Burners 101

[Mikey98118]

Safety practice always seem to go way to far, until you run into a few guys who rolled snake eyes...

[Mikey98118]

Saddles are great, but they aren't everything

To the best of my knowledge, it appears that butt-weld pipe reducers were first used to create linear burners by the Aussies; probably back in the eighties. Us Yanks started using threaded reducers for ease of construction. There have been lots of back and worth and borrowing in burner designs since them; I'm all for that. Apparently, an Aussie has now copied part of an English burner design, by casting parts to make another linear burner; hurry for him. Unfortunately, the cast saddle assembly used to hold the gas pipe on the reducer is the first and last thing about his burner that is clever.

Know a guy on another thread has posted drawings of his interpretation of this very poor burner design. Saddles for holding gas pipes (and their gas jets) on linear burners aren't new, but saddles, cast or bent from flat bar, are the logical construction method for building GOOD linear burners the easy way. Alas, it seems that a lot of people think that a slick idea will get them around the need to have a clue about the whys and wherefores of how a burner works; wrong! We still need to pay attention to all the other factors of construction, such as the proper ratio of reducer opening to mixture tube diameter, what makes a flame nozzle work, and why it needs to match up closely to the speed of indued air a gas jet generates; not to mention gas jet diameter to mixing tube diameter, and keeping track of good gas and air flow throughout the entire burner. You don't need to be a combustion engineer to get the general idea, or to pay attention when someone gives you the particulars on a silver platter. If you aren't willing to do that much, you will end up with a junk burner.

[Mikey98118]

So what is the proper ratio of opening to mixing tube diameters? It depends; a minimum of three to one (3:1) is indicated for maximum air induction on naturally aspirated linear burners. Three to one is likely to be the maximum ratio for fan-blown linear burners; greater than that ratio simply wastes fan power in forced air types, and causes a tendency to create back flow of the gas air mixture in fan powered Vortex burners.

Next we need to think about length to width in reducer shapes; longer is better. As to straight funnel versus convex and and concave walls; I have found straight reducers (ex. funnels) to be the most efficient, and slightly convex reducers to be the least likely to create too much back pressure next the a weak fan (creating a dangerous tendency to reduce flow direction and dump gas into the fan area, instead of down the reducer to the mixing tube). What about a concave reducer? What a D-U-M-B idea!

[Frosty]

Yeah, bell reducers are a really poor design but it's what's been used since the things became available. As much as I hate to say it, "If it's dumb and it works it isn't dumb." 

The thing is it only "works," it's pretty straight forward to do better than "just works." 

Yeah, weld fittings are far better than screw plumbing but folk need to have a welder, know how to use it and how to weld pipe while keeping it aligned and straight. Back when I started messing with burners, before Cruz's folder of inducer info I was looking at weld pipe fittings and believe it or not there were off the shelf "Trumpet" shaped weld reducers, an ideal shape for a linear inducer's air intake! They were made for through hull tank outlet, drain, . . .somethings. Unfortunately the smallest I saw at the time were 3" dia. on the small side. Oh well, back to plumbing parts.

At one point I browsed in junk, thrift, etc. stores and yard, garage, etc. sales for cheap horns, (brass section horns) but never saw one of appropriate size for a linear burner on any scale I could use. Same for semi air horns those those came a LOT closer and still a maybe.

Frosty The Lucky.

[Mikey98118]

I have considered jet ejectors as generally the best design for a burner; the first time I heard the idea that history has cycles, I didn't think it would apply to mechanics; wrong! My two latest burner designs are both linear burners; one is naturally aspirated with a fan powered (not fan blown) supercharger, and the other is straight forward naturally aspirated. Vortex burners (fan powered) totally maxes out every potential of linear burners. Oz burners (only naturally aspirated), should max out ease of construction for people who have very few tools. Of course, just when we think we have finished the race, something new occurs, and its back to the drawing board. I sat on the ideas behind Mikey burners for more than six months before giving in to them.

[Jbradshaw]

Here's a 3/4" Mikey burner I just finished up. Photo taken about 2 minutes into the first test fire on10 psi with a 0.030 tip. 

This weekend I'll try to get some pics of the Frosty T and Dave Hammer burners that I built previously and post them all up.

 

[Mikey98118]

I think it could use a little more tuning.

