What loco for next years little lec

[Michael CallaghanParticipant @michaelcallaghan68621]

Hi out there. I have a mind to try my hand at next years little lec. However my 3.5 gauge locos are too large to enter. Looking at past events, locos like rob Roy’s, come up a lot. However what are your views, and can anything be done with these little locos to make them more competitive. Thanks

[noel shelleyParticipant @noelshelley55608]

I would say that the first issue is the efficiency ie the conversion of the fuel to power, SO, minimise all steam losses, avoid lifting the safety valve. Insulate the boiler and pipe work and work through the steam circuit so that all portways, pipe work and valves/regulators are able to pass the steam needed, in essence gas flowing the system. The next important thing is to be able to get the power you have on to the track, adhesion aided by weight and possibly the use of steel wheels/tyres. I hope these ideas would not be considered cheating ?   Noel.

[SillyOldDufferModerator @sillyoldduffer]

I agree with Noel – the issue is efficiency.

“The winner will be the driver of the locomotive returning the highest thermal efficiency“.

The organisers provide a weighed quantity of coal, so it’s the drivers job to get every Joule out of it and onto the track.

Building on Noel’s answer:

• Careful management of the fire
• Minimise braking
• Accelerate slowly
• As the rules say “The use of the hand pump will not result in disqualification. “, use the hand pump. The engine’s pump and injector both consume power, that’s better used turning the wheels. Have the driver do the work instead – he burns no coal.

Insulate!  Full-size loco boilers typically waste 95% of the fuel and small boilers are worse.  Most of the heat goes up the chimney and not much can be done to save it. However, quite a lot radiates from the boiler shell, so insulate the whole engine thickly, at least 100mm deep.  Rename the engine “Snowball”, which is what it should look like!  They won’t be laughing if you win.

For the same reason consider a tank engine.  Heat leaking from the boiler isn’t entirely wasted because it warms the water, and less coal is needed to boil hot water than cold.

Every little helps.

Dave

 

 

[noel shelleyParticipant @noelshelley55608]

In view of Daves ideas/comments, and I have not read the rules, the idea of a “snowball” is fine, if the true scale or rivet counters don’t like it – tough ! If you use the rules to best advantage bearing in mind the purpose of the contest and win, FINE ! Noel.

[noel shelley]

On noel shelley Said:

In view of Daves ideas/comments, and I have not read the rules, the idea of a “snowball” is fine, if the true scale or rivet counters don’t like it – tough ! If you use the rules to best advantage bearing in mind the purpose of the contest and win, FINE ! Noel.

Having noted the above comments, I do remember a rivet counters dream loco winning back in the eighties made by Roy Amesbury if memory serves.

Andy

[Nigel Graham 2Participant @nigelgraham2]

I’ve never entered any competitions but reading their reports they clearly are tests of driving skill as well as the machine.

I would question the remark about axle-pumps and injectors “wasting” power, or more accurately absorbing  it.

Axle pump yes, because it takes energy in both the delivery and suction stroke, gives lumpy running especially at short cut-off, and pumps cold water.

Hand-pump less so. It takes no mechanical energy from the engine but still delivers cold water, and rather irregularly.

(Assuming in both cases the locomotive has no feed-water heater: I have not heard of any such fitting, in miniature anyway.)

Injectors take no mechanical energy, and if sized correctly to the boiler should lose relatively less heat energy than pumps because the delivery is hot. This is partly why full-size locomotives were fitted with injectors instead of pumps from very early on in their history. The secret would seem a properly-proportioned injector, perhaps even two (large and small, the latter maintaining the level on the run) and well-installed pipework.

[Chris GunnParticipant @chrisgunn36534]

The injectors will use some of the precious steam wont they? or will they put most of it back in the boiler?

Chris Gunn

[duncan webster 1Participant @duncanwebster1]

Full-size loco boilers typically waste 95% of the fuel and small boilers are worse

er… No. Full size loco boilers are typically 70% efficient, according to Jim Ewins tests so are little ones. Most of the waste is hot exhaust gas up the chimney, the heat loss from the boiler shell is small by comparison. The exhaust gasses have to be hotter than the water in the boiler, so there is an upper limit to efficiency. Using exhaust gas to preheat the water is a double edged sword as it increases the draught required, so increases back pressure, which is not a good thing. As with all engineering it’s a balancing act.. Anyone ever tried a water cooled smokebox?

By all means insulate, but as explained by Mike Tilby in ME some time ago, there is a maximum efficient thickness, above which extra insulation actually increases heat loss. Due to the increased area from which you lose the heat.

