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Naturally Aspirated Ribbon Burner. Photo heavy.


Frosty

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1 hour ago, Another FrankenBurner said:

My other thought was to 3D print a mold for the block which could add tapers or steps at the outlet to act as nozzles on each port

I’ve got some printed out, I’m going to try it on my next burner. The base of each mold is crayon thickness with a 1:12 taper. It’ll take a few weeks before it’s made, but I’ll let you guys know the results. 

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On 2/3/2019 at 5:01 PM, 671jungle said:

I have pulled it out to almost the very end (furthest away from mixing tube). The flame leans out but is not stable.

I think refining my intake will help induce more air, they are knife edged but could be smoother.

I didn't mean to come across so harshly I have cranky days. I'll try to be more patient. 

Stop trying to understand the hows and whys, for now settle for something that works well. Once you have that tinkering is a good thing. You don't want to spend as long as I did trying to figure these things out on your own. I messed with it for a couple years before Cruz gave me that box of info. 

I don't have a good mental picture of your burner and we really  need to have our terms straight. When I say, "Forward" or "Back" the reference is the direction of flow, the burner nozzle is all the way forward while the jet fittings are all the way back in the burner. Make sense? 

There are rules of thumb for the components of NA burners and they are based on the throat diameter, the "Throat" is the narrowest section of the burner fuel air mix flows through. It's typically in front of the last intake port and is the beginning of the mixing tube.

The ratio of mixing tube length is 8x Dia. So a 3/4" burner tube is 6" long, a 1/2" burner tube is 4" long, a 3/8" burner tube is 3" long. These are ideal and there is a little slack a BIT longer is preferred but not a lot. 1/2" long on a 3/4" burner is pretty much max that works well. 

Kiln washes in pottery kilns serve an entirely different purpose to a forge, not counting a protective layer against hot flux. In ottery kilns it prevents pottery and glazes from firing to the kiln and furniture. High temp release agent is also the main purpose of ITC-100, in BIG furnaces, industry buys it by the RR car load. 

Ball parking the formula below looks a LOT more complicated than a member here living in the Nederlands (I think) has mixed up and tested. He got excellent results with IIRC a couple % Bentone a clay in the Bentonite family. Vee Gum literature talks in the range of .3% - .4% making zircopax plastic enough to work like clay.

My experiment put 1 rounded tbsp bentonite in 2 cups zircopax and I spread it directly in a yellow hot forge. It not only fired without breaking it foamed a little. I thought of trying this outrageous experiment because the mud they plug the tap on a cupola melter is bentonite about tooth paste consistency, it dries and fires in direct contact with molten iron and slag without leaking. Sooooo I figured what the hey and gave it a shot.

Anyway, I don't see anything in the recipe that'd make it worse but I don't know if it makes it any better for what we need.

Frosty The Lucky.

 

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I should have specified, I have no idea about that recipe and was not suggesting it.  I was just sharing it.  The Potter's Center said they have used it as a kiln wash and it flakes similar to ITC.  They said it is cheaper for reapplication and it is tougher then ITC.  They mentioned using it in a throat arch as it could take a beating.  

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On 2/3/2019 at 1:08 PM, Another FrankenBurner said:

My other thought was to 3D print a mold for the block which could add tapers or steps at the outlet to act as nozzles on each port.

The issue I am thinking about is about burn back in ribbon burners at low pressures.  

I was looking at my burner mold tapers I had 3D printed, and I'm constructing a NARB and it occurred to me that maybe they are opposite of what they should be.  The burner works with straight tapers inside the forge, and inside the forge there is no problem with the flames blowing off the burner (i.e. igniting after leaving the nozzle hole), but at low pressures ribbon burners backfire.  The idea of putting a flare on the end of the burner nozzle is to reduce the speed of the gas leaving the nozzle and thus keep the flame from blowing off - which is not a problem inside a forge.  If at low pressures the propagation of the flame is faster then the speed of the gas, combined with the nozzle block getting too hot because the flame is too close, wouldn't it be better to make a constricting taper at the nozzle end to increase the speed of the exiting gas, both cooling the end of the nozzle more and keeping the flame further away from the block?  Is there any example of this in industrial burners that anyone has come across?

