# Some Thoughts on Troubleshooting



## steamermeister (Feb 20, 2013)

Since completing Climax #2 the burner system has needed some troubleshooting. In the test runs I did in late winter, the burner worked but the fire would go out sometimes. Other times the fire would have problems snapping back into the flue when I'd try to light it. This all came to a head though the first time bringing it to a steamup. I couldn't get it to light at all. The solution was two fold. Early on in test runs I found that the jets that came with the Roundhouse boiler kit were more susceptible to the problems described than another jet I has in my parts bin made by D. R. Mercer. I compared the D. R. Mercer and Roundhouse jets under a microscope and found the hole diameter of the D. R. Mercer jet to be .009 inches; the Roundhouse jet being .007 in diameter. Still, something had changed between my test runs and the steamup causing the burner failure. After a lot of head scratching, I determined that the biggest problem was the height of the burner in the flue. There wasn't enough space for a fire to form over the burner. Sometime between my test runs and the day of the steamup, the burner must have been bumped up just enough that temperamental operation became failed operation.

The reason the burner was so high up in the first place was because the stem passed just barely above the gear box. In order to lower it and still have enough space for the gears the boiler needed to be raised with spacers, simple enough. That said, I'm still befuddled by the jets. The locomotive works perfectly now. All the burner issues from my test runs have disappeared. What I'd like to know is whether there is any data on burner design and optimizing locomotive performance. I've searched high and low for anything on the subject but have found nothing other than that the problem may be due to a blocked or scarred jet which was not the case here. Here's the sorts of things that jump to mind: jet diameter, jet placement relative to fuel/air mixing holes, fuel/air mixing hole area, burner length, burner diameter, flue length, flue diameter, burner placement and orientation in the flue, smokebox size, stack size, steam engine intake plumbing diameter, steam engine plumbing exhaust diameter. These and many more all contribute to locomotive performance. Are there any answers out there?


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## steamermeister (Feb 20, 2013)

*Way up close*

Below are some pictures of the jets as seen under a microscope. A jet hole diameter difference of .002 made a big difference in performance.


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## steamermeister (Feb 20, 2013)

*The bigger root (cause)*

Below are some pictures of my solution to lower the burner in the flue by raising the boiler.


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## seadawg (Jan 2, 2008)

I'm waiting to hear from some respondents to this thread. I think there is little more than anecdotal evidence and would like to see more (scientific or anecdotal!).

I have a Merlin that I have been working on and the fire seemed to get weaker and weaker, so the first thing I did was clean the jet. Now I can not get the burner to light. The fuel needs to be so low to get the flame to pop down the stack, that the burner will not remain lit. I tried to get the jet back onto the same location compared to the air inlet hole, still no joy. I will look at the burner alignment itself, maybe there is no flame space as in your example.


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## steamermeister (Feb 20, 2013)

I completely agree. Despite the fact that the live steam hobby is nearly as old as the invention of the steam engine, there seems to be no published science. I've been doing this nearly 20 years now and I still feel like I'm winging it.


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## boilingwater (Jan 27, 2010)

Actually, there is science around this and math for this of course. It has to do with Venturi effect and the interaction between gas/air and pressure relative to the creation of a flame. Just like on our gas grills, someone has already done the math and the engineering. Most of us assume, the engineers did correctly and simply replace the jet with one of the same size. Others, to sometimes positive effect, have changed the jet size to influence the gas/air mixture and as result, the flame itself...So, it's a bit less mysterious than alcohol flames --at least to me-- but that's another thread...
Sam


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## steamermeister (Feb 20, 2013)

Sure, but what about folks aren't interested in copying previous work but wish to build something new and different? Everyone who builds a live steam locomotive from scratch hopes that their efforts will be successful. I think it's entirely reasonable to want to have access to that base level engineering and math in order to make educated design decisions. I am an engineer, and I still don't know where to look.


