Burners 101

[Mikey98118]

It would seem obvious that the hotter the burner the better the forge. But there are lots of factors that limit such a generality. Energy is consumed to heat a forge and it costs money no matter what the form is used; that means you have to look into what your loval markets  charge for various fuels versus the price of electricity. You also need to decide just how high the temperatures your forge need to attain, to do the work you want to accomplish.

No matter what fuel you decide to consume there are some general principles that will apply. Use of hotter fuels and/or richer oxidizers to attain high temperatures are the most expensive path to achieving that goal.

Engineering improvements are the only source of freebies you have any hope of attaining toward your goal; fortunately they exist. But, you have to recognize the principles at play in order to take advantage of them.

The smaller the area a flame is compressed into the higher its temperature will become, which means that the greater the percent of a fuel is burned in a primary flame envelope, rather than the secondary envelope the hotter its rated temperature will become.

The smaller the flame is the smaller the forge interior is needed to complete combustion, and the smaller a forge interior is the less heat is dissipated to the square of the distance rule.

Normally small hard flames tend to be faster, which means they can be aimed at a tangent to the forge interior so that they swirl around it one or more times befor exiting through exhaust vents, increasing the overall time they have to heat the forge before being lost.

Ribbon burners also enjoy the advantages of the better models of naturally aspirated burners in making most of their flames content in the primary envelope for high temperatures from small areas, but achieve it with very low flame velocity, and so need no swirling within the forge to transfer more of there energy to the work before exiting. And so it is that two very different burner types in fact are applying the very same principles to achieve desired ends.

 

 

[Mikey98118]

By the way, being present for the information age" just means that loads of it is avail at your finger tips; it does not mean that what you find is true. You can log on to hundreds of sites that show the flame temperature of propane burning in air at 3578 degrees; it can be marked so exactly because adiabatic temperatures only concerned with scientific models of a fuel's full potential energy output, and have nothing whatsoever to do with what it will be in the real world.

In the "real" world the commonly held answer is given as about 2400 degrees, because that's what a propane flame will reach coming out of a Bunsen burner; and this figure is also nothing to do with y-o-u-r real world, because you are looking to burn a fast hard flame from an appliance design to boost combustion temperature over that attained from the laminar flow type put out from a Bunsen burner. So you need to consider that figure as representing the bottom of the barrel. Not that their aren't plenty of burners around that are only achieving it.

When an air/fuel flame reaches 2800, and continuing on up to3200 degrees, there is a significant increase in oxides of nitrogen present in exhaust gases; enough that you can smell the tang of it. A very hot burner design that is perfectly tuned will give off that smell on propane, but will not do so when burning propylene (which is a hotter burning fuel); I believe that is because at that point the flame has exceeded 3200 degrees.

Not every burner I build reaches such high temperatures; they are hand made; not stamped out of a factory, so there are going to be differences. But enough do to keep my confidence strong that paying attention to detail when building a burner matters--a lot! 

 

 

[Mikey98118]

Finally, you need to understand that the burner is only one part of your forge. A great little forge will not completely turn around the performance of a junk burner, but it will help a lot. And a mediocre burner can seem exceptional when run in an exceptional forge. No; this isn't double talk. You only need enough performance from a burner to allow a good forge to do its job. Be glad of that; it means your work doesn't have to be perfect at any point along the path, in order to end up with exceptional performance. You just have to try a little harder  

[Mikey98118]

In a previous section I stated that to attain high temperatures, the flame needed to be compressed; perhaps a better way to express what happens is that the flame is folded in on itself; that is a slippery concept to get your mind around. While this trick is also found on many  flame tips in air/fuel jeweler torches, anyone can find it in action by observing a blue flame butane lighter. It is the special shape of the recess around the gas jet orifice that partially collapses what would otherwise be a cooler bushy flame into a hot little needle shape. That recess is helping the flame stay in place at the jet orifice for sure, but the reason it is so large and deep is to create enough of a shoulder for secondary air rushing past it to  push the flame wall in on its self, so the the flame is made thinner, longer, and hotter. 

