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Detonation gun

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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Unread postAuthor: paaiyan » Wed Dec 12, 2007 10:52 am

Well, I can't tell you how far it needs to compress, but I can tell you that you'd better come up with a really strong stand for that thing, that's going to kick like a horse.

It would work better if you had some sort of mechanism to lock that piston forward when the initial chamber fires, else it's going to bounce back some and you'll lose a significant amount of pressure quickly.

EDIT: My calculations could be wrong, but using Charles's law, you should reach autoignition temperature in about a 3-1 compression ratio.
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Unread postAuthor: DYI » Wed Dec 12, 2007 5:03 pm

The design I posted could reach up to 840 psig in the detonation chamber by compression from the piston. However, the entire mechanism would have to be over 20' long to achieve the desired result. However, if the compression needed was only 4:1, I could simply ignite a 3x hybrid mix in the back chamber, without need for the gas ram type design. In theory, this design could actually be feasible to build if I only need to get a 3:1 compression ratio for the oxy/hydrogen to ignite. The piston will be fairly massive, and by the time it compresses the O2/H2 enough for it to autoignite, it will have too much momentum to be stopped by the detonation in front of it, and its continued forward momentum will further enhance the firing, with even more of the gas being expelled. There would be a very substantial bumper to stop it at the end of its stroke.
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Unread postAuthor: CpTn_lAw » Thu Dec 20, 2007 4:48 am

Hey DYI, that topic kinda takes me back a few years when my physics prof showed us two different explosions; one with 02/H2, and one with O2/CH4.
the loudest was the methane one...it did detonate, as well as the di-hydrogen, but H2 dd more of a "PWOP" and methane..."POOOO" that is pictured language isn't it :D
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Unread postAuthor: BigGrib » Thu Dec 20, 2007 6:39 am

all i have to say abou this is i swear someone is gonna get dead
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: DYI » Thu Dec 20, 2007 5:05 pm

all i have to say abou this is i swear someone is gonna get dead


Ah, ye of little faith. I hope you don't mean that seriously. Because if you do, you obviously didn't read the topic before you posted, and that's never really a very good idea.

On further consideration, I've decide that due to the unavoidably light projectile mass of the detonation gun for the concept to work without an explosion on a massive scale, I'll probably just make a normal, non detonation hybrid. It will probably use a maximum mix between 20 and 30x, and should pack quite a bit of power. I'm also considering sacrificing a bit of power in the name of ease of use, and making it a piston hybrid design.

One way or another, I'm going to be building a pretty serious hybrid in the summer.
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Unread postAuthor: CpTn_lAw » Thu Dec 20, 2007 6:29 pm

just be careful...we don't want a mate to get hurt or else :wink:
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Unread postAuthor: ramses » Wed Jul 16, 2008 10:16 am

You may wish to put a bumper of some kind on the far left end of chamber II in the diagram you drew on page 2. Relocation of the C1 to near the middle of chamber II could allow air to cushion the piston. If the piston recoiled, after the half way point, pressure would build on the oxy-propane side, cushioning the right side of chamber II.

If the oxy-hydrogen fails to diesel or detonate, you could try oxy-acetylene. from wikipedia:
...Acetylene can explode with extreme violence if the pressure of the gas exceeds about 100 kPa (≈14.5 psi)...

So in theory, oxygen wouldn't even need to be present, although it would burn the byproducts of the decomposition of the acetylene, creating additional heat and pressure.

Just some thoughts, and this sounds a lot like a combustion light gas gun:
http://en.wikipedia.org/wiki/Combustion_light_gas_gun
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Unread postAuthor: bugsingelyn » Wed Jul 16, 2008 11:01 am

Ehhh...I've done some (a lot of) experimenting with H2 and O2 and talked to many chemists and chemistry teachers, and they all say that when you make H2 and O2 with electrolysis of water, it makes a "wet" mixture. Water is evaporated as the gases are made and it really slows down the burn time. So basically, the mixture in your cannon would be H2, O2, and H2O gas.

When you pump in H2 and O2 from bottles, they are "dry" gases, and it would burn much faster.

You can tell the difference when you fill a balloon with "wet" and "dry" mixtures. The wet mixture will give a low booming sound, while the dry mixture will be more of a CRACK.

Is there some way to dry out the mixture?
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Unread postAuthor: ramses » Wed Jul 16, 2008 12:01 pm

The best way to dry the mixture, if it is made outside the chamber, is ironically bubble the mix through water. This allows any water vapor to condense and become part of the liquid. A better, but much less safe way would be to put it in a bottle with some silica dioxide, that stuff in shoe boxes and stuff that says don't eat.
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Unread postAuthor: SNDM » Fri Jul 25, 2008 9:05 am

Wait, are you putting a certain volume of stoichiometric hydrogen/oxygen into the chamber and then adding compressed air in?

Or are you compressing the mixture in?
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Unread postAuthor: DYI » Fri Jul 25, 2008 9:47 am

Wait, are you putting a certain volume of stoichiometric hydrogen/oxygen into the chamber and then adding compressed air in?

Or are you compressing the mixture in?


If I was building this cannon (which I won't be) I would be adding hydrogen and oxygen (probably from compressed gas cylinders for ease of use) to the chamber in a near-stoichiometric ratio, the same way as I fuel my oxy/propane hybrids, with a manometric fuel meter.

Certain recent events have confirmed my guess that DDT guns won't work at all with heavy projectiles - unless the slug has very little mass, it won't accelerate along with the shockwave, and will be passed by, wasting most of the energy and resulting in a slow shot.
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Unread postAuthor: McFear » Sun Aug 03, 2008 3:02 am

hey DYI have you made this thing yet?
if so, how did it go.

Fear
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Unread postAuthor: frankrede » Sun Aug 03, 2008 11:27 am

McFear wrote:hey DYI have you made this thing yet?
if so, how did it go.

Fear
I think Larda's hybrid just demoralized everyone:/
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Unread postAuthor: Mr.Sandman » Sun Aug 03, 2008 11:50 am

frankrede wrote:
McFear wrote:hey DYI have you made this thing yet?
if so, how did it go.

Fear
I think Larda's hybrid just demoralized everyone:/


i wouldnt say everyone, maybe spudfarm will make one for 200x mixtures
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Unread postAuthor: Coodude26 » Sun Aug 03, 2008 12:04 pm

Mr.Sandman wrote:
frankrede wrote:
McFear wrote:hey DYI have you made this thing yet?
if so, how did it go.

Fear
I think Larda's hybrid just demoralized everyone:/


i wouldnt say everyone, maybe spudfarm will make one for 200x mixtures


That's what larda's does, sandman. IIRC. 200x mix (which is still crazy) is part of the original message, and was the challenge from DYI.


Hey, I know my stuff :D

Well most of it anyway. :roll:
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