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My thinking on the tapers, I'm not sure if they are accurate.   Balance the size and count of the ports so that the Fuel/Air Mix(FAM) velocity is beyond the propagation velocity right at the outlet.  When the propagation velocity increases due to a heated block, the flame will move back to a tighter area of the taper where the FAM velocity is faster and matches the propagation velocity.  A downside to this is that the flames would be deeper into the block to heat it more/faster. I am not sure if it could be balanced to prevent blow back or if it would just make the problem worse.   

 

 

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I didn't think you were recommending it as a replacement for ITC 100. I was just making an educated guess about it based on what little I know about what kiln washes are used for in pottery kilns. 

Actually the prime functin of a flared nozzle on a home made burner is to increase induction, reducing flame velocity is good being a flame holder is a happy extra. A low velocity flame is a good thing as it stays in the forge longer to shed more energy.

Hmmmm, AFB put a narrow spot just inside the outlets to act like a rocket nozzle? Not to be confused with the engine bell, engine nozzles are there to produce max exhaust pressure for thrust. The bell is to reduce exhaust velocity for reasons I don't understand, I just read about them. Anyway, as burner outlets the "bell" analog could be normal crayon dia. and back say 1/4" is a nozzle that accelerates the FAM which then is reduced in the bell section.

Interesting idea, I like it! How to form crayons. Hmmmm.

Frosty The Lucky.

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8 hours ago, Frosty said:

Actually the prime functin of a flared nozzle on a home made burner is to increase induction, reducing flame velocity is good being a flame holder is a happy extra.

Increasing induction was part of my mental picture of tapered ports in a NARB.  Less back pressure and more throughput, allowing lower pressures to move more air for cooling and cleaner burning while giving us the flame holding characteristics.  Tapers slow the stream as they increase in area/volume.  If looked at backwards, the further upstream you go, the higher the velocity of the FAM.  This may provide a natural brake to flame propagation backwards.   

I am basing all this thought on my experiments with tube burners.  When using a tapered nozzle, as the fuel pressure is decreased, the flame rolls back into the nozzle further wherever the propagation velocity and the FAM velocity match.  It gives the burner a larger range of operation.

As long as the velocity at narrow end of the taper is higher then the propagation velocity, the flame will not flash back into the plenum.  

The major downside and possible idea killer is the fact that as the flames move back into the block, they heat the block more/faster.  In tube burners, I have run higher end orange nozzles without flash back but with more ports giving more surface area to heat the flow, it may make the problem worse.

One possible solution to this could be to use straight ports and have the tapers only make up a portion of the length.  Another thing to balance.

 

I had previously mentioned a shoulder or stepped nozzles right at the outlets of straight ports.  Is this what you mean by a bell section?  I didn't clearly follow.  I think this would be more resistant than tapers as are stepped nozzles on tube burners vs tapered.  They require higher input velocities and the amount of step and overhang are more critical then a tapered nozzle.  The upside I can envision is that the flame would not roll back into the burner block beyond the steps unless it flashes to the plenum.  

Another possible solution.  If the ports are closer together, the block has less mass and less hot face with the same amount of cooling.  It isn't as convenient for spreading the heat to a wider area.  This may be why the Giberson burner heads have ports which are so concentrated.  It also makes it easier to balance flow distribution among the ports.  

Having more ports which are smaller provides a similar solution.  Less mass, more through flow.  

 

If we are getting crazy, striving for perfection, we could think about making the ports on the outside of the header different diameters then the inside ports to balance the flow across them.  Thinking about the logistics of using shaped ports of differing diameters to get the header flow balanced while getting the entire throughput balanced with the induction device, makes my head hurt.  

This is the greatness of 3D printing, if we actually figured this out, we could easily print a mold which matches all this.  I envision lots of experiments on the horizon.  Maybe in plaster or hydrocal.  Something cheaper then kast o lite.

Inducing enough air at lower velocities and still having enough energy to mix it all and spread it evenly across a plenum is quite a chore.  

As far as I am concerned, the Frosty NARB is "good enough."  Wide range and it makes metal hot.  Thinking and tinkering are just part of the fun. 

 

 

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AFB: I was getting lost trying to tell if you were referring to a single or multiple outlet burner too. Perhaps for discussion we should decide on specific terms for clarity? 

I didn't mess with tapering the outlets as I could control velocity perfectly well without making construction more complicated.

The first lesson I learned was factors like: ratios, mixing tube length, intake ratio, etc. do not carry over to multiple outlet burners very well if at all. Heck forge volume to mixing tube dia. ratio doesn't carry over either. I scrapped trying to determine where the carry overs were and how to apply them as working too hard for the value. 

