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More noob questions

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: ROCK SOLID » Sat Mar 08, 2008 5:35 am

i think i smell some BS from bubba 05 here to, tho he could be taking about his hybrid cannon that he rifled and he can send a TB over a mile or is that BS too :roll:
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Unread postAuthor: Hubb » Sat Mar 08, 2008 5:37 am

Now that may just be possible, depending on the mix and all.
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Unread postAuthor: ROCK SOLID » Sat Mar 08, 2008 5:44 am

well he says (bubba05) that he uses high octane fuel i dont know the mix.

but do know the mix on my cannon, a sqruit of hairspary and thats all to send a sock over 50 m im serious no BS and i dont know how far that will go for a tennis ball but at least ove 100m
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Unread postAuthor: DYI » Sat Mar 08, 2008 10:31 am

Firstly, BigGrib, oxygen is a diatomic gas, consisting only of oxygen atoms. It is quite stable, and will not violently decompose at ANY concentration. It may oxidise other materials in the vessel, including almost any solid or liquid hydrocarbon that might be present. Ethyne (acetylene) contains a carbon - carbon triple bond, which stores quite a bit of energy. It is unstable at pressures of over 15 psig in 100% concentrations, and its decomposition is extremely fast and exothermic.



I do know for a fact that a normal pressure spike from a hairspray is 300 psi bubba05 told me this cus he is my neighbour .


Considering that the maximum combustion pressure of propane (the main flammable propellant of hairspray) is about 129 psig, and that hairspray contains all sorts of other crap like water and scents, you either misunderstood bubba, or he's full of [excrement].

Now, on to your original question, yes, it is quite possible. I made a simple one myself actually, and the flammability limits of propane or MAPP are quite large in pure O<sub>2</sub>. DDT runup distance will be significantly reduced, and heat generation and pressure spikes (and therefore fatigue on the chamber) will be increased.

What mixes did you plan on using? 1x (atmospheric pressure) combustion will generate roughly 250 psi if it is mixed properly. For higher mixes, a rough estimate can be obtained simply by
((250psi x mix number) + preignition pressure). Pete was right with the
1 part C<sub>3</sub>H<sub>8</sub> : 5 parts O<sub>2</sub>.

As long as your chamber can withstand the pressure generated, and you aren't creating detonations, you should be fine. If you are creating detonations, things get a lot more difficult. Detonation guns would have problems with massive shock loads and quick fatiguing. All parts would have to be specially designed, and be replaced regularly. Ever wonder why there aren't guns powered by high explosive charges? That's why. (cue JSR providing a link to one)
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