coca-cola burner

[dian]

im building a forge that should be able to get to as high a temperature as possible. so i started experimenting with propane burners. i have built quite a few burners over time for hardening or forging small pieces and most of them are adjustable to the point where the flame goes out on the lean side. i quickly found out than more air is needed in a closed chamber than in free air so the goal is to have an even larger reserve to lean the burner out.

this is the prototype design i came up with:

 

 

im getting a good flame with the secondary (or is it primary?) intake completely closed, so there is hope for success in the forge. i like to run my burners at around 45 psi. the orifice is made with a 0.7 mm drill (0.0276") so i guess its around 0.029". im using 96% propane (the rest being ethane and butane) at 900 feet elevation.

 

what do you think?

Edited February 25, 2021 by Mod30
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[Mikey98118]

Presuming that your burner's mixing tube is 3/4" pipe, then your gas orifice diameter is right. But you haven't said how long the hole is; at that diameter it should be about 1" to 1/14" length for maximum air induction. However, If I'm seeing past the bottle well enough, air is induced into  roughly elliptical ground openings in the wall of a pipe fitting. If this is correct, and if they are the only air paths, you need to enlarge them, to achieve sufficient air flow. The large diameter of the bottle only increases air spin; not induction.  The gas orifice and flame retention nozzle should create lots of air induction. But tiny air entrances will put the brakes on that process.

On the other hand, if air also is slipping past the gas pipe, and into the end of the pipe fitting, then as near as a can tell, the gas tube is squar; this will create vortices in incoming air; creating drag, which puts the brakes on air induction. You can check for that effect by moving tghe gas pipe further away from the end of the mixing tube. Without drag, air induction would fall off seadily, with drag, there won't be a sharp decline. What to do? taper the end of the tube close to a point.

[dian]

hi mikey, thanks for the feedback

trying to understand what you are saying: what "hole" should be 1-1.25" long? the orifice?

 

[Mikey98118]

The gas orifice on my burners have been less hole than tunnel. In fact, I used to call them "accelerators" to stress the point of why I prefer MIG contact tips to mere holes in end plates. When I started making burners too small for MIG contact tips to work, capillary tube were mounted in the tips, to keep the accelerator effect going. Finally, with !/4" burners, friction losses and the tars and waxes in propane (which create cleaning problems) have made 3D printer nozzles a smarter choice than gas tunnel orifices.

[dian]

the idea might not have been completely clear from the picture. the outer bottle neck is opened up to the id of the pipe and is attached too the pipe by the short connector. (actually there is 6° taper and a corresponding chamfer in the pipe with the edges blended in.) the inner bottle neck is closed by the choke. the air enters the pipe between the two parts through the annual opening that is properly adjusted for free air operation.

as soon as the choke is opened ever so slightly, the flame goes out, so im led to believe there will be enough reserve in the forge.

this tip indeed has a short orifice. however i can screw mig tips in there as well and frankly speeking i dont notice any difference with this or other burners due to the longer orifice. if i think about it, a long orifice will flow less and if more gas velocity should be needed i can go up to 60 psi. im sure you explained your idea with the "accelarator" somewhere. where do i look, please? 

 

Edited February 25, 2021 by Mod30
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[Mikey98118]

9 minutes ago, dian said:

im sure you explained your idea with the "accelarator" somewhere. where do i look, please? 

In a book that is out of print.

[Mikey98118]

I just posted a complete answer to your question on the Burners 101 thread.

[dian]

as the experiments looked promissing i started building the burner. i made the outside intake out of kitty-litter-epoxy. it  runs on the slightest opening of the choke.

the inside shape looks like a problem because the wall has to be very thin for the secondary air (siphon?) effect to work . im trying to find/think of something out of metal. the best so far is a thermo-bottle i have, but the throat is too big. does anybody have a good idea without me having to take up metal spinning?

 

the shape, btw, with its parallel inlet and outlet walls is inspired by some rocket jets i came accross. i thought if i works well for propulsion why not as an intake?

 

 

Edited February 25, 2021 by Mod30
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[Mikey98118]

Try searching for funnels.

You have complete combustion in a primary flame envelope; a good position to start from

[dian]

this is the intake shape im trying to reproduce:

 

 

[dian]

trying to find best position of the nozzle by replacing the choke with a cardboard-choke. i figured the smaller the opening at a constant flame temperatue the more "suction" im getting. well, it turns out the nozzle can be almost anywhere, the difference being a few degrees. i then settled on what seemed slightly the best.

 

 

Edited February 25, 2021 by Mod30
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[Mikey98118]

With such a large funnel structure as an air intake, it wouldn't be surprising if you need to increase the gas orifice diameter. Just a thought.

