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Burners 101


Mikey98118

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Although I don't know if it holds true for propane burners, oxy-acetylene flames supposedly have inner cone tip temperatures of 5700 degrees F for carburizing (rich), 5850 degrees F for neutral, and 6300 degrees F for oxidizing flames.  Internal combustion engines also appear to run hotter with lean mixes compared to neutral or rich.

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Air is 70% nitrogen which adds nothing to the fire but robs heat from combustion. 

Oxy acet torches run rich. What the instructor or charts call: rich, neutral, lean, are subjective terms not the actual flame chemistry. Subjective regarding an "ideal" torch setting as regards the desired work. For example a "neutral" welding flame is slightly richer than a "neutral" brazing flame. A "neutral" cutting torch preheat flame is the leanest of any correct oxy acet flame but it's still a couple % richer than a stoichiometric burn.

Frosty The Lucky. 

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15 hours ago, Frosty said:

A "neutral" cutting torch preheat flame is the leanest of any correct oxy acet flame but it's still a couple % richer than a stoichiometric burn.

You may be right, but that seems to conflict with the information on weldguru.com:

Oxidizing welding flames are produced when slightly more than one volume of oxygen is mixed with one volume of acetylene.

"To obtain this type of flame, the torch should first be adjusted to a neutral flame. The flow of oxygen is then increased until the inner cone is shortened to about one-tenth of its original length. When the flame is properly adjusted, the inner cone is pointed and slightly purple.

An oxidizing flame can also be recognized by its distinct hissing sound. The temperature of this flame is approximately 6300ºF (3482ºC) at the inner cone tip.

Oxidizing welding flames are commonly used to weld these metals:

  • zinc
  • copper
  • manganese steel
  • cast iron

When applied to steel, an oxidizing flame causes the molten metal to foam and give off sparks. This indicates that the excess oxygen is combining with the steel and burning it.

An oxidizing flame should not be used for welding steel because the deposited metal will be porous, oxidized, and brittle. This flame will ruin most metals and should be avoided.

A slightly oxidizing flame is used in torch brazing of steel and cast iron. A stronger oxidizing flame is used in the welding of brass or bronze.

In most cases, the amount of excess oxygen used in this flame must be determined by observing the action of the flame on the molten metal."

If the "lean" flame was still richer than stoichiometric, then there would be no concern about the excess oxygen combining with the steel and burning it.   Not trying to pick a fight here.  Just striving for accurate information.

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16 hours ago, Alphafarrier said:

Where I am ultimately going with this discussion: Could the slots on a Mikey burner be significantly shorter, if a neutral burn is achieved with choke covering a lot of the slots anyways?

Where you are going is quite correct. I did not design the burners for maximum heat.; The burners in that book were the hottest design I could make within maximum SAFETY margins; a decision I don't regret. Readers on IFI are looking to make burners that are mounted in equipment. The burners in the book were just as likely to be used as air/fuel torches, out in the open .

A burner that is equipment mounted need not be as stable. So, the answer to your question is that EQUIPMENT MOUNTED Mikey burners can benefit with wider air openings. As to length, wider should be shorter. Furthermore, the original design deliberately employed over length  openings, because the burners were to be hand crafted by armatures. So what was enough, or too much on one burner wouldn't necessarily be so with the next; this is true even of the author's burners, and certainly is going to be true for readers.

I love pushing performance to the limit. However, there, unpleasant surprises can happen there; If you want a safe burner, follow the books directions. If you want every last erg of energy, welcome to the world of hot-rods. Just remember, that some surprises bite!

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No argument from me Buzz, I haven't welded or brazed with an oxy acet torch in probably 35 years and I've never welded any of the metals you listed. My last metal shop class was in 1970 so my memory is sorely dated. Anybody in metal shop got the hiss from a torch got yelled at to "adjust that torch!" 

I haven't owned an oxy acet torch in I don't know how long, not since buying the All States oxy propane rig. It's GREAT for brazing and blows oxy acet out of the water cutting and heating but doesn't weld worth spit. 

I probably shouldn't talk about adjusting oxy acet torches, I'm so long out of harness. 