An injector converts steam to hot water, you then have to burn coal to convert that hot water back to steam (as well as the extra water you’ve injected). Using an external source of power (hand pump) to put water in is clearly better than either injector or axle pump, but the work done pumping in the water is a small part of the output power.

Main ingredients I would aim for are no leaks (internal or external) enough superheat to avoid condensation, driver technique, no blowing off no spilling coal, no slipping. Does the weight limit include the tender (if not it should). If so tank engines have an advantage as they use more of the weight for adhesion, and the bigger the loco the better up to the weight limit.

[old martParticipant @oldmart]

Expanded polystyrene is one of the best thermal insulators I know but whether it would stand 120C as boiler insulation, I’m mot sure.

[Michael CallaghanParticipant @michaelcallaghan68621]

Thanks chaps, some good ideas.

[Nigel Graham 2Participant @nigelgraham2]

An injector uses a far smaller weight of drive water (as steam) than delivered water (from the tank), and should also be more efficient than a pump because it does put some of its heat back into that water.

A simple feedwater heater is more or less radiant; a coil round the smokebox wall or roof so it does not impede the exhaust fdlow. It might not be ever so efficient though.

I doubt expanded polystyrene would be very good as boiler lagging: try a piece with the water boiling at atmospheric pressure (straight from a kettle). The temperature of water boiling at the 90spsi gauge typical in model engines is somewhere around 180ºC, not 120ºC.

[JAParticipant @ja]

Are you allowed to use a hand water pump? If so, chuck the ejector and axle pump and just hand pump pump pump.

More seriously, the fire box on a model is far too small (think square/cube law). Using a normal grate will give inefficient combustion. I am told grates that reduce the air flow (for example, a Rosebud grate) give a nicer, more efficient, combustion all be it at a lower heat release. The latter can be compensated by reducing the draw bar load. Combustion efficiency can be easily measured by sampling the exhaust gas at the chimney for partially burnt hydrocarbons and carbon monoxide. These are compared with the carbon dioxide present. Steam and smoke are not relevant.

JA

[Nigel Graham 2Participant @nigelgraham2]

The competition is really more of relative efficiency than outright performance, with a strong element of driving skill. They examine small-scale replicas with many design compromises of full-size locomotives, not specifications for power-stations, and no-one expects levels of testing applicable to the latter.

 

Steam does matter – if wasted by excessive blowing-off or needlessly long cut-offs.

Smoke does matter – beyond the initial ignition fumes, it shows incomplete combustion, hence wasting fuel.

The exhaust-gas composition is not tested and really, is not very relevant; nor possible in a competition of this manner. The best guide to the state of the exhaust from a locomotive on the track, hence quality of combustion, is its colour, and that is a point made in the official operating-handbook issued by British Railways.

 

I do not know if a Rosebud or similar grate really improves combustion over a conventional grid, given both being properly proportioned.

Their users swear by them but since I have read remarks that their tapered holes (for better ash release) lift the fire by increasing the air-speed through them, for no obvious benefit, and I have seen little mention of them anyway in the last few years, I do ask. It’s pressure that lifts a load, not speed, but that needs the holes diverging upwards (think of an injector’s delivery cone), and those would soon clog.

Is a Rosebud grate’s effect influenced by the type of firebox? Do they better suit deep, narrow fires in Belpaire-pattern and LMS square fireboxes,  the wide, shallow LNER ones, or the cylindrical fireboxes on some narrow-gauge locomotives?

Surely an ash-pan damper, and its judicious use, would give better fire control but for some reason these seem unusual on miniature locomotives. Small top air feed to help complete combustion may not make much difference on a very small fire in a box with no damper and no brick arch; but excessive top air would be worse.

The coal size can affect the fire too, depending on the fire shape, but I don’t know how this managed in the “LECs”. It’s not just whether it fits through the firehole – but I’m sure we all know drivers who seem to think the door diameter is the optimum lump diameter.

 

In the end, assuming a well-built engine in good condition, I suspect what really counts is the driver’s “multi-tasking” on a track that may well give rather little time between curves and gradients for spot-on performance as both driver and fireman.

I sometimes try firing on the run round my own club’s track with fairly long straights, and even sitting directly behind our narrow-gauge outline locomotive (Kerr-Stuart ‘Wren’ class) with its large firehole, put as much coal on the footplate as fire, with the door open for longer than it should be. Our club used to own a 5″ g. tender loco which we ran on raised fixed and portable tracks, but I don’t recall anyone trying to fire it on the move.

So I admire those who manage competition-standard firing on a 5″ or 3.5″ g tender loco, in motion with a heavy train, even on a raised line!

 

I think it’s possible to over-think things. Of course we should and do want the best out of our model-building, these model locomotive efficiency trials are technically interesting and no doubt very enjoyable, but let’s not be carried away analysing the machines’ designs to the umpteenth degree when the numbers are unlikely to be more than a few % at best.

