Bad Gas Math

May 13 2008 Published by under Bad Physics

This has been mentioned elsewhere - like on the Machinist blog on Salon (where I first saw it) - but I can't resist saying something about it myself. And I'll also chip in a little bit of originality, by also criticizing some of the people that I've seen criticizing it.

The story is, there's a scammy company that sells a rather expensive device that allegedly increases your gas mileage. The way that it (supposedly) works
is that it uses electricity from the alternator to get hydrogen by splitting
water, and then adding that hydrogen to the air that gets mixed in the engine. The argument is that the hydrogen causes the gasoline to burn more completely and more cleanly, thus increasing the efficiently of the engine, which allows it to go further on a gallon of gasoline.

A local TV station in Florida claims to have tested the device. They tested the mileage of their news van using a dynamometer; then they mounted the device on the engine of their news van, and after giving it time to break in, put the
van back on the dynamometer, and tested its mileage again.

Here's where the pathetic part comes in. They reported that before mounting the hydrogen generator on their van, they got an average mileage of 9.4 miles per gallon. After mounting it, they claim that they got 23.2 miles per gallon. Ok so far? Now, they go on to say that increasing their mileage from 9.4 to 23.2 mpg is a 61% improvement in mileage.

So, our intrepid reporters don't have a clue of what percentages mean or how to compute them. You might think that perhaps they misreported the
"23.2" number - maybe it was supposed to be something like "13.2"? Nope, that
doesn't work. In fact, no plausible typo for either 9.4 or 23.2 gives you anything
close to 60%. So where on earth did they get the number from?

Being a math geek, I saw it pretty quickly; hopefully, some of you out there
did as well. 9.4 is almost exact 4/10ths of 23.2. If you take 9.4, divide it by 23.2, and then subtract that from 1, you get about 0.60. That's how they did it - they took 9.4; figured out what percent it was of 23.2, and then took the difference as the percentage improvement.

That's spectacular innumeracy. It's incredibly stupid. It's stupid in that
that's a mind-bogglingly idiotic way of trying to compute a percentage
improvement. And it's stupid in that anyone who had the slightest understanding
of just what percentage change means would immediately notice that doubling something means a 100% improvement; since 23.2 is well over
double 9.4, that means that it's got to be more than 100%. Anyone who'd say that 25 is less that 100% larger that 10 is an idiot.

What about the other side of things? Lots of people are (justifiably) skeptical of whether the hydrogen generator could possibly improve mileage. One comment which I saw (but unfortunately can't recall where I saw it now) said: "It's idiotic: it violates the laws of thermodynamics. You can't possible generate
any more power by adding hydrogen to the mix than you spent splitting the water."

Bzzt. Sorry, no.

If you were arguing that the improvement comes about because of the additional energy of burning the hydrogen, then that would be true. Burning hydrogen produces a bunch of energy and creates water; splitting water consumes a bunch of energy
in order to break the water molecules. Recombining hydrogen and oxygen to produce
water can't produce more energy than it takes to split them - that would, indeed, violate thermodynamics.

But that's not what the proponents of the hydrogen generator say. Their
argument is that the process of burning gasoline in an engine is extremely
inefficient. There's a fair bit of gasoline that doesn't get burned; the part that
does get burned doesn't always burn in the ideal way to convert the energy from
burning it into mechanical force. The hydrogen augmentation argument isn't that
you're adding energy by burning hydrogen, but that adding extra hydrogen to the
mix increases the efficiency of how the engine burns gasoline - that a larger
portion of the gasoline gets burned in the engine cylinder, and that it burns in a
clean sustained burn that maximizes the mechanical energy extracted from that
burn. There's no thermodynamic reason why that couldn't work: separated the
hydrogen and oxygen in water isn't cheap, energy-wise, but gasoline contains a
hell of a lot of chemical energy, and a moderate improvement in the efficiency of
how we extract that energy could outweigh the cost of splitting a small quantity
of water.

Mathematically, it's a stupid error - not as stupid as the percentage
miscalculation, but still pretty stupid. We can write out a simple equation that
estimates energy production from burning gasoline.

Suppose that a gram of gasoline produces a maximum of J joules when burnt.
We want to convert that from heat energy to mechanical energy. A standard engine
will do that with an efficiency, Eg, where Eg > 0 and < 1. So the engine will
produce Eg×J joules of mechanical energy per gram.

Now, suppose we add hydrogen to the mix.

Hydrogen produces H joules per gram, and in an engine, the energy of burning
it can be converted to mechanical energy with an efficiency of EH.
Further, splitting enough water to produce a gram of hydrogen has an energy cost
of C, where C>H. So even if you could burn hydrogen with perfect efficiency,
it would still be a loser energy-wise.

If burning hydrogen and burning gasoline in the engine are
independent - which is the basis of the erroneous argument - then the energy
generated by burning N grams of gasoline + M grams of hydrogen in a hydrogen
generator-augmented engine N×Eg×J + M×Eh×H - M×C.

