Gas fired engines

Is the insurance industry opposed? As others have said plenty of gas fired steam boats, camping stoves etc. SFed has regs for testing home built containers which suggests they are acceptable.

Duncan I have built a three truck shay loco ,it is 1.5 inch scale but i made it to run on 5 inch gauge track, so the firebox is 8 inchs by 5 inchs rectangular with Marty burners

That would be Australia, over-regulated to the max. "Leading the world in safety" -- and red tape.

As I mentioned yesterday book 3 covers the testing of refillable gas tanks but only upto 250mls which would be a bit small for larger locos. So I expect it is the thought of having to pay for any testing that puts Model engineers off just like the thought of engaging the services of an independent boiler inspector and your own insurance rather than getting it done by a club

So use a standard gas bottle. The only bespoke thing is then the burner assembly, which is very small volume. I really can't see why a gas fired loco is different in principle to a camping stove, so why are people saying they are banned? Is there any actual evidence of this? The most dangerous thing with a gas bottle is if they are involved in a fire and overheat. This causes them to burst causing a BLEVE (boiling liquid expanding vapour explosion). Quite spectacular, but difficult to see the relevance to operating model steam as long as you keep the gas tank away from the source of heat.

A new one on me - Marty burners thanks for that.

I wonder if making the slots at an angle to create a vortex would help.

Following on from Duncans post !

Since gas (butane & it's mixes) is readily available off the shelf in tin cans one can reasonably assume that it's storage and transport is considered safe ? The vapour pressure of butane is quite low and below freezing is zero, ask any one who has tried to use a butane room heater on a very cold day ! As has been said a 5" loco needs a lot of heat so tin cans would not last long. Gaz do/did heavy steel bottles as small as 0.5Kg and also a 1.5Kg. The thread is a standard metric hydraulic/gas size and for high pressure piping ( to 4000psi) hydraulic hose with a perforated outer case. BSP O ring fittings. All the above are commercially available, but since the regulator fits on the bottle there need be NO high pressures involved, depending on the burner type the redoced pressure will be low. Soapy water will show leaks and you will be outside. Baring idiots trying for a DARWIN award, I fail to see where the problem is ?

In frosty weather I opened a damaged Gaz canister and poured out the gas - an oilly liquid, into a glass jar ! It was still there the following day - it was to cold to boil off ! Noel.

Having looked at the Marty Burners, The burner unit in a domestic gas boiler cut down to suit the fire box in question would seem perfect, give or take tuning. I have already put one aside with this idea in mind. Noel

Edited By noel shelley on 18/03/2023 10:33:48

Edited By noel shelley on 18/03/2023 10:42:21

The firebox on the loco I'd like to gas fire is 5.875"*2.625" grate, 15.5 sq.in. If I assume 25 lbs/sq.ft/hr (which is I think a reasonable estimate of the coal actually burnt in 5"g loco working hard) this is 34,800 BTU/hr. Marty burners are 8000 BTU/hr, so I'd need 3. The site linked to above (which is excellent) recommends the burners be 1" from a wall, and 2" centres, but the 2" can be reduced if you intermesh the flames. This means I can actually get 3 in my firebox. Why haven't I done it instead of pontificating? Well the regulator is seized, and so wants sorting, and too many other unfinished projects, and I'm hoping someone else will do it and show us the way (probably the real reason). Phillip's grate is massive compared to mine, nearly 3 times as big, and the firebox is probably a lot taller, mine is 4.375 grate to crown

Fitting things which are essentially round shapes into a rectangular framework is possibly not the best, Noel's suggestion of a longitudinal tube with transverse slits might well work better. I'm off to ring my tame plumber to get him to recover a central heating burner when he next does a boiler swap.

The next problem is the gas bottle cooling due to gas evaporation. The model boat guys get over this by feeding liquid gas from the tank to a vapouriser above the flame, but in my view you might as well burn paraffin if you've got a vapouriser, much easier to handle than gas.

I've collected loads of info about gas burners from old copies of ME if anyone is interested send me a pm

Edited By duncan webster on 18/03/2023 12:14:24

I am mystified too, I even went to look at the primary legislation and it's clear that all model trains/traction engines, would be out of scope of the gas regulations and treated the same as other boilers.

There's some complications with steam-plant type model boilers, but nothing that can't be worked around with basic awareness.

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One wonders if it like the situation with welded and non-copper boilers, where they're already permitted but actually finding someone within the model engineering community who would test one under those rules is hard causing them to be viewed with suspicion and generate misconceptions.

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As JasonB points out you can already do pretty much whatever you want as long as it's safe, if you're willing to submit to a true independent inspection against the relevant regulations, (and crucially pay that inspector).

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To Hoppers about Aus, in the UK we have some of the most non-restrictive [whilst still existent] safety regulations in the world, but it does put the onus on you to prove that whatever you decided to do is in fact safe, which is often a complication as it takes resources and documentation.

(The UK approach should be contrasted with only being allowed to do prescribed things which the government has decided will be safe).

"Fitting things which are essentially round shapes into a rectangular framework is possibly not the best, Noel's suggestion of a longitudinal tube with transverse slits might well work better. I'm off to ring my tame plumber to get him to recover a central heating burner when he next does a boiler swap."