Frosty The Lucky.  

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You were, nevertheless, dead on to mention that oxyacetylene torch flames don't translate one to one with flames from an LPG fuel and air burner. There is a lot of onsite that decades of torch work brought to my burner experiments--but is was only after realizing their limits that real progress was made. Even different LPG fuels produce different flames. While propane and propylene flames are very similar (propylene appears to burn with a with a little lighter h blue; this is on/y a subjective judgement) Methane, on the other hand, burns similar to propane in low velocity stove flames, but when run through a high-speed torch nozzle, they are much lighter blue, altogether. Subtle differences are easily misinterpreted. Cold blooded testing is much more reliable. 

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What size burner? If it's a 1/2" T and you didn't mount it perpendicular to the far wall, nothing it'd work a treat. However if by dead center you mean perpendicular as in straight at it. the back pressure would inhibit the burner and you'd be pretty disappointed. 

If you try that with a 3/4" burner it probably wouldn't burn except maybe some yellow flames billowing out the doors.

Frosty The Lucky. 

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On the propagation of gas flames

A laminar gas flame, such as those in most lab burners (but not all) is a calm ongoing combustion process; mainly differing from a camp fire in its much greater stability’ The same amount of air and fuel gas, when mixed and ignited all at creates an explosion. Turbulent flames fall somewhere between these two examples. Put bluntly, a turbulent gas flame, is a controlled explosion, slowed just enough to remain a stable ongoing process.

Surprisingly, a gas flame in space, is far from an explosion; it is spherical, because no outside forces (like atmospheric pressure, gravity, or  buoyancy) can act on it. In space, a gas flame isn’t explosive because expansion is the only movement within the cloud helping to diffuse its oxygen and fuel molecules through the expanding area, which as it is distancing them from each other;  in fact, the flame is downright sluggish.

But, supposing you ran fuel gas and oxidizer through a hand torch in space; then, you should get a very familiar high heat gas flame. Why? Because oxy-fuel torches are designed to defuse the fuel and oxidizer thoroughly, and then project them out of a tip forcefully; all of which are meant to create and control a high speed turbulent flame.

    Oxy-fuel torches and air-fuel burners have thorough diffusion in common, but forceful ejection of an air-fuel mixture becomes a far more delicate balancing act between enough speed, without too much pressure. The more force in the ejected mixture the more breaking is needed by the flame retention nozzle. Even if fed by hoses, an air/fuel burner will not work in space, because it needs atmospheric pressure to prevent its flame from blowing off its nozzle end.

    Thus, torches produce flames from heating or cutting “ tips”  that were designed to use increased mixture pressures to increase flame velocity,  while air-fuel burners employ “flame retention nozzles, designed to lower incoming mixture pressures, while permitting as much mixture flow speed as possible to--but not through—the flame retention nozzle.”

    The first source of confusion about gas flames come from use of the term “flame envelope” from some experts, while the term “flame front” is used by others; they are often used interchangeably, but best describe different aspects of the flame’s edge.

          Different fuels and different oxidizers burn at varying rates. Because the potential velocity of its flame has much to do with how useful a heat source any given fuel is, a test was devised to measure velocity of a flame’s propagation through a hose, from ignition point to target instrument, so that time tests became practical; this is the origin of the term “flame front” to describe a flame’s periphery. Most flames in heating equipment combust in two or three distinct zones; primary; secondary; and sometimes tertiary. Each zone has an outer layer, called the “envelope.” So, flame envelopes are the best term to use concerning equipment design. Flame fronts are best left in fuel discussions.

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    What causes separate flame envelopes? Primarily, different fuels are being combusted, in the primary and secondary flame envelopes. Most fuel gases contain complex molecules of carbon and hydrogen atoms in varying arrangements. Usually, an LPG (liquid petroleum gas) fuel will combust in a primary and secondary flame envelope. For instance, the darker inner “cone” of a gas stove’s flame is surrounded by a lighter blue outer secondary flame; this is often the case in equipment burners too.

