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Ceramic Gas burners on Locos

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Donrecardo

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It’s been a long time since I posted on this thread as I've moved to loco's that are coal fired However, I still get the occasional query and it seems that this thread has become bit of a reference so I'll post this here.

I got my jets from a model engineering supplier but recently I've purchased a 3D printer and sought a supply of extruder nozzles so turned to Aliexpress. They arrived today and my immediate thought was "these are gas jets". I hadn't noticed the similarity before. It’s understandable really, hobby 3D printing gained a foothold with RepRap and where else would they get nozzles?

Barely US$8 for 22 "jets" with shipping.

US $2.58 11% OFF|22 Pcs Nozzle MK8 Extruder Head 3D Printer for creality CR 10 CR10 Machine Heads 1.75mm|3D Printer Parts & Accessories| - AliExpress

View attachment 120401

Pete
Under where it says 22PCS it lists the sizes like 0.02 0.04 etc but they are not , they are 0.2 0.4 ( ten times bigger ) its stamped on each jet . Also the thread will almost certainly be 6mm where normal gas jets ( at least in England) are I believe 1BA
 

Steamchick

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Hi Guys,
I have been making ceramic burners for 25 years or more, on and off. But the technology is limited by the laws of physics, so really a surface glowing the size of a firebox cannot provide enough heat to power the loco - if the firebox has been designed (sized) for coal. The coal fire, as well as providing the "red surface of coals" also gives huge amounts of hot gas - to transfer heat in flue tubes, PLUS the hot coals radiating sideways into the firebox lower walls ( a cold gas-air mix in a box for the ceramic). AND there is the soot... These soot particles, id incompletely burned in the fire box transmit with forced draught into flue tubes and continue to burn - and radiate heat - as well as provide extra heating to the gases - in the flue tubes. All in all as designed by George Stevenson, a jolly powerful heat source!
But the ceramic burner - if adjusted to a glowing surface - ONLY provides the radiant heat from that surface, as the gases are completely burned so the Carbon monoxide is consumed - which stops burning below 300deg. C -and the exhaust gas only has the small amount of residual heat from 300deg. C to steam temperature to impart as it passes up the flue tubes.
OVER fuelling ceramics - as explained by users - gives huge amounts of burning gas, but that is all, as the hot (not burning) exhaust in the flue tubes only has the residual heat of the gas (maybe 650deg C to steam temp) to impart. So you need a Lot of burning gas - and very fierce (fast combustion in the confined space of the firebox) to generate the heat and exhaust - that then needs the blower to drag it through the flues....
However: A solution is at hand, though only recent technology:
In steps:
  1. Ceramic: 950deg C max.: 120kW/sq.m.
  2. Stainless steel (wire wool) matrix: Metal fibre knitted matrix:1050deg.C. max.;200kW/sq.m
  3. High Temp. Stainless (ferro-chr. alloy)matrix (Sintered surface) 1050deg C max.; 250kW/sq. m.:
  4. Porous Ceramic burners: (Silicon Carbide porous matrix, or other modern clever materials):1450deg.C max.; 1000kW/sq.m.

Infraglow seem to sum it up in their on-line brochure: - worth a read:
Go-Gas have an interesting technical comparison table and clues about design.

Also, search for "CREMADOR - Joan Lluch": as he has made a big and powerful firebox burner... - wire mesh type: - but he has a resonant noise problem to overcome.
Note: Regular stainless steel wire wool burns-up quickly: Special alloys are used by the Burner Manufacturers.
The porous matrix materials cost $100 per small block - so I haven't bought any to make myself a burner, but the 1000kW/sq.m capability is big enough to make firebox burners suitable for boilers designed for coal firing. (8 x more powerful than ceramic burners.).
Over to you guys!
K2
 

