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 62 users online :: 4 registered, 0 hidden and 58 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

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

The Team
Administrators
Global Moderators
global_moderators.png CS

Slow Motion Combustion Video

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

Slow Motion Combustion Video

Unread postAuthor: ToasT » Thu Jun 23, 2016 6:02 am

Came across this on youtube.



Several things here, that if not of general interest, could be useful when designing combustion cannons.
Like the wall cooling effect.
  • 0

User avatar
ToasT
Corporal
Corporal
 
Posts: 63
Joined: Mon Mar 04, 2013 2:23 am
Reputation: 0

Re: Slow Motion Combustion Video

Unread postAuthor: wyz2285 » Fri Jun 24, 2016 6:27 pm

The guy has a freaking good slow-mo camera.
Nice demo of ignition position versus efficiency, too bad his mix isn't consistent.
  • 0

CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
User avatar
wyz2285
Major General
Major General
 
Posts: 2244
Joined: Sat Mar 06, 2010 7:50 am
Location: Porto, Portugal
Country: Portugal (pt)
Reputation: 12

Re: Slow Motion Combustion Video

Unread postAuthor: jimmy101 » Sun Jun 26, 2016 2:37 pm

Great example of why putting the sparker in the cleanout is a bad idea. Almost takes his hand off with the recoil.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3128
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Re: Slow Motion Combustion Video

Unread postAuthor: starman » Sat Jul 02, 2016 6:29 pm

Nice to see this stuff with the high frames per second camera. We've operated for years knowing that multiple spark gaps will allow a more complete and faster chamber burn. Also it was interesting to see the forces and "back waves" of pressure in the chamber even before the potato left the muzzle.

Also, One thing a burst disk does is allow a pressure build up and also more complete burn before the projectile begins down the barrel. I would LOVE to see the high fps with a burst disk installed.
  • 0

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

Re: Slow Motion Combustion Video

Unread postAuthor: wyz2285 » Mon Jul 04, 2016 6:38 pm


I did the same with a burst disc combustion, but my camera is not nearly as good as his.
  • 0

CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
User avatar
wyz2285
Major General
Major General
 
Posts: 2244
Joined: Sat Mar 06, 2010 7:50 am
Location: Porto, Portugal
Country: Portugal (pt)
Reputation: 12

Re: Slow Motion Combustion Video

Unread postAuthor: matti » Tue Jul 05, 2016 4:21 am

wyz2285 wrote:I did the same with a burst disc combustion, but my camera is not nearly as good as his.


nice work :D How many fps? what camera do you have, Casio?
  • 0

User avatar
matti
2nd Lieutenant
2nd Lieutenant
 
Posts: 232
Joined: Tue Oct 04, 2005 1:01 pm
Reputation: 9

Re: Slow Motion Combustion Video

Unread postAuthor: wyz2285 » Tue Jul 05, 2016 1:39 pm

Bought the Nikon J1, felt like a better bang for the buck. A wonderful camera to have around really.
The video was recording on 1200 FPS I think, the J1 can record 400 FPS or 1200 FPS so I'm not entirely sure, it has been a few years.
  • 0

CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
User avatar
wyz2285
Major General
Major General
 
Posts: 2244
Joined: Sat Mar 06, 2010 7:50 am
Location: Porto, Portugal
Country: Portugal (pt)
Reputation: 12

Re: Slow Motion Combustion Video

Sponsored

Sponsor
 


Re: Slow Motion Combustion Video

Unread postAuthor: matti » Thu Jul 07, 2016 1:19 am

wyz2285 wrote:Bought the Nikon J1, felt like a better bang for the buck. A wonderful camera to have around really.
The video was recording on 1200 FPS I think, the J1 can record 400 FPS or 1200 FPS so I'm not entirely sure, it has been a few years.


Ah ok, I have Casio (1000fps) : http://www.exilim.eu/euro/exilimzrserie/exzr1000/
  • 0

User avatar
matti
2nd Lieutenant
2nd Lieutenant
 
Posts: 232
Joined: Tue Oct 04, 2005 1:01 pm
Reputation: 9

Re: Slow Motion Combustion Video

Unread postAuthor: Futterama » Wed Jul 13, 2016 4:03 am

So basically, it's not the best idea to put the spark gap in the middle of the chamber because this can or will starve the combustion from oxygen? Or did he just have a rich mix in the chamber?
  • 0


Futterama
Corporal
Corporal
 
Posts: 62
Joined: Sun Oct 11, 2015 1:19 pm
Country: Denmark (dk)
Reputation: 3

Re: Slow Motion Combustion Video

Unread postAuthor: mrfoo » Wed Jul 13, 2016 7:53 am

I think he just had a rich mix, what you're seeing is the same effect you get in the Reynst combustor / jam jar pulse jet, and you'll see the same reignition of residual fuel thing with the ignitor at the end, although that may blow more of the unburned mixture out the end of the barrel.