A smorgasbord of burner ideas, both good and very very bad:  https://www.pinterest.com/dmasontov/venturi-burners/

[Jbradshaw]

Can you explain what it is you see in this pic that tells you it needs more tuning? I have some ideas, but would like to understand better. I plan on changing out the tip to a 0.035 tonight to see how that effects things before making any more permanent changes. 

[Mikey98118]

First, please understand that what I do not see is a weak flame. You could mount this burner ,as is, in a forge, and make the equipment quite hot, BUT it would create a lot of scale on your work, because its long secondary flame contains a lot of free oxygen, which will reach your parts before being consumed; some of that free super-heated oxygen will combine in the heating steel to quickly form scale.

Going from bottom to top in your photo:

First, I see a flame nozzle with an ORANGE end, rather than merely RED end. Burning propane can only get a flame nozzle to orange incandescence , in the open air; this is the first indication or a very hot flame.

Next, comes the base of the flame; what should be a single primary flame of blue, instead it has four zones of combustion.  The mostly white area is probably from the combustion of carbon. Carbon can only come from from deterioration of the propane molecules. I suspect that the propane and air isn't leaving that very hot nozzle area quite fast enough to prevent carbon from forming. You will note some blue with just a touch of green in it for a short distance before it thin out to only a thin "skin" on most of the periphery of the flame, and then thickens again at the iip of the flame envelope; this area is what used to be thought as a neutral flame by most people, but is actually a little reducing.

Third, we see a pure blue area at the tip of the flame, just beyond the blue-green reducing flame front; take a good long look at this flame area, because that is a truly neutral flame; this zone is what you want to have in the whole flame.

Fourth we see the area usually described as "secondary flame". Note that it is purple. I think this is do to an abundance of super-heated oxygen, which escaped the so called "primary" flame.

Again, you need to understand that, while this may seem complicated and ominous, the answer to this puzzle is straightforward. Everything we are seeing is the result of gas/air mixture speed as it enters the flame nozzle versus breaking effect by the nozzle. You may need to raise gas pressure into the burner, and shorten the amount of overhang, to prevent the faster flame front from blowing right off the end of the burner.

I would begin by shortening the amount of overhang between the end of the flame nozzle and the end of the mixing tube. You also need to make sure that the diameter of the nozzle is correct for the burner size. The orifice diameter of the gas jet (MIG contact tip) needs to be right for the burner size. In the book I recommended both MIG tips for .023" and .030" welding wire; this is because the smaller tip is just a little too small and the 030" tip is just a little too large. I advised readers who wanted a perfectly performing burner to use the smaller tip, and use torch tip cleaners to enlarge it a thousandth or two at a time, on till satisfied. The orifice size of the gas jet much match up properly to the inside diameter of the tube. You seem to have used tubing, rather schedule #40 water pipe; this is likely to change the inside diameter of your burner from that of the pipe that jet is effecting; that could end up good or bad; what we can say for sure is that it can't be predicted. Finally, my burners are set up so that you can move the gas jet back and forth in the area of the air openings to 'find the sweet spot". he burner is provided with set screws to allow the builder to make sure the gas tube is kept parallel to the burner's axis; if it isn't, or if the MIG tip isn't kept parallel to the gas tube, the flame can be partially or completely destabilized.

What you are trying for is a solid blue flame front with a rear side that is a cone shaped empty area. There should, ideally, be no secondary flame at all; this ideal is possible, but not practical. A wisp of secondary flame is feasible and  will vanish in a heated forge, where the flame will turn light blue, and elongate into a blade shape.

What else do you need to watch for? Wants you get your burner built and tuned up to a single zone of combustion, the only thing left that can go wrong is opening up the sliding choke too much; then the flame will become a darker blue, indicating excess oxygen. I once had a burner that I could open up so far that the flame turned purple, indicating that it was totally oxidizing. This is a serious problem.

Once we make the magic flame our Mad Scientist can come out, causing us to laugh insanely and burn a lot of steel; naughty, naughty! What we need to do is pay careful attention to what we are seeing in the flame, so as to prevent the nut behind the wheel from running our car into the ditch. How would I no this?  Dr. Frankenburner laughed madly and played in my garage for months...

[stockmaker]

Mikey, loved your explanation!  Wow.  I have a question for you.  Shouldn't the adjustments you suggest be performed when the burner is insides the forge?  Maybe a better question is what do you suggest be done prior to mounting in the forge and what adjustments be done after.  Thanks 

[Jbradshaw]

Thanks for the detailed feedback. I really appreciate the break down of the different zones of the flame.