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## boilingwater (Jan 27, 2010)

I am sure I could find the math for you when I get some more time. As you discovered, too small a hole and sometimes you get too lean a mixture and the flame blows out. Too large a hole and you create an inefficient flame. So, a bit or trial and error here can assist the scratch builder in determining what works best without the formulas. I remember some builders buying an assortment of jet sizes to do just that. Perhaps a bit inefficient but it can get the job done.

Sam


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## Chris Scott (Jan 2, 2008)

1. About particles or debris in a can of liquid butane and it ending up clogging the gas jet. How do the particles or debris in the liquid butane end up at the jet if what goes to the jet is a gas? A gas can carry particles but big enough to clog the jet? I suppose accumulation at the jet orifice is a possibility. The same question about debris left in the gas tank from manufacturing. Having had little if any jet blocking by debris experience other than a stray fiber(s) from the dang factory filters, which I immediately ditch, I'm just wondering. 

2. Gas of an Idea!  If clearing a gas jet using the butane gas pressure direct from the can doesn't work, try a higher pressure gas; butane-propane or pure propane. Even better if you have an air compressor and 60psi. A small soft brush to the back of the jet a couple of passes to help dislodge something stuck then repeat back pressure clearing. 

3. To see if it really is a jet problem I check the flame at the jet out of the burner. I remove the jet from the burner leaving the jet attached to the gas feed. Turn the gas on just *slightly* and light the gas  at the jet so the flame is about 1.5" and torpedo looking, steady, no flickering nor pulsing. After some practice I've gotten a bit more comfortable (brave?) I turn the gas up a little to see if the flame stays steady. 

It's a good way of checking twin jets to see if both jets and flames are working properly. I do this before boiling any water. It's easier and a lot less time consuming to verify the gas flow part of things is working than going trough the later debug process. Besides, the locomotive is clean when it's just unwrapped. 

4. Accucraft used to include a gas jet clearing tiny wire in the parts & tool kit with new live steam locomotives. It's been a long time since I bought a new locomotive. The wire was in a small baggy of its own, about 2" long wire. Did you get a wire with your new locomotives, do they still include the wire?


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## John 842 (Oct 1, 2015)

As a number of people have asserted - the mathematics to enable a burner to be designed to work without the need for experimentation and adjustment undoubtedly exists. 

However, the problem is so complex that the systems capability in the form of 'dynamic mathematical analysis' - 'variable compressible flow visualisation' - and '3-d temperatue gradient distribution' are unlikely to be found outside the design offices of people like - Boeing - NASA - or Pratt & Whitney.

Locomotive gas burner design is unique among all the component design requirements of the rest of the loco in that.....

- If the flow design of the steam passages is wrong - the loco may be down on power - but it will run.

- if the fatigue analysis of the main driver axles is wrong - they may fail at X miles instead of 2X miles - but the loco will run.

- If the lubricator design is wrong - the piston rings and valve gear will wear prematurely - but the loco will run.

- etc, etc.

- However, if the gas burner design is wrong - then the loco will simply not run at all.

The main reason for this is that the air-fuel ratio has to be in a relatively narrow band for combustion to occur and the real problems come in trying to maintain combustion when taking into account a long list of additional factors that all have an effect on the reqired A/F ratio.

The first, and probably the most important, additional limitation is when you want to enable the flame to transfer itself back from the firebox to the burner, instead of just staying in the firebox. I would very much like to see how you could calculate that. You would need to compare the 3-D profile of velocity of flame-front propagation across a non-homogenius fuel/air mixture - against the gas flow velocity profile across gas passages of variable cross-section, shape and surface finish - and then ensure that the maximum value of the former was less than the minimum value of the latter by some desirable, but indeterminate, margin .... 

Then follows a whole raft of variables whose effect would have to be mathematically accounted for .... 

- how to share the bulk of the gas system pressure drop between the gas regulator valve and the jet.

- gas velocity and hence pressure distribution through the system and how it will change according to 'fixed' variables like the profile and roughness of the internal system passages.