[Frosty]

On 2/19/2021 at 9:46 AM, dian said:

the shape, btw, with its parallel inlet and outlet walls is inspired by some rocket jets i came accross. i thought if i works well for propulsion why not as an intake?

The gasses are going opposite directions? 

If you look at commercially made burner intakes they are typically trumpet shape. The intake air passing over a convex airfoil curve accelerates it, lowers the pressure and induces a stronger spin. Just like water down a drain.

I just don't know where to find something to use as a mold to cast one and I've looked at plastic soda bottles more than once thinking about doing the experiments you are. 

I'm just mostly following along. Great job so far.

Frosty The Lucky.

[dian]

propulsion gasses exit on the big end. i think my coke funnel has the shape you are talking about. weirdly  enough they are the only ones among all the other plastic bottles, the problem being that i dont drink the stuff. the convex shape is in the throat and the rest is there to stabilize the air (and prevent wind messing with it, as i hope).

it bugged me that there was not much difference in the position of my nozzle, so i figured it might need to go deeper into the throat, leading to the tapered variety (same size orifice). this one reaches into the steel pipe itself but results were the same, i ended up with the same position as before. what i found, however, was that now i could fully open the cardboad-choke, so the suction was less and i got a lower temperature as well (10000f less).

as the nozzle is step drilled it occured to me, that it might not be flowing as much as the "stubby-nozzle". but going from 45 to 60 psi didnt make any difference.

any thoughts on that?

 

Edited February 25, 2021 by Mod30
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[dian]

cant edit post. why is that?

so the drop in flame temperature was 190°f. (had to look it up.)

[Glenn]

All posts have a short edit window. 

If you go beyond that time, tell the mods and your posts can be combined.

[Frosty]

The bell on a rocket is internally a concave surface and is designed to direct the thrust and resembles your intake bell. If you lay a straight edge on the inside, a pencil is good it touches two points and there is open space in the middle. Right?

A trumpet bell is convex, if you lay a straight edge on it it will only contact it in the center or rock like a teeter totter. Yes?

This type bell is used on horns to disperse sound waves, not focus them. 

When the intake bell is convex air coming in if forced to the center compressing making a higher pressure zone. There is greater friction as well, air flowing into it is in increasingly hard contact with the walls of the bell. Any bell beats no bell but there are better.

Air flowing down a trumpet bell is constantly trying to flow AWAY from contact with the bell and must follow it because there is a low pressure layer of air in contact with the curve. This is exactly the same behavior that makes airplane wings generate lift. Air flowing over the curved upper surface must travel a longer distance in the same amount of time and is constantly trying to move away from it causing a low pressure boundary layer. Higher pressure on the bottom of  the wing pushes the wing towards the low pressure.

The Bernoulli principle explains it with math and everything. 

Anyway, as air is drawn into a trumpet bell intake it flows faster and with less resistance because of the low pressure boundary layer contacting the bell itself. Conservation of angular momentum causes the air to form a vortex as it flows to the center and out the mixing tube. A vortex generates low pressure in it's center which causes more air to be drawn in.

I couldn't find an image I really liked to illustrate a trumpet bell. Most trumpets get polished before pics are taken and it's really hard to see details like curved surfaces in polished metal. Pic 1 shows the shape pretty well from the outside. Pic 2 is made from carbon fiber and isn't shiny so might show what makes a proper intake bell shape.

Please note a trumpet isn't likely to be the right trumpet bell to make a 3/4" burner but it's the shape you see in commercially made propane burners that aren't made from plumbing parts. 

Frosty The Lucky.

       

 

 

[Mikey98118]

Or to put things another way, the point of the intake Trumpet is to provide swirl to the intake air--not thrust.

[dian]

one could also copy a carburetor or injection stack, but how they work with gas induction would have to be seen.

 

anyway, the basis is the classic pipe-fitting-burner that produces a flame temperature of 2165/2206°f (45/60 psi). the position of the probe is optimised for each measurement and choke adjusted to max. temperature. as the flame tends to get hotter with time and there are some "inexplicable" fluctuations there is some scatter to the data and i took the highes achieved. my setup consists of an inexpensive instrument and probe, combined with a professional compensating cable (that cost me more than the rest, because i had to get it locally). therefore the absolute values are a bit questionable and i will be looking at the differences. everything with my obviously "magic-stubby-nozzle".

(1) same with shorter pipe: 0/+62°

(2) same setup with cat-liter intake (last picture): +15/+22: not much gain. this is not surprising, because all my burners can be leaned out until they go out in free air. but consider this: inspite of the minimal opening of the choke, once in my small (experimental) forge it can be completely opened up without the flame going out. thats why im trying to get more air in there.

