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Triangle strips. Anybody got any experience with 'em?

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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Triangle strips. Anybody got any experience with 'em?

Unread postAuthor: D_Hall » Tue Mar 18, 2008 9:51 am

So I've been working on the Pipe Dream design trying to firm up combustion properties and the like. In talking to an online friend on another forum....

...Turns out he's a PhD who specializes in turbulence issues while he dabbles in combustion. Woohoo!

Anywho, he was asking if I was planning to use "triangle strips" to induce turbulence in the flame front. I've not had any chance to research this at all (although the name is pretty self explanatory), but I was wondering if any of you folks have used such methods?
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Re: Triangle strips. Anybody got any experience with 'em?

Unread postAuthor: starman » Tue Mar 18, 2008 10:45 am

D_Hall wrote:So I've been working on the Pipe Dream design trying to firm up combustion properties and the like. In talking to an online friend on another forum....

...Turns out he's a PhD who specializes in turbulence issues while he dabbles in combustion. Woohoo!

Anywho, he was asking if I was planning to use "triangle strips" to induce turbulence in the flame front. I've not had any chance to research this at all (although the name is pretty self explanatory), but I was wondering if any of you folks have used such methods?


Was he aware of the fans we use in typical combustion chambers to induce turbulence? Did he elaborate on the "triangle strip" effectiveness, placement, etc. It wouldn't be hard to mock something up to test, but getting real performance data would be tedious.
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Unread postAuthor: jimmy101 » Tue Mar 18, 2008 2:43 pm

Sounds similar to Schelerin (SP?) coils.

I wonder though if any type of a restriction designed to introduce turbulance might actually hurt performance. Heat loss appears to be the major limiting factor in a typical combustion gun. If you speed up the burn rate by baffles etc. then you probably also significantly increase heat loss. There just isn't very much energy in the gases, and what energy there is is all present as very high termperature.

I don't think anyone has every tried this particular approach, or they haven't posted it here or at SpudTech.

DR did some experiemnts with pre-combustion chambers and jet injection. Idea was that the first chamber is ignited and the jet of hot burning gases injects into a second chamber generating lots of turbulance. Worked great for making a huge bang with low mass, low friction ammo, didn't do anything with practical ammo.
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Unread postAuthor: Fnord » Tue Mar 18, 2008 3:02 pm

DR did some experiemnts with pre-combustion chambers and jet injection.


Got a link by chance?

I've been thinking about building a gun that accelerates the flame front through a pre-combustion tube with a schelkin spiral (even bought most of the parts needed) but I'd like to know more about this before I put things together.
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Unread postAuthor: SpudBlaster15 » Tue Mar 18, 2008 3:35 pm

jimmy101 wrote:I wonder though if any type of a restriction designed to introduce turbulance might actually hurt performance. Heat loss appears to be the major limiting factor in a typical combustion gun. If you speed up the burn rate by baffles etc. then you probably also significantly increase heat loss.


I suppose triangle strips (or similar) made from an effective heat insulator would create turbulence without absorbing too much thermal energy.
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Unread postAuthor: psycix » Tue Mar 18, 2008 5:16 pm

I googled somewhat here and there but most of the triangle strip hits refer to something with graphical computer rendering.

Has anyone some link or pic to show what a triangle strip actually is and how it works?
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Unread postAuthor: D_Hall » Tue Mar 18, 2008 7:49 pm

Let's see if I can hit everybody's questions...

* I don't think he was aware of the fans commonly used. I mentioned them, but I've not heard a response from him on that topic (remember, 'tis a net aquaintance of mine).

* He flat out stated that the use of baffles/grids could work, but it could also hurt; that one would have to be extremely careful if one chose to go that route.

* I've not had any luck with google either.
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Unread postAuthor: jimmy101 » Wed Mar 19, 2008 2:14 pm

Here is the link to what DR (aka BewareOfDog) did
http://www.spudfiles.com/spudtech_archi ... =17&t=9011
It's a 5 page thread. Unfortunately the images appear to be missing?

The post that got him started was by man_o_brass based on a post by plasticex
http://www.spudfiles.com/spudtech_archi ... =17&t=8879

There is a bit more info on flame front accelration caused by obstacles at the Gexcon site (http://www.gexcon.com/index.php?src=han ... Bchap5.htm).
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Unread postAuthor: Fnord » Wed Mar 19, 2008 2:52 pm

I was thinking of something more like this. I don't see how DR's design would have helped a whole lot.

This would be made from abs by the way. I don't think I would trust anything brittle such as pvc, since this is essentially pushing the flame front towards DDT conditions. I doubt propane/air would create a transition in a small scale such as this, but who knows?
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Unread postAuthor: psycix » Wed Mar 19, 2008 5:51 pm

@_Fnord

That might work BUT
In the "runup pipe" the flame front is slow and slowly increases pressure over the whole chamber.
When the chamber finally ignites (quickly) the pressure raises not at much as normal due to the volume in the runup pipe.

The "runup pipe" should be small diameter since this will reduce the volume of it.
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