Burners 101

[Mikey98118]

Thought you'd like that

[Mikey98118]

Progress

The heart of a naturally aspirated burner is its gas jet. A hot, efficient, gas flame depends on adequate gas and air mixing, but it also depends on a fast flow of the gas/air mixture down the burner’s mixing tube. Initially, the home built burner had a small hole drilled into  the side of a its gas pipe, and compressed fuel gas was forced through it, creating a  weak and rapidly expanding gas stream. The low pressure area caused by such a stream was barely able to induce sufficient air to create a neutral flame. Extending that hole into a tube shaped orifice produced a fast compact gas stream, and acceleration of more induced  air; from this, all the rest of the burner’s performance springs.

 

The Bernoulli Principle is a naturally aspirated burner's  motor, but how you engineer the motor is important. Lengthening the gas orifice into a tubular exit with MIG contact tips, (and then by capillary tube), was followed by placing the tips in the end of the gas tube; that was followed by streamlining the joint between tip and gas tube, which also made it easy to position the tip end and mixing tube entrance for maximum air induction.

Recently, Curtis (AKA Another Frankenburner) has improved air intake design  as radically as the MIG tip improved gas jets; with equally startling improvements in burner performance (see the 3D Printing thread to follow his progress). Next will come homemade ceramic flame retention nozzles. There is a continuing progression in all of these improvements; each one enabling the next.

[Mikey98118]

Putting on the breaks

The fuel gas and air mixture benefits from turbulence and speed of mixture flow. Swirl provides maximum mixing with minimal breaking of the mixture flow's forward speed; this is why--so far--it is the only acceptable form of turbulence throughout most of the burner's length. The exception is in the flame retention nozzle; here, maximum breaking  and zero swirl is the goal.

[671jungle]

This design is an attempt at an “easy” screw and press together burner using the Mikey intake slots. My major issue while making burners is producing a stable accelerator. This should take care of that although sacrificing distance adjustment. Which it doesn’t need once correct distance is realized. A choke can still be applied.

The mig tip will be pressed and sealed into the 1/4” female hose barb, and the edm tube will be pressed into the mig tip. 

The 1/4” male reducer will screw into the hose barb, and the Mikey cut 1/2” pipe will screw into the other side of the reducer. Sand everything smooth and it should work? Establishing proper distance of accelerator would probably be tedious.

The resulting system would be rigid enough to be banged around and not lose tune as it is screwed together

[Mikey98118]

Maybe; These burners can be finicky about the slightest gas like in the fuel system. But if your burner develops problems do to fuel leaks, then you can use solder, silver braze, or form of gasket seal to stop the leak. Use three air intakes.

[G-son]

I just thought of using 3D printer nozzles as gas jets for small burners. I've just made a little research, but they seem to be available down to 0.2mm diameter. Not sure about the internal shape or length of the narrow passage, probably varies between different manufacturers. Do they seem suitable? Availability seems good, price okay (but not great, like the mig tips).

[G-son]

I took the liberty of making a list of Mikeys suggested MIG tip vs. pipe sizes, and added the actual pipe diameters (instead of the schedule 40 pipe sizes that aren't the real size) and the tip size in percent of the mix tube diameter. I thought it could be useful for people who build burners using other kinds of pipe or tubing, and the gas jet vs. mix tube size may be useful for people building other size burners  than the listed ones - something in the ~4.0-4.6% range seems to be right for most of the listed sizes, possibly more on smaller burners and less on larger ones. 

I just gathered the numbers in one place, everyone gets to draw their own conclusions and use it as they see fit. The information was already out there, I just try to make it a bit easier to compare and use.

[Mikey98118]

The printer jets remind me of a similar idea I had to use replacement gas jets a few years back. The printer jets appear to have the same drawback; very short orifices. If you have to mount capillary tubes in the jets to get the desired result, than nothing is gained over using a MIG contact tip.

[G-son]

Which brings us to the topic "how short is too short?" (Keep your girlfriends out of this one.)
Looking at the jets in store bought small burners the orifice seems to be quite short, a couple of millimeters at the most, and often there's a filter of sorts mashed down into the mouth of the jet too so there's no laminar flow into the orifice for sure. Not a perfect design by what we have learned around here, but it seems to work. 

With smaller diameters shorter orifices would seem to be acceptable, but how much is enough? 

[Mikey98118]

In the interest of full transparency, I admit that it is possible to use a mere hole--if it is small enough--with a very high pressure jet to do similar work to the gas jets I recommend. There is know free lunch, however; the hole needs to be about .004" at full cylinder pressure to run a 1/4" burner; That size orifice will plug closed from impurities in the propane before you can finish half a five gallon tank.

[G-son]

Thankyou, that's interesting.  

