Thanks for all your replies. I’m now getting some data, and have reports on the PRR T1, Q2, NYC S1a S1b and S2a, and C&O H8 to hand, and have ATSF and UP references on order. It will take me some time to digest and analyse everything, several weeks, if not months I would have thought. I will report back then for those who are interested.
An initial look see at the data says that on Porta’s critique ‘US exhaust design could not have been worse’ there is a case to answer; at top steam rates of 125000lbs/hr the PRR Q2 had an exhaust pressure of 31 psi, blastpipe area about 58 sqins; the Niagara already a back pressure of 10 psi at 52500lbs/hr, 44 sqins blastpipe, which means that at the quoted rating of 6000IHP the blastpipe pressure would be approaching 40psi! If it were possible to reduce that figure to 5 psi at the same steam rate (and I’m not claiming it is), you would get about another 1200IHP for ‘free’. The T1 had a back pressure of 25-29 psi at 100000lbs/hr which implies a blastpipe area of less than 50 sqins; star of the show so far is the C&O H8 which showed around 13psi at the same steam rate.
Now these backpressures look horrendous to European eyes, but there are mitigating factors. Firstly the % loss of efficiency you get from high back pressure decreases as MEP rises, and US MEPs it seems were higher than elsewhere. Secondly, these figures, apart from the H8, are probably at steam rates, which whilst achievable on test may not have been called for in daily service; remember to maintain 100mph with 1000 US short tons on the level needs only around 5500 IHP from locomotives of this size, exhaust rates less than 80000lbs/hr because of feedwater heater recycling. So an important piece of contextual evidence is what the steam rates required by the most demanding schedules were. If logs of actual running are available one can work back to required evaporation rates. (I’ve just piloted this approach by driving a brand new T1 + 1000tons from Crestline to Lima in 46 minutes, as one of its forebears did; all works well- the locomotive was not flat out. The residents Upper Sandusky were taken by fright as it passed at 111mph at the foot of the downgrade; most didn’t know that something approaching this used to happen several times as day. Lawsuits were threatened.)
If one were to set a design goal of a back pressure of no more than 5 psi at some maximum design evaporation rate- let’s say 800lbs/sqft/hr, i.e. before boiler efficiency really plummets, then a few calculations suggest that a blastpipe area sqins of 0.887* grate area in sqft- 2.14 would be required, so the target for a Niagara would be 86.5 sqins, for the Q2 about 106sq ins, about double what they had; relaxing the criterion to 10 psi gives about 60 and 75 sqins respectively. The Jabelmann exhausts on the UP 4-8-4 and Challenger, should offer a significant improvement on the Niagara and Q2 respectively, so getting these areas is a high priority to understand what US best practice was.
Exhaust design is historically a trade-off between steam raising ability and back pressure; in the UK, and I guess everywhere else, steam raising won out over backpressure i.e. efficiency every single time. This is the real constraint when aiming for lower back pressure.
Dreyfusshudson Dear Lars, Thanks for these comments. Where should I look out for the private message?- this is new to me. I would be very intertested to see the Big Boy data when we have established direct contact
Dear Lars,
Thanks for these comments. Where should I look out for the private message?- this is new to me. I would be very intertested to see the Big Boy data when we have established direct contact
On the index page, where all the trains.com forums are listed, nearer the top you'll see a clickable post from anyone who wishes to start a conversation with you. Similarly, if you click on the bold username in any text message posted here, a page will open and one of the options will be to start a conversation.