Your thought about putting a restriction in the outlets to increase velocity and prevent burn back is very interesting. I just need to figure out how to make the patterns, probably cast the wax in silicone molds. I see a direct parallel to liquid fuel rocket engines. and any time I say "rocket engine" I'm just leavint the rest off till I get to the really cool new generation. (cool metaphorically and literally)

Anyway, a rocket engine has 3 major parts not counting fuel supply. Picture a hourglass. the top section is a sphere, the restricted section is the nozzle and the bottom is the Bell. The fuel burns explosively in the combustion chamber, exiting through the ONLY path, the nozzle, exiting the nozzle produces the bulk of the thrust. However if it's allowed to vent to space directly the thrust producing high speed flames will expand in a sphere so thrust is self cancelling.  The bell directs and slows the explosion and so aims the thrust back up through the center of the engine. 

Basic rocket engine stuff right? What I didn't realize till I as linked to the new breed of rocket engine the Aerospike, that has numerous combustion chambers and nozzles directed to a spike or blade where the high speed flame rides the boundary layer and external air pressure directs the thrust. What I didn't realize was what the main function of the bell was and why modern rockets require multiple stages. Two issues, first the exhaust flame needs to exit the bell at as close to zero velocity to ambient air as possible. Left over velocity is energy that wasn't imparted to the engine. So the faster the rocket is the fster the exhaust velocity relative to the craft.

Last but not least, ambient air pressure makes a huge difference so again you need different engines. The aerospike uses the rocket exhaust itself to shape the flame but that's a different thing well worth reading about if it interests you.

So there's the parallel in my mental experimenting. The plenum is a steady pressure of extremely turbulent FAM. Zero need to think about mixing, it's done. The exits are the outlets and almost to the opening it a reduction and is accelerated. The bell on the far side is simply to provide a decompression / slow zone but still above the rate of propagation. Hopefully.

Anyway, I'm mostly skyballing here and the aparent parallel between a flared burner nozzle and a rocket engine bell struck me as possibly worth playing with.

Logic has been telling me thick burner blocks are a bad idea there is just too much thermal mass for the flow to keep cool. The flame exposure is the same, hard to change that so perhaps decreasing the thermal mass might help. Of course it might just shorten the time till it burns back. 

Frosty The Lucky.

 

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1 hour ago, Frosty said:

probably cast the wax in silicone molds

You can easily cast wax in two piece plaster molds.  Once the plaster is set, just soak it in water until it stops emitting bubbles (i.e. soaks up as much water as it can). If you just cast the plaster, it may not bubble because there is still water in it, but it will dry out and need to soak it before you can pour wax into it.  Used to do it all the time - no need for expensive silicone molds for such a simple shape and it hardens much faster!

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19 hours ago, Another FrankenBurner said:

A downside to this is that the flames would be deeper into the block to heat it more/faster. 

I'm hoping that by increasing the velocity of the exiting gas, this will allow a lower pressure operating range.  What I want is to be able to keep an even 1550F or so in the forge for heat treating...and that requires a pretty low flame even with a very rich mixture.  I could also just make a bigger diameter forge, but then it would just cost a lot to run (which is why I built this one).  

 

1 hour ago, Frosty said:

Logic has been telling me thick burner blocks are a bad idea there is just too much thermal mass for the flow to keep cool.

I agree with your thinking, but not necesarraly your conclusion.  It's the face of the block that is getting hot, I don't think the depth matters much because  I don't think that the flow of gas through the block cools it much at the face in the forge.  It's just not enough surface area or enough btu's sucked up. If it was, we would see that the area around each hole would be cooler, and it does not appear to be.  The answer to me is to increase the velocity of the FAM without changing the volume, and that will push keep the flame from back burning into the block. 

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 I wanted to be sure about what you mentioned.. 

I did a bunch of research back about 10 years ago as I was building intake manifolds based on single or individual runners for turbo charged and fuel injected cars.. 

There is a ratio of inducer to exducer  for maximum burn ratio with the air/fuel not damming..    this ratio will actually speed up the flow out the nozzle.. 

If you look at a liquid fuel mixer for a liquid fueled rocket it will show the shape for the inducer, then as it goes threw the orifice the nozzle shape has a lot to do with how the gas velocity comes out..  

