Design of boilers

[Chuck TaperParticipant @chucktaper]

Posted by SillyOldDuffer on 05/03/2021 09:45:08:

Posted by Andy Stopford on 04/03/2021 20:15:21:

Posted by Nigel Graham 2 on 03/03/2021 23:09:22:

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[Snip]

I agree!

I wonder what an engine specifically engineered to win IMLEC would look like. An engine with no obligation to resemble a full-size locomotive, or to be practical beyond winning IMLEC, and run in conditions that don't require the boiler to be certified.

I suggest:

• A tall vertical boiler balanced by outriggers
• Draught created by a tall chimney, not steam blast
• Waste steam used to pre-heat air intake and tender water
• Scale prevented by only running on distilled water
• High pressure, possibly from a water-tube boiler, with efficient superheat. (Isn't a water-tube boiler the logical conclusion to Bob's idea? It's all done with radiant heat.)
• If a fire-tube boiler is used, corrugate the firebox
• Oil burner to maximise heat and remove ash issues.
• Only burns one oil of known heat value so that combustion and heat transfer can be optimised.
• Grate area, firebox volume, and heating surfaces, calculated and proportioned to match the fuel and to optimise IMLEC performance.
• Large diameter steam pipes and a big steam chest
• Valve gear simplified to minimise friction
• Large aperture poppet valves, precision made to minimise leaks, possibly from exotic materials.
• Everything thoroughly insulated without regard to appearance!
• Optimum speed and load determined by experiment with a Dynamometer Car, and observed during trial
• Maximum automation allowing the boiler to control input and output to eliminate the possibility of a heavy handed driver wasting steam with excessive acceleration, or otherwise running the engine outside it's sweet-spot. Also manages combustion to best effect, neither underheating or overheating the boiler. Remote control and automatic shut-down
• Ideally driverless and without human passengers because they wobble, shift and raise the centre of gravity. Also, removing people means bigger risks can be taken with the boiler, speed, and balance.
• Thermal proportions, weight, adhesion, static and dynamic balance and other design features to be computer modelled to optimise performance
• Only run the engine under ideal track conditions – level, stiff track in good condition, few points, and large curve radii etc. And only run on dry, windless days.

[Snip]

Dave

Actually does sound like a great challenge or a new category!

FC

[Nigel Graham 2Participant @nigelgraham2]

Wonderful!

It's that last criterium that will prove the hardest to meet….

I like the contradiction between fitting a high boiler and even higher chimney balanced by out-riggers (on rails or with counterweights?), and hauling no passengers with their raised c.of g.

BTW… We read IMLEC report comments like "Fred stopped to drop off 3 passengers … " . Never mind the few ounces of coal consumed by the 1/8-scale loco, what of the weight of the 1/1-scale passengers? I've not read of discreet weigh-ins!.

[duncan webster 1Participant @duncanwebster1]

More power to your elbow SOD. Jim Ewins made a loco to win IMLEC, called Jimmy's Riddle. It incorporated several of his pet theories, and didn't win. I think the lesson from recent IMLECs is build it big and drive it hard.

Many moons ago there was a competition for hot air engines run at the ME exhibition (when there only was one). A good start on SOD's trail would be a similar competition for stationary steam engines, it's a lot easier to build and develop a single cylinder engine than a loco, and easier to instrument as it's not moving round a track. Steam at set pressure supplied by the exhibition management, probably electric heating.

SMEE used to have a rolling road for locos which could exert some load (shades of Swindon/Rugby) not just having it running free on rollers

[noel shelleyParticipant @noelshelley55608]

I'm three parts of the way there ! Got the the verticle boiler with tall chimney, Stuart No1, just need 2 sprockets and a bit of chain + the wheels. A bit of applied science and fine tuning and That's it ? Victor Ludorum !

[Dave Smith 14Participant @davesmith14]

SOD

Nice off the wall list. But what about the aerodynamic part of the equation. A long tall boiler will compromise the drag compared to a short thin on. Whilst drag is proportional to the square of velocity even a low speeds it will have an effect and it would be an interesting trade study to what wins out.

Dave

[Howard LewisParticipant @howardlewis46836]

The boiler will have to be computer controlled so that feed water is supplied by injector or pump, in the optimum manner (Churchward Top Feed? ) and quantity, and temperature, with similar controls over fuel supply and air through dampers (No driver / fireman so no need for firehole door – which simpllfies the stress calculations! )

And the system should take account of ambient atmospheric temperature and pressure to maximise combustion efficiency.

So fuel supply, water level and smokebox depression will be constantly monitored and adjusted.

Won't be much fun for the "controller" (formerly k a Driver ) unless they enjoy waggling joysticks, or tapping a keyboard!

Howard

[John OlsenParticipant @johnolsen79199]

If it is efficiency you are after then we need to increase the temperature difference between the hot end and the cold end. Usually this also involves raising the pressure, but I suppose under club rules you can't go past 100 psi. So lots of superheat I guess. Actually with a flash steam generator you should be able to go to any pressure you like, since there is no pressure vessel. The exhaust end needs a condenser, which needs to be as cold as possible, I guess we could carry ice, or get even more ambitious and carry dry ice, or liquid nitrogen. Although it would be awkward if the condenser iced up, i guess that would have to be prevented in the design somehow. The engine part would need to be a compound, reciprocating engines are limited in the temperature and pressure they can usefully cope with in one stage.

One thing is sure, the whole thing would be bulky, and it would not look much like any conventional steam locomotive.

It is easy to get hung up on efficiency, what really matters is a whole lot more subjective, eg how effective is this device at doing what I want at a price that I can afford.

John

[LukerParticipant @luker]

Posted by Nick Clarke 3 on 04/03/2021 09:43:55:

Posted by Luker on 04/03/2021 09:34:42:

I am not a fan of any requirements for professional or welder certification for the smaller boilers.

In the UK a non-coded welder needs to submit recent weld samples to professional inspection to comply with the current boiler code in addition to the inspection by a club inspector. This applies to all welded boilers and the material (welded steel or TIG welded copper) is not specified.

See paragraph 6.2 here **LINK**

Hi Nick,

I’ve finally had a gap at work and gone through the UK 2018 boiler test code (thanks again for the link). I found it a decent code to read. I’ve read far worse! Interesting stainless boilers isn’t specifically disallowed; it just can’t be tested using this code due to “specific” requirements. This makes sense if boiler inspectors aren’t trained with certain materials and current manufacturing practices. The code allows for a 3rd party boiler inspector to certify a published design of such a boiler provided he understands working with stainless (and is commercially certified). Boilers according to the code can be welded by “non-coded” welders but test samples just need to be commercially tested (as you pointed out), here I’m not sure if this will show any more than the standard v-sample vice bend test. Incidentally I think the section with the minimum sight glass point above the crown is a little dodgy; there should be a specified min value typically 10% top of nut.

At our club the boiler construction and testing follows and exceeds the requirements of this code, other than the use of modern materials and construction techniques. With this comes the necessary calculations and testing to make sure it is safe. As modern materials and techniques become more common place hopefully clubs will be more comfortable with newer techniques.

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