If anything, I would suspect having the ignitor in the middle would give better perfomance overall, including better combustion, as the pressure rise will be approximately twice as fast with 2 flame / shock fronts.

It's a neat video, but for someone who's pushing "SCIENCE", they did it all in a remarkably slapdash way. No metering, no pressure monitoring, no frame count of ignition to projectile leaving the barrel, not even a goddamned chrony. Cool flame video content - 10. Science content - 0.
  • 0

User avatar
mrfoo
Specialist
Specialist
 
Posts: 47
Joined: Wed Apr 29, 2015 11:05 am
Country: Afghanistan (af)
Reputation: 5

Re: Slow Motion Combustion Video

Unread postAuthor: jimmy101 » Thu Jul 14, 2016 10:17 am

He probably had either a rich mix or a poorly mixed mix. It is a "spray-n-pray" fueling method.

In my crappy videos of a clear chamber I noted that you get odd little licks of orange flame that appear to be associated with either dust or imperfections (like scratches) on the chamber wall. http://www.inpharmix.com/jps/Propane_co ... ycarb.html

You can extract some rough timings from the video. I get ignition at 5:02, projectile (rag) starts to move at 5:15 and projectile exits barrel at 5:34. You can't actually see the muzzle so I estimated exit time as the point when the gases in the chamber made a really big jump in velocity. If the frame rate is 20,000/sec, and the video frame rate hasn't been further fudged in the video and is standard 30frame/sec, then from ignition to start of projectile movement is (5:15-5:02)/20,000*30=19.5mSec. Transit time is (5:34-5:15)/20,000*30=28.5mSec. Total time from click-to-bang 48mSec, which is consistent with other measurements and the models. It looks like the barrel is a good 5 feet long so a rough estimate of the muzzle velocity is twice the average velocity; 2*5'/28.5mSec=351 FPS, which is reasonable (though seems a touch high to me).

It is cool to see that while the projectile is moving through the barrel the front flame front is moving forward faster than the rear flame front is moving backwards. That is what the combustion models we did years ago predicted.

I agree, coolness factor and video camera=10/10, actual thought put into doing the correct experiment=2/10. Kind of like Mythbusters.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3128
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Re: Slow Motion Combustion Video

Unread postAuthor: ToasT » Thu Jul 28, 2016 4:04 am

My take away from this is you ideally want to minimise the surface area to volume, ie as spherical as possible, and ignite the mix from the centre ish. This gives you the greatest flame front area, which i take to mean the greatest rate of combustion and therefore pressure.
I say ish, because maybe it is best to have it very slightly forward biased to reduce the amount of fuel combusting in the barrel. (keeping a large flame front)

This all means the wall thickness needs to be greater to support the greater stresses due to the slightly higher pressure acting on a much larger surface.
  • 0

User avatar
ToasT
Corporal
Corporal
 
Posts: 63
Joined: Mon Mar 04, 2013 2:23 am
Reputation: 0

Re: Slow Motion Combustion Video

Unread postAuthor: jimmy101 » Thu Jul 28, 2016 12:44 pm

Or, just use multiple sparks. You can decrease the total burn time by a lot with three of four ignition points. With a multiple ignition points the cylindrical chamber basically acts like a sphere.

An actual spherical chamber probably really wouldn't change the performance all that much. Indeed it might even decrease performance because the gas flow pathway wouldn't be as good as in a cylinder.

As always, the most important thing is to (1) properly fuel and (2) mix the gases.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3128
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Re: Slow Motion Combustion Video

Unread postAuthor: ToasT » Mon Aug 01, 2016 4:50 am

Yea i forgot to mention that the effects here are maybe the last few things to optimise to get the best performance. These are still things that you might want to consider even after you have picked the low, and big fruits, of additional spark gaps.

Id still be interested in seeing a simulation of spherical vs cylindrical chamber, 1 spark vs 1 spark.
  • 0

User avatar
ToasT
Corporal
Corporal
 
Posts: 63
Joined: Mon Mar 04, 2013 2:23 am
Reputation: 0

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

cron
Reputation System ©'