# Gas burner making high pitch, flute like, noise ??



## joanlluch (May 20, 2017)

I have been performing some simulation tests of the gas burner that I plan to use in my loco. The idea is to use the "open smokebox" approach that Bill described some time ago. The burner is a radiant, metal fiber type. The burner produces a bright red flame and it appears to perform really well

Cremador by joan lluch, on Flickr

However, I have an issue that I did not anticipate, and I can’t figure out how to solve. The problem is that in most conditions the system produces a very loud, high pitch, resonant like noise that resembles the sound of a flute. See this video: 

https://flic.kr/p/X62nzM

After some research, my understanding is that this is a relatively known problem that may happen sometimes while designing burner systems. The high pitch sound appears to be caused by some sort of combustion resonance that occurs with burners in constrained or long shaped combustion chambers. The actual phenomena is described here:

https://en.wikipedia.org/wiki/Rijke_tube

I wonder if someone has seen this issue before and whether you can point me with any tips or suggestions that I can try to avoid that.

I tried to make several changes, but so far I don't get with the proper solution.

Any ideas?


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## xo18thfa (Jan 2, 2008)

Put an adjustable choke on the air intake holes. Once the burner warms up it doesn't seem to need as much air. At least mine behave that way.

vr Bob


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## joanlluch (May 20, 2017)

xo18thfa said:


> Put an adjustable choke on the air intake holes. Once the burner warms up it doesn't seem to need as much air. At least mine behave that way.
> 
> vr Bob


Hi Rob, thanks for your reply. 

In my case, the hotter the burner becomes the louder is the noise and the greater is the vibration amplitude. Restricting air intake does indeed help, but then I found that a part of the flame is formed at the end of the tube (boiler), not in the firebox. 

My testing setup is extremely prone to produce this phenomena. The sound is really loud and annoying. It seems to do it whatever changes I try. It makes me think that there's a fundamental flaw in my design or the whole setup. I wonder how common is that?. 

Do you think that the size (or shape) of the pre-mix chamber has anything to do?


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## bille1906 (May 2, 2009)

Not sure of the design of your box
Is it just for testing or something you plan to use?
For sure, the sheet metal structure will amplify any noise and may be the cause of all of the noise

I would go ahead and build my firebox boiler and then try the burner in it

My ceramic burners sometimes howl for a second or two at the start and then go dead silent
As bob stated, poker burners do this all of the time and usually can be quieted down by choking off the air to a degree but this also reduces the efficiency and lighting ability of the burner


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## joanlluch (May 20, 2017)

Hi Bill, 

Thanks for your reply.

This is only for testing. It's just simply made steel sheet box simulating the inner part of the boiler, to help me understand gas burner behaviour before I make the actual boiler. The box has about the same shape as the firebox and the same section for the flow gases towards the smokebox.

As you point out, the sheet metal structure amplifies the sound. The sound of the vibrating sheet is partly audible on the video above, this can be eliminated by just wrapping the metal surface with something rigid (preventing it to vibrate), but the louder sound comes from INSIDE, just like a flute. In fact, if you add rigidity to the system the sound becomes even louder and the pitch is purer (Like the sound of an organ musical instrument).

I would like to solve this problem (or understand how to solve it) before starting making the boiler. The boiler will be a full locomotive type with wet firebox for a big 5" gauge loco, so it will be quite expensive to make. I just want to adapt the design to (hopefully) work without any forced draft, as you do on the "G" scale. I am not aware of anybody who has attempted this on a 5" locomotive.

After posting my previous message I read somewhere on the internet that by adding a section of perforated tube to the end of a the "Rijte" tube, the thermo-acoustic phenomena can be stopped by breaking the sound waves resonance. So this made me think that maybe I can have something placed on the smokebox to break this cycle. (?)


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## bille1906 (May 2, 2009)

Joan
It is close to the boiler design but not the same. The boiler will have tubes where the hot gasses flow through to the smoke box.
The design of the boiler will be the same no mater what fuel system you use only the bottom of the firebox and the smokebox will be different so i would go ahead and build the boiler and then try your burner in it. It may have no noise after that.


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## joanlluch (May 20, 2017)

bille1906 said:


> Joan
> It is close to the boiler design but not the same. The boiler will have tubes where the hot gasses flow through to the smoke box.
> The design of the boiler will be the same no mater what fuel system you use only the bottom of the firebox and the smokebox will be different so i would go ahead and build the boiler and then try your burner in it. It may have no noise after that.