- floating variables like the changing gas pressure in the reservoir as it is depleted.

- the effect of changing water bath temperature.

And so it goes on.

I came across an indicator of just how sensitive the system is recently when I was attempting to improve a Wuhu burner - if I installed the jet with teflon tape it would work OK - but if I left out the tape, there was enough gas leakage through the spiral space between the crest and the root of the thread to alter the A/F ratio enough to interfere with the flame transfer back from the smokebox to the burner.

So - I'm afraid I've come to the inevitable conclusion that 'trial and error' is the only practical solution to burner design for the foreseeable future....


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## hcampbell (Jan 2, 2008)

Just to add to the "confusion," on my Regner shay the air fuel mix to light
easily is not the same as the mixture to run well. It needs quite a bit less air to light.
This applies most of the time but on rare occasions I can just light and go.
Ain't steam interesting?

Harvey C.


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## Taperpin (Jan 6, 2008)

There are several factors to consider with "flue" style poker burners in our little engines..if designing from scratch.

[1] the model size [small NG prototype] and therefore small boiler, or larger standard gauge and large boiler etc..generally the very small boiler [40mm diameter or less ]for reasons of water capacity , will only accept a 16mm flue diameter and this is the smallest that will work reliably.

For the larger boiler 45mm to 55mm diameter a flue of 20mm works but once we go beyond 60mm then twin flues are needed because of heating surface requirements..

[2]The second constraint is the height above the poker surface needed for flame development and heating effect, which from experiment is about 10-12mm minimum.

[3] The flame height is also derived from the exit velocity at the poker slots or holes of the gas/air mixture, and this should be as low as can be built in.

[4] the jet sizing needed for a given boiler is controlled by the poker diameter[the smaller the diameter , then the total amount of gas/air mix which can be injected into the poker and slowed down enough to burn successfully ]

The jet sizing range is quite small .

example jet 0.007 or 18 Micron 5000BTU heat output ..

jet 0.009 or 22 Micron 8000BTU " " 

the 5000 BTU jet will steam any NG loco with 15mm cylinders or !:32 model with 13mm cylinders [assuming reasonable valve events] 

the 8000 BTU jet will steam a 1:32 model with 15mm cylinders and assuming reasonable valve events..or a NG large loco running slowly..

From this we can see that to get more heat onto a larger model we run up against needing a larger flue and poker/air gas mixing venturi, and explains the twin flue approach ..

The blending of the air in the mixing venturi with the gas cone occurs at the boundary layer of the cone and thus , small poker , small flue small mixing venturi equals small jet,, fitting the small boiler /flue layout. and vice versa..

Slowing the gas/air mix at the poker exit surface derives from the area of the slots or holes in the surface, too small a area =higher velocity, so slots should a minimum of 1mm or0.040 wide and half the poker depth with a total area of equal or larger than the cross section area of the venturi mixing chamber. drilled holes , same rule..

The common addition of S/S gauze or mesh externally to the poker helps by slowing the gas/air exit speed as does fitting mesh inside the burner, and I think the internal fit is better[it does not burn away].

The gas jet should have a complete seal at the point where it is mounted ,either by machined taper/chamfer or a sealant such as PTFE tape or Engine sealant , any tiny leakage here will allow gas which has not been metered via the jet to seep into the venturi mixing chamber and the mix will be "richer" than designed.

Where a steam drying pipe is run inside the flue it should be low down at one side and below the point where the flame development starts[this can be seen by looking into the flue from the smokebox end] any disturbance of the flame development will cause bad combustion and noise .

Some other requirements are that the poker must be concentric with the venturi chamber and axially aligned as well, so that the burner is level and straight inside the flue, misalignment causes "fluttering burn" and difficult light back..

The fitment of a Air Collar so the mixture can be adjusted is useful, and a very slightly 'rich" mixture helps with Light back down the flue a very short pale blue flame is slightly "lean " and may be harder to get Light back reliably.

