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Naturally Aspirated Ribbon Burner. Photo heavy.


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1 hour ago, Frosty said:

Hey gang: It's been a while since I mentioned progress and or results with the NARB. The last time I ran it at a meeting I had the reg set at about 2-3 psi. I was happy to see two 3/4" T inducers making good heat but a 40lb. propane tank not even sweating so it was drawing very little for the output. That was a pleasant result.

After about 3 hours though the left burner started backfiring, burning back into the plenum and then out the T. I couldn't get it to correct and had to shut that burner down. Within maybe 15 minutes the other burner started backfiring and I shut it down. 

What appears to have happened is the burner block got hot enough to speed the rate of propagation of the fuel/air above the speed of the mix exiting the outlets so the fire burned up the outlets into the plenum.  

Either I can try shielding the burner block from the forge heat or try increasing the fuel air flow and maybe keep it cooler.

It's too cold to do much messing around in the shop till later in the year. I'll let you know what I find out.

Frosty The Lucky.

 

Frosty I know very little about gas forges.. I do know a lot about engine porting and polishing and flow dynamics..   So I'm just spit balling here.. 

 

If you were to increase the venturi pipe (pipe going into the forge) would you get more velocity? Or increase the length of lead into the T?   A T on a intake system for a NA car would be a no, no since you would have converging airflow which would stiffle and create eddy currents as each side smacked into each other before changing direction into the main tube.. 

 

Like I said.. Just spit balling as to gas forges.. 

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Have you looked at the illustrated T burner plans? The easiest way to increase the velocity of fuel/air through the NARB is to turn up the psi. As is this pair was amazingly stable at the full stop to stop range of my 0-20psi regulator. I am disgustedly pleased with how well they burn, back firing is only an issue after they've gotten hot. I'm thinking I'll just have to turn up the pressure and keep them cooler with increased air fuel flow.

Another thought was to increase the insulation value between the main body of the burner block and the forge chamber but I'd like to take an easier route.

The issue I spent the most time solving when cobbling the NARB together was getting the flame velocity as low as possible without having it burn back. I made something like 9 models from 2" x 4" with different numbers and patterns of holes drilled through them to experiment with the optimum number of outlets.

Fewer outlets increases the air fuel velocity but increases the back pressure on the T inducer and the whole unit loses stability and it will only run at higher psi. If I need to run at higher psi anyway I might as well run a stable number of outlets and make as many stable HOT little flames in the forge as possible.

Keep thinking though, that's why I started the thread in the first place.

Frosty The Lucky.

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1 hour ago, Frosty said:

Have you looked at the illustrated T burner plans? The easiest way to increase the velocity of fuel/air through the NARB is to turn up the psi. As is this pair was amazingly stable at the full stop to stop range of my 0-20psi regulator. I am disgustedly pleased with how well they burn, back firing is only an issue after they've gotten hot. I'm thinking I'll just have to turn up the pressure and keep them cooler with increased air fuel flow.

Another thought was to increase the insulation value between the main body of the burner block and the forge chamber but I'd like to take an easier route.

The issue I spent the most time solving when cobbling the NARB together was getting the flame velocity as low as possible without having it burn back. I made something like 9 models from 2" x 4" with different numbers and patterns of holes drilled through them to experiment with the optimum number of outlets.

Fewer outlets increases the air fuel velocity but increases the back pressure on the T inducer and the whole unit loses stability and it will only run at higher psi. If I need to run at higher psi anyway I might as well run a stable number of outlets and make as many stable HOT little flames in the forge as possible.

Keep thinking though, that's why I started the thread in the first place.

Frosty The Lucky.

Yes I have looked at the plans and have seen the ratios...    

 

      So to just clarify..    A longer tube overall while maintaining the same pressure of LP/NG/Propane would increase velocity but also cooling of the burner orifices.. 

 

From what I can remember you tried different hole counts (smaller number/size) which as you stated increases velocity through the holes but increase back pressure..  This is consistent with what I wrote..   

