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Acetylene Detonation Cannon

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Acetylene Detonation Cannon

Unread postAuthor: FiveseveN » Mon Jun 19, 2006 3:14 pm

All this talk about HCCH gave me an idea.
It uses a piston to compress acetylene beyond the point where it self-detonates, thus rupturing the burst disk and propelling the projectile.
The piston is pushed by pressurized air (at around 80 to 100 PSI).

<a href="http://www.flickr.com/photo_zoom.gne?id=170710978&size=o"><img src="http://static.flickr.com/53/170710978_55e36cf4b7.jpg" width="500" height="364" alt="ADT idea"></a>

In the given example, a 3-way valve is used to feed the chamber behind the piston and then vent it so the piston can be reset. This can be substituted with a system using two ball valves (3-ways are probably more expensive and not as easy to find).
The cushion spring prevents the piston hitting the end position with too much force once the pressure in front of it becomes lower than that behind it.
Most obviously, some serious steel piping is required. And keep in mind this is just a sketch. In a practical application, the chambers would probably be longer, as would the cushion spring.

If ya'll think it's plausible, I might build this baby in the near future.
Suggestions and questions are welcome, but please refrain from asking something stupid like "is this a combustion or a pneumatic?".
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Unread postAuthor: CS » Mon Jun 19, 2006 3:31 pm

Nice idear'! Your sketches are kick ass!

Anyways, I only see a few possible problems, but wouldn’t require to much to fix. First off your burst disk would need to burst when the acetylene self-detonates and not when the pressure just builds up. So that might be a bit frustrating to find a burst disk with a balance. Second you'd need to find a smoothbore metal pipe for the piston.

I may be wrong, but I thought I recall BLB saying something to the essence that acetylene doesn’t provide the right "combustion" for our situation.

If and when you build such a cannon it'll be very cool no doubt. Not to mention that thing would be fun to build, minus the $$$. Good luck...
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Unread postAuthor: boilingleadbath » Mon Jun 19, 2006 5:43 pm

"trouble finding smoothbore pipe for the piston"
Nah, just line some steel pipe with some plastic.

About the combustion charistics of acetalene, I'v stated that it's higher pressure spike requires a more robust containment vessle for the pressure generated... so instead of running a 7x propane hybrid, you might only run a 2x acetalene one.
(numbers are bullshit. You have been warned...)

The major issue I see with the design is that you are moving the piston with pressured air: when the mixture does go off, it will be pushed back, so you won't really be able to supply much pressure.
This might have accuracy benifits, but I don't think that's the effect you are chasing...

That's simple to fix though. Just pressurize it with a (relitivly) incompressible fluid, like water. With only a small filling hole, it couldn't move very much of it during the firing cycle.
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Unread postAuthor: drac » Mon Jun 19, 2006 5:44 pm

As Pimp said, your sketches are very detailed and as always clean! It's a pleasure to look at them instead of trying to decipher something that someone scribbled down in math class.

As said above, you need to either a) find a smooth bore pipe, or b) machine your own detonation chamber. The burst disk also needs to have a balance, echoing Pimp's statement, but with a few simple calculations, it could be figured out.
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Unread postAuthor: benstern » Mon Jun 19, 2006 5:55 pm

It's a pleasure to look at them instead of trying to decipher something that someone scribbled down in math class.


I am offended!!!! :evil: :x
Just because i don't have any artiistic ability does not give you the freedom to poke fun at me.

Also, what type of pipe are you using?
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Unread postAuthor: djt » Mon Jun 19, 2006 6:01 pm

god those drawings are good...

nice desgin but your going to have to be careful that the acetalene tank itself doesnt get to the pressure needed to detonate. this cannon in definately the first i have seen based on the concept of a piston detonating acetalene.
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Unread postAuthor: SpudStuff » Mon Jun 19, 2006 6:09 pm

the actylene in the tank cannot detonate due to the fact there is no Oxygen
same reason why a can of axe of other arisol cannot explode.

for the burst disk wou might want to use the industrial ones. they aren't too expensive and then you can be shure of what pressure it will burst at.

And yes i agree nice skech
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Unread postAuthor: Pete Zaria » Mon Jun 19, 2006 6:16 pm

FiveseveN,
I think it's a great idea.

In response to the problem BLB brought up about the piston coming back upon detonation... Why not put another spring behind the piston so it can't slam back too hard, and a pop-off valve to vent the pressure, so that the piston effectively resets itself upon detonation? That would also make the 3-way valve unnecessary, you could just use a modded sprinkler.

The only other problem I see is venting the chamber between shots, but I assume you could use the compressed air tank to vent the chamber.

A few little ideas:

Put the filling shrader/QD valve on the pressure tank itself, no need to add that T.

Add a T setup similar to the kind found on most hybrids to measure the pressure created by the combustion. You know, combustion chamber > spring-loaded checkvalve > T with a pressure gauge on one side and a pressure release on the other.

Add a pressure gauge on the combustion chamber itself, to monitor the pressure of the acetylene.

It needs a safety of some sort. My only idea is to add a ball valve on the chamber that you can leave open, as a safety, to prevent the acetylene from reaching detonation pressure until you close the valve.

