooling water is OTOH is completely free, at the expense of a lower temperature differential.

    I don't think scaling the process is a problem, but bouncing down the road might complicate things. The total size/mass might end up pretty large too, but I don't have a good handle on just how big. A fridge doesn't have much cooling power compared to an AC unit, since it mostly relies on insulation and thermal inertia. The traditional ammonia cycle uses compressed hydrogen gas and ammonia, which might lead to safety concerns.

    Alternately, you could try to use a stirling engine for one or both sides of your AC.

  3. davolfman Says:

    "Peltier-device heat-recovery units"? Isn't it a heck of a lot easier (and more understandable) to call them thermocouples instead, or are you quoting?

  4. Daniel Rutter Says:

    A Peltier device is indeed, technically, made out of an array of thermocouples, but when you say "thermocouple" you're usually talking about the simple dissimilar-metals type, which is cheap and robust but which has quite miserable power output. If you put a bunch of thermocouples and a heat sink the size of a basketball on top of a kerosene lamp you can just about run a valve radio, but that same contraption would have trouble powering one incandescent-bulb turn signal, let alone the rest of the crud in a car, even if you extended it to six feet of exhaust pipe.

    "Peltier" thermoelectric devices are always made out of semiconductor junctions (and there's some technical difference between the Peltier and Seebeck effects which I haven't the physics to quite understand), and have much better efficiency than simple dissimilar-metals thermocouples.

  5. j Says:

    I nabbed a look at your "magnetic wine" review this morning, and just happened to spot this article this afternoon:

    I smiled, then I sighed.
    I'm guessing the "inventor" actually does believe it works; he probably also buys special pure silver cables for his hifi.

  6. Jono4174 Says:

    In NZ (unlike Australia), "Engine Up" is allowed to advertise on TV. (It is an oil additive which does nothing)

  7. davolfman Says:

    I never realized you could run any old peltier in reverse. I'll have to see if I have that old 40 watt I bought intending to cool my Thunderbird with.

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