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Hydrogen Oxygen and pressure

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LAN_403

Slid

Sun Nov 06 2011, 02:10AM

Registered Member #853 Joined: Thu Jun 21 2007, 03:08PM
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Posts: 14

For some time I have been thinking of ways to make rocket fuels that does not involve chemicals that are so hard to get by, for example even potassium nitrate is quite regulated here.
With electrolysis of water one will get oxygen and hydrogen. This leads me to two possible uses. If you made a closed airsealed system which leads the oxygen into one tank, and hydrogen into another tank, I guess it would be quite compressed after some time, the electrolysis doing the actual compressing. So no mechanical compressor should be needed.. Then valves could be closed to the tanks, and you should have a rocket fuel that would not last very long since it is not liquified - but it is quite simple in theory, and very cheap to reload once you have the system buldt. And it does not require any turbopumps.

The other use, If one used a closed system, like water in a airtight tank and just let the oxygen and hydrogen mix and generate a huge pressure inside, will you have made a very easy to obtain 'explosive'? It should be way more energetic than the same gases at atmospheric pressure. (I do not intend to make this, it is just a theoretical system) It is the compression that makes me wonder. I do not know much chemistry, and I can't find any information if this has already been done, or if there is a certain pressure that will lead to autoignition.

I would appreciate some comments

Ash Small

Sun Nov 06 2011, 11:18AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

If the oxygen/hydrogen is mixed, and fed to a source of ignition, it will explode (the whole tank).

The oxygen/hydrogen MUST be mixed at the point of ignition.

Also, you will need a pump to achieve more than atmospheric pressure, so your proposed system won't work.

I'd suggest you do some more research before messing around with an explosive mixture of gases.

Powdered aluminium plus an oxidising agent may be a better fuel for your purposes.

Slid

Sun Nov 06 2011, 01:15PM

Registered Member #853 Joined: Thu Jun 21 2007, 03:08PM
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I do understand the whole tank will explode, that is the point of that theoretical system.

But are you saying that when you have greater than atmospheric pressure, the gases from electrolysis cannot escape the water?

It is the bit about the electrolysis doing the actual compression in a sealed system that interests me the most.

Ash Small

Sun Nov 06 2011, 02:28PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

They will escape the water, but once the collector chamber is full, any further gas will just bubble up to the surface.

You will only get one atmosphere pressure without a pump.

Or do you mean to carry out the whole process inside a sealed chamber?

Slid

Sun Nov 06 2011, 03:29PM

Registered Member #853 Joined: Thu Jun 21 2007, 03:08PM
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Yes, carry out the process inside a sealed chamber! I do not know if there is anything preventing the pressure from rising. If there is not, the system will compress the gases by itself, which could be quite handy.

Ocean Waves

Sun Nov 06 2011, 06:01PM

Registered Member #4181 Joined: Thu Nov 03 2011, 02:39PM
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I believe the best you can safely reach is about 200 PSI with a well constructed dry membrane cell, using a farm of 120 gallon storage tanks filled to 200 psi, one could expect to get about the equivalent fuel as a few cans of gasoline, unless you are using such a system to store energy from a renewal resource generator, its not very practical to have such a system.
the hydrogen being easy compressed with a hydrogenation proof oil used the compressor, however the oxygen is much harder to handle, as ANY and I do mean ANY combustible material, will explode as the pressure increases over 1 atm. I suppose and in theory only, one could use an external drive multistage, stainless steel, rotary vane compressor lubricated by a non reactive heavy halogen based lubricant, but your would be risking the life of yourself and your nabors.

if you actual want to make a rocket, without chemicals, pressurize a section of PVC filled 2/3 of the way full of water to around 600 psi, or just below that where you brand of pcv fails, these type of water rockets have been known to reach over 4,000 feet. using carbon fiber instead pressurize it to 3,000 psi...............

I don't think that an oxy-hydrogen rock is within reach of private citizens, however, the vacuum distillation at 134 F and use in less then 1 liter quantities of 75-90% H2O2 is possible in the home rocket lab setting, simply pressurize a tank of peroxide to around 2,500 with say oxygen. Open the valve forcing the peroxide threw a fine mesh silver plated brass screen pack, followed by a nozzle, instant rocket, with good oxy fuel like performance. Probably a reasonable model could be produced out of thin wall threaded, or welded SS parts, with the need of a machined nozzle.

you could use the oxygen from your electrolyzer to run into an ozone generator, then bubbling the ozone into clean distilled water or better yet over the counter 3% sol as it has a stabilizer in it that will help the reaction will make stronger H2O2 from Ozone........as a starting point for distillation. but I don't recommend that just anyone do this as H2O2 50% and above is dangers when mishandled and the danger increases exponentially approaching 95% consentration.

Slid

Sun Nov 06 2011, 08:14PM

Registered Member #853 Joined: Thu Jun 21 2007, 03:08PM
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So I have been reading abit. Say you took an ordinary soda bottle, filled some salty water in it and glued in two electrodes and turned the power on. You will get O and H. Then you let it generate to for example 5 atmospheres. This should be a powerful bomb, easily ignited by a spark between the electrodes when laying it sideways for the water to leave them dry.
Why isn't this done, as it requires absolutely no illegal chemicals? And so easy scalable..

And forget the soda bottle, why not do the same thing inside a high pressure tank?

I do understand this is dangerous, and I do not intend to do it, but I am wondering why it isn't done.
It is the principle that interests me, if it would work in ideal circumstances, not the practical DIY dangers.

Will compressed oxygen and hydrogen autoignite at some point?

Ocean Waves

Tue Nov 22 2011, 02:43PM

Registered Member #4181 Joined: Thu Nov 03 2011, 02:39PM
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Posts: 42

slid: LoL

it will likely ignite far before 5 atm on its own, its more like turn on the power and wait for it to explode.................... an airsoft (maybe) or bb gun would also be a good way to set it off as well

a perfect mixture of hydrogen and oxygen can ignite from a simple pressure change as little as 50 torr, such a reaction is a common lab demo where a perfect mix in placed into a small jar with a balloon over the top simply tapping the the balloon with a pen causes a small ignition and thats at 1 atm!

what you are talking about, I have done safely with a std 1 gallon milk jug, my uncle showed me this trick when i was about 10, 2 electrodes trough the cap, and when the jug starts to swell fire a bb at it i suppose throwing a rock might work as well but i never tried it I always had bb gun and still do for that matter, it gives a nice loud report, with little danger

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