Developing a car to run on H2O - Engineering Discussions - IET EngX - IET EngX
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Developing a car to run on H2O


The new crisis brought up an old thought back in my head. 

10 years ago I was living in a different country, and me and a few friends of mine tried to "build" a concept vehicle that could run on H2O, obviously not directly and not that simple, but, to create an electrolysis chamber and install it on a car, maybe even with an extra battery.

The main thinking here is that if this car would be constructed, even if it wouldn't be as efficient as a petrol or diesel car, because of the lower H concentration. At the same time, there are lots of cars that have been converted to use LPG, that has a combustion formula 100: C3H8+5O2  - > 3CO2+4H20, witch clearly suggests that it will "burn" the H and O giving a "residue" 3xCO2 and 4 molecules of H2O.

If instead of this we will supply the engine with H and O the burn should simply give a clean H20 residue. 

Yes, the problem appears that the LPG has 8 to 10 H, and petrol has 12 to 32 H and diesel has 20 to 28 H. But also these fuels have a high concentration of carbon.

It the electrolysis scenario we would burn pure Hidrogen and the burn could be cleaner for the environment and also the water doesn't need any modification.

There might be other costs involved, like the cleaning of the hydrolysis tank and electrodes, but that would still be cheaper than the constant purchase of fuel. 

Anyway, I digress... This came back to my mind, but, unfortunately, I'm not a car mechanic. I was thinking to buy a cheap car as start working on it and see where I get, but like I said, I'm not a mechanic and I don't have all the required knowledge. I already designed the electrolysis tank, and I'm confident I can build a big enough version to fit a car for this purpose. 

I guess my questions are:

What would be the simplest car that I can/should use so I won't fail from the wrong reasons?

Did anyone worked on a problem like this before? 

Are there any issues that I'm not aware of? 

Any advice? 

  • The big issue I can see is where are you going to get the electricity to do the electrolysis?

    If it's from a big battery, then you might as well throw out the engine entirely, put in an electric motor, and you have a Battery Electric Vehicle.  If it's from the car's alternator, then the alternator will need more power than the car's engine is generating.

    The only thing that might work is to plug it into the mains when parked, to fill a tank with the hydrogen/oxygen mix.

    It takes as much energy to split water into hydrogen and oxygen as you get from burning the hydrogen.  So water isn't a source of energy.  Unless your process is 100% efficient (and it will never be), then trying to power a car of water actually loses you energy.

  • That's why I was thinking of having an extra battery, and maybe some extra small tank for keeping some excess Hydrogen. 

    These are kinks to be worked out through testing, obviously... 

    But splitting the hydrogen doesn't require so much energy... 

    And on the running stage the alternator should provide enough power to keep the electrolysis going. 

    It might not be as efficient as a normal fuel car, but it might work... 

    An EV is not a solution for the issue. 

    But if we look at a hybrid car, the alternator provides enough power to charge the battery so the car can run on electricity. Therefore I'm assuming that with the right combination this can be a viable solution. 

    Like I said before, I'm not a car mechanic... But thank you very much for the feedback. 

  • It would be interesting to see the numbers for what you propose. How many kWhrs of fuel do you expect to carry,  i.e. what range?  how do you recharge it? at what pressure are you storing the gas etc. All these things maybe not solved in fine detail but you should at least be calculating to the correct factor of 10 , to reasure yourself that you can avoid wasting time on tanks that are unsafe or impractically heavy, or other components that are not of the right scale.

    Remember there is no free lunch - the force needed to spin an alternator rises in proportion to the electrical load, so that you always have to  put in a bit more mechanical energy than you get out as electricity,  - the rest comes out the side as unwanted heat, vibration and stirring the air inside.  Electrical energy needed to split water into hydrogen and oxygen is one electron per hydrogen atom and there are 10 ^ 23 of the blighters in a litre of gas.
    That is a lot of amp seconds - an amp is 10^19 electrons going past per second after all. That has to come from somewhere.
    Note that the power needed to split water is the energy needed to break the bonds between H and O, plus a bit more that is lost in the electrical resistance of the liquid, so that as well as generating gas, the liquid has to be cooled if you want to do electrolysis at the sort of scale needed for a car - kilowatts.

    When you burn the hydrogen back to water you get back the energy you put in to split the chemical bonds as they are re-created, no more no less, but of course any engine will not convert all of that to torque, some will be lost as heat etc.


  • You may not realise it, but you're trying to make a perpetual motion machine, and it can't work.  You want to put water into the fuel tank, and get pure water out of the exhaust.

    But, somehow, by turning water into water, you want to extract enough power to run a car.

    The car will run until it's battery is flat, then it will stop.