(3) not relevant for what im doing here, but just for the hell of it (compare with 2165/2206):

- machined fitting: -27/-18 (dont mess with the fittings, they do exactly what the are "supposed" to do, for some reason.)

- expansion pipe: -10/+94 (maybe im onto something here)

- welding reduction: -14/-10

then the cast expansion pipes:

(4) big (16° included, length 3.15"): +81/?

(5) small (12°, same lenght): +182/+216

(4), (5) with cat-intake, all numbers referring to "2165/2206°f.

 

 

 

Edited February 25, 2021 by Mod30
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[Frosty]

Dian:  We really need to work out a common terminology so I don't have to keep asking you what you mean. 

Until then. 

I don't know why you made your mixing tube from multiple pipe nipples and couplers. In my early experimenting days I found anything but a single length of pipe inhibited performance.

I discovered that machining the threads out of either the T fitting's air intake ports or the thread protectors I use for the flame nozzle inhibited performance. I have a hypotheses and empiric results but no measurements to back it. maybe later if you're interested.

I really like the flame nozzle in your 3rd. picture, it's much closer to a commercial fame nozzle in shape. 

I much prefer to build burners that operate with a SLIGHTLY richer than neutral flame across it's operating range. I can't think of a good reason to design one to run so lean it goes out, then install a choke to correct a designed problem. I did similar things when I first started to explore the "envelope" so to speak. Envelope refers to the outer boundaries of what will or won't work, it's not a measure of performance.

 There is back pressure when you fire a burner in a forge, this is why I keep telling people not to tune burners in free air and expect them to work as expected in the forge. 

Carburetors or air intakes for injected engines have true "Venturis" but designed for a different purpose than what we need for a NA burner intake. We need one that makes it easier for the propane jet to induce combustion air intake. A side and highly valuable side benefit is inducing a strong spin to the intake air. 

The venturi in an engine is designed to maximize the strength of the boundary low pressure zone to assist in introducing fuel and atomizing it. The motivating force drawing air in is generated by the pistons making ease of flow insignificant to the root purpose of an engine intake venturi. The same principles but entirely different purposes. Make sense?

An engine type venturi might be an improvement in blown (Gun) burners but maybe probably not enough improvement to be worth the effort to develop and make. 

I really don't understand the thinking behind the spherical attachment around your gas jet. What is it for? All my experience tells me is, it severely restricts air intake. I suppose it could act as a choke but adjusting it would also move the gas jet closer to or farther from the mixing tube which alters induction rates. 

I'd make more comments and ask questions but I'm having too much trouble staying focused. It's not on you, I'm a Traumatic Brain Injury (TBI) survivor and poor focus is a common issue. I'll try to take your posts one thing at a time and see if that works better.

Frosty The Lucky.

[dian]

its all very simple:

1.  the couplers are there to be able to easily modify the length. the pipes almost touch and i dont see any detrimental effect.

2. i wanted the choke to be deep in the throat, so i can be moved out of the way and also to reduce the sensitivity. together with the position of the nozzle optimized before it has to be after the nozzle and i assumed the "ball-choke" woud flow more than a simple disc that would have to have a long stem anyway.

3. once i get the new forge built i can see what the burner does in there. however it will be much, much harder to tune it in the forge, e.g. the location of the probe has to be changed for every measurement. also because of the inertia if i were to measure forge (not flame) temperature. so far the experiments are encouraging yielding a 200°f difference to a "traditional" setup.

3. i was talking about injector stacks not carburators.

so the interesting question is: where does the increase of 200°f come from? how can it be explained?

then, and on the basis of above, where do i go from there? decrease the angle further, play with the lenght of the expansion cone, what else? (the blue flame is actually burning in the first third of the cones and what we see are the hot gasses colored by some traces of waterglass.)

any ideas on further improvement of the flame temperatures will be appreciated.

 

 

 

[Frosty]

I had the benefit of some literature that gave me the most effective ratios for these devices before I started playing with them. I haven't found a more effective ratio for the length of the mixing tube than 8:1. There is a little leeway longer or shorter but not a lot guys are getting good results with 9:1 in linear inducers but it reduces induction on a jet ejector type. For the little experimenting I did with different ratios I just bought a pipe nipple the length I wanted to try. 

I'll be very interested about how your choke concept works, I've never seen it done that way.

Yeah, injector or carburetor either one is a PROPER Venturi. I used one to illustrate how far your intake bell or the common plumbing bell reducer is from either a venturi or a proper intake bell. I was just illustrating a point.