It was really neat  to see and to run the formulas for sound wave timings and such..      You wouldn't need any of this..  Frosty worked out more the figuring but there is a size, shape, orifice size, and nozzle shape that is optimal for a given pressure..   Usually its a fairly rounded inducer with a radius orifice opening up smoothly back to full size.. 

I think something like this could be neat to work with.. 

With this said,, I haven't seen any commercial blocks with this type of arrangement..  Money? Mfg expense?   Don't know.. 

 

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Liquid Fuel Rocket EngineThe task is to design, build, and test a liquid-fueled rocket engine.  A mixture of gaseous oxygen and methanol are injected into a copper combustion chamber at high pressure.  A stainless-steel outer jacket permits cooling water to flow along the outer surface of the chamber and DeLaval nozzle.  Combustion temperatures will exceed 5000° F at pressures around 200-300 psi.  Oxygen and liquid fuel will be injected into the combustion chamber at 300-400 psi and ignited by a disposable electric probe.  A properly tuned engine will exhibit shock diamonds in the exhaust plume.

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23 minutes ago, D.Rotblatt said:

I agree with your thinking, but not necesarraly your conclusion.  It's the face of the block that is getting hot, I don't think the depth matters much because  I don't think that the flow of gas through the block cools it much at the face in the forge.  It's just not enough surface area or enough btu's sucked up. If it was, we would see that the area around each hole would be cooler, and it does not appear to be.  The answer to me is to increase the velocity of the FAM without changing the volume, and that will push keep the flame from back burning into the block. 

It's not really a conclusion, it's more of a hypothesis. I know running my mod 1 or mod 2 burners under 2 psi results in backfire in about 2 hrs. 3psi takes about 4 at 3.5psi they'll run all day. 

Agreed the block is heated by exposure to the forge interior, IR more than flame I think. Mix flowing through the outlets cools the block. Obvious I know. however the block facing the plenum has a strong turbulent flow and is exposed to the steel plenum walls. The rate of heat conducted through the Kast-O-Lite 30 blocks is only slightly less than through IFB. In a thick block the only siignificant cooling is through the outlet tubes. 

So, if instead of 2"+ the thickness can be reduced to 3/4" there will be less insultting thermal mass and the FAM will have more time and exposure in the plenum to cool the lock and shed heat through the plenum shell. 

I agree higher velocity cools better, the higher the primary pressure (propane) to a NA burner the more and faster the FAM through the device.

Like I say, this is where my little mental journeys take me. No experiments nor proofs.  Too cold to be casting refractory and no way does Deb want me playing with mud in her house.

Frosty The Lucky.

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Interesting, I used to run my multiport burner in my glass furnace 24/7 on forced air-natural gas.  Only time I ever got worried was when I shut it off altogether to cool down.   That was a Gibberson head with a commercial mixer and operating at a pretty steady temp of 2100 deg F running and up to 2350 to charge.

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1 hour ago, Frosty said:

Agreed the block is heated by exposure to the forge interior, IR more than flame I think. Mix flowing through the outlets cools the block. Obvious I know. however the block facing the plenum has a strong turbulent flow and is exposed to the steel plenum walls. The rate of heat conducted through the Kast-O-Lite 30 blocks is only slightly less than through IFB. In a thick block the only siignificant cooling is through the outlet tubes. 

So, if instead of 2"+ the thickness can be reduced to 3/4" there will be less insultting thermal mass and the FAM will have more time and exposure in the plenum to cool the lock and shed heat through the plenum shell. 

A hypothetical conclusion?  :)  I guarantee it'll either make it worse or better (or the same).  The only way would be to try it (we have no way to collect data on how the heat absorbs into the block), and that means actually making the burner since we have to run it for a an hour or so before we get blow back.  

I just looked at Joppa Glass (JLPservicesinc reminded me of them - thanks!), they have dimensions and looks like they have about a .5-3/4" thick area where the holes are.  Giberson does mention that this allows the head to stay cooler.  I believe these are made of ceramic. So maybe a thinner face to the block would be the way to go! Might be worth a try!

 

1 hour ago, jlpservicesinc said:

I think something like this could be neat to work with.. 

With this said,, I haven't seen any commercial blocks with this type of arrangement..  Money? Mfg expense?   Don't know.. 

It's an interesting shape for the nozzle.  Wouldn't be hard to mimic and make molds for.  But from your pic I see two ways to look at it.  Either 1) the large chamber is the plenum, and each hole is just a tapered nozzle, or 2) each hole has a larger tube, which constricts in the end to a small tapered nozzle.  It would take some experimentation to get right.

