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Ok, so I know its been a topic before-H20 power

  1. Apr 20, 2005 #1
    First of all, I just want to say that I stumbled upon this site and am quite pleased with what I have found, so I joined. I just wanted to say hi, I'm a college student who is hoping to become a mechE. Anyway, I have seen a few topics which discuss the possibility of using electrolysis to split water into H2 and 0, then burning it either in a regular engine which has been properly treated or some other sort of burning device (such as a pulse-jet engine). I realize that as I read in another post somewhere, water is not a fuel source, but an ash in the sense that it is the waste of burning H2. And after some of my own expirements and calculations (I dont like to take somones word for it if I can do the work myself haha) Realized that yes, you can not produce enough energy to sustain the breaking up of the water molocules because this would be like creating a perpetual motion engine. My question is how much extra electricity would it take to keep the process sustained, and could it be provided by way of converting unused energy (heat, or maybe even photo cells). and then the whole point of this is of course to have this process produce more mech energy per volt then just a straight electric vehicle otherwise, just build that haha. Maybe you could even just replace the battery ever X miles or charge it in the wall even... well thanks for listening, Im not an idiot so please feel free to correct me and let me know what you think, I will listen, thanks. --David
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  3. Apr 21, 2005 #2


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    Hello, and welcome.

    I'm not quite sure what you're getting at, sorry if I appear patronising!

    Firstly, remember that to get electricity 'out of the wall', you're usually just burning coal (a process which, at best, is 40% efficient).

    Secondly, the laws of thermodynamics give rise to the fact that you can't have an ideal process; you're always going to lose energy by converting it from one form to another. Every time you convert, you lose more and more energy. I think you know this.

    Thirdly, combustion is an inherently inefficient process; getting energy out of hydrogen is far more efficient in a fuel cell than in an internal combustion engine of any sort.

    When running hydrolysis, you're always going to put in more energy (in the form of electricity) than you'll get out (in the form of hydrogen). Residual heat energy from processes such as combustion are, indeed, a waste, but this waste heat is usually pretty useless.

    I'm not quite sure how you think hydrogen as a fuel is going to be used, do you realise that you couldn't just fill your car up with water, and have something turning it into hydrogen? If this were the case, you'd need a pretty large store of energy in the car, and you have to get this energy from somewhere (you mention a battery, or charging from the wall). If it were possible to store this amount of electrical energy in a car, then you wouldn't need to bother with the hydrogen, - you'd just stick it straight into the motors.

    I'm not quite sure I've understood you, or answered your question, but don't be put off!
  4. Apr 21, 2005 #3
    UT-3 and S-I for nuclear hydrogen production

    Electrolysis is not very efficient. The processes being explored for nuclear-powered hydrogen production are thermochemical. The two leading candidates are UT-3 and S-I:

    Regarding efficiency:

    We developed screening criteria and did detailed evaluation to select two cycles that appear most promising, the Adiabatic UT-3 cycle and the Sulfur-Iodine cycle. The UT-3 process has predicted efficiency of 35% to 40%. The Sulfur-Iodine cycle remains the cycle with the highest reported efficiency, 52%, with process improvements suggested that could increase the efficiency and lower the capital cost.
    Last edited: Apr 21, 2005
  5. Apr 21, 2005 #4
    Burning hydrogen to crack hydrogen; fuel cell efficiencies

    Coal has hydrogen in it. Coal itself can provide hydrogen more easily than can water and, alternatively, coal can be converted to gasoline, diesel, and kerosine. Wouldn't it be Rube Goldbergian to burn coal to split water to get hydrogen for transportation fuel?

    Dominic Crea says that is not true.

    It has often been said that a fuel cell is a very efficient energy converter, that its efficiency can “approach 83%”. This is actually quite true-in theory. However, when one considers all of the parasitic losses and ancillary subsystems necessary to make a practical fuel cell-powered vehicle, the real world efficiency plummets from 83% to something like 40% or lower-a number that is surprisingly close to the actual efficiency of some Diesels and other high-compression engines! In fact, the 83% theoretical efficiency is not unique to the fuel cell-it is equally applicable to heat engines, thermoelectrics and even human muscles [....]
  6. Apr 22, 2005 #5


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    Yes, that was my point! The OP's idea seemed to be based upon in-vehicle hydrolysis, using some magic portable power source.

    An interesting link sir. However, while overall efficiencies for Hydrogen fuel cells are indeed mitigated by all the supporting systems and running losses, the efficiencies still remain higher than with combustion, although by not as much of a margin as I originally supposed.

    Any stats on the differences between emissions of nitrogen oxides when comparing hydrogen used in a fuel cell or a combustion cycle, setting aside any produced while isolating the hydrogen?
  7. Apr 22, 2005 #6


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    Speaking from experience (several years with the Hybrid Electric Vehicle Team at Virginia Tech), it's true that the fuel cell's monolithic efficiency is sharply reduced by all the blowers, water pumps, power electronics, and other supporting appartus. It's also true that fuel-cell design is progressing more rapidly than the tooling and technology to build them! Smaller fuel cells which require lower pressures, have higher output current capability, and reject less waste heat are on the way, faster than we can build them. Fuel cells are really an infant technology, particularly in highly-engineered situations like automobiles.

    - Warren
  8. Apr 23, 2005 #7
    The gasoline engine - old or young

    Ditto for reciprocating heat engines. I haven't seen any camless engines, throttleless gasoline engines, electric compressor engines, engines with thermoelectric recovery, stratified-charge gasoline engines, or electro-linear engines; and the advanced engine designs such as those incorporating Miller and Atkinson cycles that are made today don't sell well in an environment in which gasoline is still virtually given away for free.

    Graham Cowan's boron engines might eventually compete well against gasoline/diesel/kerosine reciprocating engines, but simple arithmetic shows fuel cell engines never will -- even long after nuclear-recoverable oil is depleted.
  9. Apr 23, 2005 #8
    That was the introduction to his question. He said:

    Realized that yes, you can not produce enough energy to sustain the breaking up of the water molocules because this would be like creating a perpetual motion engine. My question is

    His question was, "What is the EROEI?" He wanted to know how much more energy needs to be put in to get a given amount of energy out.
  10. Apr 23, 2005 #9

    Ivan Seeking

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    According to the Scientific American state of the industry review, fuel cell powered electric vehicles are currently operating at about 36% efficiency, and internal combustion about half that, or 22% at best.

    The well to wheels efficiency of water/hydrogen/fuel cell auto is 8%. So you get 8 watts of hydrogen power for every 100 watts of power spent producing hydrogen. These are measured, not theoretical values. They attempt to include the real losses of all systems involved.
  11. Apr 24, 2005 #10
    haha thank you for helping me out hitssquad, I think I have some good info thaks to Ivan as well. I appreciate it guys
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