Since C>H, the second quantity (the hydrogen-augmented one) is clearly smaller than the first (the pure gas one). But the problem is, Eg
isn't a fixed constant over all mixtures of gases in the engine. Add more nitrogen and less oxygen to the fuel mix, and it goes down. What happens to that efficiency when you add hydrogen?

I don't know. But I do know that treating it as a constant is wrong - obviously wrong.

I'm not trying to defend the hydrogen generator. I still very much doubt that
the hydrogen generator works as advertised. I'm very skeptical of it. (If it
worked, I think we'd see companies like Honda and Toyota, which make lots of money
selling extra-efficient hybrids adding it to their cars - if you could boost the
efficiency of simple gasoline engine by as much as the hydrogen generator claims,
you'd have pretty much the efficiency of the hybrid without needing to go to the huge amount of engineering effort needed to produce an effective hybrid.) But
bad math is bad math.

55 responses so far

  • andrea says:

    holy crap! Why is more-than-doubling something > 100% so difficult a concept for people to get? You don't even have to be able to do the arithmetic in your head to realise that...
    andrea

  • Jim Thomerson says:

    I don't immediately see why adding hydrogen would increase the efficiency of burning gasoline. Adding oxygen would probably do so, as I doubt the burn as it goes on at present is at the stochiometric ratio. An internal combustion engine is basically an air pump and the more air it pumps, the more horsepower. That is a true statement, but has a number of "yes, but...."s not mentioned.

  • Jack Bishop says:

    At the risk of defending those who don't deserve it, 61% does make sense as a number describing a change in efficiency: namely, it describes the decrease in fuel consumption (which is different than what's usually described as efficiency.
    9.4 miles per gallon could also be described as 1/9.4 gallons per mile; 23.2 mpg is 1/23.2 gallons per mile. 1/23.2 is about 40% of 1/9.4, so the act of going a certain distance in a 23.2mpg car uses 40% of the fuel used by a 9.4mpg car; thus, there is a 60% decrease in fuel usage.
    I may be giving them too much credit for this, but there is in fact a sensible quantity described by that 60% figure, whether or not they know what it is.

  • Conceivably the combustion of hydrogen and oxygen at compression acts like an extension of the spark throughout the chamber, facilitating more complete combustion (assuming the fuel injectors have done their job and mixed fuel and air in the correct proportion). Or that the small amount of water produced by that combustion made for a more regulated burn - smoothly surrounding the greatest moment of torque at 90 degrees ATDC. But I'd be truly surprised if any of that really happened, and somebody will figure it out.
    More important would be that you have to add water to your splitter. Imagine the yuppies arguing over which expensive bottled water makes their car get the best gas mileage! It would be even better than thousand-dollar speaker cables giving better sound.

  • hukes says:

    My friends hate me for being so picky about percentages. They don't really care, or they don't understand (something I find unbelievable).
    These guys -at the TV station- had another error on top of their original error about percentages. It is not even 61%. According to my math and to my HP 50g calculator, their error should've been 59.48%.
    % of improvement = [1 - (9.4 / 23.2)] * 100 (according to *their* way of caculating percentages)
    Anyway...*sigh*

  • Blake Stacey says:

    Well, your engine efficiency, in terms of mechanical work out per chemical joules in, is gonna be limited by thermodynamics: ain't no beating Carnot. On top of that, there are losses in the engine due to friction, pumping issues and such, so even improving combustion efficiency can only get you so far. Self-proclaimed engine nuts concur with my skepticism.

  • Wry Mouth says:

    "Now, they go on to say that increasing their mileage from 9.4 to 23.2 mpg is a 61% improvement in mileage."
    I didn't even get past the "Read On" before I was mentally saying "Eurghhh!" Thanks for *that!*
    Certainly, I can see it as a "teaching moment" -- being a teacher and all -- and may (once I get past the chuckling) actually introduce to my 7th graders.
    ;o/

  • Blake Stacey says:

    I should add that there's some serious woo mixed up with these "Brown's Gas" claims, which makes untangling who's saying what a real pain (and why I didn't blog about it days ago).

  • Blake Stacey says:

    A master's thesis from several years ago indicates that adding hydrogen to the fuel mix is not an absurd idea (the researcher got a 12% improvement in fuel conversion efficiency, in what looks to me like a laboratory situation idealized to Hell and back). Whether the devices marketed for this purpose actually do this — they don't even claim to get their hydrogen from the same process — is an open question.
    Oh, and if somebody could get a copy of L. N. Bortnikov's paper, "Combustion of a gasoline-hydrogen-air mixture in a reciprocating internal combustion engine cylinder and determining the optimum gasoline-hydrogen ratio," I'd be much obliged. Regrettably, Combustion, Explosion, and Shock Waves is not an open-access journal.

