HOME | DD
bartpaaddiator — Boxhead
Published: 2014-10-14 11:52:22 +0000 UTC; Views: 770; Favourites: 8; Downloads: 1
Redirect to original
Description
Some pondering and thinking aloud about locomotive design. Tandem, 4-8-4, HP in the back. Most ideas are self evident from the drawing, but let me explain.Again the locomotive plays to my obsession of respecting temperature gradients. One of the main ideas here, inspired by reading the "Advanced steam locomotive development" papers, is placing the superheater not in the smokebox, but between the firebox and boiler proper. This enables not only to increase superheat temperature, but also to reduce chimney losses, by allowing for the smoke to have a lower escape temperature than in conventional superheated engines. However, this engine has a conventional superheater, instead of a firetube one as suggested by the papers (as I think its a terrible idea, for numerous reasons). The locomotive also has re-heat, placed similarly to conventional superheaters, but at a different layout, that is with the return tube placed concentrically inside of the in-tube. This enables the reheater to go "deeper" without having to worry about giving the heat back to the exhaust gases (or not as much, to be exact). An extensive water preheat system is present, with coiled copper tubes in forced circulation. There is also a rudimentary air pre-heat system, that aids the GPCS firebox by blowing an air-steam mix over the fire, the air being heated in a heat exchanger in the smokebox and sucked in through venturis powered by exhaust steam. Another idea is the presence of axle driven air and water pumps, both with variable stroke, rather than bypass valves to minimize the energy losses. The locomotive also has an exhaust steam injector.
Related content
Comments: 24
Question: How the heck are you going to get the superheater elements into location? With a 20 foot length, they certainly wont fit through the firegrate area, and with the necks up to the header, I cant see them going through the firedoor either.
👍: 0 ⏩: 1
How is it done on power plant boilers? I imagine similarly.
👍: 0 ⏩: 1
Perhaps, they might do it that way, but then again, they have massive grates, space enough to fit a rigging system, and relatively speaking, the geometry isn't quite as cramped. I just don't see your system being remotely easy (relatively speaking) or even possible to install or maintain unless you split the superheater lengths in half, then have headers at both ends of the barrel.
👍: 0 ⏩: 1
The idea here was to fit the superheater before the boiler and firebox get joined together, if it were to be built as a small livesteamer. In other cases, take the grate out, and do it from the bottom.
👍: 0 ⏩: 1
So you are saying, that if one element had to be replaced, the entire boiler needs to be severed at the flue plate? That is wholly 600% more work than needs be compared to contemporary practice.
👍: 0 ⏩: 1
Nope, you get in there from the grate side. If people can weld tanks from the inside, i don't see why this could not be done.
👍: 0 ⏩: 1
I can see how people would get in, but how do the superheater elements themselves fit through the grate? The firebox simply isn't large enough to allow a 20 piece of pipe to fit cleanly through it and then go straight into the flues.
Sure, you can argue that it would be possible for it to be inserted in sections and then welded together, but the reliability of the weld is now questionable and unable to be observed by an x-ray in a timely fashion, not to mention that the power of the locomotive is impaired due to the turbulence/slowed gas stream from the fire due to the raised portion of the weld.
Yes I am taking a basic welding course right now, and there is a huge difference between cold water tanks/cisterns and a boiler/pressure vessel.
👍: 0 ⏩: 1
The problem here which you have both not forseen and yet which will help 's side of the argument is that superheaters are not usually and never should be welded in. Among other things the welds would cause immense thermal damage to the elements and the headers and more damage would need to be done to remove them because of the work hardening.
Superheater elements are most commonly press-fit to pressure sealing seats against matching conical faces inside the headers and they are held against these seats by bolts with crossmembers which are integral to each individual element that exert massive tension that is more than enough to overcome the pressure trying to remove the end of the element from this seat. You can clearly see both the crossmembers, staybolts and nuts that hold in the elements in this photograph. www.ihpworkshops.com/header_im… The improper practice of welding superheating elements came entirely from this country's irrational overcautionary measures instituted after Gettysburg, much like the welding in of flue pipes.
