Frosty

Naturally Aspirated Ribbon Burner. Photo heavy.

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The pic looks like some of the ones on the sites describing different flames approaching "Quench Distance" velocity. IIRC with the gas jet aimed down.  Now THERE'S a coincidence. eh?

I wonder how to get colors. 

Frosty The Lucky. 

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Okay crew, I need a little debugging help!

my forge currently runs really well at 10 psi (or so I think it is doing well).  However, when I lower the psi to 5 or 6 it runs fine for a while but then blows out the flames.  When I relight the forge it runs for a bit before blowing out again.  When I add an object of of decent volume it blows out almost immediately (this could be related to the time factor, but when I relight the forge it blew out immediately and wouldn’t light until I removed the object).  

From what I have learned, the blowout indicates that I am low on outlet volume and may need another hole.  Before looking into that option, however, I wanted to tweak the burner at the jet.  I’m guessing that the blowout occurs because the fuel air mix moves to heavily to toward the air side of the equation.  That would seem to indicate that my mig tip needs to protrude a little more into the mixing tube.  Would this be a correct first step to try?

 

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The first thing I would try is to partially cover your air intakes while turning down the pressure to see if the problem continues.  If, as you suspect, the problem is too much air compared to the fuel then this could help you sort that out. 

I'm a little perplexed because your blow out symptoms happen at lower pressure rather than higher.  If you didn't have enough outlet holes I'd expect it to blow the flames out more at higher pressure rather than lower.

Too many holes would typically result in backfiring at moderate pressure once the forge is up to temperature.

Do you have much flexibility on aiming the burner head at slightly different angles to see if that makes any difference?   Does this issue happen in open air too or just in the forge?

BTW, unless I missed something all we saw in the video was a forge with a happily purring NARB in action.  Do you have video where the problem you mentioned can be seen?

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My guess would be burn back into the plenum and then it self extinguishes. Not enough air/ velocity..   But I am no expert on gas forges.. 

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Thanks for the ideas.  I fully intend on trying to get a video of the blowout.  Burning back into the plenum sounds like a possible explanation and would make sense out of the fact that it works fine once the pressure is up.  The video was at 9-10 psi.

I will try to see if it doesn’t blow out when the intakes are partially covered.  If it makes it worse then Jennifer must be correct and I should file the mig tip shorter.  This would fit into Frosty’s tuning guidelines.

I already tried putting the burner in different positions and, within the somewhat limited range of motion, seem to have had little change.

Either way, covering the intake is an easy test and modifying mig tips is nearly as simple to do.  Both are not permanent changes I will try first.

Thanks again!

Lou

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If it is burning back into the plenum around 5 to 6 psi that would suggest you have too many outlet holes.  You can test for that by plugging one or more holes with some spare kaowool (just temporarily) and see if you can turn the pressure down lower before the problem recurs.  If that turns out to be the case then mix up a little castable refractory and make the plug(s) permanent.

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Don't choke the intakes, It's burning a little rich now. Maybe take another 1/64" off the jet? The only other thing I see is the flame is aimed almost directly against the far side so there's more back pressure than necessary or might be good. Maybe angle it so it's more tangential to the wall on the right in the video?

These are home built devices, if yours won't burn at lower psi then run it where it works. I think I've told everybody what happens every time I try running mine too low. I also run my forge much more open so there's little back pressure.

Bear in mind I haven't seen it blow out, back burn, etc. my thoughts will maybe/probably change if I do.

Frosty The Lucky.

 

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Okay, here is a video of my issue.  I did file ever so little off the mig tip.  I heated up the forge and it ran for nearly ten minutes at 7 psi but then it had a blowout.  I set up the camera and started it up at about five psi.  It ran about a m8 Ute but no blowout.  I raised it up to 7-8 psi and it ran about minute with no issue.  I then gradually lowered the pressure and it finally blew at about 5-6 psi.  I think it has more to do with the burner getting hot enough until it burns back into the plenum.  My propane tank is quite low atm, I’m not certain if that can be a factor.

 

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There is smoke puffing out from behind the plenum just as it backfires first couple times.  Is it sealed completely?  If not, where is that smoke coming from?  Is the burner made as specified by Frosty's design...i.e. with 19 crayon sized holes (5/16")?  

Dan R

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A low propane tank can mess with how burners run so maybe. How about not changing the psi up and down. Just set it at 5psi and put a timer on it. Take notes.

You heated up the forge and (or then?) ran it at 7 psi for 10 minutes and it blew out.  It ran fine at 5psi for 8 minutes? Then you turned it up for a while then back down and it blew out.  

The reason it's so hard to figure out what the problem is is you keep changing things mid test. When trouble shooting change ONE thing at a time, test, take notes. With a forge you need to let it cool down before running the next test. If not you'll never know if it's an overheated burner block or the psi, or . . . some mystery thing you can't determine without eliminating the other variables.

The video doesn't show a forge at forging temperature but I do see flame hitting the pocket on the far side. I don't think that's a cause though it may be a trigger. Do NOT start changing the burner orientation, eliminate the other factors. 