Where the 200* comes from is no mystery, the air fuel ratio was closer to optimum. That's all the explanation there is nothing more.  

You are getting too involved with measuring flame temperature, there are easier ways to judge burner and forge effectiveness. Ron Reil spent years developing his linear burners to as close to an ideal air fuel ratio as he could but that sort of tinkering is his passion. Did it make a better burner? Probably yes. Was it a significant improvement? Not really there is a practical limit to how hot you want a forge to get and effectiveness isn't measured in absolute temperature.

Effectiveness is measured in how many BTUs per second of an adequate ambient temperature you can make and keep in the chamber. If the ambient temperature was the main factor I could use a butane soldering torch, butane burns hotter than propane or methane. Or even better I could use my oxy propane torch, that produces about 6,000f! Unfortunately there isn't a lot of flame there no matte what it's temperature.

Your flame is plenty hot enough to do forge(fire)welds and from here it looks like it's a large enough burner to bring 300-350 cu/in to welding temperature. Trying to squeeze the last possible temperature above the practical forge temp is the goal. It's not a bad goal but it isn't about blacksmithing it's about making the hottest flame you can. That's not a bad thing. It's just over the line of diminishing returns.

Frosty The Lucky.

 

[dian]

iv seen guys reach 2600°f (i believe with copressed air) and really wonder what makes the difference. i dont think it is a/f ratio, as i adjust this to highest temperature for each measurement.

actually im doing this for a friend. he bought a two burner forge for $ 3000 (swiss prices, you know) and cant get to forging temperature with propane. of course as much depends on the forge as the flame, but if the flame is not hot enough you get nowhere, right?. it should be much easier to tune the burner in the forge im building once it runs hot it open air. im trying to get as high as possible, because the next project will be a melting furnace for cast iron (hopefully). i mean, if i get the flame hot enough i could even melt steel.

concerning the lengh of the tube, are you measuring total lenght including the flare? i wonder how to translate this to my setup with the 4" long cone. using 3"of tube before the cone is an absolute minimum, it really only starts working with 4". thats 8"/id of 0.82" = 9.7.

 

 

[Frosty]

If someone is using compressed air they have a gun (blown) burner and it's just a matter of adjusting the fuel/air ratio. A gun burner can force the mix into the chamber and produce a lot of BTUs. It takes both, like voltage AND amperage to make electric appliances work.

If it's a good burner you can adjust the fuel air ratio and make it HOT. However it it's not making enough flame it can only get the volume so hot. A soldering torch typically has a flame in excess of 3,000f but it's not going to bring a forge larger than fits in a bean can to a decent temperature.

One of the four T burners in my too large shop forge will melt a spot in the 3,000f split, hard fire brick floor. I replaced it once but it started forming the molten puddle again. The other burners aren't that hot but I don't need them to be.

The length of the mixing tube is from the end in the intake bell to the end in the flare. Just the tube, nothing else counts. I don't measure the ID of the pipe it's not that critical. What I've found is critical is making them too long. Much more than 8:1 and friction starts to become a factor, linear type burners like yours do well enough up to 9:1. I go by what the pipe is marked which is always a little smaller than the measured diameter. If we start measuring them and making precise burners they every one would be different. There's variation from one run of pipe to another, sometimes quite a bit. Industrially the ONLY thing that has to match are the threads and being tapered they differ a little.

Casting steel is a LOT more involved and complex than just having a hot enough melter. Lots of people cast iron with Side arm or T burners and propane. How large a crucible determines how large the burner needs to be, hot enough flame is just a matter of tuning the fuel air ratio. Honest, that's the ONLY requirement for making HEAT.

Frosty The Lucky.

[dian]

i got sidetracked by other stuff and got back to the project only now. i did some more experiments back then. the highest flame temp. i achieved was 2425°.

i also tried to copy a design quite popular on youtube, without any "breakthrough". what kept me busy for a while is the fact, that the flame starts burning at the very start of the expansion tube. even when i really smoothed out the transition. then i made a burner for a smal table top oven, that has been working quite well (last picture, 12° included).

i might be a bit obsessed with flame temperature. i quickly learned, that by putting an extension (tube) on a well burning flare you can raise the temp. a little, the gas gets uniformly hot. but i decided to use burners where the combustion fully takes place in the flare, no real flame commimg out. it might be true, that the gas will burn in the forge anyway, but this way there is at least no oxygen inside.

well, in the end i found wind being quite a problem for flame stability and decided to go with a forced air burner.

 

Edited June 13, 2021 by Mod30
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