Propane/Oxygen Hybrid Idea

[Pete Zaria]

Right off the bat, this is kind of a crazy idea. If I attempt this, it will be extensively tested remotely.

My idea is to build a (hybrid) gun out of sch80, and sleeve the chamber pipe inside couplers so there's a double layer of PVC over the entire chamber. I know that will be expensive, but hopefully not as much so as metal.

I've built regulated propane meters before, so I was wondering... What if you had two meters, one for propane and one for oxygen? Instead of using compressed air to even out the propane:air ratio as in a normal hybrid, I'd like to use a small amount of oxygen. I'd still need a burst disk, I think.

The part I'm not so sure about, and would like some help on is basically, is it safe to use a small amount of oxygen, with metered propane, in sch80 PVC, pressure rated to 280psi, double-layered on the whole chamber? Could anyone estimate or speculate on how high a "mix" would be safe to run? Will using oxygen produce more of a pressure spike than compressed air would?

The ultimate goal is to break the sound barrier with a golf ball. I know it could be done with a large pneumatic with a light gas, but I don't want to deal with pressurizing chambers with a light gas for every shot. I don't have a huge budget for this project, but hopefully will in the next year or so. I figured if I'm going to build this, I should start working on detailed plans.

Please let me know if you think this is feasible. I'm sorry if I rambled.

Thanks a ton to the spudfiles community. This is the only place you can ask questions like this and get a reasonably educated answer.

Peace,
Pete Zaria.

[WOW!!]

If you want to break the sound barrier, a good sized Hybrid with propane and compressed air would work. Meabey 24" of 4" sch80. Like what DR did. But with the Oxy I dont really know how much to put in there. But I do think that the DDT rate might blow the chamber up. But I am not sure. I would build it first with just 2X and 3X if it is your first and then add the Oxy set up. Or you could go for broke and try it and see what happends.
Good luck

[Pete Zaria]

I've built several combustions and a couple of pneumatics before, but never a hybrid. I've been reading about them here and other places for a few weeks, and I'm confident I could build one. I'm a very safety-minded and paranoid person, so I'd include redundant safeties and remote detonate it the first 50+ runs.

The reason I like the idea of bottled oxygen is that you could do two onboard meters, just like for propane (but one for O2 obviously), and not have to bring along a compressor.

Keep the info coming please

Peace,
Pete Zaria.

[LucyInTheSky]

You could put oxygen into the chamber so the chamber was just oxygen, then meter 20% propane in (the right amount).

[Pete Zaria]

Does anyone have any idea about the pressure spike or pressure produced by a propane/oxygen mixture?

Thanks.

Peace,
Pete Zaria.

[boilingleadbath]

Using temperature values for combustion, taken from varius sites on the internet, it seems that it'll increase pressure about 15%, as the flame temperature is about 15% higher. (I've done a more extensive examination, but don't want to copy my post from spudtech.)

Burn rate... well, that, I don't know about.

You may acctualy have better luck using a 20%O2-80%He oxidizer mixture.
I havn't done the math, but I'm pretty sure it'll have a higher speed of sound than the O2-propane one, in addition to burning slower. (although still faster than normal air due to the lower heat capacity of helium)

[Pete Zaria]

Here's roughly what I'm planning to do.

4" x 12" PVC sch80 NSF-PW combustion chamber with 4"x2" pressure rated reducer bushing, to a 2" union, to a camlock (banjo fitting) for the barrel (10 ft stick of 1.5" SDR21 sleeved in 2" sch80 pvc). Stun gun ignition with a chamber short (for dual spark gaps), so there's only 3 holes total in the chamber: two bolts (with washers and nuts on both sides of the chamber wall) for the stun gun wires, and the gas port (diagram below). I'm planning to sleeve the entire thing either inside of couplers (with the ridges filed out) or inside of 6" ABS (to contain any potential shrapnel). I prefer the idea of double-layering the PVC using couplers, but I'm not sure how expensive that would be.

Here's the gas meter system I have in mind.