Perhaps the social aspects of the competitions are far more valuable!

[SillyOldDufferModerator @sillyoldduffer]

Well chaps, the aim of the competition is:

“The winner will be the driver of the locomotive returning the highest thermal efficiency“.

The organisers establish thermal efficiency by measuring distance, mass moved and mass of coal burnt.  No rivets  counted!

If Michael wants to win, a few extra % make the difference.  Insulation and hand-pumping pumping are two easy ways of improving efficiency.  Gets difficult after that, and then there’s no room for under-thinking.

Always best in engineering to put numbers on phenomena.  Anyone disagree with these full-size averages:

Dave

 

 

[Michael GilliganParticipant @michaelgilligan61133]

For what it’s worth … Armaflex is a MUCH better insulator than polystyrene foam

Commonly used as pipe-lagging, and easily carved to shape with a sharp blade.

https://www.pipelagging.com/pipe-insulation?msclkid=1400fde47a9916f4853e94c7f1f97248&utm_source=bing&utm_medium=cpc&utm_campaign=PLC%20%7C%20Search%20%7C%20Pipe%20Lagging%20%7C%20Variants%20%7C%20Exact%20%26%20Phrase&utm_term=pipe%20insulation&utm_content=Pipe%20Lagging

 

MichaelG.

No real interest in locomotive efficiency, but we used it a lot on liquid nitrogen lines !

[duncan webster 1Participant @duncanwebster1]

According to the interweb, armaflex max service temperature is 110C, higher than expanded polystyrene, but not as hot as a boiler. Rockwool would be my choice, but work out the most efficient thickness, probably less than you’d guess.

 

[duncan webster 1]

On duncan webster 1 Said:

According to the interweb, armaflex max service temperature is 110C, higher than expanded polystyrene, but not as hot as a boiler. […]

 

They do offer an HT version
https://www.armacell.com/en-GB/htarmaflex

MichaelG.

[duncan webster 1Participant @duncanwebster1]

And max temp for that is 150C. a boiler at 100 psi will be at 170C.

[Michael GilliganParticipant @michaelgilligan61133]

O.K. Duncan … I give up

I already said I wasn’t really interested in Locomotive Efficiency Trials

but I did assume people would be treating this as Competition, and maybe stretching the boundaries a little.

If conventional materials and lousy efficiency are the rules of the game, so be it.

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

O.K. Duncan … I give up

I already said I wasn’t really interested in Locomotive Efficiency Trials

but I did assume people would be treating this as Competition, and maybe stretching the boundaries a little.

If conventional materials and lousy efficiency are the rules of the game, so be it.

MichaelG.

On duncan webster 1 Said:

Full-size loco boilers typically waste 95% of the fuel and small boilers are worse

er… No. Full size loco boilers are typically 70% efficient, according to Jim Ewins tests so are little ones.

My mistake – should have said “full size locos” typically waste 95% of the fuel, the boiler is “only” the third worst problem.   But this is an efficiency trial, where every % saved matters.  Big picture, the difference between wasting 95% or 70% is immaterial.  They are both whopping big numbers! Anyone who wants to win the competition should try to reduce heat lost.  As I said, thickly insulating the entire engine is the simplest thing that can be done.  So do it!

 

 

Most of the waste is hot exhaust gas up the chimney, the heat loss from the boiler shell is small by comparison. The exhaust gasses have to be hotter than the water in the boiler, so there is an upper limit to efficiency.

Doesn’t matter – we’re trying to improve efficiency, not think of reasons not too.  Insulation is an easy win.

 

Using exhaust gas to preheat the water is a double edged sword as it increases the draught required, so increases back pressure, which is not a good thing.

Why would heating water with waste heat that otherwise escapes up the chimney increase the draught?

 

… Anyone ever tried a water cooled smokebox?

Good idea, condensers increase power and efficiency,  Problem is weight and complexity.  Has anyone ever got a condenser to work reliably on a loco?

By all means insulate, but as explained by Mike Tilby in ME some time ago, there is a maximum efficient thickness, above which extra insulation actually increases heat loss. Due to the increased area from which you lose the heat.

Pretty sure that’s wrong.  Any references?  What do the sums say?

An injector converts steam to hot water, you then have to burn coal to convert that hot water back to steam (as well as the extra water you’ve injected). Using an external source of power (hand pump) to put water in is clearly better than either injector or axle pump, but the work done pumping in the water is a small part of the output power.

About 3%.  It’s a worthwhile saving in an efficiency trial.