Steamchick

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Just spotted this one:
Also,I understand - from various sources - that the preferred medium for a porous gas burner is CORDIERITE porous foams. The burner comprises an air inlet at the jet, venturi, mixer tube (as "normal") - then with the mixture entering a low-density (high porosity) matrix for cold gas mixing and heating the mixed gas, followed by a higher density (lower porosity) matrix where combustion takes place: Combustion is COMPLETED in the matrix: NO extra air is required for post combustion. But the whole of the high density matrix glows brightly at 1400deg.C. (ish) with the internal combustion taking place inside the material. - like 1 big hot coal! The exhaust is supposed to be very clean. - So loco drivers will not get headaches from the CO normally blasted up the funnel in great quantities.
Bring it on?
K2
 

fcheslop

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A big advantage with a radiant burner. The velocity through the flue is slower giving a greater dwell time to absorb the heat
I have recently built a simple marine centre flue boiler and comparing it to a water tubed flue of the same size the flue with no tubes heats the water faster and the outlet temp is nearly 80c lower .Also the temp along the length of the flue is reasonably constant at 510c to 620c
Its very 16mm loco in form and for my toy boats no idea how it would scale up
Often wonder if in larger loco fittings doing away with the blast system would make a more efficient set up
Another benefit is the amount of gas used drops by about 1/3 reducing freezing and cooling of the gas tank.Using just butane with an ambient temp of 6c the plant will still run a 1/2 by 1/2 double acting wobbler at 300rpm
radiant material canbe bought from the jewellery suppliers like Cousins
For mesh you really need to consider nichrome mesh as it last far longer than stainless but I tend to get around 12 or so burns from stainless. The likes of Wilko in the UK sell frying pan cover for a couple of quid and the wire just happens to be the right size to make number 3 jets double bonus for the penny watchers like me
cheers
 

Steamchick

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Good stuff! But I wonder if there is really much heat flow from the gas to the boiler in the flue tubes? - The temperature should drop from around the 600 degrees (post combustion) to nearer 200 degrees (beyond boiler) if the heat is being "sucked" from the gas into the boiler. I would be tempted to put a wire coil inside the flue, not touching the side walls, to gain heat and radiate it into the side walls of the flue. (Black infra-red can't be seen but is still very effective). Also install some very loose stainless steel wire wool inside the wire coil. - The hottest gas will be in the middle. The coolest gas at the surface of the flue tube. You should heat the "wire wool" (or other) in the hottest gas so the heat can radiate across to the walls of the flue. That should increase efficiency of the heat flow into the boiler....

I have made Ceramic (and other) burners ranging from a no. 3 jet (0.2mm) (for Mamod boilers) to a 0.49 jet: - which was for Propane on a ceramic for a 9" dia boiler - 2 ft. tall. - That one was "short" of a lot of flue tubes, so needed the ceramic to create most heat suitable for heating the bottom of the vertical boiler, rather than the (Stevensons) loco multi-tube boiler that maximises the heat flow in flue tubes. I did some very crude calculations and decided the 9" dia boiler had very little flue CSA to take a 7kW or so simple gas burner. So I made a rectangular burner about 7" x 5" powered by 15psi Propane. - Rated at around 4.4kW. (see "International Toy and Model Steam Hospital" for the boiler). I've not seen many ceramics on models this big.
By comparison, a friend has researched the "heat" required for his 4" vertical boiler to drive his Clayton Wagon: 27kW: So it explains easily why radiant ceramics just don't have the rating to achieve the power density required for Coal-fired loco fireboxes! a 4" circle of radiant ceramic is only a single kW or so! - Good for making Tea....
However, as used in domestic central heating boilers, a 5" x 3" plaque can be used (non-radiant mode) as a surface diffuser for 25kW or so of gas flames in the water-tube boiler. - I understand successful 5" locomotives usually have around 30kW (or more?) of gas combustion in the firebox - using some very fierce multi-nozzle blow-lamps. (look-up J.E.Nystrom).
K2
 

