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oxy vs air & oxy regulator

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: Technician1002 » Wed Jun 10, 2009 12:54 am

Moonbogg wrote:
Technician1002 wrote:
Moonbogg wrote:Discussing the use of oxidizers isn't against forum rules as far as I am aware. Whats the difference between combustion and explosion? When you say explode, do you mean chamber failure? This cannon will be able to hold at least 2,000psi so I am not too worried about mapp gas and oxygen causing it to explode.

The definition of a detonation vs a combustion. The detonation may cause chamber, barrel or other failue.

The sudden and violent release of mechanical, chemical or nuclear energy from a confined space which creates a shock wave that travels at supersonic speeds. Often used interchangeably with explosion.


Right. The cannon chamber and end caps are going to be so overkill I can't possibly immagine it ever failing. OK i'll spill the chamber specs and tell me what you think.

3" SCH80 6061-T6 chamber x 12" long
1/2" thick 7075-T6 end caps (much stronger than 6061-T6)
secured with 6 #8 machine screws per cap to chamber.

It would take one hell of a blast to cause that beast to break apart. The barrel is 1 1/2" SCH10 6061-T6.

Have you seen a piston from a car that has had severe pinging? This is the result on a small scale what you want to do on a large scale.


These shock waves break things.

Knock is best defined and identified as the sound associated with vibrating pressure waves created by the burning of some part of the mixture in advance of the normal flame front. The abnormal burning in advance of the flame front creates a measurable rise in pressure that is always steeper and often earlier in the combustion cycle than normal. Under some conditions, this gradual pressure rise becomes a pressure spike with a peak value much higher than normal. This is illustrated here.

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Unread postAuthor: Moonbogg » Wed Jun 10, 2009 2:27 am

Maybe I can compromise between the two. The only thing I have against an onboard compressed air chamber is that it won't yield enough fuel loads. What if I used an onboard air chamber and enriched it with additional oxygen? Instead of the air having 20% o2 it would have perhaps 50% o2, yielding many more shots per tank fill and still keep a reasonable buffer for safety. It might even allow the use of air regulators for the onboard tank since the pressure won't be beyond 150psi or so and the o2 concentration won't be 100% but only 50%.
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Unread postAuthor: Biopyro » Wed Jun 10, 2009 4:36 am

Technician1002 wrote:
You may get unexpected combustion speed with no nitrogen buffer. It may be a true explosive mixture which is against the forum rules. I mentioned it as a safety concern. It may explode.

The rules don't say deflagration is allowed but detonation isn't. They are more to keep within the american legal boundaries, where a spudgun is still a spudgun if you don't use solid oxidiser/fuel mixes, and don't have ammo/fuel contained cartridges.

I think we need to use our own discretion in interpretation of the rules, and just because changing the oxygen percentage might (for we are speculating) cause a detonation, doesn't mean we can't talk about it.

In hybrids, DDT is actively avoided, because it's destructive power cannot be harnessed, and preventing it's disucssion would just be dangerous really.

Moonbogg: You need not to look at the concentration of oxygen, but mainly the partial pressure. It is this which will govern reaction rate between your oxygen and your seals, pipes etc.
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