A couple clarifications of things from my end. This is a 3/4" burner (I am assuming you think it is a 1/2" burner based on the comments about orifice size). I did use stainless steel tubing for the flame nozzle (1 5/16" ID 304L, the 316 was more than twice the cost so even if it lasts longer it would take me burning through 8 of the 304 flame nozzles to catch up with me financially).

After I posted the photo I realized that I forgot to do any adjustment of the flame nozzle overhang. I will play with that first and then try a different size MIG tip.

[blacksmith-450]

I have a hard time accepting (understanding) that there is as much adjustment for a burner that has 3-4 parts only. 

4 hours ago, Mikey98118 said:

First, please understand that what I do not see is a weak flame. You could mount this burner ,as is, in a forge, and make the equipment quite hot, BUT it would create a lot of scale on your work,

Running too rich brings a lower temperature, more CO and... ?

[Mikey98118]

Stockmaker asks  "Shouldn't the adjustments you suggest be performed when the burner is insides the forge?  Maybe a better question is what do you suggest be done prior to mounting in the forge and what adjustments be done after. "

There is a burner flame, and a forge atmosphere/flame/environment ; these two intertwining, yet separate things, interact. Sometimes they must be considered separately, and at other times, they must be considered together. Furthermore how often they can simply be considered together depends heavily on the burner. Every burner needs to be tuned to some extent; some of them to a great extent. Also, if the burner has been set up to run only within a piece of heating equipment, it can't be tuned out in the ambient atmosphere of the shop, if it has no flame nozzle, it must be tune out in the open, at least the first time.

Every burner I design, is meant to be tuned out in the open; once it is so tuned and mounted, the choke setting and needle valve and/or regulator setting on the gas pipe are all that can be changed within a forge or casting furnace. I design burners for maximum performance; this requires as many adjustments as possible to get the flame just right; trying to do all that inside heading equipment would be going about the task the hard way. Other burners call for other procedures.

jbradshaw,

I gave you the right MIG tips for a 3/4" burner. If you have my book or download a pirate copy, you can see it listed in the chart on page 22. A MIG tip for .023" is also listed in that chart for 1/2" burners, but only because there is no such thing a a smaller MIG tip; not because it has an ideal orifice diameter.

[Mikey98118]

blacksmith-450 writes " I have a hard time accepting (understanding) that there is as much adjustment for a burner that has 3-4 parts only. "

Unless you build one, you are doomed to go right on having a hard time understanding them.

You also write " Running too rich brings a lower temperature, more CO and... ? "

And a longer flame; sometimes a lot longer flame, depending.

That should have read  "... if it has a flame nozzle, it must be tune out in the open, at least the first time.

[Welder74]

Hey guys I'm new to all this but the building part. I built my forge , anvil and 2x72 belt grinder. But I don't know if my forge is burning right it get really hot after I turn it off. I didn't use wool insulation just fire brick and 1/4" steel plate. 

Should I insulate it???

Will I hurt it if I don't??

And will my metal to be forged get hot enough weld?

[ThomasPowers]

Not knowing how you plan to use your forge makes it hard to answer your questions about it's constructions.  Sort of like "Should I use my vehicle for racing or for carrying heavy loads?"

Use of kaowool insulation makes a forge that heats up faster and uses MUCH LESS PROPANE; but is less rugged. So for a hobbyist kaowool often makes a lot of sense (and dollars), for a person sharpening jackhammer bits the extra heat transfer from hot brick and more rugged construction might be best.

Hot enough to weld depends on a lot of things; the people I know that use a firebrick forge to weld in often tell me that it takes an hour or more to heat the forge up to welding temperature and then it can weld like crazy the rest of the day.

[Mikey98118]

So far as the as the burners are concerned, they are producing soft flames that are slightly reducing.=; this is shown by their color.

[Mikey98118]

 Mixing tube length

  One of the first burner design principles I learned was called "the nine diameters rule of thumb," which stated that the length of a mixing tube, in a linear burner, should equal nine times the inside diameter of the mixing tube. Later on I incorporated that principle to include the area forward of the air intakes to the end of rest of the tube, on my jet ejector style tube burners (AKA Mikey burners). Generally, this rule of thumb works out well, but like any rule of thumb, it can be bent somewhat to suit particular needs. Nine times the diameter can be lengthened to ten, to smooth out a rough working burner, or shortened to seven diameters to deliberately shorten the length of the flames in burners mounted within a forge, if its flame is too close to the work pieces.