  • John D. says:

    Turning from the math to the energy aspects of this, the best article I've seen that breaks down alternative energy efficiencies vs. conventional is Don Lancaster's "Some Energy Fundamentals"
    http://www.tinaja.com/glib/energfun.pdf
    While it doesn't go into this specific idea, of course, it does give you the pros and cons of hydrogen vs. gasoline vs. solar, etc. And at his website, meny items like this story get almost a "Good Energy Bad Energy" debunking in his in his "What's new" blog. (Don's an old hand at amateur tinkering with years of experience, and tells you exactly why most amateur energy ideas end up pie-in-the-sky.)
    Oh and, Mark, about computer languages, Don Lancaster likes to do all his general programming in straight Postscipt! His many PDF articles sure are tiny and hand-crafted...

  • Blake Stacey says:

    To electrolyze 1 mole (18 g) of water takes 237.1 kJ (at 298 K and 1 atm, but that seems reasonable if you're not operating in the hottest part of your engine). This produces 1 mole of diatomic hydrogen gas, which will occupy 22.4 liters at the aforesaid temperature and pressure. A typical claim for a "Brown's Gas" fuel additive device is to deliver 2 liters of hydrogen every minute. 2 L/min is 0.098 mol/min, which would require 21.1 kJ/min or 0.353 kW to hydrolyze.
    The manufacturer claims (see the first link I gave above) to deliver 2 L/min of hydrogen gas by pulling 30 amps from a 12-volt battery. Power is voltage times current, so we're talking 360 watts here: the reputed power demand matches the stoichiometry, but I don't know if a car's electrical system can actually deliver that on top of the other demands already placed on the alternator. Isn't a 100-amp alternator already pretty heavily loaded by all the other bling a vehicle is trucking around these days? Don't ask me — I'm a theorist!

  • Dave M says:

    But bad math is bad math.
    No it isn't! Oh wait, you're right, it is too. My bad.

  • Old Bogus says:

    Wonderful thrashing around! In a modern vehicle engine the oxygen sensor will reduce the fuel richness so #2's objection is irrelevant in my interpretation. Like those fancy "pulse" plugs and other ignition aids, H2 enhances the ignition process in the cylinder and makes the gasoline deliver its punch quicker. Assuming the engine parts can handle the added thrust.
    How much actual current does electrolysis add to the alternator load? This is actually a high resistance circuit since little current flows without tangible results. Which end up shortly in the energy cycle.
    About the real subject at hand; during a political meeting I attended recently, the moderator mentioned that a motion on a particular subject required a 3/5 majority. I couldn't resist, since a previous motion required 60%, shouting that I though it required 60% instead. He had no idea those were the same things. Damned liberal arts majors (which must include reporters)! The more technically inclined attendees appreciated the humor but the majority in attendance just didn't get it.
    Is this a great country or what?

  • Joe Shelby says:

    Well, I don't see it either. My understanding of gas burning inefficiencies is that the main bottleneck is the time limitation of the cylinder cycle combined with the relatively low levels of heat involved. if you could burn for longer you'd increase burn efficiency but not the way the engine is designed - you'd need more cylinders to keep the engine's timing cycle running at optimum speed for the expected acceleration.
    since this stuff can't change the cycle speed, i'm guessing it instead has to change the burn efficiency by increasing the temperature (which is certainly possible).
    yet, if you burn hotter, you risk increasing the heat enough to start burning the metal of the engine. i'd actually worry about my engine if this hydrogen thing worked as advertised.
    maybe the right combination of oil and radiator coolant might hold things off or keep it stable, but it'll still wear out the engine faster unles the cylinder steel is changed.
    now, a new engine design that takes advantage of this approach and makes cylinders more easily replaceable (rather than costing $2K, mostly in labor, whenever there's a problem) might solve that. it could all add up to a viable solution if someone did the research, but this as described today I see as too risky.

  • Hypercubed says:

    If I'm not mistaken they are calculating the money saved per mile. At 9.2 and 23.3 mpg the price per mile is 43 and 17 cents per mile respectively (assuming $4 per gallon). (17 - 43) / 43 = -60%. The answer is the same regardless of the gas price. Assuming that people travel the same number of miles no matter what mpg they are getting they save 60%.

  • Bob Iverson says:

    Perhaps they are wrong twice in the same calc?
    If you reverse the digit right of the decimal the botched calc come out as...
    (23.4-9.2)/23.4 x 100% = 60.68% which appears to match.

  • celeriac says:

    Fuel consumed per mile is a much more practical way (in terms of planning a fuel budget if you're going to be driving to work, to give a trivial example) to describe fuel efficiency than its reciprocal anyway. Especially as liters/100km is the standard measure of efficiency in metric countries. Their reported numbers indicate a 60.52% savings in fuel costs before you round to 2 sigfigs. Your suggested retroactive explanation gives 59.48.