This means that replacing a superheating element is as easy as unscrewing the nut of this bolt (after penotrant has been applied due to the nonsense going on in the smokebox) and removing the element by knocking it loose, then replacing it and retightening this nut. It works in exactly the same way as a ground union. I am faithful that with modern engineering and some beefing up this same design can be used in a radiative superheater in the firebox.
Dimensionally, it seems that removal of Bartek's superheating elements can be achieved quite easily through the firebox grate area upon removal of the fire arch. Each element, being planar in one dimension, can be turned sideways and removed through a long narrow hatch designed into the ashpan without any removal of the boiler from the frames.
👍: 0 ⏩: 2
Sorry about any confusion, if any, that arose. I was not speaking of the attachment to the header, as Bartpad certainly mentioned, I was just severely worried that installation simply would not fit. I expect this design could be installed and maintained easily in, say, a UP 4000, but almost certainly not in smaller, more prolific equipment that would be more common, like a CNR JS or SY, where I expect greater superheat would be of much more benefit.
👍: 0 ⏩: 1
Thankfully Bartek's fireboxes tend to be on the large side.
👍: 0 ⏩: 0
One issue I have, is that superheaters are very commonly welded. Unless you of course mean welding the bolted parts like the pipe connections, which is stupid beyond comprehension, and I have never encountered that in my life - maybe this is where the confusion comes from? In Poland by the end of the steam service even the drums were of a welded design, this worked, and enabled the use of steam engines without hiring any contractors or importing any parts - something that I consider to be the biggest advantage of a steam locomotive over other forms of traction, especially in the "third world". In fact, friends of mine have supplied the information on how to weld superheater elements to the Bosnian workshops in order to keep steam working, as the locals had an issue with getting the parts. Welding, as much as you don't trust it personally, is a great means of 'democratizing' manufacturing technology, and for that reason I support it in practice. That is not to say that I would not favor press fitting if a new engine were to be built. And to reapeat, I don't mean welding the bolted pipe unions, and I had no idea this was a practice...
Thank you for explaining this to the guy, this was essentially what I was trying to say, but I forgot of that discussion entirely. You have given a concise answer, which even helped me figure a few things out.
👍: 0 ⏩: 1
Oh I was specifically talking about welding the pipe connections. I do understand that many headers and sometimes element ends, if built-up, were welded and heat treated. While the bolted pipe unions should always be pressfit, I myself am used to cast headers of very thick metal but I can see how these could be made of welded construction.
👍: 0 ⏩: 0
Well, this is very cleverly designed! I like your approach to superheating!
👍: 0 ⏩: 1
Thank you. I since have realized certain faults with some of the components, but hey, thats what such designs are for.
👍: 0 ⏩: 1
It's interestingly shaped. If this thing were to have a condenser tender, it'd be perfect.
👍: 0 ⏩: 0
Bartek I have been meaning to say this engine reminds me very much of www.ipenz.org.nz/heritage/docu… I believe within her box is an exhaust steam feedwater heater, not nearly as developed as your system
👍: 0 ⏩: 1
I actually know of this engine, but believe it or not, it has not came to my head when drawing Boxhead (or Boxhead-Johnson as an intrusive thought actually named it, but I redacted that due to the obvious phallic connotations XD). I would actually need to read up about how the preheat worked here, as it seems like an interesting specimen.
👍: 0 ⏩: 1
That is hilarious, and it most certainly is. I know next to nothing about the Kb as of yet.
👍: 0 ⏩: 0
Oh man I have been WAITING EAGERLY for more drawings from you. One thing, I see you have her listed as a 4-8-2, but she appears to be a 4-8-4. Was this a mis-type?
