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Post by runner42 on Mar 21, 2015 5:14:48 GMT
Joan,
if the anachronistic PLC controlled steam locomotive had a presence in days gone by it wouldn't have the charm and attraction that causes many of us to re-live those past halcyon days of steam. The absence of the conventional valve gear would make it much less animated, which is one of its most endearing features. I look at my Doris with her Walschaerts valve gear and see poetry in motion.
Brian
PS A 4-6-0 or 4-6-2 with tender and outside valve gear is the quintessential steam locomotive.
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Post by joanlluch on Mar 21, 2015 11:43:05 GMT
Joan,
if the anachronistic PLC controlled steam locomotive had a presence in days gone by it wouldn't have the charm and attraction that causes many of us to re-live those past halcyon days of steam. The absence of the conventional valve gear would make it much less animated, which is one of its most endearing features. I look at my Doris with her Walschaerts valve gear and see poetry in motion.
Brian
PS A 4-6-0 or 4-6-2 with tender and outside valve gear is the quintessential steam locomotive. Indeed Brian. That's why I intend to have my locomotive fully mechanical with conventional valve gear and so on. In my opinion a Baker valve gear, which is what I am using, has even more "poetry" in it. However, as an exercise, making a PLC controlled locomotive can be still an interesting one, because that involves other skills such as (at least) PLC programming. Such a PLC locomotive could be a life of trial and error on mechanical designs, software patterns, and all sorts of engine optimisation. Definitely, not something to be dismissed as not interesting.
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Post by Deleted on Mar 23, 2015 9:17:00 GMT
Joan,
if the anachronistic PLC controlled steam locomotive had a presence in days gone by it wouldn't have the charm and attraction that causes many of us to re-live those past halcyon days of steam. The absence of the conventional valve gear would make it much less animated, which is one of its most endearing features. I look at my Doris with her Walschaerts valve gear and see poetry in motion.
Brian
PS A 4-6-0 or 4-6-2 with tender and outside valve gear is the quintessential steam locomotive. Indeed Brian. That's why I intend to have my locomotive fully mechanical with conventional valve gear and so on. In my opinion a Baker valve gear, which is what I am using, has even more "poetry" in it. However, as an exercise, making a PLC controlled locomotive can be still an interesting one, because that involves other skills such as (at least) PLC programming. Such a PLC locomotive could be a life of trial and error on mechanical designs, software patterns, and all sorts of engine optimisation. Definitely, not something to be dismissed as not interesting. Nobody ever believes this when I tell them but there is really little scope for improving the thermal efficiency of a modern design simple steam locomotive . Optimised but simple mechanical valve gears , cylinders and boilers already do all that is reasonably required of a working engine . The only way of getting even a little bit better performance is to introduce higher pressures and temperatures of steam and compounding and generally have a more complicated engine . Experiments with high pressure/temperature steam , gassifier combustion , marine style high performance boilers , compounding and complex valve gears have all produced useful results but usually at great cost . Performance of a steam locomotive does not just come down to thermal efficiency . The thermal efficiency of a simple steam locomotive is poor at best .What matters is effectiveness of an engine in service .
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Post by Deleted on Mar 23, 2015 9:56:46 GMT
The subject of using marine style boilers on steam locomotives is of interest though for reasons other than simple thermal efficiency .
Designs of British locomotives reached their practical limit of size with the Duchesses - in cross section they were tight to the loading gauge and their length was the maximum that was sensible to use .
If a simplified form of marine boiler could be devised which gave increased steam production but in the same envelope as a Duchess boiler then a more powerful engine could be built .
Experiments with complex versions of marine boilers on locomotives were mostly unsuccsseful but there is certainly scope for using some of the general principles of marine boilers but in a simpler way .
Water circulation is critical to getting good steam raising in any boiler . The use of marine style flow return tubes is certainly something worth exploring .
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Post by Deleted on Mar 23, 2015 10:13:25 GMT
I think design of the Hush Hush engine was something like 90% deductive/adaptive and 10% inductive/inventive . The designer certainly knew what he wanted to achieve from a theoretical point of view but he used mostly existing technology in his attempt to achieve it .