Crandell
Dear NM Coot,
Thanks- understand and largely agree with what you write. Will check out the reference if I can get it. One of the first books I bought on US railroading was Duke and Kistler's photographic treatise on the Santa Fe in California, and I remember being very struck by the fact the 4-8-4s ran the 1765 miles from Kansas City to Los Angeles, over as many obstacles as you would care to mention. Inspired by the photograph of 3777 climbing Cajon Pass with 11 vehicles unassisted, I had a go at producing the power map for a 29xx class, again using guesses for many key parameters (Seems I can’t post this Excel graph)
I then got a crew with a miraculous ability to work at a constant 65000lbs/hr to the cylinders to drive 2926 all the way from Seventh Street, San Bernadino to the Summit, using this map. This is what I got:
Engine
2926
Tare wt
650
gross wt
700
Engine wt
429
total wt
1129
Miles
instant ihp
speed mph
total time
av speed
av ihp
av edhp
av dhp
height ft
av grad
0
San Bernadino
0.01
00:00:00
1060
0.8
Seventh Street
1946
22.38
00:02:48
17.19
1422
1339
875
1086
160
7.5
Verdemont
4252
28.37
00:15:38
31.32
4260
4035
2604
1706
57
10.4
Devore
4269
29.05
00:21:39
28.92
4266
4008
2576
2001
52
12
Keenebrook
4205
26.12
00:25:00
28.56
4251
3995
2567
2171
49
14.1
Old Keenebrook
4159
24.48
00:30:06
24.76
4165
3942
2517
2423
44
18.6
Cajon
4304
30.62
00:40:07
26.94
4219
3980
2550
2903
23.7
Alray
4188
26.42
00:51:51
26.08
4196
3963
2536
3487
46
26.8
Silverwood
4383
34.34
00:57:34
32.53
4349
4057
2624
3751
62
27.45
Summit
4447
39.03
00:58:41
34.90
4412
4092
2658
3794
81
It’s so long ago I can’t even remember where I got the heights and distances from- probably off Google Earth, so it’s all very approximate, but this is another illustration of where I’d like to get to.
In addition to Farrington, The Big Three, you might want to check Brasher, Santa Fe Locomotive Development. There is quite a bit in it but not in easy to use format. Another series that might be useful is the "Loco Profile" series published by Profile Publications. There are issues on NYC Hudsons, Nord pacifics, LNER A4, the American 4-8-4, and many others. The ultimate of course is La Locomotive a Vapeur, by Andre Chapelon. There is an Engilsh edition translated by G W Carpenter. If anyone knows high efficiency steam, it is Chapelon.
I think it was Churchward that said he could improve the efficiency of any engine by 10% simply by painting the funnel blue. His point was that day to day operation depended much more on correct operating procedues than pedantic design detail. If a crew believe they are being closely watched, they'll do things right. And of course what's best depends on whether you want speed, drawbar effort, water economy, simple maintenance, etc.
The objective of the boiler is to produce steam faster than any combination of engine parameters can consume it. The objective of the engine is to produce an effective output using all the steam the boiler can produce. To pass great quantities requires large cross-sections through-out the exhaust path. Higher superheat gives more fluid steam. Numerous designers got the passage part right. Fiddling with just the exhaust outlet is only a part of the answer. High superheat in daily practice really is more a matter of cost and reliability than it is pure engine efficiency.
Having said this, few steam locomotives operated near their maximum for any length of time. The NYC Niagaras were great but for day after day long, high speed runs, you have to give the blue ribbon to the ATSF 4-8-4s.
First of all, let me express my appreciation for all the comments you have all made- a very considerable efforts in some cases. Thank you very much indeed. I will try to produce a single response to all these points, starting with some generalities, then getting to specific individual comments and queries later.
Let me start by referring to Feltonhill’s comment ‘I’m not sure where this discussion is going’ and reiterate my hope as to where it might go. What I have done, as Paul Milenkovic observes it to link together a series of engineering models of the key components of drawbar efficiency; engine efficiency, boiler efficiency, and Locomotive resistance (LR); the first is a fully worked through first principles model, the latter based on detailed estimates of the likely magnitude of the components of LR; the boiler efficiency model is simply an empirical model based on test results.
Now such theories are wonderful things, and the question is rightly posed, but what of the experimental data? As I reported, I have explored the value of these models by comparing their predictions to a wide range of UK data collected at the test plant, about 1500 2 hour long test plant runs, about a dozen different locomotives from different builders, with different design philosophies, plus road testing. The models predict the outcome of these tests remarkably well. In this one ought to bear in mind that there are differences of 5% or more in measured efficiencies of different members of the same class, both ostensibly in ‘as new’ condition (a fact not reported), for reasons I think I understand, and tests also showed that between visits to the shops, efficiency could deteriorate by 10% or more. This needs to be borne I mind when trying to validate the models against data. Also, it was not unknown in our country for enginemen to waste steam through safety valves, draincocks whistles etc., use it for auxiliaries such as braking, worst of all actually using precious steam to keep passengers warm.
