Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 34 users online :: 4 registered, 0 hidden and 30 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

massive chamber and small barrel diameter

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
Sponsored 
  • Author
    Message

massive chamber and small barrel diameter

Unread postAuthor: jackssmirkingrevenge » Mon Nov 10, 2008 5:27 am

What would happen if you had a large (several litres) chamber that only had a small vent to exhaust out of? I'm thinking (if the word really applies) combustion burst fire BBMG here :D

Would the hot gasses have time to cool and lose pressure?
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Skywalker » Mon Nov 10, 2008 9:37 am

Yeah, it would work, but I doubt you'd get the same power equivalent out as you would if you shot a single large projectile. I haven't done the math, but you do loose heat energy from the combustion gasses the longer they stay in the chamber. I think it's "worth a shot" though, not very complicated!
  • 0

User avatar
Skywalker
Sergeant Major
Sergeant Major
 
Posts: 177
Joined: Sun Aug 05, 2007 7:22 pm
Reputation: 0

Re: massive chamber and small barrel diameter

Unread postAuthor: starman » Mon Nov 10, 2008 10:34 am

jackssmirkingrevenge wrote:What would happen if you had a large (several litres) chamber that only had a small vent to exhaust out of? I'm thinking (if the word really applies) combustion burst fire BBMG here :D

Would the hot gasses have time to cool and lose pressure?


Why would you want such a lopsidedly large chamber size for a BB sized barrel?
  • 0

User avatar
starman
Donating Moderator
Donating Moderator
 
Posts: 3041
Joined: Wed Dec 12, 2007 12:45 am
Location: Simpsonville, SC
Reputation: 0

Unread postAuthor: Ragnarok » Mon Nov 10, 2008 10:49 am

I have severe doubts this would work. The combustion gases lose their temperature very fast - they have little mass compared to the walls, grammes compared to kilos.

Think in terms of a completely closed chamber. The combustion pressure fast dwindles to nothing, you're not left with a chamber full of any more than mildly warm gases after that first instant.

You might get quarter second bursts, but I wouldn't hold out for any more than that.
After about half a second, the temperature of the gases will have dropped back so far that you won't be able to do anything with them.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: jimmy101 » Mon Nov 10, 2008 12:04 pm

Like Ragnarok said, the heat loss is too fast. For a typical size closed chamber the pressure will drop by 50% in 0.1 to 0.2 seconds. By one second after igntion the chamber pressure is basically back to atmospheric.
(From here.)
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3129
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Unread postAuthor: psycix » Mon Nov 10, 2008 2:14 pm

But it will surely spit out a few BB's before the pressure drops to zero.
  • 0

Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

Spudfiles steam group, join!
User avatar
psycix
Donating Member
Donating Member
 
Posts: 3684
Joined: Mon Jun 25, 2007 7:12 am
Location: The Netherlands
Reputation: 0

Unread postAuthor: FishBoy » Mon Nov 10, 2008 3:49 pm

I think it should work, the question is how long of a burst would it give.
I think if you set it up with a vortex block or cap it should work decently, you would just obviously have to refuel it after each burst. For fast refueling I would use pre-metered propane "cartridges" similar to what someone did when they made the triple thunder advanced combustion guns.
  • 0

"You polish a turd, it's still a turd"

Remember DYI!!!
User avatar
FishBoy
Colonel
Colonel
 
Posts: 575
Joined: Tue May 27, 2008 5:51 am
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: jimmy101 » Mon Nov 10, 2008 5:22 pm

psycix wrote:But it will surely spit out a few BB's before the pressure drops to zero.

"A few" being the important phase. Lets see, at 50 RPS (typical BBMG). Figure you have decent pressure for 100mS followed by another couple hundred mS as the pressure drops down. That'll give 5 rounds at high pressure. Small ID of the barrel is going to suck heat out of the gas flow like crazy, so figure you might get another 10 or so BBs before the pressures gone.

Be interesting to see if it is worth it. Off hand I would think just putting 50 BBs in a sabot and firing'm like a shotgun shell would be easier.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3129
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Unread postAuthor: jackssmirkingrevenge » Mon Nov 10, 2008 5:41 pm

jimmy101 wrote:Be interesting to see if it is worth it. Off hand I would think just putting 50 BBs in a sabot and firing'm like a shotgun shell would be easier.


That's basically the conclusion I reached ;)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Ragnarok » Mon Nov 10, 2008 6:02 pm

jimmy101 wrote:Off hand I would think just putting 50 BBs in a sabot and firing'm like a shotgun shell would be easier.

I've been longing to do this for quite some time. I was thinking something like skeet/clay pigeon shooting with two launchers, one with BBs, one with water balloons...
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], Yahoo [Bot]

Reputation System ©'