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hydrogen power

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: sgort87 » Sun Dec 23, 2007 6:30 pm

The Gort smells trouble. You guys need to watch it. Put a bad name to spudding and I'll be upset.

Realize that these guns with high power are more powerful than you may think. As the pressure builds, it compresses the rest of the unburned gas as it goes. The last part of the combustion process in the chamber becomes a pure fuel and gas mix at a high pressure. That's basically a hybrid with a pure mix.

crap like this is the reason people get hurt. Just be safe and responsible with it is all I ask, along with doing all your math and reasoning correctly.
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Unread postAuthor: rp181 » Sun Dec 23, 2007 6:32 pm

i mean im getting it to ignite 3 times before refueling.
I am getting the water out, not letting it build. I doubt i will be using this long, its experimental

heres a pic, as i said, very small:
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Sorry for bad qualtiy, taken with webcam the jar is electrlysis, water is black because carbon bits flake off after extended use, need to replace. Can't get clear pic of actuall electrolysis.
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Unread postAuthor: sgort87 » Sun Dec 23, 2007 6:36 pm

RP, I just reread your post about the back plug not blowing out. In a normal mix, that plug will blow out. Your mix is bad if it is weak like you said.

Please describe (exactly) your electrolysis setup.
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Unread postAuthor: rp181 » Sun Dec 23, 2007 7:36 pm

3x4 carbon rods, each row has 3 rods touching each other directly, and the rows are seperated by about 1cm. The first and third rows are connected by a jumper (insulated), as with the second and fourth.

I dropped the rods in a jar, and added water (warm) with a little baking powder. in the end, the water was almost at the top, but not quite. the tube for output is about 2cm below the lid.

As if right now, im feeding in 12v, 4.5A. I might just keep filling the chamber until the hydrogen pushes the oxygen out, and use air instead.

EDIT: I filled the chamber by timing, first let fill for 1min, then 2min, etc... at around 10min, it didnt work, but after blowing in a little, it ignited and was very loud, this was a dry shot.
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Unread postAuthor: DYI » Sun Dec 23, 2007 9:48 pm

If you didn't first purge the chamber with an inert gas, the mix is going to be WAY off. Which is a very good thing, because using PVC with oxy/hydrogen is just asking for trouble.
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Unread postAuthor: Novacastrian » Sun Dec 23, 2007 9:55 pm

I can't wait till you get the mix right. Not that i think we will hear about it! :lol:
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Unread postAuthor: DYI » Mon Dec 24, 2007 10:08 am

I can't wait till you get the mix right. Not that i think we will hear about it!


Oh, we'll probably hear about it. Either in the "Share your Spudding Accidents" thread, or in another "more bad publicity" thread.
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Unread postAuthor: sgort87 » Mon Dec 24, 2007 11:57 am

The carbon rods are your problem. If you wanted to just produce hydrogen, it would work, but since you are catching what's coming off both electrode sides, you aren't getting a pure mix. When using carbon electrodes, the oxygen rod isn't just making oxygen; it heavily produces carbon dioxide. In other words, you have hydrogen, CO2, and a little bit of oxygen. It's going to continue to be very unimpressive unless you get some stainless steel 316 electrodes which will produce pure hydrogen and oxygen.

After remaking your electrolysis rig, use a metal chamber and stand back when firing.
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Unread postAuthor: Hotwired » Mon Dec 24, 2007 5:59 pm

An interesting little snippet I found said that an oxygen/hydrogen mix produces up to 500psi and about 20x that if it DDT's.

Stay safe :o
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Unread postAuthor: DYI » Mon Dec 24, 2007 6:24 pm

Your interesting snippet is inaccurate. DDT is dependent on run up distance as well as pressure. You could get a .5x O2/H2 mix to detonate if it was well mixed and had enough run up distance.
Conversely, you could pressurise O2/H2 to more than 20x, as long as it was done slowly and with a heat sink. I also kind of doubt that pure O2/H2 at 1x produces 500 psi. A perfect O2/C3H8 mix won't produce over 250 psi, and C3H8 creates higher combustion pressures than hydrogen.
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Unread postAuthor: Hotwired » Mon Dec 24, 2007 6:44 pm

*shrug*

The guy who runs powerlabs does seem to know his stuff and that snippet was from him.
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Unread postAuthor: DYI » Mon Dec 24, 2007 6:48 pm

The guy from Powerlabs probably does know his stuff, but his knowledge runs over a much broader area, so he can certainly be excused for not knowing the obscure specifics of oxy/hydrogen combustion.
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Unread postAuthor: rp181 » Mon Dec 24, 2007 7:33 pm

Ok, thanks.
I might be building an all metal one with a pure mix, but i can't find stainless steel 316 sold other than industrial use.

My current setup shoots a spud over 100 yards, plenty good for me.
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Last edited by rp181 on Tue Dec 25, 2007 11:16 am, edited 1 time in total.
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Unread postAuthor: Hotwired » Tue Dec 25, 2007 5:00 am

Found a thermodynamics calculator to check.

Gave up until I can find a manual for it.

Still, steel should cover a whole load of possible combustion pressures including hybrid mixes so go for it :)
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Unread postAuthor: jimmy101 » Tue Dec 25, 2007 3:38 pm

rp181 wrote:As if right now, im feeding in 12v, 4.5A.

You might want to use a lower voltage. In an electrolysis cell any voltage over what is needed for the desired redox chemistry just goes into unwanted side reactions.

IIRC, water electrolysis only needs 1.5~2V. Putting in 12V doesn't help. So, you might try using 1.5V batteries. A generic C battery will supply ~10 amps (but not for very long). A lower voltage might reduce the degradation of the carbon elecrode and reduce the formation of CO2.
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