I would go with eight diameters on a "T" burner, just as Frosty recommends. Nine diameters works best on a Mikey burner, or a typical linear burner, and fourteen diameters on a Vortex burner. Different designs have different needs. One rule of thumb is that it is much easier to shorten a mixing tube, than to stretch one. Consider rules of thumb as ballpark figures for beginners; something that is wise to adhere to, at least until you know enough to experiment intelligently; and when might that be? Not until you thoroughly understand what you are looking at, when you view your burner's flame. After eighteen years, I'm well along, but still learning...  

[Jbradshaw]

On 5/20/2017 at 3:43 AM, Mikey98118 said:

 

jbradshaw,

I gave you the right MIG tips for a 3/4" burner. If you have my book or download a pirate copy, you can see it listed in the chart on page 22. A MIG tip for .023" is also listed in that chart for 1/2" burners, but only because there is no such thing a a smaller MIG tip; not because it has an ideal orifice diameter.

Thanks for pointing me to that chart.  I forgot about it. My confusion came from page 56 where a 0.030 and 0.035 tip are called for in the build instructions.

I moved the flame nozzle and am getting a much better flame (still with the 0.030 tip). It has a nice clear cone at the base of the flame and a smaller (but probably still too large) more orange secondary flame. Unfortunately I can not seem to get a proper photo using my phone. Being cognizant of the lessons above, the digital image and what I am seeing with my eyes are totally different colors. I will try to get a  better photo with my camera. 

[ede]

Jbardshaw,

What thickness 304 did you end up using for the nozzle?  I believe Mikey's book calls for .120", I ended up using 316 ss .065 because it's what I had.   Nice work! 

[Jbradshaw]

Ede,

i used 1&1/2" tubing with 0.095" thick walls for an ID of 1&5/16". I used this ID because the chapter notes stated it would slightly increase performance and decrease fitting work. More performance for less work sounded like a good deal to me!

[Mikey98118]

jbradshaw,

In the first place you are quite right; there is a discrepancy there. Figures in the individual chapters were derived as I worked on each burner, to produce the best possible results. However, while I used 30 PSI as my top figure for their stated abilities, I actually tested them clear to 54 PSI; the limit that my damaged 0-60 regulator would reach. I then chuckled to myself about sand bagging the figures, to protect my tender author's backside.

While the chart appears early in the book, it was one of the last things I produced, and reflects the best figures for a 0-30 pressure range, thus I outwitted myself; not for the first time, and certainly not for the last.

Please show us a photo of the corrected burner flame, with a little write up of how easy it was to make such a giant difference; this would be so helpful for others in your position, and the author will keep his big mouth shut if it isn't absolutely perfect.

Thickness of the wall in stainless steel flame nozzles usually reflects the heaviest material that is easily available in stainless steel,. I prefer a minimum of 1/8" but .065" will work okay.

[Jbradshaw]

Mikey comment away. Anything I can learn to improve my skill set is a positive to me. 

Here is the burner pictured above after minor tuning, same light (LED shop light on the other end of the one car garage and an overhead 100w incandescent bulb), same camera (iPhone 6). I moved the flame nozzle back from about 1&1/2" overhang to about 1&1/8" overhang. This is held in place with set screws so is very quick and easy to adjust. The other change was I small movement of the accelerator tube.  This is held in place by a single collet nut. So loosen and then tighten the nut back up. 

The flame is more blue to my eyes than this photo shows.

 

[Mikey98118]

Okay, what I'm seeing is a slightly reducing flame, that is almost correct. How can you tell this? Compare its tinge of green in the primary flame, with the perfect blue color around the flame's periphery, which turns into a short secondary flame on its tip. I would suggest that you drop down to the next smaller MIG tip diameter; when you do, don't be surprise if you need to lengthen the amount of nozzle overhang again. You are VERY close now.

[Mike Hall]

I have my burners built and I'm looking for a high pressure regulator. I talked to a guy this morning that has a regulator that can be adjusted. He said it can be adjusted from 20-45psi. Should I consider this or just find a regulator set to 30 psi?