When used in a forge or furnace, the high pressure area created by combustive gases, who haven't yet exhausted out of the equipment vent, complete the work of extra wide shoulders on my step nozzles to thin the flame from a fat sort of Christmas tree shape into a stiletto of flame.

I suspect that the multiple holes in ribbon burners. combine with the flat face surrounding them, to give a shoulder effect, producing the nice pencil flames, which I cannot otherwise account for.
 

[Ironhorse07]

Thanks for these excellent write ups. I am In the process of gathering parts and knowledge to put together a 20 lb bottle build and In my searches for information I have seen a.lot of contradictory information and 'rules.of thumb'. These write ups on theory help to explain the how and.why It works and help me to weed through the fact and fiction on the Internet to make informed decisions with my build. Thanks again.

[Mikey98118]

Ironhorse07,

thanks for your timely reply. It seems a little unusual not to get one sooner, although it made it easy to keep the write ups in sequence. But, now questions and answers time is overdue; the kind of information that generates is just as valuable in its own way. Besides, I like things a little rowdy

[Frosty]

If anyone is wondering why I'm not taking part in this thread don't. I'm sponging information and thinking off Mike. While our goal is the same we do it differently and if I can make a fast easy improvement on the oh so easy to build T I'm all over it.

Mike, can you draw a diagram of what the step in the burner nozzle is doing? A lot of us, maybe most visualize things and pics not only speed up getting our heads wrapped around the idea but really helps control misunderstanding.

Thanks Brother.

Frosty The Lucky.

[Mikey98118]

Frosty,

Figure 2-8 on page 26 of Gas Burners for Forges, Furnaces, and Kilns shows a cutaway view of it. I will put it here as soon as I can figure out where all those drawings wondered off to...in the mean time its available to view and download from the Net.

 

[Ironhorse07]

I am in the process of collecting parts for a 20 gal. propane tank build which will use a t-burner. I think I might have a way to make adjusting the gas jet easier without adding complexity to the design. I hope to get the burner put together in the next couple days. Sorry for the highjack, I will start my own thread with the build. now back to our regularly scheduled program....

[Mikey98118]

It isn't a a hijack; what is on your mind is exactly what this  page is about, so lets discuss it. As mentioned earlier, there are several good burner designs around; two of them are even fan-driven. The burner is but one part of a good gas forge; that doesn't mean you have a lot of parts to get perfect in order to reach your goal; it means that you have lot of parts to share the opportunity to help get you there.

This is the plain truth; not happy talk! It takes a dreadfully bad burner design to actually screw up a proper gas forge. That doesn't mean that folks won't have some frightening moments, where they think they've managed to do just that, while they are trying to tune their burners

So, if this is true, why did I go through all that trouble and strife to come up with superior burners to begin with?!?!? Am I just a perfectionist? Why, yes,  that is exactly how it came to pass! Oh, it matters how good your burner is, of course. But that matters because of efficiency issues like gas economy, heating time, and how clean your flue gases are. It doesn't matter much about reaching the magic moment, when your forge turns yellow inside, and you're dancing around on the shop floor.

Of the good naturally aspirated burner designs, the overall easiest to build, and get right, is the Frosty "T" burner, which doesn't mean that it's dead easy. Every design is going to have some sticky point to get passed; and in this one it's getting that one hole you need to drill dead bang in the right place. It isn't easy for most guys to line it up properly; not least of which because pipe fittings are steadily dropping in quality. But, adding a short nipple between the "T" fitting and a four hole (as in round) flange fitting should ensure that it can be adequately secured on the the drill press, and that the hole will and up at the right point, no matter how far off of square the "T" fitting's casting turns out to be.

Probably the next most popular design is the Zoeller Modified Side-arm burner; its virtue is also its vice; the special "T" fitting that makes it run so well also happens to be a top quality  American made part--so, no nasty surprises with fit-up or performance with it; unfortunately, you can only buy it from one source I know of: Zoeller Forge; single source parts always make me nervous; still, if it was easy everybody would be making forges...