 

I surmise that: If the stove or burner isn’t running properly, a three envelope flame may appear. The inner cone may be white, surrounded by a darker blue secondary envelope that is larger, less and sharply defined; in this case (and other examples of poor combustion) much larger, and fainter, tertiary flame will usually form.

A two envelope flame is burning both carbon and hydrogen atoms in the primary flame. The secondary flame is burning carbon monoxide (a byproduct of incomplete combustion in the primary flame with, a combination of leftover oxygen from the primary combustion process and ambient oxygen from air, when coming out of a burner). A white primary cone is burning more carbon than hydrogen, as the fuel breaks down; the secondary flame while then burn carbon monoxide and hydrogen. When combustion is far enough out of balance, a third flame envelope will develop, consisting of leftover byproducts of incomplete combustion and super-heated oxygen atoms, mixed with air; I believe it shift from blue to purple is caused the an abundance of super-heated oxygen atoms, which escaped the first and second combustion envelopes. I believe it is faint, because the gas molecules that are still combusting, are now expanding through the secondary air too fast to maintain a cohesive envelope any longer.

    A more common example of a three envelope flame has a darker blue inner core of incomplete fuel combustion, surrounded by a secondary lighter blue envelope of incomplete carbon monoxide combustion, and a faint purple tertiary combustion ‘envelope’ of carbon monoxide, escaped super-heated oxygen atoms, and air.

    What about orange-red tertiary flames? I believe that the orange tint is due to calcium atoms from new refractory are burning off along with the purple tertiary flames. This is a completely separate problem, that can occur without a tertiary flame involved at all; in this case, the flame can run from orange to yellow, and from faint to opaque.

    This section is made up of supposition; I could be wrong; comments?    

 

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I recently installed a new kitchen stove in our house.  Being rural we run it on propane and it came with the orifices and "tuning" pictures of the flames for me to install and tune.  I was rather amused how my time with propane forges played into getting our stove working correctly! (And, yes, we were trying to get away from white flames.)

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I am currently waiting on a shipment of supplies to finish my forge body build. In the meantime, I was hopeful to get some feedback on my attempts to build a burner. If this is not the correct thread, I would be happy to create a separate thread.

Because I’m working on building a mini forge, I’ve been attempting to build a 1/2” T burner. (If I can ever be successful at that, a 3/8th’s may be in the offing as well). I have also read so much in that last week that it is all getting jumbled together, so please, please do correct my equipment choices.

Current Specifics:
- ¾” X ½” X ¾” T
- 6” barrel/mixing tube
- .25 Mig tip (cut down and de-burred with a mig tip tool)
- The below pictures were taken operating at 10 PSI. The flame blows off the end of the burner at about 20 PSI
- Not shown is a quarter turn cutoff valve upstream of the burner

I’m having some difficulty translating what I see in pictures online to what I am observing in person and I would be happy for some guidance on whether the flame in the pictures is lean/neutral/rich. I am aware that those characteristics will change when I actually run a burner in the forge. I'm mainly just looking for a point of reference, so that I can better classify what I am seeing in person.

I am primarily working with hand tools at the moment and the attached pictures represent the best of multiple attempts that I have been able to produce with a ¾ X ½ X ¾ T fitting. I have tried using the neighbor’s drill press; however, those attempts have come out significantly worse (operator error).

I have been having difficulty with alignment issues and frankly have been getting frustrated. I can change flame alignment (quality?) by rotating the burner body (approx 25 degrees of rotation) around the mig tip holder and am aware of what that means in terms of my fabrication technique. At the moment I am considering just finding the best alignment and soldering/brazing the tip holder in place if if the attached pictures are decent. I would the use needle nose pliers to to remove and adjust mig tip length for tuning it with the forge.

Thanks!

4.jpg.1717598c210a9aeb452fa975fece51b2.jpg

1.jpg

2.jpg

3.jpg

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No, that flame isn't even acceptable; its heavily reducing. In other words weak, cold, and spewing out carbon monoxide. The "T" burner is inexpensive and simple to build, compared to any other high performance design I know of; but it has to be built and tuned according to directions. You have a problem; are you going to do what you need to succeed with that burner, or not? That's where you're are at. Others have been here, and faced the same choice.