You could integrate the acetylene system and safety into a T to reduce the number of holes in the chamber.

I don’t know what you’re going to use to hold the burst disk. Let me know what you figure out for that.

I think you could safely build this out of sleeved sch80 PVC. Two layers of sch80 should be pretty safe, unless you intend to use this as a hybrid.

This project intrigues me. I’m really curious to know how this ends up. If yours is successful I might consider building one.

Peace,
Pete Zaria.
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Unread postAuthor: FiveseveN » Mon Jun 19, 2006 6:30 pm

@BLB: I was actually thinking that using a compressible fluid actually is a plus:
1. It dampens the recoil.
2. It (somewhat) protects the chamber and piston from the shockwave
Actually... I have no idea how a projectile will behave after being subjected to a tansonic shockwave. Will its momentum overcome any benefits of detonation as opposed to deflagration? Will the air between the projectile and the burst disk be enough to buffer the shockwave and overcome momentum?
As one can see, there are many variables, the most important one being "am I over-estimating the power of HCCH?!"
So, BLB, seing as I was never good at stoechiometric calculus, could you figure out just how much energy a spontaneous detonation of acetylene can output?
@pimp and drac: I already have a smoothbore extremely thick steel pipe, only problem is it's only about half an inch ID. If all else fails, I think I've seen some scrap excavators and such. Their pneumatic cylinders would be absolutely perfect for a chamber :)
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Unread postAuthor: djt » Mon Jun 19, 2006 6:38 pm

are you planning to use calcium carbide to produce the acetylene? because if he does then yes there will be air coming in the chamber. when he opens the acetylene tank to put the water and calcium carbide in spudstuff. unless its not enough air to detonate. but in that case you would have to be careful in the sense that if you open the ball valve from the acetylene tank to the chamber too long it will build enough pressure to detonate and WILL have enough air.
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Unread postAuthor: FiveseveN » Mon Jun 19, 2006 6:59 pm

Damn, you guys replied before I got a chance to. I must excuse myself for double-posting, but editing my previous post would probably make it too long.
So then:
@SpudStuff: Actually, it's not at all the same thing.
Spontaneous detonation is one thing, ignition is another. You need oxygen or another oxidizer for ignition, but not in this case. (The acetylene tank would probably be contaminated with some air anyway).
But the acetylene tank is isolated by its ball valve that is only open while filling the chamber.
Now, @Pete Zaria:
...put another spring behind the piston so it can't slam back too hard, and a pop-off valve to vent the pressure, so that the piston effectively resets itself upon detonation? That would also make the 3-way valve unnecessary, you could just use a modded sprinkler.


My first thought was to use a spring to push the piston forward and cushion its "feedback", but using pressurized air better in the long run. Making all the parts needed for the spring system would actually cost more than a ball/butterfly valve that I already have, plus it's actually less efficient.

The only other problem I see is venting the chamber between shots, but I assume you could use the compressed air tank to vent the chamber.

If you're referring to the acetylene chamber, it would be no problem at all since the piston would be in its frontmost position at the end of the shot, and the barrel screwed off, so one can just blow into the chamber or expose it to the atmosphere and brownian motion will do the rest.

As for design considerations, as I stated before what I've drawn is just a sketch. The final outcome will depend chiefly on the materials I can gather.

Acetylene in the tank/chamber will not reach anything near 2 atm prior to triggering since it will be produced by adding small amounts of water to carbide.
Adding a pressure gauge to the chamber won't do much good, since the spike will be faster than the needle on the gauge can even think about moving :)
Anyways, thanks for your input and indeed this is an interesting project. The variables involved alone are enough to keep me awake untill I finally get to experiment with the design.
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Unread postAuthor: boilingleadbath » Mon Jun 19, 2006 10:48 pm

Indeed, the spike is too short lived to acctualy do much good.
The only advantages of detonation over normal combustion is a greatly decreased time for it to occur, and a slightly higher efficiency. These are important when prepelling very light projectiles, such as mere air, which is why there is a significant amount of interest in pulse detonation engeins (kindof the big brother of the pulse jet).
The benifits for heavy projectiles are much smaller.

The shockwave proper is too short-lived to make defences against. Your piston might as well be welded in place as far as it is concerned; it's not going to move very damn far in the hundreth-of-a-millisecond timescale the shockwave is in contact with it. (take numbers with salt)

Anyway, I wouldn't trust triggering the system mearly by pressure. Build in a spark plug incase the intended method fails... I wouldn't try to 'defuze' the situation any other way.
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Unread postAuthor: huse_spud » Mon Jun 19, 2006 10:52 pm

I like your drawings. they are sexy.
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Unread postAuthor: FiveseveN » Tue Jun 20, 2006 5:57 am

Lol, huse_spud. Do you think my Maria Teresa is sexy, too? :D

So yeah, It'll be using a liquid instead of air to drive the piston.
One could "defuze" it by venting the back chamber, then removing the barrel. With minor modifications (add a tee w/ a ball valve tot he acetylene feed par example), the acetylene chamber could be vented directly.
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