SpudFiles

Just an interesting idea that I have had for a while, but never really posted:

I've heard of high explosive detonations propelling objects at amazingly high speeds, and was wondering if I could replicate something like that. Now, any monkey can fill a steel tube with flash powder, stuff in a projectile, ignite the powder, and get torn in half by a hail of supersonic shrapnel. However, replicating this with only gases, and without the horrible gruesome death part, would be a real challenge. The idea is that the supersonic detonation wave can propel lightweight objects at extremely high velocities. I think I could achieve this with a pressurised mix of O2/H2 in a long, thin chamber, ignited from the rear. I am considering building something like this, but I would first like some advice from the resident genii of Spudfiles to see if it is a viable design.

Questions:
1. I would likely use 2024 aluminum for the chamber, about 1/2" ID, 2"OD, and 36" long. Would this setup be capable of withstanding repeated detonations?
2. Would stoichiometric O2/H2 pressurised to ~30 psi preignition be very likely to detonate in the aforementioned setup?
3. Would a detonation of this mix have a decent chance of propelling a <1 gram projectile down a small diameter barrel to hypersonic speeds? I'd be aiming for >Mach 3 ( what I can't do with helium powered pneumatics).

Useful answers or speculations on the above questions would be appreciated. I would obviously include shrapnel shielding and (very) remote ignition on the design if I were to build it. Comments made in reference to how I will be blown to small meaty chunks when I set this thing off are hereby limited to 5 per page.

The setup MAY be able to handle repeated detonations, but how are you planning on sealing one end of the pipe?

Sounds... interestingly suicidal... but if you can get it to work WITH OUT dieing. you would be a spudgunning god in my books. * drools at hypersonic speed *

Can you weld aluminum?
Its the easiest welding I have done(using a wirefeed)

ISP of H2-LOX rocket engeins is 530 seconds, IIRC.

... so that sets an absolute upper limit on your attempts, based on the highest velocity one can get H2-O2 exaust to go, of about mach 15.

Other than that, yeah, sounds safe... actually way over built. I've seen research papers on detonation set up DDT scenarios in <i>polycarbonate</i> tubes with ID/OD ratios larger than your gun.

well, first off hypersonic is > Mach 5 not Mach 3

also did you type the pipe right? according to you it would be 1.5 inches think, where do you plan on getting something like that?

but i have wondered about H2/O2 pressurization.

for safety i think you should electrolyze water inside the chamber then use the same electrodes for ignition to reduce the amount of things going into the chamber, also this makes the mix perfectly stoichiometric.

With something this dangerous i would use a wired remote detonator.

Just so you know, hypersonic- while literally greater than Mach one in it's etymology- should be more than Mach 5.

an O2 and H2 mix is likely to ignite/explode itself as far as i know...

POLAND_SPUD wrote:an O2 and H2 mix is likely to ignite/explode itself as far as i know...

That would be the entire point of this experiment Mr spud

Well, the chamber would be machined from a solid rod, so the back would be closed already. The front would be threaded, and then have a high pressure brass bushing going to a 3000 psi aluminum union. After that, a short barrel, probably 1/4 or 1/8". With the threads, if (read "when") this thing explodes into its individual components, I may be able to salvage some of the rather expensive bits (like the 3000 psi aluminum union which costs ~$75 )

This may be a project for next summer. I need to be far away from any civilization when I try this, so my back yard (my only firing range in the winter) is out.

Any ideas for a homemade sparkplug that won't get torn out on the first shot?

EDIT: wow, lots more posts. I was hoping for hypersonic, but at least Mach 3. Mach 15 is an upper limit that I doubt I will ever have to worry about though. If you think that the chamber is really overbuilt, I could always increase the ID to 3/4 or 1", making it easier to work the electrodes. Electrolysing water inside the chamber is an interesting idea. I could simply continue until it autoignites, or failing that, use a second set of electrodes for ignition. I could first use the hole for the ignition electrodes to measure the rate of pressure increase from the electrolysis, and use that as a basis for when to ignite the mix ( because it would destroy one gauge every shot, and that would get expensive).

You should screw the sparkplug in from the inside of the chamber. No way it's going to blow out then. That's what i do in my Hybrids.

i mean he has to put enough H2 and O2 into the chamber but the problem is that once he try to fill his chamber with them there would be an explosion - he doesn't have to ignite it, it would explode instatntly

No it won't, the Hydrogen Oxygen mix needs some kind of ignition source.
It probably would explode under enough pressure- but the pressure in this vessel would be non-existent before ignition i think. Just need a bleed valve, or a vaccum before you start the electrolisis.

P.S. Heres a pic of the "sparkplug" i use in my hybrid.
http://i182.photobucket.com/albums/x281 ... rid002.jpg

That is why I would be electrolysing the water in the chamber to start with, rather than pumping it in. And detonations are a whole different animal from what we are used to. They can blow out all sorts of unexpected things, and a 1" ID chamber is too small to screw in sparkplugs from the inside.

Inject the mix slowly, put enough pressure in at once and you may exceed the energy of activation without any heat or spark.

EDIT: Okay, I just saw DYI's post, disregard the above^^.