[jwmelvin]

1 hour ago, Mikey98118 said:

 .004" at full cylinder pressure to run a 1/4" burner

Two thoughts: (1) seems reasonable to run a regulator so perhaps we’d end up with a more reasonable hole size at, e.g., 5 psi; and (2) is the idea with a long tube that you are using the length to create a pressure drop, or that the length conditions the flow in a desirable way?

[Karl Stoeckle]

I am working on reducing my accelerator orifice for a 1/2" Mikey burner.  I am thinking of buying capillary tube from Ziggy's with OD of .064" and ID or .020" and then drilling out to .028" with # 70 drill (.028").  What do you think? Thanks. Karl

[G-son]

We want the air and the gas to mix as good as possible, if I've understood correctly this is usually achieved with a rotating flow (a.k.a. swirl) or some other kind of turbulent flow through the mixing tube, correct?

 Is there such a thing as too much swirl? (I think someone has said there's no such thing in a naturally aspirated burner, but that implies there can be such a thing somewhere.)

Has there been any known attempts using multiple gas jets in a burner to create/increase swirl? Say, for example, one gas jet in the conventional location, and one or more (possibly much smaller) jet placed at an angle somewhere in the burner to cause the air-gas mix to rotate as it goes down through the burner?

[jwmelvin]

That’s an interesting idea. Perhaps tough to tune but with small enough jets maybe possible. 

[Mikey98118]

On 5/25/2019 at 5:13 PM, jwmelvin said:

Two thoughts: (1) seems reasonable to run a regulator so perhaps we’d end up with a more reasonable hole size at, e.g., 5 psi; and (2) is the idea with a long tube that you are using the length to create a pressure drop, or that the length conditions the flow in a desirable way?

"It seems reasonable that..." is often a good departure point for an adventurer; sometime also to success--sometimes

[jwmelvin]

I was just curious why you would be discussing full cylinder pressure. 

[Mikey98118]

On 5/25/2019 at 6:56 PM, Karl Stoeckle said:

I am working on reducing my accelerator orifice for a 1/2" Mikey burner.  I am thinking of buying capillary tube from Ziggy's with OD of .064" and ID or .020" and then drilling out to .028" with # 70 drill (.028").  What do you think? Thanks. Karl

If you intend to build smaller burner later on, that could make sense. You could also fill the orifice of a MIG tip with solder, and drill out a smaller hole through a lot softer material. What works out easyest in the situation is what I recommended; that will depend on the tools you have available

7 minutes ago, jwmelvin said:

I was just curious why you would be discussing full cylinder pressure. 

All cylinder-mount Propane torches are exposed to full cylinder pressure; most of them modify flow with needle valves; this does NOT modify that pressure. Thus, their gas jets are designed to run at extremely high pressure. When we look to make end runs around limitations, we must use the techniques we find available.

[jwmelvin]

Ah, got it; handheld cylinder.

A needle valve modifies pressure, but does so as a function of flow rate. So it may be valid to approximate the jet pressure as the cylinder pressure when one uses such a small orifice and runs the needle valve fully open. 

[Mikey98118]

A needle valve modifies flow. Beyond the valve, pressure will drop somewhat, depending on how far it is opened and how high the pressure is coming from the fuel cylinder. Down stream from a pressure regulator the amount of change a needle valve can give is great. Modification on a cylinder mount needle valve is small enough that the gas orifice must be used to help the valve to do the job.

The question isn't whether or not the systems works, but how well it works. Everything is a trade off.

[671jungle]

I think i have a winner for a stable gas jet. 

Turned the mig tip in the drill against a file just enough to get a good press into the 1/4" female hose barb with a vise.

The mig tip will be fitted with an edm tube to extend the jet to proper distance. The edm tube can be drilled out to suite burner size.

The 1/4" male - ? female adapter will allow for all burner sizes(MikeyBurners).

This design should be rigid enough to be used as a handheld if needed.

[Mikey98118]

Yes, this will work just fine with orifice diameter of .020" and down, becuase the smaller the gas jet the the less need of a gas tube feeding into it.

[Another FrankenBurner]

The jet position will not be very adjustable with this configuration.  As it looks, the jet will land quite a bit further back within the burner then Mike's recommendation of 1/4" to 3/8" behind the front edge of the air inlets for his burners.

[671jungle]

On 5/29/2019 at 12:37 AM, Another FrankenBurner said:

position will not be very adjustable

these brass tubes come in different sizes and are thick and sturdy enough to be drilled out and pressed.

Inserting them into the mig tip will extend the jet orifice to the proper length. it will take some playing around with to realize positioning. 

It will be permanently tuned to neutral. A choke will richen it up when needed?? At least that is my idea im going for ease of construction and   eliminatingshakey/touchy burner parts.

[Mikey98118]

3 hours ago, 671jungle said:

Inserting them into the mig tip will extend the jet orifice to the proper length. it will take some playing around with to realize positioning. 

Yes, and everything becomes a trade-off among ever tightening circumstances with small burners