Mikey98118

Burners 101

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I made a real nozzle for my burner; it is stainless with the following dimensions: 1.224" ID; 1.375" length; step transition from 0.930" ID mixing tube that is 12" long. (That's a ~32% diameter expansion, or 73% area expansion; a half angle of 6.1 deg from the step to end of the nozzle ID.)

I tested three configurations for the inducer: vanes, no vanes (plain bellmouth matching the shape of the vanes bellmouth), and fins (circumferential fins on the perimeter of the bellmouth, with a rear cone holding the accelerator):

plain.thumb.jpg.93d3f123403e2b763a521a16a73d7ea8.jpg

vanes.thumb.jpg.238778b4608e7cd9a8647649e2053c4a.jpg

fins.thumb.jpg.e88980451d29ff9e11a50482e520bc14.jpg

I tested each, starting with a 0.030 MIG tip (not the tapered kind). The vanes made the flame more stable but I think that's because the plain (no vanes) inducer was flowing faster. I did not experiment with the nozzle extension at all, but that also could help stabilize the plain inducer. I tried a 0.035 MIG tip on the accelerator as all of the flames seemed to be pretty lean (I could make them change by choking the inducer with my hand), but I'm pretty sure that the 0.035 tip was too big. The finned inducer ran a lot richer than the other two so I didn't spend much time with it. One thing I did notice was that the bellmouth inducers were not very sensitive to axial position of the accelerator nozzle. I do plan to taper the accelerator nozzle just for any bit of efficiency it can give. And i will make a frame that holds the accelerator in position.

I'll put the pictures below and a video at the end; I appreciate any thoughts you may have on what aspects to try next.

5 psi

843574205_plain.0305psi.thumb.jpg.85250326936737633c92405a6a7df290.jpg

1257175322_vanes.0305psi.thumb.jpg.1d63392386ed4f11b6d497800de339f2.jpg

286718132_vanes.0355psi.thumb.jpg.87efaf83164d75e4da78b5b291051917.jpg

1113688637_fins.0305psi.thumb.jpg.b0218d129235ac0ffc89ff7c41089b4e.jpg

10 psi

1587659805_plain.03510psi.thumb.jpg.b9555ec68dddf75f3fce79a295a47be6.jpg

850266170_plain.03010psi.thumb.jpg.4a1d3214ce0e098bbafb188aca430600.jpg

1278789310_vanes.03010psi.jpg.5824d3dfb1a1480cd7f6322c38ea3ef4.jpg

356170018_vanes.03510psi.thumb.jpg.4b578f4071e9c22c5f791c96d73c42d7.jpg

553788925_fins.03010psi.thumb.jpg.5f9b5af88a7ba20e983395a182e2976e.jpg

Thanks,

-jason

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A little more info: This morning the flame was not stable (too lean) with a cold nozzle. I extended the nozzle as far as possible but it didn’t help. A 0.035 tip was stable but rich so I tried a tip cleaner on a 0.030 nozzle and now it is like the 0.035 nozzle. I guess I was too aggressive. I have another 0.030 tip but I can see I will have to get more. I may switch to hypodermic-tubing-based tips to have better control over the gas jet. 

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7C703F25-03AE-43E9-B137-FC2D58F5E933.thumb.jpeg.f6119ed171b5666cff67c3109b9b32b7.jpeg

I made a frame to hold the accelerator. It still blows itself out with a 0.030 tip and runs rich with a .035 tip. 

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Good looking flames.

The last image, it looks like the jet assembly might not be concentric with the mix tube:

960363935_holdercopy.jpg.8111ab01d4a63c4c4c901f6314983e4f.jpg

Could just be an illusion of lighting.  Worth verifying though.  If it is not concentric, it can wreak havoc.  One easy test would be to disconnect the brass tube at the elbow and hold the burner up to the light looking in from the nozzle end.  Look for light through the jet.  The jet is small and long so it is very obvious when things are not right.

As to the flame lift, you need to slow the FAM(Fuel Air Mix).  The FAM is moving forward faster then the flame is backwards.  We want a balance.  A larger jet (like you were thinking) might slow it enough.  A nozzle which has a larger diameter or longer overhang could do it as well.  Your overly long mix tube might also be causing enough laminar flow that it is punching through the center of the nozzle.  Maybe?  

I find the 030 no vane 5 PSI flame shape interesting.  It widens after the nozzle and then to a point.  Football like.  

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2 hours ago, Another FrankenBurner said:

[re concentricity] One easy test would be to disconnect the brass tube at the elbow and hold the burner up to the light looking in from the nozzle end.  Look for light through the jet.  The jet is small and long so it is very obvious when things are not right.