I’m interested in finding out how well these models apply to US types. The stimulus was the Porta comment I quoted, which implies that there might have been major scope for improvement; I’m a bit sceptical about this. My hunch is that latter day US designs would all have efficiencies within 10% of each other, and at most the best could have been improved by 20% by the kinds of technologies advocated by Wardale and Porta, half of this from the GPCS firing system, significant, but not game changing I think.
What I therefore need is US data of two kinds.
Firstly, input data for the models. The prime need is for information on blastpipe dimensions and superheat levels, for the work I have done shows these are the things which will most impact engine efficiency. The engine efficiency models also require detailed knowledge of 19 separate dimensions of the motion, to calculate accurately the openings of the ports during the engine cycle; I also need to know lap, lead, exhaust lap, port width, the perimeter of the ports (i.e. % of valve circumference with open ports), clearance volume, operating pressure, cylinder diameter and length. Hoping to keep things simple, I asked just for superheat and blastpipe dimensions. I have access to some of the other data, and can work my way round what I don’t have. This would allow first pass estimates of engine efficiency to be made.
The second need is then for US test data to see how well, or otherwise, these predictions fit with experimental reality; in this it should be noted that as well as taking into account the variability in different class members, in the UK there were in initial plant testing some very basic problems in measurement- fortunately there’s enough raw data available to be able to pinpoint what these problems were. So measurements are not always as reliable as they seem. There is evidence of this in the Altoona test results too.
Even if such test data were not available, I think these first pass calculations would allow one to say how much scope for upward improvement existed, and give an idea of how much the engine efficiency of latter day US designs in fact varied. I would be happy to publish the results of these calculations in this forum on a ‘for what it’s worth’ basis. The quality of the output will depend on the quality and amount of input data I can get- garbage in, garbage out. To improve estimates of boiler efficiency and LR would require more data still, though for first pass estimates, I think what I have is good enough. I am acutely aware that there are aspects of US practice that my models may not incorporate.
One final generality. My interest is in how much efficiency can be improved, as Wardale, Porta and the 5AT group, with whom I am in regular correspondence. However, locomotive efficiency is but one element in the overall financial mix. My understanding is that even in diesel days, US philosophy has been to send out freight trains with just enough power to get over the road without stalling (I exaggerate). Working heavy trains at low speeds leads to low drawbar efficiency, as my illustrative calculations show. Drawbar efficiency could be improved simply by running shorter, faster trains; even then this is not the full story, because if you run faster you need more dhp-hr to cover a given distance, so putting coal consumption up. How this all pans out is a question for accountants; all engineers can do is provide an accurate assessment of efficiency over a range of operating conditions, to allow you to estimate operating costs. Overall it appears to have made sense to run longer, slower trains, thus depressing drawbar efficiency.
Now to specifics.
Firstly, Juniatha, March 26th 09:31. Thanks again for such a detailed set of comments. I’d obviously be very interested in knowing the dimensions of the of the Jabelmann arrangement. It was watching the soft exhaust of 844 and 3985 on You Tube that led to me wonder about Porta’s assertion. With respect to your question about draughting, estimating this is not part of the process. I have done some work, based on ideas of the author of the engine efficiency programme, to attempt to work out what the entrainment ratio (ratio of flue gas to exhaust steam) of a front end is, hence how much coal can be burned. This foundered on the inability to estimate how much the chimney is able to flatten the ‘peaked’ velocity profile of the exhaust leaving the blastpipe. Others are working in detailed computational fluid dynamic modelling to address this. The engine efficiency programme only needs to know the blastpipe pressure, which is determined by the flow and temperature of the steam. Since the programme does not know this at the outset, it does a series of iterations until the flow and temperature match the flow into the cylinders, and efficiency of expansion.
On the steam rates, I’m in no position to challenge your assertion that the UP types can and did exceed 100000lbs/hr, but it would have been very uneconomic (though see comments above about economy). However, I think a distinction needs to be drawn between what could be done, and what was regularly done. If I may illustrate; in this country, we had a class of 10 wheelers, the Scots, that had small grates (31 ¼ sqft) relative to the amount of work they were expected to do. Consequently, the specific evaporations they achieved were higher than any other type. On their best runs they sustained about 1650IHP and produced shorter term bursts of 1750 IHP. This translates to about 700-750lbs/sqft evaporation. Crews claimed they ‘wouldn’t steam’ (I think they meant they burned too much coal!), and one was sent to the test plant where they got 1020lbs/sqft/hr on second grade coal, the highest recorded there. One of the class is still working one of the many steam specials we have. Without wishing to suggest anything other than top class professionalism, crews love to thrash their steeds. In 2009, it delivered a short term effort of 2350IHP needing nearly 1150lbs/sqft/hr, 50% more than they habitually delivered, higher than anything else I can find in UK history, but hardly representative!