    Of course it's better to claim that "being a math geek," you "saw it pretty quickly" and claim that correctly calculating cost savings indicates "spectacular innumeracy."

  • Morgan says:

    @celeriac (#16)

    Now, they go on to say that increasing their mileage from 9.4 to 23.2 mpg is a 61% improvement in mileage.

    "Mileage" is not "how much it costs me to travel a mile", so unless Mark is misquoting here then his point stands and your criticism is unfounded.

  • Mongrel says:

    This is a good site for 'fuel saving gadgets' information. To quote from there regarding fuel burning

    And it is a firmly established engineering fact that, on any reasonably modern engine under normal operating conditions, the burn is already at least 98% complete. The unburnt fuel in the exhaust (even before the cat) represents 1 or 2% at most of the input fuel.

  • Rick Pikul says:

    Re #17:
    Mileage can be reported either as distance per unit of fuel, (typically miles per US gallon), or as fuel per unit of distance, (typically litres per 100 kilometres).
    This comes about because mileage is really a ratio of distance to fuel used, and thus can be expressed as a fraction with either term as the denominator.

  • AJS says:

    No, it's to do with your stupid American measuring units. Or more strictly, to do with the necessity to convert them to and from proper measuring units.
    In the rest of the world, fuel consumption is measured in litres per hundred kilometres. (So, smaller = better.) I suppose litres per megametre (or even just metres to the minus two) would be nicer mathematically, but 100km. is more representative of an actual journey and litres are what the pump uses to measure what it dispenses.
    Now, 1 mile per gallon = 4.5 litres per 1.6 km.
    = 281 litres / 100km.
    9.4 miles per gallon = 4.5 litres per 15.04 km.
    = 29.9 litres per 100km. (If any vehicle of mine was using that much juice, I'd be looking to make sure there was not a hole in the tank.)
    23.3 miles per gallon = 4.5 litres per 37.28 km.
    = 12.1 litres per 100km.
    Which is only 40% of what it was before.
    Hence the 60% improvement: it's using 60% less fuel to travel the same distance. (Error almost certainly due to my premature rounding.)
    Now, I'm guessing that the equipment that they were using simply measured the fuel consumption in l/100km. in the first place, and they converted the figures back to miles per gallon.
    But because the American standard is to measure how far you can go on a standard dose of fuel, as opposed to how much fuel you would need to cover a standard distance -- which is the opposite way around to how the rest of the world does things -- it messes up the figures.

  • Mark C. Chu-Carroll says:

    AJS (and others who made the same point):
    You're probably right about the cause of the error. I just immediately homed in on the ratio the way that I did, because I noticed the closeness of the ratio of MPGs.
    So it's likely an issue of units. Still a stupid error - but a different stupid error.

  • JakeR says:

    AJS:
    Now, 1 mile per gallon = 4.5 litres per 1.6 km.
    = 281 litres / 100km.
    9.4 miles per gallon = 4.5 litres per 15.04 km.
    = 29.9 litres per 100km.

    Not in the USA. A gallon here is 3.78 l, so your conversion to l/100 km is off by a factor of ~1.2; therefore 9.4 mpg = 24.9 l/100 km, still pathetic, I admit. FWIW the US method of calculating mileage (why do you talk of mileage in terms of km--don't you really mean fuel consumption?) is more useful in the front end. We don't say, "I'm buying X amount of fuel so that I can go Y miles;" we say, "I've filled the tank (or have some fraction of a full tank left) so I know I can go Z miles, and my destination or a known fuel stop is safely within that range."

  • Dave S says:

    There is an episode of Mythbusters where they tested one of these commercial hydrogen-generating devices in an episode where they investigated myths abouting improving your mpg.

    AFAIR the device could not generate much hydrogen over a sustained period of time, and didn't produce a significant change in fuel efficiency. Still, worth watching for the bit where they ditched the device and pumped pure hydrogen from a tank into the engine. Pretty flames!

  • Blake Stacey says:

    In response to my own comment #8, I'll add that I have the article now. Take-home message: yes, adding a few percent hydrogen can be beneficial in the lab. What this means on the street, and whether any particular device actually does the job to a practical extent, is left as an exercise to the interested reader.

  • Kevin S says:

    Just to add a MechE note to an otherwise mostly theoretical discussion...
    Hydrogen doesn't improve combustion efficiency per se. Its main function is to reduce the auto-ignition tendencies of standard hydrocarbon fuels, so it's an octane booster. What that boils down to is that you can run leaner mixes at higher compression ratios without knocking. Leaner mixes are more efficient, since you more completely combust the fuel. Higher compression ratios are more efficient for a whole lot of reasons. The adiabatic heating of the more compressed air increases the evaporation of the fuel, creating a better mix that combusts yet more completely. Plus, it quite simply creates a greater distance to extract work from the pressure of the expanding gases. So increasing the octane of a fuel lets you use the fuel more efficiently, and if you're getting your octane boost from electrolyzed water or catalysis of lower octane fuel, then so much the better.
    Sadly, all the above benefits of higher octane fuels and using hydrogen as an octane booster are completely pointless if all you're doing is strapping a doodad onto your stock Honda Civic for a quite prosaic reason: it was designed to run on cheaper, more knock prone regular gasoline. So it has a fairly standard compression ratio and an ECU programmed for using richer mixes than are strictly necessary, etc. So unless said hydrogen doodad comes with a new engine or a voucher for milling down the head of your current engine and retuning the ECU, then it's going to do very little to actually improve the mileage of a car.