One other thing that can be done is have a 2 stage flue "1inch" diameter where the burner is fitted [the back 3rd of the boiler , stepping down to 3/4 inch at the front, this gives a little more heating surface with more flame space and thus more heat input.

All this is empirical but the it may help some understanding of what happens in our little engines..


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## steamermeister (Feb 20, 2013)

Thanks for the advise. This is exactly the kind of information I'm looking for.


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## steamermeister (Feb 20, 2013)

I have to revise my claim about the current performance of Climax #2. It runs perfectly when the air is no wind; preferably indoors because the slightest wisp of breeze blows out the fire. I have run it on a track indoors and it doesn't blow its own fire out by being in motion. I've attempted to make shields out of mesh and aluminium foil for the burner stem but to no avail. Has anyone else had this issue? There's a steamup this weekend that I'd like to run it at and I'd prefer to not invest in a terrarium.


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## thumper (Jan 31, 2009)

*Gas/air mixture*

I have an Accucraft Caledonia which I have had difficulty lighting. The jet is clean, I don't have a microscope, but when held up to a high intensity Cree LED, the light is clearly visible through the jet. 

The fuel I use is the Primus Propane/Isobutane/Butane all weather mix No. 2202 (can't find the percentages) which is particularly good for cold weather.

The burner lit easily, but when the smokebox door was closed, the flame usually went out, probably because of the difference in the fuel from regular butane.

At this point, I thought the only issue left to examine was the fuel to air mixture. Because the loco was cold, I tried partially covering the air inlet at the back of the burner with a finger while lighting the burner. Bingo, the burner light as usual, and when the smokebox door was closed, it stayed lit. PROBLEM SOLVED, but this fix was only temporary. 

For a permanent solution I cut a 1/8" wide strip of thin brass to wrap around the back of the burner. The strip could then be slid over the air inlet opening so as to adjust the air to fuel mixture of the burner. 

Now after adjusting the brass strip, the Caledonia's burner lights and stays lit every time.

Regards,

Will


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## Chris Scott (Jan 2, 2008)

https://primus.us/pages/primus-gas










*Primus Safety Data Sheet  * (required for all hazardous products by federal law)
http://images.clasohlson.com/medias/sys_master/9271722016798.pdf
I find it surprising the SDS does not list the specific gases and gas mixture/composition. It is unusual at the least.

Listing the Primus gas mix percentages as well as characteristics of other products. Curious, the Primus SDS (for their 3 products does not list the specific gases and mix , nor could I find it on the Primus web site, I wounder where they got their information? Power Gas Red can now appears to be a Silver colored can.
*Adventures In Stoving*
http://adventuresinstoving.blogspot.com/2011/11/whats-best-brand-of-gas-for-cold.html

Primus website also has a video comparing the three products:





This website provides useful background:
*Liquefied Gas Stoves:* Liquefied Petroleum Gas (LPG) Burners aka Canister Stoves and Gaz Stoves
http://zenstoves.net/Canister.htm#Canister


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## thumper (Jan 31, 2009)

*Warning - indoors operation of butane fired locos*

Chris, I agree that it is strange for the MSDS to NOT show the percentages of different fuels from PRIMUS.

One thing the MSDS does say, and that should be known by all is that burning these fuels produces CARBON MONOXIDE. PRIMUS cautions against using it in enclosed areas such as tents. We're not using tents, but many of us do test our equipment indoors.

As a safety precaution, I've now placed one of my several CO detectors near my work bench and rolling road.

Regards,

Will


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## steamermeister (Feb 20, 2013)

I've added some mesh over the burner inside the flue held on by wire and now I think it's good. I did a run in the garage to make sure I hadn't un-improved things (it worked the same as before) and then took it outside for a second test run after it cooled down. Despite being windier than other times I had tried to run the fire only went out once while it was building pressure. After that it ran fine. More test runs to come before I let it loose at the steamup but I'm encouraged by the results so far.


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