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38 minutes ago, Mikey98118 said:

No, that flame isn't even acceptable; its heavily reducing.

Perfect and thank you! - seriously. For whatever reason, it has been really hard for me to pick up in differences in flame attributes in pictures (unless grossly different) and even harder to compare those what I am seeing in person. Now that I know what at least what one aspect of what not working looks like in person I have a little better basis to judge what I am doing :)

I'll likely have questions for folks, but i need to better wrap my head around some concepts first. My thanks!

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About the mixing tube length. The ratio is, D x 8.  1/2" x 8 isn't 6" is it?

Keeping the jet mount fitting from moving can be a problem. I had luck with one I couldn't keep from jiggling by peining around the tapped hole with a blunted punch to drive the hole more closed. Made the hole a little smaller without messing up the threads. 

The first flame pic shows the jet to be slightly out of alignment, down in orientation with the camera angle. The flame is rich, possibly partly due to the misaligned jet. The too long mixing tube is also a problem.

The last pic is crazy too rich, you could cool hot steel with it. 

Frosty The Lucky. 

 

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About the mixing tube length. The ratio is, D x 8.  1/2" x 8 isn't 6" is it?

- No it is not, and that's on me.....as if the rest of this build. My thanks you for pointing out the error.

Keeping the jet mount fitting from moving can be a problem. I had luck with one I couldn't keep from jiggling by peining around the tapped hole with a blunted punch to drive the hole more closed. Made the hole a little smaller without messing up the threads.

- Thank you for the tip about peining around the tapped hole. I will try that and may also have another solution if that does not work.

The first flame pic shows the jet to be slightly out of alignment, down in orientation with the camera angle. The flame is rich, possibly partly due to the misaligned jet. The too long mixing tube is also a problem.

- It is out of alignment and is likely in the main due to being apparently unable to drill a plumb hole and in part due to the fact that I over tapped the jet mount hole. Then again, if I hadn't over tapped the hole I also wouldn't have any ability to adjust alignment whatsoever and would be blowing even more gas out the side of the air intakes. I'm not being flippy here, I am appreciative of your observation and thankful I could at least correct a little bit for the purposes of having an example to ask about.

The last pic is crazy too rich, you could cool hot steel with it.

- The pic is of the same burn as the previous pics (no adjustments), just with the lights out. In addition to correcting the alignment and tube length issues, would I be correct in understanding that, given it is too rich, I would need to introduce more air into the mixture by either reducing the tip length and/or reducing the diameter of the tip opening?

 

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Do you or a friend have  a drill press? If so use the floor flange drill jig trick I came up with a while back. It works a treat, I can't trap a hole straight worth beans.

There's a trick for using a hand drill but it's complicated and you need a good hand with the tap a couple times.

Frosty The Lucky. 

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I do, and have made attempts with the drill press and your floor flange suggestion; however, I still need to work on my technique... I can manage straight and in line with one aspect of the burner orientation but have yet to hit dead center. I know this is a family forum so I am resisting very hard at making jokes at my own expense.

I did want to ask on a related, but slightly separate burner, experiment if the attached picture was movement in the right direction? By the picture it still looks too rich to me, but in person it appears more blue than portrayed.

IMG_2243[1].jpg

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Panik, I hope you don't mind but in an effort to learn I've grabbed your last two flame images and cropped them for comparison. I'm trying to see the differences and having them side by side and cropped helps.  

I'm hopeful that one/some of the knowledgeable folks here could take a moment and point out what they are seeing and compare between the two. 

 

What I see is that the second, improved flame has a smaller tertiary part that is "more solid" than the first flame.  I see the secondary envelope as being more robust also, with a wider and more consistent tip on the second.  I also see, again on the second, a more dense primary flame, like a pencil tip, that is solid all the way through as opposed to hollow in the middle right as it exits the burner flare. 

 

I'll admit that was easier to see once cropped it and ran thru my default "filters". Changing saturation and color let me pick out the different parts more easily on the original flames.  These photos I've reattached are simply cropped, no color changes done. 

Screenshot_20200508-222225_Chrome.jpg

Screenshot_20200508-222252_Chrome.jpg

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