Burners 101

[Mikey98118]

I just order the usual bag of printer nozzles through Amazon, and have found way more size choices then needed in them. Their tolerances are just fine. The whole bag costs less than a bag of five MIG tips.

[Skidpad13]

Mikey, although it is now "old tech" I am going to finish your earlier design burner (with your clarifications to the dwgs I posted last week) and document the build process both on video & with updated mechanical dwgs. That being said, I'm very, very interested in the 3D print concepts & will follow that conversation with great interest and anticipation. You guys have forgotten more about burners and FAM theory that I can fit into my brain housing group.

On the subject of ordering nozzles from Amazon, I got confused at first & thought that you meant the actual 3D printed assemblies were available. However now I realize you're referring to the hot end nozzles. I have a bunch of E3d nozzles from a dual extruder build I was pursuing a few years ago. Now I just have to find that box...

Thanks again for everyone's humor, patience, & wisdom. Cheers!

[Mikey98118]

The drawings will be welcomed by all those people who can't buy the book at a decent price anymore

[Hawkbox]

3 hours ago, Mikey98118 said:

I just order the usual bag of printer nozzles through Amazon

Oh you're using the nozzles for the 3D printer, yeah that makes more sense. I was trying to figure out why you were 3D printing nozzles.

[dian]

mikey, i have recently scaned though a book my michael porter. would that be you, by any chance?

On 2/14/2021 at 11:16 PM, twigg said:

Lol Thomas

Dian, if you're thinking of the equations for compressible flow, remember there's friction and probably turbulence in the nozzles / mig tips (especially the mig tips!). If no energy is lost to heat or eddies, then 2:1 pressure ratio would get you to Mach 1. I suspect the flows are highly compressible, but I wouldn't want to bet either way whether or not they get sonic (especially in the mig tips!). Maybe you can make a burner with a de Laval nozzle for an accelerator, huh? (That doesn't sound very useful, I'm just pulling your leg)

yes, laval nozzle (orifice) in a lavale nozzle (burner) would be the ticket. there is a flaw, however, the flow returns to sub sonic on the exit.

[Frosty]

On 2/14/2021 at 12:04 PM, ThomasPowers said:

Been *years* since the last time I went skinny dipping. 

I haven't had any skinny to dip in decades either.

If I were a nudist others would need to carry See Sick bags in auto dispensing magazines.

Frosty The Lucky.

On 2/13/2021 at 9:30 PM, dian said:

maybe i missunderstand, but it appears that at a pressure ratio of a little over 2 the flow is sonic through an orifice.

A little over two WHAT? This is an international forum with, around 50,000 members in about 150 countries. You can't assume anybody knows what you mean, especially measuring systems are concerned: length, weight, pressure, temperature, etc.  Heck there are ways of measuring pressure I know of in the USA without getting into the metric system. Even similar systems are different English SAE vs American SAE have differences. 

If you'd please clarify for us a lot of us could follow along and maybe have useful contributions.

Frosty The Lucky.

[dian]

a ratio has no units. a ratio of two is when something is twice as large as something else. a pressure ratio of two means that one pressure is twice as large as onother pressure. if you have propane with a gage pressure of 15 psi the absolute pressure is 30 psi. atmospheric pressure is 15 psi, so the pressure ratio of propane in the orifice of the burner is 2 or 2:1.

[Frosty]

Okay, that is more commonly expressed as 2:1 and a little less confusing. When talking about doubling it's commonly expressed as 2x. The multiplier followed by an x. 

Thanks, I appreciate the clarification. I'll go back to following the discussion.

Frosty The Lucky.

[twigg]

4 hours ago, dian said:

yes, laval nozzle (orifice) in a lavale nozzle (burner) would be the ticket

Dian, I was joking earlier. I can't tell if you were also joking, it's hard to figure people out over the webs! I have no idea if a de laval nozzle would actually be useful in a burner or not (but I suspect it would be counterproductive). That comment earlier was meant as banter. Sorry if I wasn't being clear. There are loads of good burner designs on IFI that will get a forge plenty hot and that are much simpler to fabricate than a de laval nozzle. The designs in Mikey's book are among them.

[Mikey98118]

On 2/16/2021 at 10:28 AM, dian said:

mikey, i have recently scaned though a book my michael porter. would that be you, by any chance?

If the book was titled Gas Burners for Forges, Furnaces, & Kilns the answer is yes.

[jlpservicesinc]

Mikey, where do I find the book your involved with?  Great thread. 

[Irondragon Forge ClayWorks]

It's available as a free download in PDF form. I googled the title and added download to the search string.

[jlpservicesinc]

Probably help if I knew the name of the book and knew what to google.  I 've scanned the thread but no smooch..  

I'll look some more.. 

