Mycelium

Burner chuffing

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Greetings IFA,

I've posted here once before with my initial attempt at building a pair of Venturi burners (that were rather crude). After several months of diversions and learning new skills (basic machining and TIG welding) I've looped back around to attempt #2 with better results but still not quite functional.

Forge body:

Standard 20lb propane tank lined with 2" of Kaowool coated with a refractory stove paint and a Unicast 3000 bottom.

Burner:

Propane line hooks up to 1/8" brass fittings that are T'D inside the 2" pipe nipple. There is a grub screw that allows me to adjust the position of the gas line. I have a very crude

A 0.023" (I have tried 0.030" and 0.035" but the 23 seems to produce the most stable flame) MIG tip is used as the injection orifice and the tip of it is about 0.4" from the throat of the 2" to 3/4" bell reducer (still had the threads on the inside which I could machine off if necessary).

The burner pipe is 6" long and there is a 3/4 to 1" reducer on the end as a flare. The flare is currently pulled back into the Kaowool liner.

Propane source:

Standard 20lb propane tank with a 0-30psi adjustable regulator and standard flexible line (not ideal I know but once I have the burners working I'll look at hard plumbing).

 

Does it work? Kind of.

It will light and I can get the flame to burn in the flare. I can even heat steel up to forging temp.

However after about twenty to thirty minutes of run time the burner starts to chuff which so far as I can tell is the flame chasing up the burner tube ( carefully peering down the back end of the burner confirms this). 

After reading numerous threads on others experiencing this problem there are several things that can cause this:

1. Regulator freezing up and causing the gas pressure to drop off

- I have tried running the forge with the tank in a bucket of water and still only get about a half hour of run time before things start chuffing.

2. Back pressure from combustion gases cause turbulence and interfering with the propane/O2 mixing.

- Once the chuffing starts I have tried opening the forge up entirely and it seems to help initially but still ends in things chuffing.

3. IR radiation off the opposite wall heating up the flare and the burner pipe causing the propane to ignite in the tube.

- I do have my flare pulled back into the Kaowool though the rim of it is still exposed. I suppose I could get in there with some extra wool and paint to cover up the rim a bit better.

I am not entirely sure how to proceed in troubleshooting. Suggestions are appreciated.

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2 hours ago, Mycelium said:

Standard 20lb propane tank with a 0-30psi adjustable regulator

That is your major problem. There is not enough surface area for the liquid propane to turn into a gas fast enough at high pressures. Putting the tank in water will help with freeze up only.

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2 minutes ago, Irondragon Forge & Clay said:

That is your major problem. There is not enough surface area for the liquid propane to turn into a gas fast enough at high pressures. Putting the tank in water will help with freeze up only.

So I need to be running off a bigger tank or a different reg?

31 minutes ago, timgunn1962 said:

Turning the pressure up often works.

 

I have tried that and it doesn't make any difference that I am capable of detecting.

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3 minutes ago, Irondragon Forge & Clay said:

A bigger tank will help. I started with a 20lb tank and had similar problems. When I switched to my 115 gallon they went away.

Alright, I'll see of I can russle up a bigger tank. My local makerspace has a big tank for the oxy-propane torch.

I've not had a reason to examine it's fittings closely but I might be able to hook up to that for a test run.

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I can run a pair of 3/4" Ts off a 20lb. tank for a couple hours before they start to slush up, that's not your problem.

Who's burner plans did you use or is this something you came up with yourself? 

The things that jump out at me is that long nipple on the intake end. The only practical reason I've ever come up with is to move the jet farther away from the mixing tube. You're eliminated that possible benefit by putting the supply so far down.

On top of that you have a stack of fittings evidently intended to put the jet INSIDE the mixing tube.

It's burning rich in the pics because it can't possibly induce enough intake air, cranking up the psi won't do it the propane stream can't expand enough to make a difference just going faster only means more fuel in the mix.

You might try losing all the fittings below the cross pipe except the bushing with the jet screwed into it. See if that leans it up. The next step I'd try is cutting off as much of that nipple above the cross pipe as I could. 

Remember trouble shooting rule #1. Change ONE thing at a time, test, observe the results, compare to the previous test, take notes and only then make another change. I prefer making several small changes over making one big one.

Try searching out Ron Reil's burner plans I believe they're archived on the ABANA site and follow his plan as close to exactly as you can. Ron and I don't make the same kind of burner but his work well and is a design proven by a good 30+ successful years.

If you want to make a T burner the plans are in the propane burner section of IFI.

Frosty The Lucky.

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I've read through Ron's website a few times actually. As for the running of the gas line through a pipe nipple rather than the bell reducer I've seen in a few places I decided to opt for that as it would be easier to dis/assemble.

Adding the extender fittings actually improved the performance of the burner. With just the bushing that the MIG tip threads into I was lucky if I could get the flame to stay in the flare for five minutes let alone 30 before it started to chuff. The tip isn't quite in the throat of the reducer though. It's maybe half into the body. I haven't tried it with just one of the spacer fittings (there are two). Maybe its a matter of meeting in the middle. TBH, where that fuel injector nozzle needs to be in relation to the burner pipe is what I've been haziest on in the whole build.

Chopping off the back half is definitely another good idea.

I will however test one things at a time and dropping a fitting before I go chopping anything.

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The rule of thumb for jet hold back from the throat is 1/2 the mixing tube diameter. Eg a jet for 3/4" tube should be held back 3/8". This is the departure point and will need adjusting for your build. 

When I build a 3/4" T, the 1" x 3/4" T has about 2x the air intake port size and I run my jet around 1/2" - 9/16" back. My T burners draw a huge amount of combustion air which allows me to run 0.035" contact tips for jets without running high pressure. This results in a LOT more fuel air at a lower velocity. 

There are fundamental differences between a Linear burner like yours and a Jet Ejector like I build. I don't know why they're so much different but they are. The important basics are the same though, a good flame is a good flame and the adjustments are the same in principle. 

Frosty The Lucky.

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