  • Tegumai Bopsulai, FCD says:

    Brown's Gas page at PhACT

    Wowza, I just found a video on YouTube entitled Reduction of radioactivity of Americium 241 with Brown's Gas flame
    The guy doing the demo is Teh Stupid. He thinks filter paper is going to stop gases. Aside from being scientifically unlikely, the video is pretty amateurish as well. For example, they show us the Geiger counter dial without showing what the probe is aimed at.

  • red faced reporter says:

    let me just go ahead and apologize on behalf of dumb reporters everywhere. as a whole, reporters are embarrassingly poor at math (to my horror, they're open about it and tend to laugh). i had a recent colleague who couldn't compute percentage changes either. i had to explain it to her every time a new batch of crime stats came out. and she was canuckistani, so their ed system must be as bad as ours.

  • KeithB says:

    Blake:
    I imagine that this would work best in a classic hybrid where you tailor the engine to work in a very narrow range to simply top off the battery.

  • dale says:

    Just by crossing the border from the US to canada your cars miles per gallon automatically improves as the imperial gallon is 4.54 litres per gallon (Interesting coincidence - a Pound is about 4.54 decagrammes)
    ''she was canuckistani, so their ed system must be as bad as ours.''
    Actually, even though the Canadian system is modeled after the US system, Canadian students tend to do much better than their American counterparts in most international exams. For example the 2007 PISA international rankings of 15 year olds had Canada ranked 5th in mathematics and the US 35th.

  • jre says:

    About 25 years ago, as part of getting an ME degree, I did a lab on combustion engine efficiency. My classmates and I started up a small-block Chevy motor on a dynamometer, ran it unitl it reached operating temperature, them measured all the gazintas and gazoutas. Gasoline was admitted through a graduated cylinder. Torque was measured at constant rpm. Temperature, flowrate and composition of exhaust gases were measured. Heat rejection from the radiator and the engine itself were recorded. At the end, we took our numbers, ran a balance, and determined how accurately we had managed to capture everything (pretty well, as I recall).
    One take-away message was that the loss of chemical energy from incomplete combustion is relatively small. As Blake Stacey correctly pointed out above, Carnot efficiency is set by the maximum and minimum temperatures between which any heat engine shuttles energy. If you can do better than that efficiency, you have a source of free energy. No modern engine has combustion efficiency so poor that you could double gas mileage, or even come close, by making the gas burn better.
    Shortly after my lab, a friend of mine told me about the 100mpg carburetor that the big oil companies had paid to have locked up in a safe somewhere in Detroit. I tried to explain why it couldn't be so, but I think he still liked his version better.

  • Mark P says:

    Here is my standard anti-journalist rant: as a former reporter, I can vouch for the fact that journalists are, as a group, the least well educated of all professionals.
    If you increase the operating temperature of the engine, does it cause an increase in emission of oxides of nitrogen? That's the bane of diesel engines.

  • Alex Besogonov says:

    Hydrogen generators DO work for diesel engines, particularly for high-powered truck and heavy machinery engines.
    They do not produce over-100% MPG increase, but a much more plausible 6-15% increase in real-life use. Nothing earth-shattering, but still not bad.
    See: http://www.umpquaenergy.com/, http://www.hydrogen-boost.com/Diesel.html, etc.

  • AJS says:

    dale wrote:

    Just by crossing the border from the US to canada your cars miles per gallon automatically improves as the imperial gallon is 4.54 litres per gallon (Interesting coincidence - a Pound is about 4.54 decagrammes)

    A pound is nearer 4.54 hectogrammes, and it's no coincidence. A fluid ounce is the amount of water which weighs one ounce at some predetermined temperature and atmospheric pressure, and a kilogramme is the mass of a litre of water (which fits exactly into a cube, 10cm. on each side) at some (other) predetermined T&P. A gallon of water = 8 pints in a gallon * 20 fluid ounces in a pint = 160 fluid ounces, which weighs ten pounds (16 ounces in a pound). And it sort of makes sense that 4.5 litres of water would weigh 4.5kg.

    Not in the USA. A gallon here is 3.78 l, so your conversion to l/100 km is off by a factor of ~1.2; therefore 9.4 mpg = 24.9 l/100 km, still pathetic, I admit.