Increasing the hole count would decrease pressure inside the block as there is an increase in flow because of more holes..   More holes would mean an increase in pipe length to create the same volume at a higher speed of air flow..   Or you can go up a size in pipe diameter but you would now have a slower air flow but more volume.. 

 

It's the balancing effect you have been looking for.. ????????????????    This balance when the burners are getting hot is what you are after..    If there is an increase in air flow this would help to cool the burners better  just like an A/O torch so to speak but would also increase velocity at the burners (faster air flow).

So, with this being said.. Why would you want a slower flame velocity??????  I understand flame front and heat kernel  but if the forge maintains the same volume (area/floor space, etc, etc) so to speak wouldn't you want the flame kernel to be nearly in the same spot to heat the metal????  

 

Instability is because there isn't enough velocity to keep the air from stalling in the tube and the gases are in a reversion process inside the tubes..  If you increase gas pressure this makes the tube induce (venturi effect) more air as it pulls it downward with the fuel increasing both air speed and volume.. 

lengthening the Tube would give the same effect as turning up gas pressure but without the increase in gas pressure... This would just increase the velocity of the air..   

Sorry, just trying to wrap my head around the total package you are trying to achieve.. 

 

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I guess you have read the Illustrated plans, I'm blaming the tree!

The basic ratio for linear or ejector type induction devices holds pretty consistently at tube length = 8 x it's narrowest ID. There's wiggle room but more than 9x and friction starts to reduce efficiency, much less and propane doesn't mix well with the air so you get a weird atmosphere in the chamber.  

The reason I was looking for the lowest practical flame velocity is to keep the fire in the forge as long as possible before it exhausts. As Mike keeps pointing out dragon's breath is heat and fuel wasted. I couldn't intelligently argue with the logic so I started designing to maximize it.

If I forget who you are again, throw a big stinky cyber-sock at me will you?

Frosty The Lucky.

 

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Frosty thanks for bring this subject up again as I am ready to make one of these NARB forges.  I have been slowly gathering parts and pieces for some time.   I am ordering refractory from Wayne tomorrow.    In my case, being a hobbyist blacksmith I doubt I will ever run mine for 3 hours straight on any day, so I don't see the overheating problem as a major issue right now.   When I get finished  with it in a month or so I will post pictures.

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16 hours ago, jlpservicesinc said:

LOL.. Thanks for taking the time to get back to me..  Certainly helps with my education in this realm..     I believe the answer will come as one of those.. Ah ha moments and then it will be all clear.. 

Looking forwards to the results.. 

:)

Ah heck if I didn't get back now and then nobody'd talk to me. It was a good question, logical and would be true were we discussing a different kind of device. NA inducers have their own rules and I was gifted a bunch of paperwork by a coffee shop buddy years before the internet went public. 

Stockmaker: 3 hrs isn't that long to be running a forge even as a hobbyist but there's no good reason to keep the psi turned down so low, I got carried away. There's a focus a lot of the guys making burners have on low psi performance, Ron Reil makes a big deal of how low he can run his. My burners usually don't like less than 9psi +/- so I got excited by a type that was so stable at such low pressures. Lower than my regulator will deliver in fact. 

Just because a piece of equipment works at an extreme doesn't mean that's where you should run it, how often have you pegged your speedometer going grocery shopping?

Please feel free to give me a shout if you have questions during the build.

Frosty The Lucky.

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  • 2 weeks later...

Seeing this thread gives me a strong feeling. Today I'm tired and not good with words, so it's quite hard to explain, but being here at the time of such innovation feels like being part of something big. Maybe this wont change the world, maybe this isnt the first NARB in existence, and probably isn't completely tuned yet, but I can certainly imagine in some years looking back at this moment when new people make their own and ask for assistance.

It is as if seeing progress itself being made, which is quite rare in this particular ancient craft. I mean, this is seeing a new possibility open up, and here we start seeing one of the first examples of a NARB, which is pretty much a new concept for forges.

I can't really explain it. Maybe tomorrow I'll have the right words. It's just that being present through the whole process, from "Ribbon burners are blown ->What if...? ->Experiments ->Results!! NARB!!" makes one feel part of it, and awed at the same time.