 

[MonkeyForge]

"gas burners for forges furnaces & kilns" if i recall correctly. Happy hunting.

[Mikey98118]

 

bUT, while chock full of usefull information abut my burners and how to build forges and casting furnaces, it is  seventeen years old. We have learned lots of stuff that isn't in the book. One of the reasons I haven't tried to have it republished is all the rewriting I would need to do to stay current.

[jlpservicesinc]

Found it..  Looks great.. Only a few pages in and ton's of info and food for thought.. 

[Mikey98118]

The main changes aren't in the burners, but in forge building materials, and how that affects forge designs. What is in the book is perfectly adequate, if all you want is results, but there is no satisfaction to the mad scientist types (totally guilty here)

[pnut]

The reason I wanted to read and ultimately did read your book wasn't for the how but for the Why. I wanted to understand why burners behave the way they do and I found it very helpful. 

Pnut

[Mikey98118]

Nothing is stopping you from asking questions right here. The worst thing said will be  "I don't know." Maybe someone else will

[Frosty]

If Mike can't, I'll be more than happy to say, "I don't know." 

Frosty The Lucky.

[Mikey98118]

Not to mention several sharp minds on the group.

[Mikey98118]

Understanding flames & equipment atmospheres

When looking at the flame from a really powerful burner in a cold forge or furnace, It will appear much as it does out in the open air, but within moments it will lengthen and become smoother in outline, as the equipment starts to super-heat; it will also lighten in hue to blue-white. There will be little to no secondary flame within the equipment, even while it is cold; lesser burners will make more complicated flame envelopes, but this is the ideal; these facts also hold as true for multi-flame ceramic burner heads as they do for single flame burners.

    You need to remember that there are at least two different flames going on within the average gas forge or furnace; the flame being input by the burner, and an internal atmosphere, which may extend to an output flame leaving the equipment via the exhaust opening. When blacksmiths discuss terms like dragon's breath it is such an exhaust flame they are speaking of; a very different animal than the burner flame. Not that both flames aren't equally important clues to burner performance, but they need to be treated separately for clarity. So, what amounts to a perfect exhaust flame? No flame at all.

    If we are speaking about the burner flame, straight blue from a single combustion envelope is the goal, but many older burner designs have a white inner flame ahead of a blue secondary flame, followed by a darker larger and less substantial appearing blue or purple tertiary flame from the combustion of secondary air. Buy or build a good enough burner to see no white in the flame, and then tune it well enough to have little or no secondary flame.

    The next question tends to be "how dark a blue?" Different fuels give off different hues, and lean flames are always a darker blue than neutral flames in any given fuel. In fact, a burner can be run so lean that the primary flame turns purple from the amount of red that excess superheated oxygen gives it. On the other hand, any slightest tinge of green in the flame is an unmistakable sign that it is way too fuel rich; such a flame will also be pumping out lots of carbon monoxide.

    The simplest way to judge a neutral flame is that it’s blue is a lighter hue, and it has very little to no secondary flame; any darkening beyond that is from too much oxygen; it is called a lean flame as it is thought to be lean on fuel as compared to air input. In the end, you must tune a burner back and forth between rich and lean to educate yourself on what constitutes the best flame from your burner; you can do this out in the open air, or in the equipment while it is warming up.

    You can also get thin yellow and red streaks in a perfectly tuned burner's flame, due to breakdown products of oxidation from some alloys of stainless steel, mild steel, or cast iron in flame retention nozzles. Flame nozzles of #304 stainless can put on quite a show that way; it's harmless. #316 stainless nozzles make fewer streaks and last longer.

Fuel rich (AKA reducing) flames, range from the faintest tinge of green in a blue primary flame envelope (AKA flame front) to bluish green flames that are pushing so much incompletely burned fuel into your shop's atmosphere that you feel like gagging. If the burner’s choke is completely closed the burner will make a lazy yellow flame like burning wood.

Neutral flames range from light to medium blue; they are neutral throughout this tint range for all practical purposes; what that means is, although their combustion chemistry is changing, you can't appreciate the difference without calibrated instruments.

    So how can you know when the blue leads the neutral range and inters oxidizing? The answer is that you can’t without a fair amount of practice. Eventually, you will learn to compare the flames from your burner at one time and another, so as to tune it perfectly.

Oxidizing (AKA lean) flames start just beyond medium blue, go through dark blue, and extend into purple. While learning to discern the boundary between neutral and oxidizing flames, it is helpful to use small pieces of fresh ground steel in the forge, how fast and how much it scales—in the forge—gives you a faithful comparison, as you self-educate about flames. 