As to the flame lift, you need to slow the FAM(Fuel Air Mix).  The FAM is moving forward faster then the flame is backwards.  We want a balance.  A larger jet (like you were thinking) might slow it enough.  A nozzle which has a larger diameter or longer overhang could do it as well.  Your overly long mix tube might also be causing enough laminar flow that it is punching through the center of the nozzle.  Maybe?  

I find the 030 no vane 5 PSI flame shape interesting.  It widens after the nozzle and then to a point.  Football like.  

Thank you; that's a good idea for aligning the accelerator tube. I got it roughly close but wasn't too careful. I will align this one but when I made the next version I will do something a little more precise and elegant.

I do have more mixing tube coming so i can try some different lengths. I will also try a larger/longer nozzle.

2 hours ago, Another FrankenBurner said:

A larger jet (like you were thinking) might slow it [the FAM] enough. 

Why does a larger jet slow the FAM? I was thinking maybe the issue was not enough fuel, so the lean flame wasn't as robust, but it was a guess based on the richer flame from the larger jet having greater stability. A larger jet seems like it will induce about the same amount of air, but with more propane in the mix. 

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Edit: I see that Mikey's nozzle based on sch 40 pipes would be an area that is 2.8x the area of the mixing tube. Mine is only 1.7x, so that could explain my flame blowing out. I will try a larger nozzle (seems like I want about 1.5" diameter).

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I found that schedule forty pipe worked out perfectly for flame retention nozzles for years (pipe comes in stainless steel too), BUT, once I started playing with vortex burners, larger diameter nozzles became possible. In other words, think larger diameters--not smaller :)

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1 hour ago, jwmelvin said:

Why does a larger jet slow the FAM?

The larger jet does not slow the FAM.  You are correct on that.  I stated that poorly.  I think you are also correct that a larger jet induces similar amounts of air.  The only minor slowing I was talking about is caused by running lower fuel pressures for the larger jet for the same heat.  You have to induce/mix enough air at the lower pressure for the bump in jet size to be a good route.  Jet size should not be used to control FAM velocity, only fuel to air ratio.  I only suggested it as you stated you thought the burner was running lean and it maybe could help with the other problem.   Also, with the metal nozzles, I think more heat going slower heats the nozzle faster.  It might be why your rich flame with the 035 didn't lift.  A hot nozzle holds the flame better.  If you start the burner at a lower pressure for a minute and then turn it up, you will get much better flame hold.  I don't like to have to tinker with settings to get a burner to run so I prefer a larger nozzle which the flame won't lift off, no matter what I do.  It's a balance though, too big and the flame rides back in the nozzle to overheat it.  The nozzle also affects induced air volume.  Bad nozzle balance/design/setting can make a great burner seem like a bad burner.  

 

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Wind breaker, 1-1/4" stainless tubing with 2" of push fit flaring to ~1-1/2", It appears to be burning happy from what I can tell and no more fluttering. I have been thinking about adding thin mesh air filters to test if it promotes a cleaner burn without restricting too much airflow.

Picture #1: Two PSI cold burn.

Picture #2: Ten PSI cold burn.

Picture #3: Full Burner.

Picture #4: Looking down wind breaker.

Thanks Corey.

 

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DSCN0008.JPG

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Can one of you experts explain the phenomenon where there is a low-pressure threshold, below which the flame front transitions from just inside the nozzle exit to right around the mixing-tube exit (and turns rich)? I guess it has to do with nonlinear air induction?

Normal pressure (above ~1-2 psi):

927493312_normalpressureflamefront.thumb.jpg.f0c3c337a0721aa24232d0f8b1605ade.jpg

Very low pressure (below 1 psi):

342789528_lowpressureflamefront.thumb.jpg.02dbc6b4c055930525b7f698c8a8ba5a.jpgm

With the larger nozzle, my burner lights easily when cold and seems pretty stable over 2-20 psi. I did change to a shorter mixing tube, which is steel tube that is 0.87" ID and 8" long (right around 9x ID); I didn't immediately notice a difference from the 0.93" ID, 12" long nozzle but didn't really compare. The nozzle is 1-1/2 sch 40 pipe (304 SS), so is 1.6" ID, and to get a stable flame requires it to extend past the end of the mixing tube about 1.9". Because I was just experimenting, the nozzle doesn't contact the mixing tube until well back of the mixing-tube exit, leaving a dead space around the exit. I'm not sure if how that affects flow.

744588874_nozzleconfiguration.thumb.jpg.27ea78d2f368284ba0234582d010184a.jpg

Any comment on the flame?

785581717_20psi0.030tipvanes.thumb.jpg.13175cc68f04d30800bf9afcecbae9a3.jpg

I made the accelerator connection better by drilling into a plug and soldering it to the brass accelerator tube:

1679063064_acceleratorconnection.thumb.jpg.6bd380c492e8ede08e84c26b2546a00c.jpg

Thanks for any thoughts.

