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Hybrid Hydrogen Fuel Canisters

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Hybrid Hydrogen Fuel Canisters

Unread postAuthor: fogus » Tue Nov 11, 2008 6:35 pm

In my quest for an ever simpler means of construction, I thought it might be fun to try hydrogen/oxygen, created from the electrolysis of water.

I would be using this mix to fill my charges (same charge as seen here: http://www.spudfiles.com/forums/files/f ... _1_162.png except I would not be fueling it with propane, but rather adding water through a secondary valve)

I heard some complaints about hydrogen made from this process being overly moist. Could this be helped by running the process at near 0C (causing the moisture to condense more readily)?

If I had a charge of 75 cubic inches and I wanted to get a 12X mix inside it, how much water would I use?

Does anyone have suggestions on what would make a good electrode?

When using hydrogen, or any other fuel, what is my best way of staying away from DDT? What shapes/pressures cause DDT?

Thanks!
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Unread postAuthor: Lentamentalisk » Tue Nov 11, 2008 8:26 pm

with pure hydrogen and oxygen at a 12x mix you will get DDT. You will get DDT at much lower mixes. You will also get spontaneous detonations of your fuel canisters, because in order to fill your much larger chamber to 12x, you will need to have the fuel canister at 120x at the least.

Do not attempt this.

Hydrogen/Oxy cannons are great, but I would stick away from high mixes, and storing them for sustained periods of time if at all possible. Also, storing hydrogen in steel pipes for long periods of time greatly weakens them, as it seeps in between the bonds, and reduces the structural integrity.

Either store the fuel and oxidizer separately, or try something else.
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Unread postAuthor: rp181 » Tue Nov 11, 2008 9:15 pm

What lent is talking about is hydrogen embrittlment.
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Unread postAuthor: Lentamentalisk » Tue Nov 11, 2008 9:19 pm

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Unread postAuthor: fogus » Wed Nov 12, 2008 12:28 am

Lentamentalisk wrote:You will also get spontaneous detonations of your fuel canisters, because in order to fill your much larger chamber to 12x, you will need to have the fuel canister at 120x at the least.

Do not attempt this.


No no, I wouldn't do that. I want to use a 6-12X charge mix to fill a 1X (atmospheric) chamber. These charges are used as a fuelling method only and are not more compressed than 12 to 1.

Does anyone have a suggestion on what would be the best electrode to use?

I was thinking of epoxying in some stainless steel wire through small holes in the bottom of my PVC charges and then wrapping them in some configuration.

How fast will stainless steel corrode in electrolysis? Could I get one 12X charge out of some length of 1/16" stainless steel wire?
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Unread postAuthor: Lentamentalisk » Wed Nov 12, 2008 12:43 am

Well ideally you would use platinum, but I am guessing that that would be a little out of your price range. Other than that, you are pretty much confined to stainless steel, as most other metals will react with the electrolyte in the water. I suggest that you do a little bit of reading on electrolysis before considering this any farther.

I would be very weary of storing even 12x canisters, as PVC tends to shrapnel, and I really do not trust hydrogen/oxy mixes to not spontaneously combust at those pressures.

I really suggest that you capture the hydrogen and oxygen separately, and then add them each as their own canister.

edit: What determines the speed at which the water separates is:
1) the electical current running through it
2) the surface area of the electrodes (wire has a very low surface area per length, but high per weight)
There are other factors, but I don't think any of them are as important, but as I said, read, read, read, and then come back to us when you have a more complete understanding. I often spend weeks reading up on a new subject before I post my ideas.
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Unread postAuthor: rp181 » Wed Nov 12, 2008 5:38 pm

normal steel works, but for the electrolyte use sodium hydroxide (carefull, powerfull base!). Its in home depot labled "crystal drain opener" Also, include a bubbler, so if its ignited the whole thing wont blow and spray caustic soda everwhere. It also helps get the water out of the gas, throw some ice cubes in the bubbler.
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Unread postAuthor: fogus » Wed Nov 12, 2008 10:35 pm

Thanks guys,

Lentamentalisk, what kind of calculations can be used to find the spontaneous ignition point of hydrogen/oxygen?

Off to do some more reading on electrolysis (please don't think I just randomly throw out ideas I have not done any reading on)...

rp181, does sodium hydroxide totally prevent corrosion?


To test a theory on how much to use, I'll throw my reasoning out:

I wrote:If H2 hydrogen is at a density of 2g/22.4L = 0.09g/L and O2 oxygen at 32g/22.4L = 1.43g/L, then the mix of the two would be 0.76g/L at 14.7PSIa.

If I wanted a 12X mix at 1L of volume then I would want 12L*0.76g/L = 9.15g of water.


Is this right?

Thanks guys.
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Unread postAuthor: psycix » Thu Nov 13, 2008 3:06 pm

The sodium hydroxide is there to make the water conduct electricity, while not electrolyzing by itself.
It does NOT prevent corrosion of the electrodes, heck it will even react with some types of metals (aluminium). You will need to use electrodes that do not corrode. Best would be platinum (expensive!), but you could also use carbon rods (but they WILL break down and cause black dust in the water) or stainless steel rods/plates (probably the best option).

Do NOT store large amounts of hydrogen and oxygen.
Do NOT store them mixed together.
Do NOT store them under high pressure, as they will get even more dangerous.
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Unread postAuthor: Biopyro » Thu Nov 13, 2008 3:21 pm

If I were you, I wouldn't be storing it at all in your own homemade container.
Your best bet would be to use it as you generate it, maybe store in a ballon and place it in the chamber. Then you pop the balloon and fire.

Hydrogen undergoes DDT very easily, so I wouldnt be using DWV eh?
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Unread postAuthor: jimmy101 » Thu Nov 13, 2008 4:15 pm

psycix wrote:The sodium hydroxide is there to make the water conduct electricity, while not electrolyzing by itself.
It does NOT prevent corrosion of the electrodes, heck it will even react with some types of metals (aluminium). You will need to use electrodes that do not corrode. Best would be platinum (expensive!), but you could also use carbon rods (but they WILL break down and cause black dust in the water) or stainless steel rods/plates (probably the best option).

Do NOT store large amounts of hydrogen and oxygen.
Do NOT store them mixed together.
Do NOT store them under high pressure, as they will get even more dangerous.

Sodium Hydroxide (NaOH) will significantly slow down the corrosion of the electrodes. Stainless steel, even zinc plated iron, will last a while in an electrolysis cell filled with several molar NaOH (or KOH).
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