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Venturi forge with excess blue flame


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Hello all, new here and looking for some help, a friend and I built a dual burner Venturi propane forge.  We are having a problem no matter how low of psi we are getting a ton of excess blue flame. 

here’s some specs

approximately 680cuin

inside is lined with 2” of mat with rigidizer and refractory 

dual devil forge burners

20lb propane tank with regulator(kept in warm water)

each end has about a 8”x4” opening with firebrick as doors

in the two pics the regulator is at 5psi and 10psi, with the chokes open about 3/16” 

All advice appreciated 

 

 

 

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I'm a forced air burner owner... but looking at both those pics- it looks as if the chokes are relatively closed off. They regulate the air flow into the burner. Tried opening them all the way up?

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1 hour ago, Welshj said:

I'm a forced air burner owner... but looking at both those pics- it looks as if the chokes are relatively closed off. They regulate the air flow into the burner. Tried opening them all the way up?

So even when I open them there’s lot much change. Maybe even a little more flame

 

20 minutes ago, Mikey98118 said:

Not to mention that all secondary air is also closed off; it looks like someone worked overtime to create a problem.

if your referring to the firebrick doors, there’s not much difference with them off, they really help stop the flame from going straight up

i I’ll get a pic with both these changes and have it up soon

Here’s chokes fully open and no doors

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No; I'm referring the the fiber insulation crammed between the burner's mixing tubes and the burner openings in the forge shell. If those were perfectly constructed Mikey burners, that would be okay. Most burners NEED some secondary air, which the flame will induce, unless the opening has been blocked off.

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2 minutes ago, Mikey98118 said:

No; I'm referring the the fiber insulation crammed between the burner's mixing tubes and the burner openings in the forge shell. If those were perfectly constructed Mikey burners, that would be okay. Most burners NEED some secondary air, which the flame will induce, unless the opening has been blocked off.

With those open heat would come up the sides of the burners

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1 minute ago, Adamsnj112 said:

With those open heat would come up the sides of the burners

Than you have other problems with the burners; you need to address them, first; that will probably take a while, and you will need more input from others who have those same burners, and have gone through the same problem.

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21 minutes ago, Mikey98118 said:

Than you have other problems with the burners; you need to address them, first; that will probably take a while, and you will need more input from others who have those same burners, and have gone through the same problem.

I don’t think heat escaping and coming up the sides is a burner issue, heat rises and the heat is going to escape through any opening 

there’s also a problem sometimes where the back burner (left in pics) will flutter

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Yup; that's your problem alrighty! So, what to do? First attempt at a fix would be to replace those A-W-F-U-L flame retention nozzles. You can search through the Burners 101 thread  to find out how to build a slide-over Mikey style nozzle; If your burner is the right size, you can order a flame retention nozzle from Larry Zoeller Forge. Or, you can use one burner to heat up the nozzle from the other one, and pound out a four times longer increase in the nozzle,  to reshape that trumpet end design.

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I don't pretend to know every minute detail about some other burner design's flame; only the only the obvious, which are:

(1) The primary flame envelope isn't blue, nor even blue-green; it is green, showing it to be heavily reducing.

(2) Even though a lot of its color is wiped out by sunlight, the distortions caused by the secondary flames in the photo show it to be about one-foot long; again indicating a heavily reducing flame.

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7 hours ago, Adamsnj112 said:

With those open heat would come up the sides of the burners

It doesn't with my single burner forge while it is running. Some burners are designed to run with secondary air. A reducing flame needs more air or less fuel. How about a picture of the inside of the forge.

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5 minutes ago, Irondragon ForgeClay Works said:

It doesn't with my single burner forge while it is running. Some burners are designed to run with secondary air. A reducing flame needs more air or less fuel. How about a picture of the inside of the forge.

I will try this out tomorrow and post some more pics

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So with the insulation removed around the burner and the burners about an inch into the mat, the nozzle got red hot in seconds 

also here’s some more pics of the forge setup

the burner tubes are about 1.3” and the bell is 2” at the end of the flare, the burner holes are 2”

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13 hours ago, Adamsnj112 said:

Mikey I’m a little confused now, wouldn’t a reducing flame be more controlled from the choke (limiting air) than from the nozzle?

how does the nozzle control how much oxygen is being combusted?