Understand your comments about Porta.
Comments on US draughting systems; understood and agreed; it is just how much more might have been possible with better draughting that interests me.
According to my programme, if you had a blastpipe area equivalent to a 10” diameter single pipe you could get 8000ihp from a Niagara, 45% cut off at 100mph, cylinder rate about 117000lbs/hr if superheat were 750oF, quite possible from a 100 sqft grate + feedwater heater, but not I think a regular practicable proposition. Because of the need to have sufficient cylinder volume to develop high power at low speeds, all engines can deliver far more power than their boiler could hope to produce at high speed: the issue is boiler capacity, not engine power.
I’m not saying that lap, lead etc. make no difference, just that the effects are not that large, this on the basis of analysing UK style dimensions; it might pan out differently with US dimensions, though I doubt it. There is a well told story in this country about how changes to these settings led to a massive improvement to the efficiency of the original Doncaster Pacifics. One of the ‘high priests’ of valve gear design in this country, and a Doncaster man too, saw the results of the programme I am referring to just before he died, and, understanding the basis of the calculations, had the grace to admit that the explanation put about for the previous 75 years had to be wrong; the benefit was all about the redesigned gear being able to operate in shorter cut off, compared to the long cut off/ low steam chest pressures allowed by the original design. I have corresponded with Wardale, but not on this subject.
There is indeed no magic in 30% cut off; it is just that if you plot efficiency vs cut off, you find that the decrease is relatively small increasing from 15 and 25%, and then progressively begins to get bigger and bigger for each additional % cut off- 30% is an arbitrary breakpoint between ‘not much difference’ and ‘quite a lot’ of difference, and beyond 40%, ‘very big’ differences. As in Germany, drivers in this country often, for the practical reasons you describe, drove on part throttle, and longer cut off than they needed to, offending the purists who correctly said that the most efficient way was full throttle, short cut off; however, providing cut off was not much above 25%, any efficiency losses were marginal; test plant results confirmed this.
Poppet valves are another big discussion point; maybe this should be shelved.
On the point about it being cylinder back pressure, not blastpipe pressure being important for efficiency, I agree. However, what the programme I am describing demonstrates is that to all intents and purposes the two are the same thing, or at very least, highly correlated.
With respect to your comments on the SSCs of the UP types at 5000 IHP being too optimistic, this is entirely possible! As I indicated in my comments, the input values I chose for superheat and blastpipe area were completely made up; I am looking forward to repeating the calculations with the correct values. The first column of my Table shows that develop 5000IHP at 100 mph is about 30%; the exact figure will depend not only my guesses about superheat and blastpipe dimensions, but also other guesses that I have made with respect to engine and valve dimensions. The allowance for feedwater heater on boiler efficiency is a bit of a botch; I am in essence assuming that the amount of heat from coal needed is about 10% less than that would be needed to produce the flow of cylinder steam in no feedwater heater were present; this is just another assumption that needs tightening up if one were to do more accurate estimates. No account is made of the steam required by auxiliaries. This may sound like a damning series of admissions, but remember my purpose was to illustrate what could be done, if the relevant data were available, not to produce accurate estimates, these will come later if the necessary data is available. Having said that, I do believe the drawbar efficiency estimates are in the right ball park, and the changes I alluded to with respect to speed realistic.
The same goes for you questions about resistance; the underlying formula for resistance I use does separate mechanical and rolling resistance as you suggest. I think the approach used to define mechanical resistance, developed by a friend, is sound, and with data about the mass of parts of the motion, pistons, valves, journal sizes, spring forces etc, could be applied to US designs. I am not confident that my extrapolation from UK locomotives is sound; this is another big project to put right, but I think we are only talking of 10-20% deviations from the figures I quote, so I am I the right ball park at least.
I am wondering, having written this, if it would not be better rather than to try to do a broad brush survey of many types with partial data as inputs, to take one example for which all the details are known, and for which there is test plant data- e.g. the Niagara as mentioned, just to see how applicable the models are to US practice. It all depends on the data which is available.