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fcheslop

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All good stuff and very interesting
The idea for the small plain flue is to keep gas velocity low allowing more dwell time. It seems to work from the rough ars££ experiments I can conduct
Using different burner ideas the flue exhaust has dropped about 140c and the gas consumption has also gone down. The engines rpms have gone up to near what I need for this wee boat. May have to take it to Roker for a test run when she is finished although a Stirling engine based on the Glasgow engine is on the bench.
Nothing new the loco guys have used the idea for sometime in the small scale stuff
The Clayton is greedy for steam or at least my engine is. Although she has not been steamed for over 20 years and needs a full rebuild. Maybe someday it will happen.
I only build the smaller stuff now just cannot afford the big toys and no longer wish to be in a model engineering club
keep well
 

HMEL

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Gentlemen:
I have been fascinated by these series of posts. I spent a good deal of my career doing combustion/ steam calculations. So I will comment. If you know the required steam flow per unit of time you can calculate the heat input. The flue gas heat loss is significant due to the water of combustion. So when you calculate the heat required for steam generation you must divide by that efficiency to get fuel actually fired. Its very difficult to get efficiencies above 85% unless there is a condensing heat exchanger involved in the unit. Only in modern furnaces are you likely to find that. Dividing the calculated steam heat requirement by the efficiency gives the minimum burner size for the system. After that its a matter of how well the boiler is designed to capture the heat, and how much excess air you are using in the combustion chamber.
 

Steamchick

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Tell us more... I use "Model boilers and boilermaking" for a basis of my calculations, along with some theoretical gas consumption tables per jet size, and a huge fudge factor (<70% of expectations become reality). The biggest difficulty I find is in estimating heat losses... so I really go to town with complex insulation on my boilers. (Just a sheet of "bought insulation" is laughable to me!). I feel boiler and pipework losses are the most neglected areas of model engineering.
Any advice is welcome!
I am also a believer (as an ex-design-engineer) in calculations predicting optimistic results in the hands of the inexperienced. I spent some of my life being inexperienced in most things! (Now I reckon I'm inexperienced at everything).
Ta, K2
 

Steamchick

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K.N.Harris advocates the only air in the fire-box should be primary air, as any un-used secondary air will reduce efficiency of the boiler. Many (especially people converting coal-fired boilers to gas) want lots of excess secondary air... ceramic burners lend themselves to zero secondary air when we'll designed and in a suitable boiler. But (Imho) boilers designed for coal firing seldom offer optimum heat transfer for gas firing. Not being a chemist, I can't calculate the volume of gas passing through flues for gas and coal fires of the same thermal output, but I guess the coal fire produces denser gas with all the carbon dioxide produced...so can get "more power" from the same flue CSA. Alternatively, gas needs bigger flues for the same power as a coal fire. - Is that correct?
K2
 

wazrus

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A most interesting thread. I had come to conclude that gas burners as applied to model steam locomotives were something of a black art, even given that there's a gentleman in Finland who has used 'in flue' burners, which I realise aren't necessarily the subject of this thread. I have two 'gas specific' boilers in 4mm copper, flanged and almost ready to silver-braze. Both have 38mmx3mm copper tube flues. There are two flues in one boiler, three in the larger. The larger boiler is about 180mm diameter. I have fiddled for ages with all sorts of burner lashups and I feel the stainless steel mesh, as a sort of 'glow cone' in the flue works, but is perhaps not the way to go. Interesting, though is the idea for nichrome mesh, but just where does one get that? Nichrome wire I do have, but mesh?
I've made many and varied gas jets for all sorts of positions and I've become fairly adept at drilling 0.4mm holes in brass jets. But 0.4mm doesn't seem to be small enough. Then there are jets available for 3D printers which look promising, but I doubt they'd be small enough, either. The ceramic burners, in conventional fireboxes being discussed, seem not to be able to supply heat in the flues and that was another part of my reasoning for the 'gas specific' (or 'in flue' burners) design. The Finnish gentleman suggests as few flue tubes as possible, as does Kozo Hiraoka in his Pennsy switchers, both of which are coal fired. What I'd like to find is a design for 'in flue' burners. I'm weary of the empirical methods. I have more than few failed experiments! There are a few designs for poker burners on the 'net. Ron Reil's come to mind.
I live in Australia and even given our abundant supplies of coal, it's difficult to source good steaming coal. Some clubs do actually import Welsh coal. We once had a supplier of 'char' who has since ceased trading, therein lies yet another part of my reasoning for gas specific boilers. These boilers are very much simpler, particularly in flanging and staying. I use the Australian Miniature Boiler Safety Committee's methods for calculations and I find the AMBSC specs. to be indispensable.
 