Naturally aspirated burners all use the gas jet to induce air into the burner. BUT, the flame retention nozzle's increased area, creates a venturi effect, which also induces air into the burner. We aren't done yet. The flame also  induces secondary air into the forge." There's a whole lotta inducin' goin' on" :)

The choke does act to limit air. A great set of brakes, does not a hot-rod make. You wants a big bad induction under the hood, yes? Smoke them tires, baby. I say, I say, smoke them tires!

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1.3" mixing tubes? You're measuring the OD aren't you? ID matters, OD is meaningless except for mounting hardware, maybe. 

The nozzle flare is worse than none at all. The taper is too short to do any good, however it IS abrupt enough to cause bad turbulence and interfere with induction. Those flares are making it burn worse. 

Two burners may also be too much for your forge., especially if they're aimed straight down on the forge floor as it appears in the pics. This WILL cause back pressure which also interferes with induction. 

Mike's more knowledgeable regarding linear burners than I so I'll try to stay out of this thread unless called on.

Frosty The Lucky.

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Frosty, 1”ID sorry

see pic below I reshaped the one cone to be more cone like. I did a quick test burn at 10psi 

1st pic is reshaped cone second is stock bell

 

as for the top down vs a side burner I was thinking that, I may get some bungs and try welding them in would 45 deg or horizontal be better?

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You have two different examples of not good enough. Don't be discouraged by this, but try to lengthen the cone even more. Try not to expand the diameter of the flare's edge will doing so. Before reshaping the other nozzle, cut the trumpet shape down by about three-quarters, and then lengthen what's left.

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Is this just bad forge design with the burners on top? Like I said earlier when I ran it without insulation around the burner the nozzles got red hot in under a minute, the flame almost comes out hits the bottom ceramic plate and shoots either right back or out the doors

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I knew I should've kept my fingers out but oh no, not me. <sigh> Enjoy your Valerian Mike, I'll see what I can do.

Adam: No, it's not necessarily a bad forge design, it has a few issues is all. Unfortunately issues are cumulative so several little ones are more effect than a biggy. We'll get back to the forge later, I prefer to solve problems one thing at a time and get used to the idea, blacksmithing is failure analysis. Few things actually go like we expect so we're always tweaking.

Extend or expand your sketch of the 1:12 taper until you can match the narrow end of your nozzle flare to it, THEN compare the larger end. Lining one side of your flare to one side doesn't reflect the ratio properly. 

The real flare is from the BEGINNIG of the flare to the open end. Counting squares says your nozzle is 2 1/2" long but the flare is barely 3/4" long. I can't guesstimate diameters from this angle. for the sake of discussion let's say the narrow end is 1.25" and the wide end is 2" the ratio looks to be 1 : 0.5 It's doubled in size in a little under half it's diameter, not 12x it's diameter.  Remember, it's the length of the FLARE that counts, not the entire nozzle. 

Your better flare is so abrupt it's causing turbulence of the ungood kind. You can see it's not working properly in the pic. The flame is expanding to the limit of the nozzle but it's misshapen and bushy. The color says it's very reducing. I hope you aren't testing these indoors it's generating Carbon Monoxide (CO) in dangerous levels for a wide open garage. Stand upwind outdoors. 

The nozzle with the trumpet bell isn't working at all, the flame has separated completely, it's so badly made it might as well not be there at all. It might be too crappy to make things worse even.

Next time, widen the nozzles from one end to the other but not so much. The flare can be less than 1 : 12 and work a treat, it's a greater rate that kills performance. I just use a thread protector on my burners, no flare at all they just step up a diameter that falls within the ratio. Check out Mike's step nozzles, they work beautifully and are much easier to make.

Stop worrying about PSI. it doesn't really mean anything. Once you have the burner tuned properly you can adjust the heat output by adjusting psi at the regulator. All that gauge is good for is repeating a particular temp range without having to eyeball it. What it's doing for you right now is confusing you and distracting you from the problem.  Do yourself a favor and cover the gage with a paper bag or tape. Your ears will tell you more instantly than a gage can in an eternity. Honest. 

Let's get back to the forge later, I'm wondering it I've talked myself in enough circles for a while right now. If I contradict myself I'm blaming the tree. I'm a TBI survivor, I tried to catch a falling birch tree with my head, a practice I highly discommend.

Frosty The Lucky.

 

 

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