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Oxy/Fuel hybrid

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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Oxy/Fuel hybrid

Unread postAuthor: SpudBlaster15 » Wed Aug 29, 2007 12:31 pm

I have been searching for a means of making my hybrid easier to fuel. That means no air pumps, and no compressors.

Small disposable cylinders containing ~29 liters of oxygen are available at hardware stores. They require a reverse threaded torch head, but I have one on hand. I am pondering the possibility of using the pure oxygen from these cylinders as the oxidizing component of the fuel mixture in my hybrid. Obviously, I wouldn't ignite a 4x mix of oxygen/propane, as transition to detonation is highly likely. My question is, what would be a safe mix to use in a hybrid constructed entirely of steel, brass, and copper; with a chamber volume of 18 cubic inches?

Assuming deflagration, GasEq shows that a chamber containing a 2x mix using oxygen and propane would experience roughly the same pressure spike as a chamber containing a 4x mix using air and propane. However, the flame front speed in the former chamber would be MUCH higher. This could increase performance, however, I am unsure as to whether or not the reaction will have sufficient run up distance to transition to detonation in a ~10 inch long chamber. Any thoughts?
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Unread postAuthor: paaiyan » Wed Aug 29, 2007 12:35 pm

What exactly do you mean"transition to detonation"? I'm not quite understanding you.
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Unread postAuthor: SpudBlaster15 » Wed Aug 29, 2007 12:44 pm

DDT...
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Unread postAuthor: iPaintball » Wed Aug 29, 2007 1:31 pm

It would probably be safer to cut the chamber down a little bit, but I wouldn't worry running a 2x mix.

Paaiyan, he means DDT, or Deflagration to Detonation Transistion.
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Unread postAuthor: Fnord » Wed Aug 29, 2007 4:52 pm

18 cubic inches isn't a whole lot to cut down...
I really doubt you'll get DDT'd, even at higher mixes(3-4x)
As always, you would probably be wise to put a layer of brick between you and the gun when dealing with unknown variables.

It would be nice to see a small, portable hybrid around here. Maybe you should make a small metal piston valve for it too.



Edited notes:
The run-up distance to ddt in normal air pressure was somewhere around what, 30-35 feet?
Noname achived ddt with 5 feet of pipe at 6x, which was the equivalent of 30 feet of atmospheric mix.
These numbers seem fairly porportional, so it could possibly be assumed that you could calculated the approximate run-up distance needed by the amount of oxygen/propane that the flame front travels through.
In this case, the number would be divided by ~4 to account for the pure oxygen enviroment.

This is just a theory (I wish gas laws were really this simple:), and the actual results would be heavily influenced by other vairables (temperature, for example).
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Unread postAuthor: DYI » Wed Aug 29, 2007 8:32 pm

It obviously would transition to detonation more easily due to the lack of buffer gases, but I have no idea how quickly. I would bet that BLB will have a pretty good idea though.

Congratulations for being one of the 1% of the members of this site who won't get flamed for posting a topic named "Oxy/Fuel Hybrid".
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Unread postAuthor: noname » Wed Aug 29, 2007 10:18 pm

I've said before, I'm not sure if DDT did occur. I just said that I think it did, because the pipe bulged a bit.
Oh, also, apparently someone put a stick of Sch 40 pipe in the Sch 80 rack, so it was Sch 40 pipe that bulged. Don't blame for the mix up; I haven't seen steel pipe with writing/pressure ratings or schedule or anthing on them.
SpudBlaster, might as well try it. It should be fun! And totally new if you can get it to work.
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Unread postAuthor: SpudBlaster15 » Wed Aug 29, 2007 11:33 pm

I am going to buy an oxygen cylinder as soon as I receive my paycheck on Friday, and then I will rig up my old remote ignition setup and test fire the launcher several times at a 2x oxygen/propane mix. I might even try 3x, if I am feeling insane enough.
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Unread postAuthor: Novacastrian » Thu Aug 30, 2007 1:42 am

[quote="_Fnord"]s.

It would be nice to see a small, portable hybrid around here. Maybe you should make a small metal piston valve for it too.

Have you seen my Hybrid, it is small and portable.
Look at 1st Hybrid in the showcase



:twisted:
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Unread postAuthor: TwitchTheAussie » Thu Aug 30, 2007 3:46 am

Let me say it in a true Aussie fashion. Just do it. From a distance and behind a brick wall but do it anyway.
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Unread postAuthor: SpudBlaster15 » Thu Aug 30, 2007 11:29 am

Novacastrian wrote:
_Fnord wrote:s.

It would be nice to see a small, portable hybrid around here. Maybe you should make a small metal piston valve for it too.

Have you seen my Hybrid, it is small and portable.
Look at 1st Hybrid in the showcase



:twisted:


There are plenty of small hybrids in the showcase.

Your hybrid still needs a pump or compressor to operate, and is thus not considered truly "portable". A launcher with everything it needs to operate on board is the the only thing that is really portable.
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