Ok I see your point. I am still considering whether I should have (a) flue tubes in the traditional way as per the normal coal-fired boiler design, or (b) to have an enlarged kidney-shaped section with water tubes in it, before the hot gases enter a shortened flue tubes section, or (c) to have said kidney-shaped section with water tubes going all along the length of the boiler up to the smokebox with no flue gas tubes section.

I am a bit concerned that with the normal coal-fired boiler design (a), the pressure drop along the boiler may be too high for the open smokebox (without draft) to work properly. The safest design in this regard is of course (c), but I guess this would be at the expense of some efficiency loss. The primary reason for I decided to try with my metal sheet setup was to understand better how critical was the section available for gases through the tubes for the several possible scenarios. Then the "thermo-accoustic" noise issue came totally unexpected!. I guess I will continue with my testing of the several scenarios and will ignore the noise issue for a while.


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## xo18thfa (Jan 2, 2008)

joanlluch said:


> Hi Rob, thanks for your reply.
> 
> In my case, the hotter the burner becomes the louder is the noise and the greater is the vibration amplitude. Restricting air intake does indeed help, but then I found that a part of the flame is formed at the end of the tube (boiler), not in the firebox.
> 
> ...


Yes, that's what happens. Choke off some of the air reduces the noise. But then too much choke is inefficient. It's really a trial and error thing. 

Talked with Bill at the steamup last week. He said the length of the mixing tube should be at least 6 times the inside diameter. That's very true for a poker burner otherwise they don'y light very well. Bill says its true for ceramic too. Don't know if that affects noise however.

vr Bob


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## bille1906 (May 2, 2009)

this is an excel file that I use for designing my boilers. I made it up so long ago that I forget where I got the formula. I think Martin Evans.
It is for coal burners but it works fine for ceramic too.
If the tube is too small and long, it will choke things out
If it is too big and short, it will lose heat out the stack


od id Ideal length Surface area per inch
0.311 0.250 4 0.977
0.375 0.311 6 1.178
0.500 0.436 12 1.571
0.625 0.495 16 1.964
0.625 0.561 20 1.964
0.750 0.620 25 2.356
0.875 0.745 36 2.749
1.000 0.870 49 3.142
1.250 0.120 1 3.927
1.375 1.245 101 4.320
1.500 1.370 122 4.712

This program lumps everything together so you can't see the columns but on the first line od is 0.311*** id 0.250*** ideal length 4 ***surface area 0.977


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## SalM (Jan 2, 2008)

I looks like the heated air and the cool air to support combustion are using the same path.

If you can raise the whole assembly up off the burner base about 1/2 an inch and see if it is now quiet.

Cold Air flow up from the bottom of the burner and heated air out the open end of the asm. Air movement all in one direction.


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## Steamchick (Aug 19, 2020)

*My experience. Ceramic burner 4" diameter -like a siren!*

When I made a 4" ceramic burner for a vertical boiler I had a "100 dB siren" - that I found was caused by a tiny partial of dirt glowing red hot inside a hole in the ceramic. This caused flash-back then was blown out, only the fash again repeatedly at high frequency. This was amplified by the boiler - like a trumpet - and the note could be changed by adding length to the chimney. CLEANING the ceramic was the answer. I GUESS your metal fibre radiant is doing the same type of thing? E.g. there may be an odd wire that is near a bigger hole that allows the flashback buzz? Can you line it - at a cooler zone in the mixing chamber with a fine gauze to prevent the flash-back "buzz"? I did various changes to the Inlet and this changed the siren noise, but didn't eliminate it. I even added a rubber diaphragm on the end of a tee- piece on the mixing tube, nearly worked..... but cleaning the ceramic was the real fix. 
I do like your burner. As I want a bigger radiant for 4in dia boiler, can you send some sizes? To save me "reinventing the Wheel", or in this case, the fire!
Enjoy! 
Steamchick


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## Steamchick (Aug 19, 2020)

Just thinking about the sonic design of the test rig? - The air column is obviously being excited by the burner, so to make it "sing" at a note you cannot hear, just open the shutter on the fire hole where you ignite the burner.... - does that change or cancel the note?
A bit like the thumb hole on a flute/clarinet?
K


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## Steamchick (Aug 19, 2020)

Just thinking about the sonic design of the test rig? - The air column is obviously being excited by the burner, so to make it "sing" at a note you cannot hear, just open the shutter on the fire hole where you ignite the burner.... - does that change or cancel the note?
A bit like the thumb hole on a flute/clarinet?
K


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## Steamchick (Aug 19, 2020)