    Flame color isn't the only sign of how well your burner is doing. The amount of secondary flame is also an important indicator; the less secondary flame the better. There is such a thing as perfect performance, which includes no secondary flame. Perfection is often the enemy of practicality. A small wisp of secondary flame is often better than no secondary flame at all; this is because air/fuel flames fluctuate more than oxy-fuel flames, so the "perfect" flame is likely to be slightly oxidizing part of the time. Since a wisp of secondary flame will burn up completely in the forge or furnace, it is better than added scaling on work pieces during heating, or oxidative damage to super-heated crucibles. It should go without saying that tertiary flames indicate poor burner construction, or a very bad job of tuning.

    So what is the practical upper limit for secondary flame? Is there flame coming out of the exhaust opening? Then your burner is either tuned to rich, or its gas pressure is turned up to high.

    Even with the best possible flame (that you can detect visually), there will be some super-heated oxygen molecules that haven't had time to combine with fuel gas molecules before escaping the primary flame envelope; not enough that you can see secondary combustion going on. But, any super-heated oxygen that impinges on super-heated metal, will joyfully combine to rapidly create scale, and burn away some carbon content in ferrous metals. What this means is that a few inches distance between the visual end of the flame and your work pieces, or crucible, is highly desirable. Hot crucibles are inclined to suffer damage in the presence of super-heated oxygen, leading to spalling, cracking, and early crucible failure.

    It is an advantage to build a tunnel, oval, or “D” forge with the flame angled away from heating stocks (and between the crucible and wall in furnaces), or with the ceiling at least far enough from the work in box shaped equipment, to keep the flame from impinging on heating stocks and crucibles; increased room for the flame is one of the reasons for including a plinth in your casting furnace. Since different burner designs create different flame lengths, and since they also vary by how far the burner is turned up, there can be no pat answer on the height of a box forge or the thickness of a plinth in your casting furnace; these are judgement calls on the builder's part.

    Most people find little reason to turn a burner on full blast, so the flame can be measured for length at a maximum of 20 PSI, and that can be used for a good height measurement in box forges. You want the length to be at two-inches beyond secondary flame tips. No practical forge can include further length for tertiary flames, so construct and tune your burner well enough to avoid making them. Crucibles are tapered at their bottoms and should be raised on plinths to help keep the flame from impinging on them, since most casting furnaces are round and have a burner placed low on its vertical wall, and aimed horizontally at a tangent between furnace wall and crucible walls.

    However, flame length is most important if your burners are top mounted and facing toward the equipment’s floor. Some people mount their burners high up on sidewalls facing horizontally across a box forge or furnace, to get around early flame impingement altogether; this saves heating stock, and also lowers thermal damage on walls (which can be further away the work, for the same cubic inches when ceilings are lowered; a win-win use of space).

    Is an exhaust flame just the tail end of the burner's flame? It can be just that in equipment that is loping along, with interior surfaces that are only at red or orange heat. But in a forge or furnace that is turned up into yellow to white heat ranges—no. In fact, the goal is zero output flame; just clear super-heated exhaust gases. When your forge or furnace is capable of radiant-oven performance, then everything about the exhaust discharge changes.

    With the average forge or furnace, a small amount of blue exhaust flame has been considered normal--in the past. But in really hot equipment, should you keep turning up the input flame beyond its ability to completely burn internally, you still won't get blue exhaust flames; some of the yellow-white “atmosphere” will overflow out of the exhaust, and complete combustion within a few short inches, but without a trace of blue or purple flame (which indicates a probable buildup of carbon monoxide).

    What is different? The forge or furnace itself is changing the combustion equation by super-heating any byproducts of the primary combustion envelope. How is this possible, since immediately after combustion, exhaust gas temperatures naturally decline? Intense radiant energy from incandescent surfaces is being bounced back and forth through those gases. All of the interior becomes an ignition point; not just refractory surfaces. Thus, secondary combustion is speeded up, ensuring left over products of the primary flame envelope have the time to completely burn off.

    If the equipment is red-hot you should consider heat losses in combustion byproducts to be multiplying faster than radiant energy is being added. In pale-yellow to white-hot forges, combustion losses are being subtracted while radiant energy is multiplying temperature gains. It isn't possible to understand internal combustion processes in a modern forge or furnace as just a chemical process, because of heat gain from highly radiating surfaces; such equipment is as much radiant oven as flame appliance.

     So, exhaust flames from your forge can simply be the result of fuel that hasn't combusted, as in the case of fuel gas pressure being turned up way too high. The more common cause of yellow exhaust flames is a large secondary flame (from a poorly designed, constructed, or tuned burner), which cannot be completely combusted within the forge interior.

    I have noticed that fairly opaque looking yellow to orange flame can be made from some kinds refractory that is probably "cooking off" calcium from its binding agent; these flames will not abate until the process is complete. As the flame turns from yellow to orange, it becomes more transparent, and may even seem to sparkle in a manner reminiscent of fireworks, if the forge is running hot enough at the time.

