self venting combustion

[singularity]

i had this idea a while ago but i didn't post it becuase it seemed like it would because i thought it would be to complicated to be worth it but i have some extra time so here we go...

<img src="http://i78.photobucket.com/albums/j85/i ... ustion.jpg">

its a pretty basic concept build a combustion with in a coaxial and use the barre as a combustion camber. now the coaxial would be constructed like a normal pneumatic piston or diaphragm gun, and it would store air just like one to... accept there would be no pilot valve. the force of the combustion gases would force the piston back ward both giving the projectile a little extra speed and completely venting the camber. of course for this to work you would need a consistent combustion (metered propane) and would need to get the air pressure just right. im sure i forgot something so feel free to ask any questions...

[Jumpin Jehosaphat]

You would transfer kinetic energy for moving the piston that could have been used to propel the projectile. Interesting idea though, it seems like it would work, but it would sacrifice some power I think.

[sandman]

everything happens so fast that i doubt that this would help. But i am very intrigued by the thought

[singularity]

do you think the use of a burst disc would help?

[Jumpin Jehosaphat]

I'm not sure... It seems like you would have to do some ridiculously accurate calculations for this to work without significant power loss. I also think the vent chamber would block off where you probably want your propane meter to go.

[singularity]

that is easy to fix, just move the ammo up and have the propane meter more towards the front of the gun... im thinking metered hydrogen would work better for this...

[Spedy]

Heh, makes me think of a 2-stage hybrid. first combustion, then air pressure.
Very nice idea, I want to see this ina cannon some time.

[psycix]

This is a very interesting design wich makes me think of other things.

What about having 2 chambers.
Chamber A is connected to the barrel. (barrel may be bolt-action reloading)
Chamber B is larger and holds a fuel mix under some pressure. It is connected to A with a valve between.

-A is filled up -> fires projectile
-open valve for a short time -> Mixture flows from B to A
-Bolt action reload
-Fire again!
With a large clip for projectiles and a large tank B you would be able to do some repeated fire for a long time.

[TechnoMancer]

but the mixture in B is more unstable than fuel on its own and air on its own and so you run the risk of tank B blowing up!!!

[psycix]

Tank B can be risky yes, but ive seen other topics with a bulk tank for quick loading.
A solution might be to put a huge (but weak) burst disk on tank B, if it blows, it will just send alot of hot air someway.
But a fuel mix will never ignite without any reason. Theres no ignitor in it and just make sure sparks are impossible.

Isnt that a good idea?

[dongfang]

Hi

How about a fast, big and light check valve in a chamber that is too small by the usual C:B rules: The projectile, and the inertia of the gases in the barrel will suck the valve open and draw fresh air into the chamber ....

Regards
Soren

[psycix]

That will decrese performance ALOT
And sometimes it may be so much the projectile will be stopped in the barrel or even sucked back in the chamber then.

[iknowmy3tables]

hey is the air part pressurized then that would be really cool

[boilingleadbath]

psycix, depending on the amount of turbulence in the inlet stream, such a system may only require a B:C ratio of (1.25+1):1.
That's basically a .45:1 C:B ratio... which, even without the vent in the back, only decreases muzzle energy ~20%.

With a vent in the back, the 'negative' pressure will not be as great, and so the decrease in muzzle energy will be much less pronounced.

Of course:
1) The prior statements are for a best-case scenario.
2) This has been discussed before
3) It does not belong in this thread

[psycix]

psycix, depending on the amount of turbulence in the inlet stream, such a system may only require a B:C ratio of (1.25+1):1.
That's basically a .45:1 C:B ratio... which, even without the vent in the back, only decreases muzzle energy ~20%.

With a vent in the back, the 'negative' pressure will not be as great, and so the decrease in muzzle energy will be much less pronounced.

Of course:
1) The prior statements are for a best-case scenario.
2) This has been discussed before
3) It does not belong in this thread

Oh yeah I fergot that the negative pressure would be removed a bit because of the venting in the back. Without that I would vacuum a bit.