Bill Allen: is there an error in the line - 1.250 0.120 1 3.927?
Also from my Boiler design book it insists the tube length is less that 80 diameters of the bore to prevent gas dynamic back pressure from the tube friction. Otherwise suggests that more than 50 diameters long is better for heat exchange.
I guess this differs between gas and coal (ash containing) exhaust as the heat content of the gas is different depending on the fire...? And glowing embers give even more heat to the flue tubes on coal fired boilers, especially with forcing. (This can't happen with clean gas combustion). 
But I haven't seen any rules for "radiant elements in fire-tubes"? - Although with radiant elements the heat is almost all radiant so Stefan's law manages that, and any flue tubes can be shorter as there is so little residual heat in the burnt gas.
I guess someone may have studied this and developed the equations/model, but I have yet to find it. Maybe I should write the text book?
Stupid idea,
K


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## bille1906 (May 2, 2009)

Good catch
Should be 
1.250	1.120	600	82	3.927


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## Steamchick (Aug 19, 2020)

I'm pretty sure you'll get so much heat from the radiant burner that the flue gasses won't have mush left to give to water tubes or flue tubes. Simply the thermal capacity of the exhaust gas from about 800C to whatever temperature comes out of the Chimney. But the Radiant will heat every surface it shines directly onto. - and 90~95% of the radiant the Heat will be absorbed by the metal - probably black copper oxide on the surface?So I would go for large and shortish flue tubes. Not the 80 x internal diameter of coal-fired boiler max length, but more like 20~50 x the tube diameter. AND make the flue CSA equal to about 2 to 4 times the area of the burner.... Try a shutter in your mock-up boiler to see what works and doesn't choke the burner. You can even fit a water gauge (U-bend) on the fire-box to see what pressure (in inches of water) you develop in the firebox when the exhaust is choked to the chimney size? Without forcing, it is flippin' difficult to get gas exhaust out of the firebox! Ideally, the exhaust temp from the chimney will be the same as the temperature of the boiler (at pressure), but as the chimney will be such a small hole that will be the limiting factor as to how much gas you can burn. Loco chimneys (post Rocket) were short, as the length didn't go under bridges, so there is no natural draught up the chimney. - Hence the development of various blast pipes! - Which was also the problem when they made engines with large condensers, so they lost the exhaust steam that would have been used for the forced draught.Incidentally, thinking of musical instruments, did you try a small vent-hole (say 1/2" diameter?) in the side of the firebox? - I think that cured my similar problem...? - Does opening the fire-box door stop the noise?
Sorry to hear of your health issues, I appreciate your conversation whenever you can add a post.
K


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## RP3 (Jan 5, 2008)

While your design is somewhat different, in our scales (1:32 and 1:20.3) our gas burners are generally either a poker burner or a ceramic burner. To date, the ceramic burner locos I'm familiar with(Accucraft & my Aster conversion) have required an auxiliary air source such as a suction fan during starting or a steam blower after pressure is raised to keep the ceramic burner from going out. Even the Aster gas plate burner used on the JNR C62-2 required additional air from one of these two sources. I am guessing that you will likely face the same issue.

Good luck with your project.

Ross Schlabach


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## bille1906 (May 2, 2009)

Ross
Accucraft does use a ceramic burner that requires a blower but is now looking at my design for their C18 which does not require a blower.


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## RP3 (Jan 5, 2008)

Bill, That is really interesting that you have been able to create a ceramic burner that doesn't need supplementary air. I made a ceramic burner to replace the pitiful gas plate burner in my Aster JNR C62-2 and it required a fan or blower as I stated in my posting. Since my burner operated fine just being tested on my workbench but needed extra air when inside the firebox, I wonder if the issue is backpressure from the boiler itself restricting the exit of the spent gases. 

The challenge with gas burners of the past has been their gross inefficiency without some way to create radiant heating. The early workarounds involved wire tents around the poker to create some radiant heating, and yet their function still required careful boiler flue design to extract the maximum heat transfer. Now that we have ceramic burners which yield plenty of radiant heat in the firebox proper, I wonder if the focus going forward will require less emphasis on flue design to extract more heat but more efficient airflow to avoid backpressure in the firebox.

Time will tell.

Ross Schlabach


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## bille1906 (May 2, 2009)

Ross
Look at some of my builds and the construction is shown. I don't post every step of the builds to reduce redundancy and keep them short, but checking out a couple of builds should help you out

The problem with bringing cold air into the firebox is that you lose some heat. That is ok with meth and coal as the air becomes part of the flame .
In my design, the air is drawn into the jet holder by venturi action under the ceramic plate. this is why the dimensions must be correct and four air holes in the tube.
I seal the bottom of the firebox and leave the smokebox unsealed. No blower or draft tube is required.