Steamchick

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Hi Wazrus. My experience. In the UK there are model suppers (e&@y) that will sell jets 0.15mm and 0.2 mm and above for £2.50 inc. P n p. But I buy cheap Chinese drills for 0.25 mm and above and drill my own jets. Not perfect, but I buy 10 drills for the price of 1 jet, so I' m on a winner at 2 or more jets per set of drills.
But I wonder at the power you need for that decent sized boiler at 180mm diameter. Jets basically limit the gas that you can have. So look-up some tables for the BTU per jet size, convert to kW, and assume you need over 30 kW of burning gas to power a loco big enough for your boiler, and I guess you'll need 2 or 3 burners at 0.4mm jet! So why do you want smaller jets?
I also think for you dia 35mm fire tubes you need blowlamp type burners, with cones of radiant material. What may work for you is a few coils of nichrome wire. Say that you have 0.5mm wire. Make coils at 10mm, 14mm, 18mm, 22mm and 26mm, and with some wire spacers fit them inside each other, and use a propane blowlamp into the flue tube with the coils, and see if you get a good glow for a long length. The dire is the have visible red heat for 2/3rd of the flue tube length, but use the coils full length as even the black heat from wires will pump lots of radiant heat from the gas exhaust into the flue metal walls. Check exhaust temp of the exhaust from the flues, then you can compare wire heat exchanger configurations. Remember. Gas below 350deg.C. will stop burning, so if the gas temperature is over 350 just after the last flicker of flame, then you have burnt all the gas. Otherwise you'll be creating a Carbon Monoxide exhaust. That is dangerous, so please experiment outdoors, or have a CO detector (and believe it!) If indoors.
For those that don't know. CO in any amount causes permanent brain damage. In your life, the more CO you inhale the quicker you'll bring on dementia, so avoid breathing it wherever possible. End of safety message.
The alternate way to have a gas burner is to have a very large surface area of radiant: e.g. a large flat ceramic or wire mesh radiant burner the whole length of the underside of a long horizontal boiler, with all the gases directed to one end and through longitudinal flue tubes. My stationary boiler is this configuration, but most locos would not suit this (conventional designs that is!).
Cheers.
K2
 

Cogsy

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For those that don't know. CO in any amount causes permanent brain damage. In your life, the more CO you inhale the quicker you'll bring on dementia, so avoid breathing it wherever possible. End of safety message.
This is overstating the risk and being alarmist in my opinion. Obviously too high a concentration is very dangerous but there is a threshold where damage starts to occur and we are all routinely exposed to at least some CO as a product of almost all combustion processes (including the humble log fire). To suggest that minute amounts of CO exposure contribute to dementia is completely unfounded in literature. Even brain injury organisations do not make such claims : LINK.
 