    Ah; well, I suppose selling short gallons is as good a way as any to keep the price of a gallon down. And since the whole of the rest of the world are measuring their fuel in litres, it makes it that little bit harder to tell if you're being ripped off or not. But 24.9 litres is still an awful lot of juice to be using just to travel 100km. For comparison, a brand new Vauxhall Astra (1.8 litre petrol engine, 5 gears) would use 9.7 litres per 100km. (urban) -- figures from http://www.vauxhall.co.uk website.

    FWIW the US method of calculating mileage (why do you talk of mileage in terms of km--don't you really mean fuel consumption?) is more useful in the front end. We don't say, "I'm buying X amount of fuel so that I can go Y miles;" we say, "I've filled the tank (or have some fraction of a full tank left) so I know I can go Z miles, and my destination or a known fuel stop is safely within that range."

    In the UK, they used to measure fuel consumption in miles per (4.5l) gallon. But litres per 100km. really makes much more sense. After all, you already know in advance how far you are going to have to travel; so the l/100km. figure lets you know with just a simple multiplication and a shift how much fuel you will need to complete your journey.
    Still, none of this really changes the facts, which are (1) incredible amounts of bollox are talked about energy saving, both by people who simply don't understand the science and by people who have a vested interest in others' misunderstanding of the science; and (2) you can make all manner of mistakes if you are not scrupulously careful when converting between SI and US measuring units.

  • SteveM says:

    No, it's to do with your stupid American measuring units. Or more strictly, to do with the necessity to convert them to and from proper measuring units.
    In the rest of the world, fuel consumption is measured in litres per hundred kilometres. (So, smaller = better.) I suppose litres per megametre (or even just metres to the minus two) would be nicer mathematically, but 100km. is more representative of an actual journey and litres are what the pump uses to measure what it dispenses.

    I'm going to assume that Americans tend to drive much farther (per trip) than Europeans. So the more important thing for Americans is to know how far they can go on a single tank of gas. Thus miles per gallon is the more convenient unit. So even if the US was metric, I would still prefer kilometers per liter over liters per kilometer.

  • themadlolscientist says:

    @ #23: That Mythbusters episode was the first thing that came to my mind. That hydrogen-producing device barely managed a pathetic tiny bubble every second or so. BUSTED!
    What's really pathetic about that hydrogen-generator crap is that people who ought to know better are falling for it. A couple of months ago my mom forwarded an e-mail about the rising cost of gas, and my brother the certified auto mechanic replied with a link to something like this.
    BTW, my bro is also a Fundy Mental Case. (How many ways can you spell "gullible"? Meow meow meow meow...) He reminds me of the White King (IIRC) in Alice Through the Looking Glass, who made a point of boasting that some days he could manage to believe six impossible things before breakfast.
    Jesus, save me from your followers! Amen.

  • Flex says:

    themadlolscientist, I believe that was the Red Queen who was able to believe six impossible things before breakfast, although your brother may not like the comparison.
    IIRC the white knight was constantly inventing things which didn't work well, if at all. Like the potable beehive strapped to his horse, lucky for the horse no bees moved in. Or the helmet which was so large he kept falling into it, but was intended to act as a stablizer to keep him from falling of his horse. He was a dreamy sort of inventive fellow, and mostly harmless.
    Darn it! Now you've made me want to re-read it yet again. And sir, I thank you for it.
    BTW, I just recently was reminded of a bit from Slyvia and Bruno where (to paraphrase):
    Two prim misses
    Reach a confusion.
    This logical structure is known as a sillygism.
    Cheers!

  • noahpoah says:

    ...the energy generated by burning N grams of gasoline + M grams of hydrogen in a hydrogen generator-augmented engine N×Eg×J + M×Eh×H - M×C. Since C>H, the second quantity (the hydrogen-augmented one) is clearly smaller than the first (the pure gas one).
    Bzzt. Sorry, no. You haven't stated anything about the relative magnitudes of J and H, E_g and E_h, or N and M, so C > H doesn't have any clear implication for the relative magnitudes of the hydrogen-augmented and pure gas terms. Bad math, indeed.

  • Antendren says:

    Because it's irrelevant. His claim is correct.

  • JohnW says:

    Clearly, from a thermodynamics standpoint, energy additivity is not an explanation. So, could addition of one of these dissociators improve the efficiency of the burn? Perhaps it is the addition of oxygen, not of hydrogen, that causes the perceived increased efficiency. Given that one of the discussants has done the experiment and can't see an improvement that large in efficiency, I think not. By the way, why are you spending so much time railing about the poor math abilities of the press. You knew in grade school that they couldn't do math.

  • Ed says:

    I guess no one need worry about obtaining a Physics, chemistry, or Mechanical Engineering degree anymore. Just submit your problem to Mythbusters and their word is gospel.