Last, but not least, is the Ron Riel burner; this is the only linear burner in this list, because jet-ejector type burners usually leave them in the dust; but their is a modification that you'll find in the Ron Riel  burner pages that soup them up quite a bit; if you combine it with a step type flame nozzle, it screams.

[rjs]

Mikey said:

"Probably the next most popular design is the Zoeller Modified Side-arm burner; its virtue is also its vice; the special "T" fitting that makes it run so well also happens to be a top quality  American made part--so, no nasty surprises with fit-up or performance with it; unfortunately, you can only buy it from one source I know of: Zoeller Forge; single source parts always make me nervous; still, if it was easy everybody would be making forges... "

Mcmaster carr carries a range of reducing t fittings in schedule 40  a 1-1/4   reducing to 3/4 is priced at $13.17.   I have not seen these and do not vouch for the quality or suitability of these fittings however mmc has a good reputation.

Bob

 

 

[Mikey98118]

And then we come to my own fourth generation burner design; commonly called the Mikey burner. It is a jet-ejector design that is built from threaded pipe parts, but is NOT easy to build. It is easy to get right, because all kinds of protection is built in. An entire book is devoted to building it correctly, with the right sizes for the right equipment to put it in, and how to build them too! Since you can all find free copies of Gas Burners for Forges, Furnaces, & Kilns on the Net, I'm not about to go into it again here.

But what is worth mentioning is some improvements that came out after publication:

(1) By upgrading the 1/8" schedule #40 by 4" long pipe nipple in the book to a 1/8" schedule #80 by pipe nipple, you can directly thread the MIG tip into it, avoiding all that brazing work, and upgrading its performance enough so that a 3" long nipple can be used. You can buy schedule #80 by pipe nipples  from McMaster Carr.

(2) When the book was written, 4-1/2" angle grinders were much less expensive then hand operated rotary tools; this is no longer true. Furthermore, Dremel has invented their EZ Lock  spring loaded mandrel and special cutting wheels system, which takes the mystery out of cutting sheet metal with a rotary tool; these tools make it much easier to cut out the rectangular air openings then it was in my day. Finally, diamond coated accessories make it easier to bevel the opening then jewelers files were way back then.

[Mikey98118]

Thanks to rjs, I went back to McMaster Carr, and this time stumbled on the proper name for this pipe fitting; it's called a "Why" fitting, and is available in every size you'd need to build whatever burner size you want-- even down to a 3/8" burner:  http://www.mcmaster.com/#standard-metal-pipe-fittings/=12kwyxw

rjs has made my day!!! This means that I will be able two add two different easy to build micro burners on the list

[rjs]

34 minutes ago, Mikey98118 said:

Thanks to rjs, I went back to McMaster Carr, and this time stumbled on the proper name for this pipe fitting; it's called a "Why" fitting, and is available in every size you'd need to build whatever burner size you want-- even down to a 3/8" burner:  http://www.mcmaster.com/#standard-metal-pipe-fittings/=12kwyxw

rjs has made my day!!! This means that I will be able two add two different easy to build micro burners on the list

LOL,   Thanks Mikey,  and those weren’t even the ones I was talking about.  These are the ones I spotted:

http://www.mcmaster.com/#standard-metal-pipe-fittings/=12kxr9c

Bob

 

[Mesquite0]

Bah-da-ba-ba-baaaaah. I'm lovin it you guys!   Thank you for spreading the knowledge. Im a total newbie. Been messin around with a bunch if different designs just for fin while i get a forge underway. 

 

Just a thought i'd like to throw out there, and it seems you are already touching on it heavily, is that these designs are an expression of fluid dynamics? A heavily studied field. One of the more interesting concepts i've come across is "vena contrata". 