Thinking back to LBSC's designs for parafin firing, after a venturi it was a longitudinal tube with transverse slits. Substitute gas for vaporised parafjn and thè job is done.

BTW, Duncan I think you are a bit light with 25 lbs/sqft/hr for 5" gauge. 40 would be a better design value based on my analysis of IMLECS.

Martin

So would the boiler need a redesign to get the best out of gas firing? There won't be much in the way of radiant heat going to the firebox sides and different flue tubes may be more efficient but until someone does the design and gets it approved that will be another stumbling block

Forgive the intrusion please …

This, which crosses the Flintshire countryside kinda puts things in perspective

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Not sure what pressure it runs at … but that’s a lot of gas !

MichaelG.

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Edit: __ and maybe coming soon:

https://www.dailypost.co.uk/news/north-wales-news/energy-boss-how-firm-refill-21573018

Edited By Michael Gilligan on 18/03/2023 14:02:19

Fellow club member ran his two Folwer ploughing engines on gas he had no problem with his engines or gas bottle getting tested or insured. The only drawback was running the engines on the rally field they struggled however when he ran them static they performed OK The small sized cylinder was stored in the riding trolley.

I meant burnt usefully, not ejected unburnt down the tubes or into the ash pan.

In Australia or at least in NSW all of the fitting must be approved by the AGA and you must have a blowback valve also a thermocouple in the instalation.

Duncan, I know you will know this but for the benefit of others who might be looking at gas firing in the larger scales there are a few obstacles to overcome:

1. You don't get the full benefit of the "calorific value". That is because CV is based on cooling all the products to ambient, which would condense out the water vapour and reclaim the latent heat. Gases like propane and butane have roughly 3 times more hydrogen by weight than "coal", so that loss of CV becomes a lot more important. That is why we all have condensing boilers at home. (Actually I have a heat pump, but thats another story)
2. Burning a nice blue flame is efficient combustion, but it doesn't radiate so the firebox surfaces are not working as they would with nice bright flames and a yellow hot bed of carbon. That is quite a loss in heat transfer.
3. Tubes in coal burning models are actually sized to prevent blockage with ash etc. (No I don't believe Jim Ewins or Keiller when it comes to boiler tubes!) So for an optimum gas fired boiler you would really want smaller tubes and more of them.
4. Coal is very forgiving of air control, whereas with gas or oil you need more active control of the air. I think a bank of Marty burners are likely to be running with significant excess air drawn up between the burners, which is dropping the combustion gas temperature and making for poor heat transfer again. Those of us with silver hair remember the fun and games the Festiniog had when changing to oil firing. So some experimentation with dampers and ashpans is likely to be the order of the day.

That is not to say it won't work and can't be done, but as Harry Wilkes' post shows, it can give performance problems. So I would not want to set too low a design target knowing some of the problems that lay ahead. 40 lbs/sqft/hour is pretty much mid range of IMLECS that I have analysed for 5" gauge engines.

Martin

I said it wasn't going to be easy! If using the Marty burners I'd be tempted to have a plate with 3 big holes to restrict secondary air so it has to pass through the flame, but I think the central heating boiler approach is more promising. Is it worth trying a thin stainless divider down the fire tubes to increase the Reynolds number? This has been reported as beneficial when people have taken superheater elements out, just down the big flues, but with gas and so no cinders it might help in small tubes. I'd still have elements in the fkylues of course, but again the lack of radiant heat might affect superheat as well. You're beginning to see why I haven't started, I anticipate problems, and I've got enough projects on. For a start I'd be happy if it just pulled me and perhaps one passenger, I think getting the high output you can get with coal is a long term project.

For give me gentlemen IF I have misunderstood BUT 40lb/sqft/hour from IMLEC ? Even big 5" locos were recording under 2Lb for 30 mins, so given a grate of 20Sq/in 25 or 30 I would fall for but 40? Getting the heat out of the flame would require a fire box crown with a load of 1/8"(3mm) copper rivets, say 1/2"long to be soldered in to draw the heat into the copper and possibly shorter fire box legs, even may be a dry back. It's one thing to convert and make the best of the job but if one was starting from scratch one would NOT use a design for coal firing. My thoughts would be half the heat would be drawn by the "crown sheet" a little from the fire box and the rest via small diameter firetubes and thought given to superheat. The crown sheet, think chip shop gas frier, or old fashioned cast iron boiler ! The boiler could even be easier to make, a thick crown sheet and smaller flat surfaces. Yes Jason ! The bottom of the fire box would have a little ventilation, but most would be top air.  This thread has enough ideas to make a superb gas boiler between us ! Noel

Edited By noel shelley on 19/03/2023 19:58:47

Not sure you would want a "firebox" of any sort if starting from scratch. Why not three large flues with cross tubes down the length of the boiler and a big burner for each. Much like a big version of the horizontal boilers we se used in model boats, this sort of thing at 3, 6 and 9 o'clock. Burners where the firebox would have been and a dummy backhead for the fittings.

I have fitted an arch in the firebox and also fitted turbulators in the tubes to slow the flow and get the maximum heat and find that you need the blower turned up to help draw the flame so you get a nice blue flame and a complete burn it is a bit of a learning curve ,but you do not have any ash plus you wont have to clean the tubes constantly ,i also run a separate carriage dedicated for the gas bottle only.