The only part I haven't really figured out is how I'd vent the chamber between shots. I don't want a cleanout type cap on the back, I have a feeling it'd blow up eventually. And a pressure-rated ball valve for a vent would be pretty expensive, wouldn't it?

Everything else seems pretty self-explanatory. Stun gun ignition with a 50' cable for remote detonating, chamber fan, etc...

What I really like about this design is, there's no compressor required. And, I can buy propane tanks for $3 and oxygen tanks for $6 at Home Depot, so operating costs would be very low.

I'll be starting this project as soon as budget allows, hopefully this winter. I'm hoping to do it for under $300. I already have some of the parts, though. Does anyone see any major flaws, or improvements to be made? Thank you very much.

Peace,
Pete Zaria.

[schmanman]

Use all steel instead of sch 80. you wouldn't have to worry about it exploding as much, or at all.

[Shrimphead]

The problem I see is the union. You can't sleeve that into anything. And they have failed in hybrids before I think. And I can't remember whose sch 80 hybrid it was, but it apparently had DTD happen and that caused the shapnel to fly 90 away IIRC. So I would suggest a longer barrel unless you are protected in some way.

[ProfessorAmadeus]

Yeah a unoin has exploded before and it was blown to lots of pieces. Hers a link http://www.spudfiles.com/forums/viewtopic.php?t=231&

[Pete Zaria]

I'm doing a CAD drawing of the design, and modeling the cannon as best I can with GGDT and some spreadsheets on O2-enriched hybrids.

Question... Which is safer for reducing the chamber to the barrel, a reducer coupling (McMaster # 6826K158) or a reducer bushing (McMaster # 4881K666) ? It seems like the chamber to barrel reducer must take a holy crapload of abuse, so I wanted to know. The reducer bushing would reduce the chamber volume slightly, so I'd like to use the reducer coupling if you think it's just as safe. Thanks again for all the info, guys.

What do you think of my idea for a meter system?

Peace,
Pete Zaria.

Edit: OK, here are the crappy Visio drawings I did.

4" x 2" sch80 combustion chamber sleeved in 4" couplers.



Meter system. Propane pipe will be half-inch, 8" long, O2 pipe will be 1", 8" long. 2 shots of O2 for every 1 shot of propane, both at 50 PSI, should be the correct mix. Meter drawing is not to scale.



Chamber detail and wiring diagram.
I'm going to connect the onboard control box to the remote detonator box via a molex cable and 50' cord. Since I only need 4 wires, using a molex for a quick disconnect seems perfect. Everything is pretty self-explanatory here. The quick connect at the back of the chamber will go to a 4" x 24" PVC air tank (attached to the stand) for airing out the chamber between shots. The gas meter will sit on top. The propane, oxygen, and air (vent) tanks will be mounted to the stand. I'm working on a design for a stand, but haven't had any great ideas yet.



Please give me feedback. This is going to be a big, expensive project and I'd like as many opinions as possible before I build it. Thanks a ton.

Peace,
Pete Zaria.

[Pete Zaria]

OK... So I just priced out the entire thing on McMaster. I know I could get a lot of the parts locally, but I wanted to see how much it would cost.
I realized that for only $50 more, I can make the entire chamber (including reducer and union) out of black forged steel rated to 3,000 PSI. Might as well do it. I figure I could run 6x mixes with that. I'm working on a way to get the gas into the chamber without welding, and I think I've found it.

Now to save up $400...

Peace,
Pete Zaria.

[WOW!!]

Looks good. The only thing i would change is make the union 2.5" for better flow. And I would go with the bell reducer, because it has less surface area if that makes sence?

[spudmonkey]

uhhh....dude i fire my sch80 cannon with oxy & mapp there isnt much oxy in one of thoes containers, im out of town right now so i cant tell u how how many oz are in it but i know that it isnt as much as propane or mapp, with me using it with the torch that u have to use it with for a little while then usin it in my cannon i ran out in about a week i fired it maby 30 times in a farily small chamber 21"X4", just thought u might wana know tha