  • Jan says:

    Some speculations why this device might work:
    Maybe due to the addition of H2 you create a shitload of hydroxyl radicals that are extremly reactive. This can lead to a faster burning of the fuel early in the combustion cycle. Releasing the energy of the fuel in a shorter and better defined time might (or might not) increase the efficency. Adding hydrogen is in my opinion more a kinetic than a thermodynamic effect.

  • eddie says:

    I did a wee bit research on these things and decided against them, despite some actual plus points that are there.
    On the plus side, adding electrolysed water to the gas mixture in your engine does increase the oxygen proportion of your air over the normal oxygen nitrogen mix. Also, adding hydrogen gas to the hydrocarbon mix increases the combustion rate, like adding naptha to palm oil. Not sure about overall burn efficiency.
    On the negative side, your car would need to carry an awful lot of water around with it;
    1l of liquid H2O equates to roughly 1,800l of H2 plus O2 gas. A 2l engine, running at 6000 rpm will get through 1,800l of gas in about 9 seconds.
    What proportion of the elecrolysed gas is added to normal air intake?
    And you'd have to disable or alter your car's oxygen sensor or it will see the higher oxygen as a cue to enrich the fuel.

  • Anthony says:

    (1) "A local TV station in Florida claims to have tested the device. They tested the mileage of their news van using a dynamometer;"
    Ok, so the engine was probably cold before that test.
    (2) "then they mounted the device on the engine of their news van,"
    I'll guess the let it cool down before mounting the device.
    (3) "and after giving it time to break in,"
    ok, so it's definitely warm again
    (4) "put the van back on the dynamometer, and tested its mileage again."
    Now testing with a warm engine.
    Don't engines run more efficient when warm? If they really did compare cold to warm, that could at least partially explain their results.

  • mstump says:

    The hydrogen generators do in fact work, Wal-mart has been outfitting their fleet of trucks in order to increase efficiency. They did a cost/benefit analysis and determined that with the hydrogen generators and other improvements that they could possibly halve their fleet wide consumption of fuel. Keep in mind that Wal-mart has the largest private fleet of trucks in the US and they could possibly save tens of millions each year. Keep in mind that they are burning diesel, and not petrol so results may very.

  • Stephen says:

    If this thing worked, it would not surprise me that Detroit, Toyota, etc., would not pick it up. For example, turbo chargers are known to increase fuel economy by about 20%. They do this by getting more oxygen into the cylinder. At one point, people tried heating the air that goes in, with the idea that it would be closer to combustion temperature. Performance went down. So, they tried cooling the air. This improves performance. That's because cooler air is denser, hence more oxygen. Internal combustion engines are gasping for air. This isn't news.
    Diesels get about 20% better economy than gas engines. Turbo Diesels get some of both.
    And some turbo diesels get sold. Not that many. Why not? Automakers aren't in the business of educating their customers. Not unless they can make a buck. So diesels are much more popular in Europe, where there's more demand. We'll be there in the US soon.
    Why do hybrids work? Well, by introducing regenerative braking, energy that would be lost can go into acceleration. But the real deal is that if some of the power needed for acceleration can come from some other source, then the main engine can be smaller. Why is that good? Well, it takes about 15 HP to cruise down the highway. A 150 HP engine isn't very good at delivering 15 HP. A 100 HP engine with a 50 HP assist is better. (I've no idea what the real numbers are.)
    Why are hybrids selling? Mainly because Honda educated the market, and other automakers noticed it sells, and at a premium. So, there's money to be made.
    I expect that cars with some electrics will eventually get solar cells. Back of the envelope calculations suggest 10% to 15% of highway power can come from there. If it's sunny. More if it can be stored in a battery while you're at work. You won't want to park in the garage.
    My own car gets 44 MPG. It's a 1.9 liter with a 5 speed manual. Nothing special. I bought it used. So i get good economy without paying much of anything. I consider the 70,000 miles i've gotten from it to be good value. I expect another 70,000 miles. Then $900 gets me a new engine, and another 300,000 miles?

  • Schmeer says:

    Blake,
    Don't forget that the alternator would produce alternating current. So make a slight adjustment to your method and calculate AC power not DC.

  • Prometheus says:

    @ #20
    I'll never understand the practice of measuring fuel consumption in L/100km. Nobody goes around measuring speed in s/100m.

