Gas burner making high pitch, flute like, noise ?? - Page 2 - myLargescale.com > Community > Forums

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Old 08-19-2020, 07:00 AM   #11 (permalink)
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Thumbs up 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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Old 08-20-2020, 04:12 AM   #12 (permalink)
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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?
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Old 08-20-2020, 05:51 AM   #13 (permalink)
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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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Old 08-20-2020, 06:00 AM   #14 (permalink)
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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,
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Old 08-20-2020, 07:44 PM   #15 (permalink)
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Good catch
Should be
1.250 1.120 600 82 3.927
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Old 08-25-2020, 03:45 AM   #16 (permalink)
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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.
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Old 09-03-2020, 01:15 PM   #17 (permalink)
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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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Old 09-03-2020, 01:38 PM   #18 (permalink)
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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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Old 09-04-2020, 11:42 AM   #19 (permalink)
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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.

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Old 09-04-2020, 02:05 PM   #20 (permalink)
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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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