  • But splitting the hydrogen doesn't require so much energy... 

    And on the running stage the alternator should provide enough power to keep the electrolysis going. 

    I think you'll need to do a bit of fundamental work on that bit.

    But if we look at a hybrid car, the alternator provides enough power to charge the battery so the car can run on electricity.

    A mild hybrid draws off some power from the powerchain (usually from a dedicated motor/generator) to charge a traction battery - but only during deceleration or breaking, and can then return that power for short periods during acceleration, which saves fuel. Plug in-hybrids need the battery to be charged from the mains if they're going to go any reasonable distance in electric mode. There may be pure hybrids - where the ICE just drives just a generator which in turn drives an electric motor (much in the style that diesel railway locomotives have done for generations) - which gain efficiencies by running the engine in its most efficient speed/torque range regardless of  demands of the wheels, but all these things are either about harnessing existing waste energy or improving the efficiency of the internal combustion engine. None can ever provide more energy out than went in in the first place.

       - Andy.

  • Hi, 

    Thank you very much for all the feedback, I know all about electrolysis, and I'm aware that there will be a lot of energy being lost, contrary to some believes I'm not suggesting a perpetual machine in any way or at any level. 

    Actually after all the feedback here I have a clear plan on what I'll have to do.

    I will start at a very small scale to test my electrolysis tank in real life conditions and improve at the small scale one step at a time as needed. I'm not jumping at large scale straight away, the investment would be too high. That's why I'll start at a small scale and based on the readings I will know how to go on larger scale. 

    But, at this point I want to thank everyone, even if the feedback wasn't positive or helpful form everyone (sometimes even outside the subject), it got my brain working and that helped more than anything... 

    Once I'll start the project and have real results I'll post here for more feedback. 

  • When you burn hydrogen you get water... That's not a perpetual anything, that's just chemistry... 

    C3H8+5O2 - > 3CO2+4H20

    From this formula you can clearly see that when you burn LPG you get CO2 and water... The hydrogen burns in presence of oxygen creating water... Simple chemistry. 

    Perpetual motion machine it would mean that it won't lose energy, but this one will, maybe even a lot of energy... 

    The whole idea behind it, is that even if you have a small range, because water is everywhere and it doesn't really require processing it would be a lot cheaper to run... The fact that it produces water as waste it's a bonus that shouldn't be overlooked. 

  • That is the chemistry we all agree on, and when O2 and 2 H2 meet we get 2 2 H2O and 280kJ of energy per mol of water created (1 mol of water is 2 mols ( =2 gram) of hydrogen atoms,  and one mol = 16 grams of oxygen atoms.

    Splitting the water again, takes the same energy, plus some losses.

    1 mol of any sort of molecule that is a gas at room temp takes up about 22-24 litres at one atmosphere pressure

    The bit that is worrying some of us is your assertion that you can use the car engine alternator to split water  back into gas again at any useful rate at all.

    I'll spell out the sums that others are doing in their heads.
    A typical car alternator runs out at about 1kW, though larger ones are available, and needs about 1.5kW of shaft power to do so.  That is kJ per second, so perhaps a couple of grams of hydrogen every 280 seconds, if all was loss  free. More like a few grams of hydrogen an hour would be more realistic.

    In contrast a car engine is going to burn some kg of fuel per hour, as you need to be able to put 10s of kW to the wheels.

    Now a system where fixed wind turbines or solar panels split water into hydrogen and water, and then you tanked this into a vehicle that burnt it would be a more realistic proposition - but of course the real source of power is the nuclear fusion in the  sun  - but that is burning to waste any way, or a from winds and tides a gentle reduction in  the moon's kinetic energy, at a rate that need not bother us.

    It may well be possible to dispense with tanking the oxygen, and just take up that from the air, but the hydrogen will have to be carried on board - and as it does not liquefy at any sensible pressure, then that probably means high pressures and corresponding heavy tanks.

    As I said in my first post, you need to get a decent grip on the numbers, and a far more detailed one than my coffee break analysis above.

    I do not want to put you off, but I want to warn you away from things that have potential to be a huge disappointment and waste your efforts


  • The only way that this could work is that you have the electrolysis tank in a fixed place and the car on the road, but I wouldn't exactly want a tank full of a hydrogen/oxygen mixture anywhere near me.

  • indeed, though I suppose if I was the worrying kind I'd also twitch about a volume of blended alcohols and octane with enough chemical energy to put my body into free space or to launch a large part of the whole car into a geostationary orbit, suspended in a single skin sheet steel tank spaced  a few inches above an abrasive road surface that moves  under that tank at speeds of up to 70mph (honestly officer, only up to, never beyond - ahem...). I'm not the worrying kind...