Steamchick

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Sorry Cogsy,
Seems I have the wrong answer again..., I just remember what my school chemistry teacher told us about smoking. The CO combines with haemoglobin to form Carboxy-haemoglobin, which in turn blocks oxygen transmission to the brain - causing headaches, permanent brain damage, and potentially death... But I have no idea what concentrations we normally live with - having grown-up with coal fires, dirty vehicle exhausts, paraffin heaters in the front room, smokers everywhere until less than 20 years ago, and the teachers (most of whom smoked) said there was enough CO in a cigarette to cause "some" damage...
When I have a major blow-lamp job that sets-off the CO alarm in my garage, (Rarely!) I do the sensible thing and get out and ventilate the garage. - Because I don't know any better... But my model boilers (burners) don't set-off the CO alarm.
And I was told that my Mother's dementure in Old age was caused in part by a lack of oxygen to the brain, that occurs as the body ages. But I haven't studied dementure, just know it isn't good.
I'll have a beer and crawl back into my corner... - or does the alcohol affect the brain?
Cheers mate!
K2
 

fcheslop

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No need to drill 0.2mm holes for jets ,Simply drill to 0.4 and swage the hole down around a correct sized bit of wire. My lathe wont go fast enough to drill .2mm . The loco guys have used the idea for years
I tend to make 10 blanks drilled at 0.4 then swage them to the size I need
On my simple marine boilers I find the burner csa should be no more than 1/3 of the flue area. They must be only fed by primary air or at least the ones I make?
The nichrome mesh is available on ebay and is sold for something to do with those ecig thingy ma bobs.
I do use steam tables and start any boat build with a scale speed in mind and start with the prop this gives rpm this gives steam consumption and so on
with a good bit added for losses
A wee video of an experimental Cracker
And a wee plant for a 10 inch Puffer
Just built for the fun of it
A pic of the simple marine boiler
keep well
cheers
 

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HMEL

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Tell us more... I use "Model boilers and boilermaking" for a basis of my calculations, along with some theoretical gas consumption tables per jet size, and a huge fudge factor (<70% of expectations become reality). The biggest difficulty I find is in estimating heat losses... so I really go to town with complex insulation on my boilers. (Just a sheet of "bought insulation" is laughable to me!). I feel boiler and pipework losses are the most neglected areas of model engineering.
Any advice is welcome!
I am also a believer (as an ex-design-engineer) in calculations predicting optimistic results in the hands of the inexperienced. I spent some of my life being inexperienced in most things! (Now I reckon I'm inexperienced at everything).
Ta, K2
Will start with the burner size. Boilers design is part art and part science. So to start off with will go with a small boiler that needs to have its fuel input evaluated so we can estimate the burner size. We want to know in calories or btus how many are needed. At this point it does not matter what the losses are we want the theoretical heat input. Forgive me but I will use the btu system. Its the same method for the metric system.

Lets say this model boiler has a steam output of one lb per hour and its operating pressure is 5 psig or about 20 psia (absolute). From the steam tables found in textbooks or now on line we determine that this lb of steam has 1157 btus per lb of energy. Now technically I should give credit of the energy of the incoming water and it will range between 18 and 150 btu per lb depending on the water temperature. but to make my life easier for this simple example I will ignore it. Now we know from various calculations of combustion that the water of combustion will comprise a major heat loss up the stack.
A good coal will be about 85% whereas gas might be in the range of 78%. So because I know nothing is perfect I choose a number of 75%. I take my 1157 and divide by .75
That means I have to deliver 1542 btus in fuel whether I burn coal, gas , or oil. For grins I want coal and it has a heat value of 10000 btu per lb. And for one hour of operation I will need about .15 lb of coal for my steam engine to operate for one hour. A gas burner would be a little trickier because we have to consider burner size operating pressure, but it can be done. Ceramic heaters would also have to put out 1542 Btus in an hour.

But this is an area I do not know very well. I would think that a ceramic heater would not be capable of as much thermal radiation heat transfer. A furnace is designed to absorb this heat with the rest being absorbed in the back passes of the boiler. The flue tubes absorb heat by convection heat transfer. You want these to be as clean as possible with an acceptable pressure drop.

So I hope I haven't taken the fun out of making a model steam boiler. But I will tell you even the big boilers face issues in the design and start up. And we only just covered the numbers for fuel input.
 

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