Cause and trigger are two different things. For example; the Cause of the wreck was a low front tire. The person's been driving on it for a week without problem though, then one day he swerves to miss a dog. The hard turn rolls the low tire off the bead and Triggers a loss of control. SMASH! 

Make sense? 

You have a problem and nothing obvious leaps out at me. You need to be methodical trouble shooting it. Pick a psi at one end of what you've been playing with, 5 or 8, light it and leave it run till it blows out, write it down. Let it cool completely, the burner block is the thickest heaviest solid piece of HOT in the forge, give it time to cool. Set 1 psi different, light it leave it run till it blows out. write psi and time down. etc. etc. 

My multi outlet burners will run at crazy low pressure but not for long though it burns back for a few seconds before blowing out. They run fine at 3 psi for a couple hours, then burn back and blow out. 5psi and they run all day. Once it burns back it doesn't matter how high I turn it the block is too hot and it burns back.

Dan just posted. I saw the puffs of smoke(?) but was following another thought and didn't think about the smoke. I just looked more closely. Hmmmmm. The obvious thought (residual moisture in the blanket) isn't it or I doubt it anyway, it's too persistent for steam. If there were a leak allowing fuel air to escape into the blanket I don't think we'd see smoke but I suppose it could trigger the blow out. 

Frosty The Lucky.

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I’ll eliminate all but one variable and run tests.  I get it completely, Frosty.  I have a mind for science!  Dan, the smoke/steam is (I believe) from the moldable refractory I used to build out the pocket for the burner.  It could be a cause of a problem, but I don’t believe so.  I’ll consider it a constant in my tests for now and follow Frosty’s advice by timing at different psi settings.

To be honest, I’m glad to be working through this problem.  If it went smoothly I wouldn’t have learned nearly as much and, by virtue of my posting here, others wouldn’t benefit.  I’m looking forward to the feedback from my next steps.  

Edited to add:  Frosty, as an aside, I changed the pressure because I was trying to induce the desired blowout just to get footage of it for your viewing pleasure.  I’m not even certain if my particular blowout issue is a common “type” of blowout.  Still, your advice to eliminate variables is well taken.

You have my sincere thanks,

Lou

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Steam or smoke from the moldable makes sense. I figured you were just getting carried away, it happens to us all. 

I know what you mean by things going too well. Just think how jumpy it made me feel to be so successful with the NARB so soon out of the gate! :o 

You're more than welcome, it's our pleasure. 

Keep us in the loop please.

Frosty The Lucky.

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2 hours ago, Frosty said:

I do see flame hitting the pocket on the far side. I don't think that's a cause though it may be a trigger. Do NOT start changing the burner orientation, eliminate the other factors. 

I agree with Frosty, but he knows better.  I don't think it's burner orientation either.  Looks to me more like the block overheating and allowing it to backfire.  Similar to what mine does at 3-4 lbs after about an hour.  

I would like to know the hole size, and if there is any flare on the ends (or something similar like the edges of some of the holes broken off).  This might allow the flame to burn inside the  nozzle holes, thus heating up the block or a section of it.

As for smoke, it was just odd to see it puffing out just at blowout.  I'd just look to see where it is coming from.  If it's between the nozzle block and the pocket, no problem, it's probably as you thought.  It's coming out the back side, so I can't see.  

Follow Frosty's advice.  He's got good experimental procedure under his belt.  You probably know this, but for others reading this: observe, take data, make a hypothesis as to the problem, change one variable at a time to test it.  And since we are all lazy...change the easiest variable first unless something really jumps out at you.

Dan R

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Sections of the block do get red hot relatively soon into a burn.  I’ll try to get footage of that as I’m doing some of the testing today.  I’m thinking about running it at 5,7, and then 10 psi and timing it for blowout.  Depending on how that goes I’ll think about blocking one of the ports on the burner block and running the same tests again.

 

 

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If getting hot is making it blow back then you need to establish a flow rate to keep it cool enough.

I just had to resign myself to the limits of the NARBs. I HAVE been kicking around ideas for making more heat resistant versions but nothing within reason is coming to mind. Heck, believe it or not I was thinking of ways to preheat the flow but that was before reality explained things.

Frosty The Lucky.

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I've been having trouble with backfiring, which I suspect was from unintentionally enlarging the ribbon holes while attempting to remove the crayons. Before firing up the forge today, I plugged a couple of the holes with kaowool, and that seemed to help a lot.  

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If it backfires without being HOT the mix velocity is too low, (below it's rate of propagation) blocking outlets will speed it up as you've observed. The hotter the block gets the higher the rate of propagation so ultimately you may need to block more outlets. 

Frosty The Lucky.

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1 hour ago, Frosty said:

If it backfires without being HOT the mix velocity is too low

Given the success of my 1/8" hole burner (no blackburn at any pressure over shutting off or at any heat, and which, by the way has stopped singing when I turn it on for some reason), I'm wondering if the size of crayon holes are just too large.  They work, yes.  But is the size ideal?  Everybody has followed Wayne's original design which did work, was groundbreaking, and uses crayons which are easy to get - but no one has questioned it since.  People have just assumed it is ideal and copied it.  From what I've read, it seems that either naturally aspirated or with fan, ribbon burners generally backfire at pressures under 3 lbs or so when they get up to heat.  Perhaps the basic assumptions about how the ribbon burner is made should be questioned.  When I look at industrial burners, or burners at for Glass like Jappa Glasworks, the holes are much smaller, often a honeycomb or pinholes.