    This doesn't preclude other colored flames, such as purple and blue from being present in the orange exhaust, but they are an indication of poor combustion, and must be ignored until the refractory finishes out-gassing. It is best to address one problem at a time.

Caution: Blue exhaust flames are a sign of a reducing forge atmosphere, which even a perfect burner will give off, if its air intakes are choked enough. Be aware that blue exhaust flames will be accompanied by carbon monoxide production.

    The reason flames, whenever practicable, are aimed on a tangent, is to cause their combustion gasses to swirl around equipment interiors; creating a longer distance from burner flame to exhaust opening. A longer exhaust path increases the amount of "hang time” for combustion energy to be deposited on internal surfaces. That seems obvious doesn't it?

    What isn't so clear is that the heat gain isn't added by hot gases blowing a few inches farther at high velocity; it’s due to a continuing drop in velocity over that added distance. Combustion gases begin to slow as soon as they leave the flame envelope, but gases from small flames decelerate much faster than those from large flames.

    The smaller flames of two 1/2" burners will use the same amount of fuel as a single 3/4” burner, but will drop velocity much faster in a five-gallon propane forge or casting furnace, greatly increasing efficiency; because they can burn faster/hotter without creating a wasteful tongue of fire out the exhaust port.

    What about people who want to build a two-gallon forge or furnace from a non-refillable helium or Freon cylinder? They will need two 3/8" burners to do the same trick. Someone who wants to forge hand tools or cast jewelry in a one-gallon paint-can or three Lb. coffee-can will want two 1/4" burners to run their equipment proficiently; the 1/4" burner is also ideal for a so called “two-brick” forge, or tomato can jewelry furnace, which so many people attempt to run from a store-bought propane torch; without making the necessary modifications.

    The law of diminishing returns reduces fuel savings in miniature equipment, but faster heating time, and increased portability remain major advantages. Portability? Yes; miniature equipment isn’t all that portable, if it must be fed from a five-gallon fuel cylinder, which is nearly impossible to legally transport in your car.

    Do multiple flame burners (ex. Ribbon burners) take deceleration even further? Yes, they sure do; unfortunately, ribbon burners themselves tend to be large. Over time, compact ribbon burners will be perfected, but first there must be a lot more interest in doing so; there isn’t much, because ribbon burners provide the most advantage when heating large equipment.

 

This is only an introduction to the subject, and from only one point of view.

There has been no mention of laminar versus turbulent flames, or different fuel gases, let alone oxygen enricnment, or preheated air

[Skidpad13]

I feel both enlightened & a little woozy from all this knowledge. Mikey, you are the best kind of wizard there is. Thanks!! 

[Leather Bill]

Thank you Mike.  I learned more from reading that than I have from hours of reading through hundreds of threads finding bits here and there.  I just sent your post to the printer.  I would love to see someone talk about forced air or as Frosty call's them "gun" burner to explain why it doesm't rush flame through and out of chamber leaving little heat in stock.  As an aside,do you see ribbons or other approaches soon making present tube burner design obsolete?  When you prefect your present burner built around hand torch nozzle,do you think it has poential of using multiple to replace single tube burner in small forge?  Frosty here's something I'm sure has concerned you but I haven't heard any  ideas on why it happens.  The solution is usually change in mig tip size.   I have noticed burners of same desighn often act different when time come's to tune. Is it possible that texture/imprefections or what we might call inside surface of body pipe,reducer,nozzle ect might accont for some of the inconsistancy?  An automobile brake wheel cylinder hone could make short work of cleaning inside pipe. I need to stop before I cause us to case rabbits.  

[Mikey98118]

12 minutes ago, Leather Bill said:

As an aside,do you see ribbons or other approaches soon making present tube burner design obsolete?  When you prefect your present burner built around hand torch nozzle,do you think it has poential of using multiple to replace single tube burner in small forge?

No; it simply isn't a question of the best burner for every task, nor any other practical matter. The bottom line is what people feel like building. People get into blacksmithing or most any other metal work, basically because they feel like doing so; they aren't inclined to be preached do about "what's best for them. " That's before we even get into practical considerations, which boil down to "no one shoe fits all" There is no such thing as the perfect burner for all tasks.

My present burners are designed to be used in pairs, on small equipment, as a matter of convenience. It boils down to a balance between construction ease and cost, with additional costs for upgrading the fuel system later, versus ease of use. Multiple burners are best served with a manifold and copper tubing. I'm not a big fan of copper tubing, nor a critic of it. Whatever serves you best at the time. I'm into more choices. What people choose is up to them.

Larger burners are best serve with hose, valves, regulator, and refillable fuel cylinder.