Cheddar Models Ceramic Fluetube Burner Resonant Howling

[Chris Cairns]

Whilst I've been aware that others have suffered from this phenomenon, until recently I've never suffered it with my Cheddar Models collection.

I have run 2 Pintail engines with a vertical boiler on Butane/Propane mixed gas which have had no burner problems, although a fellow member advises me he gets it occasionally on his Pintail powered steam lorry.

Whilst I've never suffered it with my Cheddar Iver, both fired on butane only & butane/propane mixed gas, a fellow owner got in touch for some advice recently including a howling burner.

I have suffered it on my Cheddar/GRS tram and originally I noticed that the gas jet had been pushed well into the mixer tube, and it was fitted with an air control ring. However it was running too rich and putting the jet to the correct position increased the howling.

Chris Bird has written on-line that he has reduced his howling burner by turning the gas control valve down, but on my Cheddar/GRS tram with the gas set at the lowest setting to hold the required pressure whilst running (approx. 20-30PSI) the burner still howls.

By accident I found that placing a piece of kitchen paper towel over the top of the chimney stopped the howling completely. So it was finding a suitable piece of mesh to replace the paper towel.

I have some stainless steel 40 mesh which did stop the howling when placed on top of the chimney. However it is too fine to allow the lit gas to pop back to the burner on light up. As I use a piece of silicon tubing supplied by Cheddar Models to collect the condensate when first running these locos I made a hole in the mesh (just over 7mm diameter) which allowed the silicon tubing to be fitted onto the exhaust pipe during warm up, and the hole is big enough to allow the lit gas to pop back to the burner OK.





In use I've found that there is less of a wet exhaust steam now than previously (the flue below the mesh is obviously hotter now) and you only get a noticeable steam plume at the end of a run when the gas has run out (running indoors). I'm keeping the gas control valve at the lowest setting possible just to maintain the required pressure. However there is now no more howling from the burner.

I suspect that a less fine mesh would probably work just as well but I do not have any available to experiment with.

Although Jerry at Clevedon Steam (a former Cheddar Models employee) sells a replacement gauze fluetube burner apparently his selling point "When used on Cheddar locos, the familiar howling noise is eliminated " does not apply to the Cheddar Iver.

Chris Cairns.

(spelling)

[MDLR]

In use I've found that there is less of a wet exhaust steam now than previously (the flue below the mesh is obviously hotter now) and you only get a noticeable steam plum at the end of a run when the gas has run out (running indoors).

Does it taste OK? (The steam plum............)

(grabs coat, runs out of door...............)

[Dr. Bond of the DVLR]

What is gas burner howling caused by in the first place? Is it similar to the flame hum you'd get in a 1:1 scale firebox when the ignition and pressure waves get too close?

[Chris Cairns]

Does it taste OK? (The steam plum............)

Nice One Brian!

I've been editing a newsletter all evening so my eyes have grown tired of proof reading, and of course the spell checker was not to know that I actually meant plume instead of plum. Now suitably edited.

What is gas burner howling caused by in the first place?

For these Cheddar Models burners that is the 64 Million Dollar question Zach, which sadly due to the early demise of Cheddar Models (2005) before the wealth of knowledge was built up on Forums like this one, has not been satisfactorily answered.

Unfortunately with the Pintail vertical boilers & the Tram boiler it is impossible to see what is happening to the burner when it is fitted inside the fluetube. You could remove the smokebox fitting on the Cheddar Iver but as my Iver has not suffered from a howling burner then that would not help in my case.

I'm now wondering if it is something to do with the secondary air holes on the side of the burner but as it gets very hot shortly after lighting up I've yet to work out a way of blocking one of those holes without getting burnt.

Chris Cairns.

[Dr. Bond of the DVLR]

it is impossible to see what is happening to the burner when it is fitted inside the fluetube.

Sounds like a quantum effect then!

[Keith S]

it is impossible to see what is happening to the burner when it is fitted inside the fluetube.

Sounds like a quantum effect then!

Indeed. You are probably expecting sound waves when you are observing it. Try observing it the way one would if one was expecting to see sound particles instead. Obviously one can't hear sound particles so your problem should be solved in that case. I recommend mesh with a very narrow slit rather than a hole.

[GTB]

What is gas burner howling caused by in the first place?[/url]
Seems to be some sort of resonance effect, more like a flute than an organ pipe I suspect. Moving the position of the jet relative to the air inlet holes can reduce the howl on a poker type burner, but that also screws up the gas/air ratio. Using mesh also reduces it, but again that can screw up the flame stochiometry and make it harder to light.

A blowtorch burner like the Cheddar ones could easily set up the visible standing wave you sometimes see in a rocket exhaust, but there's no way you'd see that looking into the end of a boiler flue. Heisenberg still rules.........

Is it similar to the flame hum you'd get in a 1:1 scale firebox when the ignition and pressure waves get too close?

Model coal fired locos can do that as well. We had a 12" gauge loco that hummed a bass note when working hard, but it stopped if you cracked the firedoor to add a bit of top air. The grate was enlarged during the last rebuild for other reasons, so the air velocity through the firebed is now lower and the sound has disappeared.

Just what are you studying at Uni?

Graeme

[Dr. Bond of the DVLR]

I'm doing chemical engineering. I was surprised by how much a working knowledge of steam locomotives has helped me this year!

[GTB]

A colleague I worked with over many years trained as a chemical engineer and I picked up a lot from him that we weren't taught in a Chemistry course.

Good Luck with your studies....

Graeme