Main ingredients I would aim for are no leaks (internal or external) enough superheat to avoid condensation, driver technique, no blowing off no spilling coal, no slipping. Does the weight limit include the tender (if not it should). If so tank engines have an advantage as they use more of the weight for adhesion, and the bigger the loco the better up to the weight limit.

Of course, but do everything else as well.

On duncan webster 1 Said:

And max temp for that is 150C. a boiler at 100 psi will be at 170C.

Put a layer of glass fibre, aluminium foil or wood between the Armaflex and the boiler.   And, the Armaflex only has to last until the competition is won.

I’m happy with both reasons for entering the competition:

• bring an unmodified engine to see how it compares with other engines.  Fun and interest.
• turn up determined to win with a engine modified to maximise thermal efficiency, with a driver trained and practised in getting the very best out of the loco, plus a team who clean the track just before the engine as in curling.  Bribe the judges, water everyone else’s coal, WD40 the track before their turn, and force them to waste coal by delaying their start and making them brake by wandering in front of the engine.  Dick Dastardly in Wacky Races taught me all I know…

🙂

Dave

[Charles LamontParticipant @charleslamont71117]

Locomotive Management, Hodgson and Lake, p 34:

“It is a very good practice before starting out to throw a few bucketfulls of water over the coals, both on tender and tank engines, to keep the dust down. This not only lays the dust but also prevents fine coal from being drawn through the tubes before becoming ignited.”

[duncan webster 1Participant @duncanwebster1]

No need to take umbrage Michael, I’ve never said that insulation is a waste of time, merely that you’d need to use something that can take the highish temperature, and then suggested something with a similar insulating value. Insulation is not however the holy grail, it is a small part of the losses, and so reducing it will have a small effect. I gave a reference to the sums earlier, I know it’s counter intuitive, but you can have too much insulation. I haven’t attempted to work out the optimum for a say 3.5″ pipe (,typical boiler on small loco).
A shell and tube feed water heater designed to extract more heat from the exhaust gas will impose a pressure drop on the gas flow and so require a greater smoke box vacuum, so higher exhaust back pressure. Taking some of the exhaust steam and using that to increase feed water temperature will reduce the steam mass flow up the chimney, so you again need higher back pressure. Either might still increase efficiency overall, it’s a balancing act. Apart from Crosti boilers, which were not a resounding success in the UK, feed water heaters were not found to be worth the complication involved in the UK,  what were a success were exhaust steam injectors, best of luck getting one to work in small scale. A simple coil of pipe in the smoke box, or even water jacketing it might be worth a try as it wouldn’t significantly restrict the flow of exhaust gas. LBSC once proposed a baffle part way down the water space around the firetubes to give a sort of counterflow effect, inject cooler water at the front and restrict circulation and it extracts more heat. He got ridiculed, but I don’t see why it wouldn’t work.

A condenser is going to increase the mass of the loco, there is a weight limit in this competition.

I don’t know what SODs 70% refers to, I said boilers are 70% efficient, not that they waste 70%.

Working at higher pressure reduces the heat required to convert boiling water to steam (latent heat reduces until you get to the critical point, where it is zero), and increases the work you can extract from that steam, but it means you have to run at shorter cut off, which reduces port opening, increases wire drawing. As everything, engineering is a balancing act. A high pressure 2 cylinder compound might be worth a punt. Three cylinder is less mechanical efficiency, and more weight. If working with an overall higher expansion ratio you need more superheat, or reheat.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the explanatory notes, Duncan

… I realise that I am out-of-my-depth

I have never taken anything more than  casual interest in model steam locomotives or their efficiency.

I only mentioned ArmaFlex as being a  much better insulator than expanded polystyrene … and very easily worked.

Beyond that, and the technical details,  I can contribute nothing useful to this discussion.

If I was more involved, I would probably take advantage of the invitation in their Remarks

MichaelG.

.

.

 

 

[noel shelleyParticipant @noelshelley55608]

The idea of wetting the coal always seemed to me strange. If only to keep the dust down and your not paying for the coal is one thing, but the fire then has to vaporise the water in the fire box to burn = wasted heat ? I seem to recall a test done ( in full size )where wet and dry coal were compared and the dry coal worked much better !

A tip for Dave Dastardly, as you pull through the starting point for the last circuit turn on the track lubricator to dribble 220 gear oil on the starting point and first 100 Yds having first got the first run ideally or an early run if the judges are to expensive to bribe, this should spoil the chances of a large part of the rest of field. Contaminating the feed water so it primes badly will help as well.  Good Luck.  Noel.

PS to see how well the track lubricator works visit the Wells Walsingham Light Railway where even a 10.25″ Garratt struggles up the slope due to the lube system on the loco. Or is it to stop corrosion of the rail due to the proximity to the sea ?

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