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It is the opposite of the flame lift you were seeing with the smaller nozzle.  Normally the FAM is screaming down the mix tube.  The nozzle is an increase in sectional area which causes the FAM to slow down enough to not lift off.  With a fuel pressure set below the threshold, the FAM velocity slows enough that the flame front can flash back into the bigger nozzle which I think also tanks the induction volume.  It is still fast enough in the mix tube to keep it from flashing all the way back.  

What is your end goal?  If you are after a burner which is hot enough, you have it.  Or are you a fellow tinkerer after knowledge?  

It's a good looking flame, nice job.

 

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5 hours ago, Another FrankenBurner said:

What is your end goal?  If you are after a burner which is hot enough, you have it.  Or are you a fellow tinkerer after knowledge?  

It's a good looking flame, nice job.

I am, as you suggest, looking to understand more about the various design parameters. I am gathering materials for my forge and will begin assembling that soon but I figure I should learn as much as possible along the way. I’ll likely make a forced-air oil burner too, to see what I can learn from that. That will be for a melting furnace. 

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Blue flame oil burners do exist ($1$1$1) but are expensive and high maintenance. Other oil burners are hot, but very bad for air quality in a shop. Guys have been trying to get around these limits since the nineteen forties...

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A fellow on Kodiak Island uses a blue flame oil forge but it's a furnace burner firing into a 55 gl. drum lined with fire brick forge. It takes about 45 minutes to come to temp but he can cycle a large quantity of steel through it fast. I can't say what he forges or if he's still alive, I haven't heard from him in maybe 11 years. 

It's the only home built oil fired forge I now of that works well. It's a pretty industrial scale though and in a wide open shop.

Frosty The Lucky.

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Lots of hobby casters have built oil fired casting furnaces in pursuit of "free" fuel; some of them have been fairly clever, and of course, what you can do for a casting furnace can be done for a forge. However there is a vast gulf between "free" and practical :)

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You don't have to stand by a melting furnace while it works though, forges tend to exhale right on you. Nothing like waste oil burners for mystery atmosphere.

Frosty The Lucky.

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The way oil burners work is combustion of an energy rich fuel; the downside is built into the upside; it's a package deal :unsure:

Nevertheless, some guys have dealt with the problem by using dual chamber casting furnaces; if combined with a baffle wall at the exhaust port that could work. The better solution is "just don't go there to begin with."

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The two combustion chamber waste oil burners tend to be iffy at best. The best I've seen pictures of are hot enough to light flammables in proximity before the output nozzle. The state heavy duty shop bought a waste oil furnace to recoup some of the money it spent just disposing of waste oil with hopes of saving on heating oil. Turned out service calls to keep it functioning cost more than both put together. The filtering and treatment system was another financial burden that required regular expert maintenance. 

It was insane but they tried to make it work for a few years, after I retired I heard they had it removed, junked because nobody else wanted it and had natural gas run in instead. Running a feeder line that size isn't a trivial matter either. 

I had a neighbor (call him Flash) who used to fire pottery with waste oil. A pulled extension cord caused a huge cloud of oil vapor which detonated scorching about a 50' dia. circle in his lawn. It was a super simple burner, a pinched line dripped oil on a hot fire brick in front of a blower output. When the cord pulled and the blower went off waste heat melted the pinched end off the tube and dumped flow of waste oil on a HOT brick. I wasn't there but the neighborhood kids used to watch from up the road a ways. They said the fireball was like an atomic bomb. Just a typical FAE mushroom cloud. Wish I'd been there to see it. Neighbors said it wasn't the first time either.

The oil boiler burner forge ran on fuel oil.

I'm thinking I'd rather not be neighbor to a waste oil fired anything.

Frosty The Lucky.

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Your experiences and stories are helpful, thank you. Sounds like I’ve had better plans than a waste-oil burner. 

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What makes #316 SS better than #304 for flame nozzles?

#304 stainless steel contains 20 % chrome and #316 only has 18% ,so why do #316 flame retention nozzles outlast #304 nozzles? #316 has 3% Mo added; #304 has none. Molybdenum increases lattice strain in the alloy, thus increasing the energy required to dissolve iron atoms from its surface at high heat, and thus slowing down oxidative loss to flame corrosion.

I just wanted to get in that fun fact before ceramic flame nozzles make the difference irrelevant :)

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9 minutes ago, Mikey98118 said:

I just wanted to get in that fun fact before ceramic flame nozzles make the difference irrelevant :)

What, we're not even going to discuss the advantages of monel or inconel nozzles?! :o So what if it's crazy expensive you can leave it to the grandkids.

Frosty The Lucky.

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No; that ship is leaving the dock. Next year we'll all be using ceramic flame nozzles, and forge tiles. "Resistance is useless," saith the Borg :P

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