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## Steamchick (Aug 19, 2020)

Hi Joan, Some interesting ideas here, but you are fighting laws of physics.
Good points: The coal fires in boilers use the exhaust to develop the "updraught" and increase the pressure difference between the firebox (grate) at atmospheric pressure and the smoke box, to force the fire. This is where Mr. Stephenson (George, I mean) achieved his efficiency to win the Rainford Trial. The combination of multiple fire tubes and high draught meant he had a smaller, and more compact locomotive, which was always going to win the technological race. BUT the gas burner - even a very good radiant like yours, is basically running on the Gas pressure providing a tiny "push" for the gases to pass up the flue. Unless you plan to use "standard" forced draught on your locomotive, you must increase the cross-sectional area of the flue tubes considerably for a gas burner arrangement. If you Quadruple the CSA of the flues then you stand a good chance of a successful gas powered boiler, otherwise the exhaust steam must be used to force the draught. Typically, a 3 1/2inch or 5 inch boiler is running a forced coal fire at something like 30kW of heat, so you can imagine how much is simply blowing up the chimney! A large proportion of that heat transfers to the boiler in the firebox by radiant heat - as will your burner - but the coal exhaust has a lot of heat carried up the flues in the smoke and ash - glowing red hot or still burning. - This is something you will not have so after maybe 50 diameters of flue-length there won't be much heat left in the flue gases. 
Therefore - as per many Americans and others - using gas for the fire you will need shorter flues and more area. I have seen loco boilers for GAS firing with twice the firebox volume and half the lenght of lue tubes, and these were 2 to 4 times "normal" (coal-fired) boiler practice. The real problem comes at the chimney, which can't be made so big, so it chokes the exhaust anyway. So forcing the draught is probably the best plan for a locomotive?
Forcing will also change the pressure characteristics of the "musical device" so will change the sound. Hopefully, from your Rijkes tube "fog-horn" to a sub-sonic, or ultra-sonic sound so we can't hear it. Of course, the flue tubes will also act as a musical damper, especially if they are lots of different lengths. If you have a single large tube for the gases, with water tubes crossing, I fear you won't change it much from the current Rijkes Tube and resonator.
The physics of the air-hole/choke is simply that you are changing the density of intake and exhaust gases, so excited by the burner interface, you simply have different notes resonating in the "musical device".
Personally, I would make a conventionally styled boiler thus:
Firebox = Approximately half the length of the total boiler length. - with as big a surface area of burner as you can achieve? - Include some water tubes or Thermo-syphon?
Flue tubes: At least double CSA of a conventional boiler. Even at the loss of surface area, the tubes should be maybe 40 x tube ID in length? Make perhaps 3 or more lengths of tube by extending some at the ends to project into the firebox and smokebox? - These will make different notes and interfere with the primary resonance to reduce the overall effect of the Rijkes tube. (as designed into many car silencers, etc.). 
Chimney: Maybe a double chimney - and forced draught pipe - will help eliminate resonances and noise from the Rijkes tube flame-front of the burner? - The double chimney could maybe have 2 lengths or diameters to further "break-up" the resonance tube effect?
I feel that the steel wire radiant element is a "prime-mover" of the Rijkes tube effect, and possibly extra thickness of wire may cause the "pressure interface" to be less well defined? can you add more wire wool to try and change the effect? Also try some flue-tube mock-ups to see how that changes the effect?
I hope this is of some help.
Ken


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## Steamchick (Aug 19, 2020)

Incidentally, I make ceramic burners ( for stationary boilers) and the limiting factor for almost all burners is the ability to "exhaust" the fire-box. A closed firebox is most efficient - with all - but no excess - air through the burner. But this (laws of Physics) forms the Rijkes-tube resonator we have here. Any by-pass air simply damps-out the resonator - to the point of no resonance - by changing the gas pressures across the burner "interface". e.g. Opening the fire-box "lighting hole" door should prove that easily for Joan's mock-up boiler. 
But I see the limiting factor of loco boilers to be the Chimney Cross-sectional area. It is small compared to flue-tube CSA, so needs the exhaust (or blower) to get the exhaust out of the firebox, to permit correct firing of any burner.
Has anyone clever at CAD done a gas model of the boiler? Maybe I'll have to "learn-how" as this is what is really needed. For example: look at your fireplace and think how different the burners and flues are for Coal fires, Log-burners, and Gas fires... Gas is really innefficient when you try and make it like a coal fire, so what are we doing with "coal-fired boilers"?
k


