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Supersonic non-hybrid combustion gun - it's feasible!

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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Supersonic non-hybrid combustion gun - it's feasible!

Unread postAuthor: dongfang » Sun Aug 27, 2006 10:08 am

Hi,

If any of you have wondered if it is possible to shoot > Mach 1 with a butane gun, I found the answer a few months ago: It is.

The gun is made of unrated PVC pipe (somehow I'm still alive, but rated pipe is just too hard to get by in Denmark -- nobody does DIY plastic plumbing).

The chamber is 105 cm long, 110 mm in diameter (a long and narrow thin-walled pipe will withstand more pressure than a short and chubby one, for the same volume). The sparker has 4 gaps, evenly spaced. There is a PC fan at the breech end.

The barrel is 5 meters of 50mm OD pipe. I did some calculations, and found out that with the reletively low pressure of a combustion gun, a barrel of this length was needed.

With a perfect air/propane/butane mix, it would shoot about 280 m/s with a light plastic ball.

With about 40% oxygen in the chamber and a double gas charge, the ball comes out with at least 380 m/s (Mach 1.13) (I put a magnet in the ball and shot it through two electromagnetic coils, starting and stopping a microsecond timer. The coils were 75 cm apart, measuring _before_ the muzzle. At the muzzle, the velocity is yet a little higher).

Sonic booms are LOUD, even for small plastic balls ;)

Safety mesaures included hanging heavy rugs over the chamber, and firing the thing from a gooood distance.

Next thing must be to find out if it can launch a potato at those speeds as well. It will require more pressure, that means, more oxygen and more fuel in a better chamber.

Good fun it was anyway.

Søren
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Attachments
IM001864_small.JPG
The beast
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Breech end
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Gas meter device. It is basically a bottle with a hole in the bottom and a hose through the cap, immersed in water.
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The barrel fits loosely into the socket glued to the front of the chamber.
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Soon a place where you would not want to stay.
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Breech out.
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Inside the chamber
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The arsenal. Hydrogen peroxide and yeast make cheap oxygen. Acetylene was dropped after initial experiments (in air, it performed only marginally better than butane anyway. Acelylene was NOT!!!! tried together with oxygen enhancement)
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Coils in place around the barrel, and connected to mach meter.
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75 centimeters in 1974 microseconds. The mach meter was designed for oranges, but it works for other ammo, too ;)
Last edited by dongfang on Sun Aug 27, 2006 4:55 pm, edited 3 times in total.
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Unread postAuthor: Mihlrad » Sun Aug 27, 2006 11:31 am

Em, you said you used oxygen... that would make it a hybrid no.
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Unread postAuthor: ProfessorAmadeus » Sun Aug 27, 2006 11:33 am

Yes and your doing it in unrated pipe. YOUR CRAZY :shock:
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Unread postAuthor: )DEMON( » Sun Aug 27, 2006 11:39 am

Great work, not many cannons go supersonic. You should consider moving on to metal so you could really have some serious fire power.
What are you shooting at?
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Unread postAuthor: Torch » Sun Aug 27, 2006 11:45 am

Very nice gun sir. If you were to use a burst disc you might get higher speeds but im not 100% sure on that, correct me if im wrong :). Also I dont think you woul dget to many shots out of it, because the pipe might start to weaken over time..Stay safe! Peace!
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Unread postAuthor: dongfang » Sun Aug 27, 2006 11:53 am

I think my neighbors would wear out before that pipe :wink:

I guess I will try with 60% oxy and a spud, while standing pretty far behind the breech (the safest place near that gun :P ) If it blows up, well, there is only one sound barrier and it has broken it.

I think (don't have anything empirical to back it) that burst disks help only if you have problems with flame propagation (there are points in the chamber too fra from a spark gap). It did have such a problem with this gun originally, but the quad sparker solved it.

Søren
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Last edited by dongfang on Sun Aug 27, 2006 11:59 am, edited 1 time in total.
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Unread postAuthor: SpudStuff » Sun Aug 27, 2006 11:56 am

Sweet. You should really liik into metal or sch 80 pvc because what you have is not pressure rated. good job on the supersonic though
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Unread postAuthor: dongfang » Sun Aug 27, 2006 11:56 am

EEeeeeehh .. oxygen enhancement makes a gun hybrid?

Isn't a hybrid gun a combination of a pressurised gun and a combustion gun? -- the pressurization being a different way to stuff more oxygen into the chamber? I don't pressurize; I increase oxygen concentration instead.

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Unread postAuthor: noname » Sun Aug 27, 2006 12:23 pm

Mihlrad, if you don't have any oxygen, there's no ignition. A flame needs 3 things, fuel, oxygen, and a spark. Using oxygen doesn't make it a hybrid. In a hybrid, the gun is pressurized to a point just below the burst point of the burst disk, then propane is injected and ignited. The sudden pressure flare from the ignited propane plus the already pressurized chamber ruptures the burst disk. BOOM
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Unread postAuthor: CS » Sun Aug 27, 2006 12:37 pm

dongfang, weve already had a discussion on the issue. The reason you use compressed air is for the ~21% oxygen it contains. Yes, a hybrid utalizing compressed air in a controlled state would be more powerful then that of one using pure oxy and fuel. That is because that the extra nitrogen and such in the compressed air provides pressurazation behind the projectile. ~10PSI per each 'X' value.

Either way, nice gun. Id say on the performance side rather then safety :-p
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Unread postAuthor: dongfang » Sun Aug 27, 2006 12:38 pm

noname, I guess we still need to say that the pressure in the chamber will -- hopefully -- rise to something significantly higher then when the bursk disk burst (because of continued combustion). If not, one might as well save the propane and add a little more air instead, right?

I wonder about one thing, though: Is a stoichisometric mixture really the best? It will definitely be the mixture that leaves the least residual oxygen and fuel in the chamber, but that is not an issue.

It will also be the mixture with the highest combustion energy, but will it make the biggest BANG? In my experiments with the gun above, I got the best performance somewhat below stoichisometric. I still wonder why.

BTW DEMON, I shot at wooden boards and chipboards. It can shoot a candle through 46 mm of chip board, with no oxy injection. I shot a candle right through my neighbor's old ink jet printer, too.
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Last edited by dongfang on Sun Aug 27, 2006 12:39 pm, edited 1 time in total.
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Unread postAuthor: Flinchy » Sun Aug 27, 2006 12:39 pm

i like how creative your cannon design looks. it looks like pretty much everything you have you built from raw materials. what did you use for your ignition source? a stun gun? an ignition coil? or what?

-Flinchy
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Unread postAuthor: dongfang » Sun Aug 27, 2006 12:43 pm

Flinchy: A BBQ sparker. I tried to get an auto spark coil to work, but it was too weak. And my friend, who knew about the project, tossed out his old 32" CRT TV the same weekend -- not even bothering to salvage the flyback!!!

Søren

PS Yes this is not kit-gun land. Most materials, apart from the barrel and the wood for the support, were something that we didn't need anymore.
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Unread postAuthor: Bluetooth » Sun Aug 27, 2006 2:46 pm

How the he!! did u get 4 sparks out of a bbq igniter???
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Unread postAuthor: dongfang » Sun Aug 27, 2006 3:03 pm

A good igniter and careful adjustment. One day, in humid weather, it would not work unless I shorted one of the spark gaps, though.

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