As I have discussed earlier in this thread, I have a successful NARB that runs a burner with 124 holes @.125".  I have now run it for more than one multi-hour sessions and done fluxless forge welding in it.  Another thought, I just pulled out a box of Chanukah candles that measure at .325" diameter at the base and taper to .25 at the wick.  If you cut them off at 2" they start at about .290" at the base.  A tapering hole (decreasing in size from plenum to nozzle head) would increase the flow at the nozzle head pushing the flame away and limiting backfiring.  

Just my 2 cents.

Dan R

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This seriously worth the experimentation.  I only had the time to run one test today and, at 5 psi, it backfired at 4:20.  I’ve decided to not bother with testing at higher pressures and, instead, to block off ports incrementally to see if I can increase that time.  Currently the blue flames appear to start inside the ports.  I’m going to see if I can’t increase the airflow until they stand just proud of the holes.  I’m thinking this will be a good place to start.

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45 minutes ago, Lou L said:

block off ports incrementally to see if I can increase that time

Lou, how many holes did you make in the burner? 19?

 

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Yup, I followed the plan as closely as possible.   I have 19 holes made with crayons.  I’m thinking that the severity of my problem may be related to the forge design itself as well.  Where I cast the back wall of the forge it bumps out into the chamber just enough to create a shelf that overlaps the edge of the burner.  It may created a little hot pocket of air that increases back pressure.  By blocking off the jet that is closest to that side, I’m hoping to reduce the effect.  I’ll find out today.

I hope that makes sense.

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I experimented a couple weeks ago with smaller holes.  I used a soft fire brick and drilled holes in it using a piece of 3/32" welding rod which I ground to a chisel point.  As Dan has already indicated, the turn down capability of the smaller holes is fantastic even after the forge is hot.  I doubt soft IFB is a good long term choice for a burner block, but it was sufficient for testing purposes.  I still need to do some more experimentation to find the right number of holes for my setup, but the concept appears to be sound. 

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854299926_Image2019-04-08at10_52PM.jpg.7908359fd1803b6ce013193f3f430b81.jpg1194388628_Image2019-04-08at10_53PM.jpg.b5318b55dd62c9426c2b80cf59c5689d.jpg

Heres a couple screenshots from a book I stumbled across. I've only had time to give one section a quick look but I think some of you guys would find something useful from this book. I think some real fine tuning could be done with the holes sizing and location in all homemade ribbon burners, NARB and blown. I've been lurking for a while, can't wait to make a NARB and hopefully get a frankenburner attached to it one day. I don't have any welding equipment so I am mulling over no weld solutions (haven't thought of a good one yet) or get a cheap arc welding machine, might get some use out of it for future projects too.  

 https://books.google.ca/books?id=SAjLBQAAQBAJ&pg=PA450&lpg=PA450&dq=ribbon+burners&source=bl&ots=Xzg9dR9RQ_&sig=ACfU3U3-l01c3SLLKJHBkVx453ACa2wX4g&hl=en&sa=X&ved=2ahUKEwifqrTL77_hAhWEvZ4KHZjzAO4Q6AEwR3oECGEQAQ#v=onepage&q&f=true

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Vincent, thanks for that research help.  I believe it supports an explanation for everything we have been working out in this thread.  You have a good no weld option that someone on here has already used.  Search online for a “T-type threaded conduit body 3/4”.  That’s what I’m thinking of using for my next burner.  

 

Back to my testing.  All, strange results!  I blocked off one jet on the burner and more than doubled my run time of 4:20 at 5 psi to 9:35 at 5 psi before blowout.  I then blocked a second hole and ran it again.  This time it blew out at 7:20 at 5 psi.   When it cools I’m going to try it with three holes blocked just to look for a pattern.  After that I guess I will run the same series at 7.5 psi.  So far I see no logic.

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On 4/8/2019 at 7:06 AM, Lou L said:

I’m thinking that the severity of my problem may be related to the forge design itself as well.

If the burner is built to Frosty's plans, and runs smoothly outside the forge, process of elimination suggests the forge itself or a forge/burner interaction.  Though the forge looks normal sized, what are the dimensions of the inside of the forge?  How many cubic inches?   I believe that the 4x4 pine ridge burner is recommended for a forge no less then .75 cu ft. (that's about 1200 cubic inches).  A 4x4 burner equates in size to a 2x8" burner, but it depends on number of holes, and the pine ridge is a forced air.  Given that, my forced air ribbon forge is a 2x8, with around 20 holes and has 340 cu inches volume inside (about 6 diameter x 12" long) and it seems to run fine, backfiring at low pressures like 3-4 lbs only after around an hour of run time.  I don't know what size Frosty's forges are.  

Could be a back pressure issue since ribbon burners are supposed to have problems with back pressure.  Or you may have just created a "perfect storm" situation, where a number of variables come together to cause the problem.

Dan R

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