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## bille1906 (May 2, 2009)

Ken
You seem to know a lot about the subject but I can tell you that from experience doing ceramic burners in locomotive style boilers that using larger flues is a big mistake. The hot gas will pass through the tubes so fast that a great percentage of the heat will just go out the stack
I use the ratios suggested in Martin Evans books (for coal burning boilers) to produce very efficient ceramic boilers and have had problems whenever I tried something different


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## joanlluch (May 20, 2017)

Ok, I'm the original author of this thread. After years of inactivity due to my medical condition I managed to get some recovery and I'm now working on my locomotive burner again. By trial and error I found that reducing the premix chamber volume on my mockup boiler setup, the noise essentially disappeared. Unfortunately, it has returned (with a revenge) on the final design. See video. I'm now lost again on what to try next..






Just for context, the test consisted on heating the boiler with the safety valves removed, as I was not interested on steam pressure development but just testing the burner behaviour.

The noise is that unbearably loud, it's unbelievable. I also post a frequency graph made with my smartphone. The pitch tones appear to be very clean, and actually they sound as pure as an organ. 










Any further ideas or suggestions on what to try to remove that annoying noise would be appreciated.

Cheers


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## MGates (Mar 16, 2016)

Your video on YouTube is "private" and we are unable to view it. You can change it to "unlisted" and it will be viewable with the link, but will not be searchable on the website if that was your original intent.

-Mike


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## joanlluch (May 20, 2017)

MGates said:


> Your video on YouTube is "private" and we are unable to view it. You can change it to "unlisted" and it will be viewable with the link, but will not be searchable on the website if that was your original intent.
> 
> -Mike


Opps sorry, it's "Unlisted" now. Hope you can watch it now

Cheers


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## bille1906 (May 2, 2009)

Joan
What is the ID and length of your tubes?


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## joanlluch (May 20, 2017)

bille1906 said:


> Joan
> What is the ID and length of your tubes?


I attempted to have them shorter and wider than an equivalent coal fired boiler, so length is 390 mm and inner diameter is 14 mm


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## Steamchick (Aug 19, 2020)

All. I can happily report that this problem has been resolved. Joan has managed - with a lot of hard work, head scratching and proper methodical study and effort - to eliminate the problem.
Essentially, by improving the air intake to increase the gas-air pressure pre-burner, there are small flames exuding from the wire matrix which increase the effective length of the heated interface. This stops the Rijke's tube resonance from occurring when the thickness of the heating zone becomes longer than a wavelength of the oscillating gas through the heating interface. Sounds very scientific. It is! - But it is like a hot-air engine having a stroke between hot and cold zones. When the stroke is too short to get the heat exchanger from hot to cold and back again, it doesn't work. When the stroke is long enough to completely transit from hot to cold and back then it works. So does Rijke's tube resonance. When the oscillating gas can transit for hot to cold and back again, it sounds - and resonates very loudly. When the cold to hot interface is too thick for the gas to travel across and back it cannot sound.
I hope you have enjoyed this science lesson as much as I have enjoyed working with Joan to resolve this problem. All credit to him for his successful result and a great locomotive.
K2


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## Steamchick (Aug 19, 2020)

xo18thfa said:


> Yes, that's what happens. Choke off some of the air reduces the noise. But then too much choke is inefficient. It's really a trial and error thing.
> 
> Talked with Bill at the steamup last week. He said the length of the mixing tube should be at least 6 times the inside diameter. That's very true for a poker burner otherwise they don'y light very well. Bill says its true for ceramic too. Don't know if that affects noise however.
> 
> vr Bob


Bob, This was the clue to resolving the problem. THANKS! Basically, by richening the mixture, you are creating CO combustion flames beyond the thin wire matrix that causes the noise, so the CO flames actually prevent the noise from occurring.
Incidentally, A US Dept of Commerce paper (from 1921) states the mixer tube shall be at least 7 times the tube diameter. It also describes the optimum venturi - and Joan proved it works well!
Finally, 1 problem I have seen with many commercial ceramics, is that the mixer tube is OK for a smaller jet, but chokes - and becomes too rich - with larger jets. Each jet needs a different mixer tube diameter and length, and the burner holes also have an optimum size. To little gas and air mix and they flash back, too much and the flames lift off. So the whole burner needs designing properly - and the US paper describes it very well.


https://nvlpubs.nist.gov/nistpubs/nbstechnologic/nbstechnologicpaperT193.pdf


Ken


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