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14 hours ago, Another FrankenBurner said:

f you are asking me, I am talking about the shape of the ports.  Usually ports are just straight cylinder voids left by removing crayons.  I am talking about either a taper, a partial taper, or a step of some kind.  

Go with steps.

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6 hours ago, D.Rotblatt said:

It's an interesting shape for the nozzle.  Wouldn't be hard to mimic and make molds for.  But from your pic I see two ways to look at it.  Either 1) the large chamber is the plenum, and each hole is just a tapered nozzle, or 2) each hole has a larger tube, which constricts in the end to a small tapered nozzle.  It would take some experimentation to get right.

this was the image that was easy to find..     The reason why Liquid fuel , Air flows like a liquid so the characteristics are pretty close with flow dynamics..       This shape of the chamber, orifice and nozzle could be changed so there is no boost...   This example is for boosting the flame stream for lift/push..    

this example uses a water cooled jacket with a copper burn chamber.  

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Sorry for the confusing post.  I promise it sounded legible in my head when I wrote it.   :P  

As to specific terms, I can use whatever anyone likes.  I generally try to adapt to the terms being used in the discussion.  I am mostly just going to lurk until I have built a couple so I am not just another guy talking without knowledge. 

It's a fun topic.  

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On 2/5/2019 at 7:23 PM, D.Rotblatt said:

A hypothetical conclusion?

Yes, almost exclusively hypothetical; I'm almost Holmeslian in my use the hypoductive method. 

The thread is rapidly leaving me behind and I don't have a way to experiment. I found myself making comments and jokes rather than making contributions. I think the idea of putting a restriction in the outlet tubes near the flame face has merit and well worth experiments. 

Come next spring I'm probably going to experiment with a heat shield flame face on the burner block and a much thinner  block. That's not final of course the discussions is going strong enough I'm probably going to see ideas I like better. 

Fun thread indeed. Thanks guys.

Frosty The Lucky.

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On 2/5/2019 at 7:00 PM, Latticino said:

nteresting, I used to run my multiport burner in my glass furnace 24/7 on forced air-natural gas.  Only time I ever got worried was when I shut it off altogether to cool down.   That was a Gibberson head with a commercial mixer and operating at a pretty steady temp of 2100 deg F running and up to 2350 to charge.

I suspect that a Gibberson multiport burner head head has more internal area for the fuel/air mixture to  cool, since it is also the plenum chamber, and less refractory area for the equipment to heat; yes, no, maybe?

The barbeque tiles (I got a box of them) have smaller holes than guys are making by employing crayons; this should permit higher flow speeds for the same BTU output, with much less cubic area for heat gain; a better direction?

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44 minutes ago, Mikey98118 said:

The barbeque tiles (I got a box of them) have smaller holes than guys are making by employing crayons; this should permit higher flow speeds for the same BTU output, with much less cubic area for heat gain; a better direction?

I also bought a box of them tiles. I cut one row of holes off and put it in a bag balm tin and sealed it off with kitty litter and slapped a 1/2" ejector to it just to test. It ran very well, I think. I don't  know much though.

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1 hour ago, 671jungle said:

I also bought a box of them tiles. I cut one row of holes off and put it in a bag balm tin and sealed it off with kitty litter and slapped a 1/2" ejector to it just to test. It ran very well, I think. I don't  know much though.

It was your post that set on to them; thank you. I'm a big fan of shortcuts through purchased parts. I had already planned to build a muli-hole burner this summer, but similar to a Gibberson burner head. It would have been made in two parts; the plenum chamber section, and a face plate with multiple flame holes, then mortared together with refractory cement. These plates have changed my plans a lot :)

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2 hours ago, Mikey98118 said:

I suspect that a Gibberson multiport burner head head has more internal area for the fuel/air mixture to  cool, since it is also the plenum chamber, and less refractory area for the equipment to heat; yes, no, maybe?

That's what I think too, maybe, yes, no?

2 hours ago, 671jungle said:

I also bought a box of them tiles. I cut one row of holes off and put it in a bag balm tin and sealed it off with kitty litter and slapped a 1/2" ejector to it just to test. It ran very well, I think. I don't  know much though.

Yes, pictures please!  I'm with Mike, if we can buy a burner block instead of having to make one I'll be . . . Happy.:)

Frosty The Lucky.

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