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Post by Deleted on Mar 23, 2015 10:31:53 GMT
there have been quite a few recent developments. i have been very privileged to have got to know Jos Koopmans re loco draughting, and he has completely overturned the traditional thinking on how draughting actually works in practice, plus found out that miniature locos actually lead the way in this respect because the margin for error is far less than in fullsize due to a number of factors. as a bit of an aside, i always think that a firm understanding of cube laws etc and how velocities apply to miniature require far more attention than has often been the case. Jim Ewins had something to say on both, but i have a feeling Michael could say a lot more! cheers, julian Conventional thinking on locomotive draughting is all wrong because it assumes steady state conditions . Nothing could be further from the truth could it - Whumff - pause - Whumff - pause ! Need to take account of events in cylinders , boiler , smokebox and chimney over a full wheel revolution to get anywhere near understanding what is actually going on . Could discuss steam flow and scale effects at length if anyone interested .
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Mar 23, 2015 10:48:16 GMT
i for one would be very interested in michaelw explaining all about steam flow and scale effects.
it is an area of design that is sadly overlooked and mis-understood in miniature.
michael's above posts are very interesting.
cheers, julian
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Post by Deleted on Mar 23, 2015 10:56:28 GMT
me too....always willing to learn.....
Pete
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Post by joanlluch on Mar 23, 2015 11:56:36 GMT
Hi Michael, Yes please.
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Post by Deleted on Mar 26, 2015 15:27:58 GMT
Only a few people have been interested in design as an abstract subject but several more have expressed an interest in theory and design of steam engines . So I have altered the thread title to something more suitable and we'll take things from there .
Please ask any questions you wish and I will attempt to answer them .
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Post by chris vine on Mar 26, 2015 18:53:33 GMT
Hi Michael,
Yes the flow of steam/combustion gases in a steam loco is anything but steady state. however I think it would be seriously difficult to analyse it mathematically and you would end up using a sophisticated fluid dynamics computer simulation program.
What would be interesting is how much the boiler (just as an example of part of the whole machine) would differ in design from what was used in practice - because of taking the pulsating flow into account.
In reality, a thousand different designs of steam loco were built in the UK, some better than others. They were all tested (in the flesh) with pulsating flows, so the designs were validated - some better, some worse. Of course this is a very inefficient way of designing a good boiler!!
However, I wonder if you sat with a computer (and modern software) in a darkened/isolated room, how much better your design would actually be? One of the biggest difficulties is to define the problem for the computer to solve!!
All very interesting stuff, Michael. Keep it coming!
Chris.
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Mar 27, 2015 22:20:39 GMT
Michael.
You raised the point about the pulsating blast not being a steady state condition. True at low speeds.
It must be remembered that the smoke box, tubes and firebox form two interconnected Helmholtz resonators. Without calculating but using my memories of loud speaker enclosure design I would say the resonant frequency of these two chambers would be much lower than the blast frequency for a loco at speed. A lot of work, Koopmanns et al, has been done on blast design but I have not seen any reference to tuning to optimise for the resonant effects I mentioned above. Compare this with the IC fraternity who spend a lot of effort resonating their induction and exhaust manifolds. Regarding the marine boiler I suppose you mean water tube type hence the reference to Hush Hush. From my work with water tube boilers, albeit limited, I suggest that drum volume and maintaining water level will be a problem. Water level in such boilers cannot be maintained by simply responding to a gauge glass. Even on small WT boilers feed forward control loops are used to balance steam use with water in.
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Post by runner42 on Mar 28, 2015 6:33:59 GMT
Michael wrote: Performance of a steam locomotive does not just come down to thermal efficiency . The thermal efficiency of a simple steam locomotive is poor at best .What matters is effectiveness of an engine in service .
Can you please amplify what features of a steam locomotive contribute to its effectiveness. I ask this so that I have a layman's (non engineer's) understanding of what may be presented later.
Brian
PS Ian is resonant effects a good thing or a bad thing?
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Post by Donald G on Mar 28, 2015 9:19:34 GMT
Michael
Please do keep these extremely interesting and informative post going.
I am very interested in the draughting side of it
Donald
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Post by Deleted on Mar 28, 2015 9:32:48 GMT
Thanks for the interesting questions and points raised . I'll put together a response asap .