 

This is a realized aperture area decrease in relation to the design of its opening due to localized belocity increases around the opening that can be rectified witha "flared" opening. In this meaning the flare is best as a parabola. Check it. 

i

This issue was addressed as "eddies" in the current. I think the visuals help to show what mr. Mikey meant

[Mikey98118]

No; a vena contracta might give interesting results if installed at the opening of a compressed air burner body, with a gas jet introduced just beyond it, so that gas/air mixing could benefit from the eddy currents generated by it. In any naturally aspirated are standard fan-blown burner, those eddy currents would interfere far too much with flow to be anything but a burden. Even then, I would only use it to generate flow to a ribbon burner's head, since this is the only kind of burner that  both makes compact flames and benefits from posotive pressure in the mixture flow; all others require a low pressure high speed flow.

[Mesquite0]

Oh. Ok. Thats interesting how that works. I had looked into this when designing a shops ventilation system. It was particulqrly interesting that the given flow of a ventilation system would be effected (upwards of 15% loss of airflow) based just on the design of the intake manifold. I was bringing this point up because i thought some problems folks are having problems might be related to the smoothness of transitions. Little bumps or restrictions that would be easy to brush off might be having a larger detriment on the shstem. So these eddies are generated leas in a jet induction system vs a forced air scenario?  

 

Thanks for all of your hard work!  I am new to this hobby/proffesion (depends on the individual) and i am so thankful and impressed how all of you folks share your knowledge so freely!!  

[Mikey98118]

Eddy currents are mostly made by complete innocents of what generates them, such as round  shaped air openings (not to mention whole fields of them).

Surprisingly. lips and threads from pipe fittings have a much smaller negative impact; not that I approve of them either, but it is difficult to argue with success. And there are plenty of sloppy burners around that are successful...

[Frosty]

Welcome aboard Mesquite-O glad to have you. If you'll put your general location in the header you might be surprised how many of the Iforge gang live within visiting distance.

You have my sincere thanks for the term "Belocity", I love it and have no doubt places to insert it into conversation will come up often.

It's a common misconception to think naturally aspirated burners operate using Venturi's effect, they don't. What's happening is similar but the difference is significant, as significant as the fact that Venturi only restated Bernoulli's principles for limited conditions and effect and got his name in the books.

Frosty The Lucky.

[Charles R. Stevens]

Mike, I don't know if this is what is happening with the treads, but have you considerd the "golf ball" effect? The small divits creat small edies that the rest of the air slip over more efficiently than an otherwise smoth serface. I know that some experiments with vehicles and aircraft have been conducted (for all I know new aircraft, ships and subs may be using it).  

[Mikey98118]

Charles,

You are a dangerous man; you need watching, you slippery character! Here I am, trying to take care of business; juggling all them facts an figures, and trying to heard cats into playing nice...and you mess up my brain with visions of vibrating golf ball burners...I need to go lie down and take a little nap now

[Frosty]

Oh WELL DONE Charles! You're bringing out dimples Mike didn't even know he had!   

Any ideas how to dimple or texture the inside of a burner tube? In addition to the lower friction the boundary layer turbulence will induce the low pressure zone will enhance propane air mixing. Propane mixes much easier at low pressure, think evaporate . . . sort of.

Frosty The Lucky.

[Buzzkill]

Well, if you cast the burner tube (or most of it) you should be able to put whatever texture you want in it.  It would also be easy to cast the flare at the right ratio.  Instead of a ribbon burner you could cast a single hole of the right size in a block.  Just a thought.

[Frosty]

That's an option, any ideas about the mold media?

Frosty The Lucky.

[Buzzkill]

I have almost no experience with something like this so I'm just spitballing at this point.  It seems like this may be a good candidate for 3D printing to make the texture in wax, cast in refractory normally used for ribbon burners, then melt the wax.  A close nipple with some pins tack welded on could be set in one end and oriented properly with the wax.  That would let you screw a T on to the end.  Like I said though I have no practical experience here.  I just wish I had the time and money to play around with some of these ideas more.