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chamber size, the point of diminishing return

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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chamber size, the point of diminishing return

Unread postAuthor: uncomplientspud » Wed Jun 04, 2008 3:17 pm

Hey there guys!

Alright i have a question for you tater gurus. At waht point does the chamber size get too big, and yeild less than impressive results? I currently have a 182 ci or 2980 cc chamber. I was thinking of increasing to 4 l, however if i don't get any real performance gains, i will just stick with what i got.
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Unread postAuthor: SpudFarm » Wed Jun 04, 2008 3:33 pm

what is your barrel? when you hit a ration of about 3:1 it wont go much up
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Unread postAuthor: uncomplientspud » Wed Jun 04, 2008 3:42 pm

Oh, sorry, i don't think i made myself clear. This would be assuming that the C:B ratio is the same. My question really is, is bigger better? Will a cannon with a .8:1 ratio and a chamber of 3 L be outperformed by a gun with a .8:1 ratio and a chamber or 5 L
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Unread postAuthor: SpudFarm » Wed Jun 04, 2008 3:47 pm

of course. then you have a small gun and a "huge" gun.

put it this way. what will be most powerful of a gun that is 1foot and a gun that is 900foot with the same ratio?
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Unread postAuthor: Spuddin » Wed Jun 04, 2008 3:48 pm

i had this same problem, my C:B ratio was about .7:1 with a 4" chamber an 3" barrel. poor perfomance. so i got a idea of using a baffle to increase the chamber pressure "combustion". i had no idea if this would work until i tried it and it made a huge diff. i took a piece of plywood and cut it out at 4 inches to fit inside the chamber. i cut a 2 inch hole in the middle of the wood to simulate a 2" barrel instead of a 3". forced the board down the chamber against the barrel and kaboom. i dunno if this helps your problem.
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Unread postAuthor: SpudFarm » Wed Jun 04, 2008 3:52 pm

i think i bail myself out of this.
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Unread postAuthor: uncomplientspud » Wed Jun 04, 2008 3:58 pm

lol, i think i this is just unclear in general. Spud farm, thanks for confirming what i was thinking. Spuddin......i am have no idea at all what you are talking :shock: . but whatever it is you are doing, just make sure its sade pal
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Unread postAuthor: BigGrib » Wed Jun 04, 2008 4:21 pm

Dude here is a quick and easy answer to your question


Will a cannon with a .8:1 ratio and a chamber of 3 L be outperformed by a gun with a .8:1 ratio and a chamber or 5 L


Yes
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 04, 2008 5:05 pm

Download GGDT, you'll be able to get a rough percentage idea of what the gain in performance will be.
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Unread postAuthor: jimmy101 » Thu Jun 05, 2008 1:32 pm

Or, better yet, download HGDT, you'll be able to get a rough percentage idea of what the gain in performance will be.

Even though HGDT is still a beta, and is is really designed for hybrids, the current version looks like it works pretty well for generic combustions.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 05, 2008 2:28 pm

Whoops, didn't realise this was in the combustion section :oops: this forced leave from spudfiles is making me lose it :?
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Unread postAuthor: Boom_erang » Thu Jun 05, 2008 2:52 pm

Spuddin wrote:i had this same problem, my C:B ratio was about .7:1 with a 4" chamber an 3" barrel. poor perfomance. so i got a idea of using a baffle to increase the chamber pressure "combustion". i had no idea if this would work until i tried it and it made a huge diff. i took a piece of plywood and cut it out at 4 inches to fit inside the chamber. i cut a 2 inch hole in the middle of the wood to simulate a 2" barrel instead of a 3". forced the board down the chamber against the barrel and kaboom. i dunno if this helps your problem.


That's very interesting. I think it points to the fact that the chamber must be fairly "sealed" for there to be an adequate pressure buildup during combustion. And it makes sense. I would say that this is one reason why the softball cannon in another thread works as well as it does. In other words, a large-ish chamber with a small-diameter barrel (but long) would in some ways out-perform something that the chamber-to-barrel diameter was similar, despite the volume of the chamber.

I do think a short, squat cylindrical chamber with the same volume will out-perform a long, skinny chamber of the same volume, as well.
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Unread postAuthor: xpitxbullx » Thu Jun 05, 2008 4:37 pm

I'm only guessing but I think with multiple spark gaps properly placed, you can make it extremely large.

For example, place one spark gap per every 100 cubic inches.

I'm sure it could reach an unsafe point. Smaller chambers can take more pressure.

Jeff
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Unread postAuthor: FLONE » Fri Jun 06, 2008 4:46 pm

[quote

I do think a short, squat cylindrical chamber with the same volume will out-perform a long, skinny chamber of the same volume, as well.[/quote]

Is that a practical thing to do? A 4" chamber would be tiny and a 6" chamber would take 2 and 1/2 men to lift it.
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Unread postAuthor: Boom_erang » Fri Jun 06, 2008 5:30 pm

FLONE wrote:

I do think a short, squat cylindrical chamber with the same volume will out-perform a long, skinny chamber of the same volume, as well.


Is that a practical thing to do? A 4" chamber would be tiny and a 6" chamber would take 2 and 1/2 men to lift it.


I'm not sure what you mean?

If you had to choose between say a 3" chamber that is 18" long vs. a 4" chamber that is 10" long (this comes out to about the same volume) then the shorter, 4" chamber would outperform the longer 3" chamber. Both of those are practical to build.

-B
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