  • Howard C. Shaw III says:

    #36, noahpoah, are you sure?
    "You haven't stated anything about the relative magnitudes of J and H, E_g and E_h, or N and M, so C > H doesn't have any clear implication for the relative magnitudes of the hydrogen-augmented and pure gas terms."
    N×Eg×J + M×Eh×H - M×C
    He did say something about Eg and Eh - they are both between 0 and 1. We don't need to know the magnitude of M, because it is constant in the equation, so assume 1, i.e. 1 gram of hydrogen.
    Then what we are really asking: is Eh×H - C positive? Well, H

  • OrchidGrowinMan says:

    In the test, did they hook up the device to the alternator or the battery? I ask because it COULD work by converting battery-stored power to hydrogen fuel, reducing required gasoline consumption. At least for a few minutes. Not practical.
    HOWEVER, it is more efficient to store energy as hydrogen fuel than in a heavy battery. Hybrids COULD be designed to use their regenerative brakes (and solar cells?) to electrolyse water and store the hydrogen (and oxygen?) for use in the engine later. You'd still need electrical storage (or a fuel cell) so that the vehicle could avoid the inefficiency of a combustion engine at low speed and idle, so a "three-way" hybrid, with energy stored in hydrocarbon, hydrogen and battery might have an efficiency edge: Lighter battery, moderate storage space for hydrogen.
    OT, but I notice that hybrids I have ridden in keep their batteries full. If the botton 90% of the battery is never discharged, then why haul it around? I would want a plug-in hybrid that would "know" my usual route, and prepare for the long downhills by leaving "space" in the storage for regenerated energy, and which would have depleted its storage by the time I get back to my charging station. If it "learned" my route, and anticipated an impending long downhill (GPS?), all the better.
    For the "three-way" idea, maybe it could obtain water for hydrolysis by condensing it from the exhaust?

  • Torbjörn Larsson, OM says:

    Batteries works more efficiently and live much longer when fully charged. And having differently sized batteries on store for swap would be prohibitively expensive.
    Though I think your idea of learning typical route (and user) "profiles" and use, for say precise mileage prediction, would be a neat feature for a hybrid.

  • OrchidGrowinMan says:

    Torbjörn,
    Ignote "wear-out" and consider that you had two batteries, one 10% and one 90% of the total. You charge-up and fully discharge the 10% one each trip, but never charge nor discharge the 90% one at all: in fact it's not even connected. Except for possible aging effects, that is the same as having a single 100% battery and only using the top 10%. Now maybe a Pb-acid battery used at 10% lasts "forever," and at 100% has a short life: that would explain the observed usage pattern. But, for example, Li-Ion batteries don't work that way: the amount of TIME they spend at various states-of-charge is what determines their wear-out (and temperature too). The wear-out rate is fastest at 100% charge, decreasing to a minimum at an intermediate level (roughly 50%), and increasing to a lower peak at "0%" (actually, this level is around 15%, but discharging it further really hurts it). So a Li-Ion battery with 20% of the Pb-acid battery capacity would work ~the same, but would be roughly 10% of the weight.
    The point I was making is that 100J stored in a battery "weighs" much more than 100J stored as hydrogen (or gasoline). If you know you're going to have to burn some fuel, then the regenerated energy would be more efficiently stored as hydrogen. Then you don't need as heavy a battery to store all of it. Less weight is good.
    The point of the car learning the route is that part-way down the big hill, the regeneration stops: the battery is full, and braking just makes heat, not reusable energy. When I get home, if the battery is not empty, there is no room to put the (presumable cheaper, someday) energy from my electrical outlet. If it detects a (or one of several) "regular commute," it can run a plan to arrive with empty secondary storage. If it sees (via GPS) on a map that I'm likely to soon go down a long hill, either a usual route or a novel one, it can use some extra stored energy to optimise storage space for the anticipated regeneration. Of course, sometimes it will be wrong, and the gasoline engine will have to be used more ("cache miss"), but the math is straightforward, similar to a computer processor's caching strategy.

  • Torbjörn Larsson, OM says:

    But, for example, Li-Ion batteries don't work that way

    I'm aware it was a simplification. I was getting at basic design criteria for hybrids.

    The point I was making is that 100J stored in a battery "weighs" much more than 100J stored as hydrogen (or gasoline).

    That was your other point.
    Hmm, not necessarily, as water tank, hydrogen generator, possibly a hazardous gas compressor (I wouldn't want one in my car) and hydrogen tank would weigh a lot.
    Anyway, you wouldn't be able to generate much hydrogen in the short time you break in traffic. Hills where you don't need an engine are rare.
    But this isn't for me to analyze any longer, now it is for you to construct.

  • Militant Agnostic says:

    jre at # 30 nailed it - combustion efficiency is so high already that there is very little to be gained by improving it. The only place where significant gains can be made are by increasing the amount of heat that gets turned into mechanical work by improving thermal efficiency. As Blake Stacey pointed out you can't beat Carnot which means the only way to gain efficiency is to increase temperature.
    Virtually all gas saving gizmos are attempting to inncrease combustion efficiency (which most of them don't anyway). This is why they are all frauds.

  • Bill says:

    I would say what you saw was a info-mercial posing as news.The news crew when proforming the test was given the 61% fig.and was told to work to it.The math was some how done wrong work up to 23.2 not down from 23.2 to 9.4.That aside how would hydrogen efect the octane rating.Engines now ajust timing to compinsate for lower octane which means more power or less power.

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