 

PS: NARB sounds a lot like "Narf!" from the two little cartoon mice Pinky and the brain.

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Thanks Andres, I wish I deserved a "1st. do to it" award but naturally aspirated "multi orifice" burners have been around a long LONG time, any gas range is filled with them. I only adapted the idea to make it a reasonably easy home build. 

Well, in truth I am kind of proud of being able to follow the process from concept through experiments to success. Being able to stay on task that long is rare for me since the TBI accident, I get distracted very easily. I have to admit I was beyond happy to discover these things are as stable as they are and was frankly silly excited so I shared the whole thing with the IFI gang.

Thanks again Andres.

Frosty The Lucky.

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On February 18, 2017 at 4:16 PM, Frosty said:

naturally aspirated "multi orifice" burners have been around a long LONG time, any gas range is filled with them.

Frosty, a question on that front: I've been assuming that gas stoves and grills must not be inducing any/all/most of their combustion air (my stove doesnt look like it induces any...) mostly because of their low pressure operation. I was guessing they would just combust with the free air at the flame point.

Is that right? 

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If you look carefully at the entire burner assembly for your stove, I think you will find that there is a section at the back of the burner where air is induced into the mixing chamber to join with the gas prior to the burner face ("flame point").  These often have adjustable chokes to allow you to properly balance burner operation for stove configuration and burner size.

See "air shutter" in the image below:

how-to-repair-an-oven-5.jpg

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Cool, by time I checked you guys had answered the question for me. :) 

Natural gas operates at pretty low pressure, especially compared to what we run in a forge. Regardless, without air mixed with the fuel your range flames would be yellow and feathery like an untrimmed candle.

As far as I know all gas burning appliances can be converted between Methane and Propane which have much different air fuel ratios so the appliance has to be adjustable. Change jet and adjust the choke does it.

Frosty The Lucky.

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Thanks everyone.

So, if a Natural gas stove and grill can run NA, inducing enough air for combustion, then what stops a NG forge burner from doing the same?

The only guess I have left is that there would be a max orifice size (and thus max burner output) that can work at NG residential pressure...?

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natural gas residential pressures are measured in inches of water column; 14.7 pounds, a not unknown pressure for some forges for welding, is 32 FEET of water column.  If you have high pressures that is energy that can be used to power the mixing of gas and air and to push it down the tube.

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10 hours ago, ThomasPowers said:

natural gas residential pressures are measured in inches of water column; 14.7 pounds, a not unknown pressure for some forges for welding, is 32 FEET of water column.  If you have high pressures that is energy that can be used to power the mixing of gas and air and to push it down the tube.

...yet my stove and my BBQ apparently are managing to push enough gas and air down their burner assemblies - so it's obviously possible to some extent.

I've resisted bringing my furnace into the discussion, since it has a dedicated draft inducer, but older lower efficient furnaces did not - using nothing more than the residential NG gas pressure they were more than capable of producing a small forge worth of heat.

I speculate it's about size - even a small furnace has multiple large burners.

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Yes it is all about size, specifically BTU output per crossection area of burner outlet.  If you look at the older furnaces you reference you will see relatively large banks of burners.  I expect if you were to line the entire interior of a smaller forge with castable multiport burners you could get away with using residential pressure natural gas and NA burners.  Of course that might provide a problem for insulating the chamber... 

By all means build one and try it out.  Would love to hear back on your results.

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  • 5 months later...
9 minutes ago, Donniev said:

Frosty what ended up working out for you to prevent the burner block getting hot? Did just turning up the pressure work as you'd surmised earlier?

It did indeed, 6psi ran for 7hrs. flawlessly. It was also REALLY stable in some pretty hard breezes. One sputter when a stiff breeze blew straight in the door. 

Frosty The Lucky.

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Me too- I'm going to make one soon, right now I'm just reading everything and trying to grasp what's happening. I'm not someone who just wants to follow step a,b, and c for a forge build and call it a day, I want to understand what's going on and why, but at the moment I feel like I'm trying to fit 10 gallons of information into a 5 gallon bucket

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