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Hybrid Confusion

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: Killjoy » Sat Jan 06, 2007 1:26 am

that is why im building the hybrid out of steel with all parts rated to 3000 psi (its over kill, but hey i got a good deal).
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Unread postAuthor: reaper613 » Sat Jan 06, 2007 2:49 am

some ppl will tell you that acetylene self detonates at 15psi, i say they are over selling it. acetylene just becomes a little unstable, i know some guys that run 25psi acetylene in their cutting torch lines. now when building a hybrid i say use nothing but steel because then you can use whatever fuel with high power mixes and you actually get somthing that earns the name hybrid (not just glorefied combustion) also make sure your valves can hold the pressure your gun is putting out, none of us want to hear about the guy with a ball valve in his skull on the 6o'clock news. looking forward to seeing your gun killjoy
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Unread postAuthor: frankrede » Sat Jan 06, 2007 3:46 am

High explosives: They undergo detonation at rates of 1,000 to 9,000 meters per second.
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Unread postAuthor: Killjoy » Sat Jan 06, 2007 8:17 pm

thanks reaper, im heading up to salvage yard soon, which gets all of its stuff from this government lab , so everything is in top condition, and the guy who owns it sells all the stuff at like a 1/10 of its value (which is till alot in some instances). I should have it down by mid febuary. Still, can somebody give me an idea of how to meter the oxygen for my cannon?
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Unread postAuthor: pbmann123 » Sun Feb 04, 2007 7:47 pm

Ethyne is not a high explosive and no more so when mixed with oxygen. It's an unstable molecule so its use in a hybrid is not suitable as it decomposes at pressures near or exceeding 15 psi. So to go for a two times mixture with a chamber pressure of 14.7 psig it would more than likely decompose the acetylene prematurely.

Also the flammability limits of Ethyne go from 100% - 2% of atmosphere. This means that it could go off in your meter pipe, or in the chamber while you are still tweaking something on your stand/test apparatus. Boom good bye hand.

One of the other problems associated with Ethyne is the extremely easy D.D.T. ( detonation deflagration transition) poses a threat to shatter what ever container you are using. The pressure spike doesn’t have to exceed the rating of the vessel but if the shock wave is fast enough it will shatter the material like glass. This is not worthy of harnessing as a means of propulsion because the event is so fast that it releases its energy in less that the time your projectile could move a more than few calibers, and then the vacuum begins to take effect.

The method by which a hybrid work is as follows:

The fuel metering pipe is of a fixed volume and assumed fixed temp. The only variable is the pressure, and by using P1V1= P2V2 we can find out how much fuel is contained in the pipe at x pressure. We adjust x until it meets the amount that we require for our chamber 4.19%.

This is where a hybrid differs, we inject twice the normal amount of propane, and then we double the pressure of the air in the chamber, doubling the amount of air in the chamber, thus reaching stoichometery again. And because of the pressure increase we need a burst disk. It has been proven that using a burst disk which ruptures as close to the nominal pressure of the chamber before firing is going to give the most energy transfer to the projectile because it allows the expanding gasses to push the projectile all the way out the barrel.
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Unread postAuthor: Killjoy » Mon Feb 05, 2007 4:55 pm

well im not using acetylene any more anyways cause its so damn expensive where i live and i decide the risk factor was to high, so im using prpane and oxygen instead, and i already figured out how to meter the oxygen for the propane, now i just got to finish welding the cannon and building the stand, and im all set. thanks for the input you guys.
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Unread postAuthor: LGM » Mon Feb 05, 2007 4:57 pm

If you're feeling stupid, hydrogen can be pressurized…
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