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Post by ejparrott on Mar 28, 2015 10:09:42 GMT
Michael Please do keep these extremely interesting and informative post going. I am very interested in the draughting side of it Donald And me! Very relevant to the work I'll be putting my Manning Wardle to, and also David's 9F...and my Std 4...and my Duchess.... I just like to make my engines work hard!
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Post by joanlluch on Mar 28, 2015 17:28:46 GMT
I also want to add something for commenting about boiler design. The question relates on the actual design of gas tubes -the ones going from the firebox to the smokebox- in a boiler. (1) Some time ago I made a spreadsheet to calculate the required surface to heat a boiler starting from a gas burner flame. I am not a great expert on heat transfer but I think that I can at least understand the basics of it. Heat transfer in any heat exchanger or heater basically depends on the exposed heat transfer surface and the said "Overall Heat Transfer Coefficient". In turn the later depends on the convection thermal conductivity of the involved fluids (in this case flue gases and water) the flow regimes, and to the pipe material and its thickness. The later is not very significative if we consider any metallic material such as Stainless Steel or Cooper. The "Overall Heat Transfer Coefficient" is mostly determined experimentally and some tables can be found in books or the internet which provide typical values for common heat exchangers. Such as tables for the pipe wall exchanger type. www.engineeringpage.com/technology/thermal/transfer.html (2) In addition, Common Practice used in model engineering exists to suggest what a proper design would be. John's baguley made the effort of collecting such common practice information in his blog site. www.modeng.johnbaguley.info/Loco%20design/design1.htm . According to this, we should keep some set of factors that make a boiler a successful one. Said factors help to determine the number of tubes, and their length to diameter ratio. (3) Figures found on the internet for "Overall Heat Transfer Coefficient" such as the ones referenced above (1) , when inputed to my spreadsheet give results that are not that far than the ones predicted by the Common Practice (2) mentioned above. HOWEVER: Observations from the real world do not seem to match in all cases any of the above. (A) For example, a kitchen gas burner heating a kettle uses a lot less surface to boil the water. The surface under the kettle is very small, but water is still heated very effectively with only small heat loses. (B) Another example is Accucraft gas fired steam locomotives. Such as this one www.youtube.com/watch?v=OyLUiO2OMnk .The boiler of such a locomotive simply consists on two concentric tubes. A gas burner is placed in the inner tube, which heats and water/steam in the cavity between the two tubes. Occasionally a few water tubes traverse the inner tube. Looking at this case it is very clear that the total heat transfer surface is a lot smaller than a conventional boiler with conventional fire tubes. But the locomotive seems to raise steam and to work well anyway. My only explanation for cases A and B is that the "Overall Heat Transfer Coefficient" is in reality much higher than estimated, for some reason. As a consequence, there should be the possibility to design and build a much simpler type of boiler -with a lot less surface- and possibly no fire tubes. Or in other words, maybe this boiler was already thought of and it is what an Accucraft locomotive uses (?) I have been thinking for some time on the subject of making a simpler boiler design, and I will make tests at some time based on some ideas I have. But I can not try everything or spend a lot of money/time on this. Fresh ideas or theoretical background on the subject of simple boiler design is something that interests me. Joan
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uuu
Elder Statesman
your message here...
Posts: 2,808
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Post by uuu on Mar 28, 2015 17:54:23 GMT
If you can get hold of the book "Model boilers & boilermaking" by K N Harris, there's a chapter on boiler types, including simple ones. This is a field that was explored in the period 1900 to the 1920s, and there was a debate known as the "battle of the boilers" that raged at that time. Although the complex "locomotive" style boiler is now almost universally favoured, KN Harris seems to be quite even-handed in discussing the simpler types.
I expect you may generate some quite heated argument here!
Wilf
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Post by joanlluch on Mar 28, 2015 19:09:27 GMT
Hi Wilf. Thanks for the book reference. I just ordered the book from TEE Publishing. The same book is available from Amazon UK at higher prices and "customers who bought it" seem quite satisfied with it :-)
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Post by Deleted on Mar 31, 2015 19:46:04 GMT
Apologies for break in the proceedings . I've just had my worst ever cold and it brought me to a standstill for a couple of days .
Got some interesting answers in preparation though !
I blame the cold on a recent installation of a program that uses cloud storage - I hear that the cloud is full of viruses .
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