I love, love, love this engine. The first thing is I love and also have had the idea in the past of putting the superheater where it belongs, which is either in or just in front of the firebox in the combustion chamber. It is far more efficient and there is far more to be gained. The only reason I have never done it in my fictional designs is because I do not trust myself to come up with a way for it to tolerate the immensely increased temperature stresses, because I am far more expert in traditional design and metallurgy than I am with modern ones. THe other thing was of course the elongated steam passage involved, but I see you have accounted for that by placing HP cylinders at the back end of the engine, another ingenious move! Firetube superheaters tend not to be good ideas, you made a good decision using an element type.
I also find it very interesting how you have incorporated the preheater into the blast petticoats. You may have to gang the tubes up or specially shape them but I believe this CAN work.
I also cannot believe I never thought of variable stroke or variable eccentric throw water and air pumps. That is a much more elegant system than bypass valves (other than priming the pump when dry, in which you do need a bypass valve for the water pump) Furthermore I have designed a succesful variable-throw eccentric for any use, and I know it works. I am kicking myself for not coming up with the pump idea myself..............
👍: 0 ⏩: 2
Thank you. I am happy that you like it, and it is quite a compliment to hear that you like my pictures.
The superheater demands a sort of extra smokebox for it as you can see. Other than that it should be no trouble to make. We have materials durable enough to sustain overcritical boilers these days, so I don't think that placing a superheater there should be an issue. The only problem is access for cleaning etc, hence the 'empty' chamber.
I envisaged them coiled around the petticoat for simplicity, but now, i wonder if it could work another way.
This was sort of an epiphany for me, which i thought of when thinking of IC engines (i often perform the mind exercise of trying to-reinvent it). The key for having it work with compressible fluids is to have the expansion link standing straight at BDC.
The concentric superheater was also a random thought, and I wonder what you think of it, as I actually want to try it out.
👍: 0 ⏩: 1
You are very much welcome.
Large smokeboxes also double as a good extra vacuum reserve. ENgines that burned hard coal were typically retrofitted with larger volume smokeboxes by adding to their length. THe larger it is, the better the engine tends to draft and handle dirty exhaust between cleanings.
I see what you mean about the material.
As for the petticoat, you see the inner walls must be totally flat and flawless surface in order to draught well, which is why caked on tar and exhaust particles on the inside edge will actually affect their performance. Because wrapping pipes around their insides would fowl the draught capability, and wrapping the pipes around their outsides would yield little heat transfer, the thing to do would be to make the piping FORM the petticoat, by having pipes smithed into a cross-sectional shape of a half-moon, with their flat sides ganged together so precisely that they physically make the inner wall of the petticoat upon which the venturi acts. THey would be brazed together and reinforced with barstock along their back sides. That, or cast the petticoat as a solid piece with these coiled pipes as simply passages within it. I have actually been thinking about this all day as I travel the city to assist in making your design a reality.
I have many times thought of the expansion link method in adjusting pump travel, but recently an idea came to me that trumps even that, when I stumbled upon a unique reversing gear. A valvegear that reversed by using a sliding collar that travels along the crankshaft, working a system of angled wedges that slide upon similarly angled faces on the eccentric disc, and slide the eccentric laterally across the shaft, so it is either 0 or 180 degrees in relation to it's original position on the crank, however any degree of adjustment between these two postions puts the eccentric with less and less of a throw, until straight neutral is the eccentric disc is directly centered upon the shaft like a flywheel, and there is no reciprocating motion coming from it at all. THe pump version of this eccentric would simply be one that goes from center outwards, rather than from center in both directions.
Can you further describe the concentric superheater to me?
👍: 0 ⏩: 0
Mis-type indeed. I have another drawing coming up in a minute, so if you could wait...
👍: 0 ⏩: 1
Aye captain, although I will see it when I return late tonight.
👍: 0 ⏩: 1
Well to bad, cause it's on now.
👍: 0 ⏩: 0