Feltonhill, March 26th 2.01pm Good to know the T1 and Niagara reports are still around- how can I get hold of them? This would go a long way to answering my query. I might be able to source the Santa Fe book over here. I got to know Phil Atkins well when he was librarian at the NRM, and if he still has the same e:mail address, I’ll see what he can add. (He was the one who hired a pick up truck and went to the Rugby test plant just before it was bulldozed, and saved all the raw data and correspondence associated with UK testing- probably the only surviving raw data we have). I’m not sure what gives the impression that I have used total evaporative heating surface- the surface area referred to is that of the grate.
With respect to combustion chambers, there were some attempts to incorporate these into UK fireboxes, but not I imagine of the size possible in the US; I’m not familiar with the theory but suppose the idea was that the more space you have the greater the time for combustion to complete. Now, Orsat analyses of smokebox gases showed that it was rare on UK designs for combustion to be incomplete, except with respect to unburned particulate coal, so if they did have an effect on combustion it would be to burn some of these small particles; however, given that the extra lifetime of these particles in the firebox would be small, I am not sure there would be much benefit- that’s where the US data would be most helpful.
The Professor who produced the first principles model of the engine began by trying to do a first principles model of the boiler. He abandoned the attempt because he felt he couldn’t do a proper treatment of radiation vs convection- if it wasn’t robust, he didn’t want to know. I think there is an even more fundamental problem that he didn’t address, namely the loss of unburned coal from a lump coal firebed. You can measure it, but as far as I’m aware, no research was ever done to try establish the principles involved (there is some work quoted by Wardale, but I think this is the wrong concept).
Your description of the changes to the Y6 fireboxes is of great interest to me, because there is something about US boiler design I don’t understand. In this country, 19th century engineers believed that a long distance between tubeplates was a good idea to maximise heat capture. When superheaters were added, this meant that whilst the steam was hot near the firebox tubeplate, as the flue gases cooled along the length of the flues, they actually began to cool the steam in the superheater! Bad news. Boilers tubes reached a maximum of 22’ here; it took about 30 years to figure out that if you wanted top superheat, it was inadvisable to go above 17’. And, in fact if you work out how much residual heat there is in the flue gases, the extra amount you extract between 17 and 22’ is pretty small anyway. So, looking at the massive size of some US boilers, how, I ask, did they manage to get top superheat levels?
Your SSC figures for the UP types give about 15.6lbs steam/hp-hr; with the original assumptions I used I get 6000IHP at 70 mph in ca 33% cut off, 89600lbs/hr to the cylinders: at this stage this is remarkable agreement! So we’re not too far apart, though I’m a bit better at 14.9 lbs steam/ihp-hr; from what I read, my blastpipe pressure of 19.7 is way too high, which seems to suggest the superheat is not as good as I suppose.
Lars Loco 26th March 5.34pm
Interested in how the discussion on 100000lbs/hr pans out- see my comments above on ‘normal’ vs ‘maximum possible steam rates’
Lars Loco 26th March 6.26 pm
I’m more than happy to share the engine efficiency programme with you, if you can suggest how I can get it to you; as far as I know Microsoft won’t even let you send zipped .exe files now. It’s only 500KB!
I can also send two published papers from its author, describing its fundamentals; there is also one from me describing how I went about applying it, though I have to say this is rather long! I should also say that I’ll send you a 1 sider on what’s wrong with it- its author would have wished for nothing less than complete honesty, but this is not to undermine its value. It is in my view a complete game changer in our understanding of steam engine efficiency, provided it is handled with care.
Paul Milenkovic March 27th 12.53 am
Thanks for your supportive comments; as outlined above, you are correct about the gist of what I am trying to do. I have Wardale’s book and it is indeed a treasure trove. The point about Wardale however is that he is very proud of the fact that he designed his 5AT using only techniques which were available in the steam age! He has used the programme referred to above to check out his calculations on the 5AT, and found good agreement, though I have the suspicion he prefers the old ways!
Thanks again for all your responses; 9 in 24hours; that’ll teach me to go off enjoying myself doing other things!
To Lars Loco: Oh yeah, I've seen "The General"! A very funny movie, but seeing that old 4-4-0 get wrecked on the burning bridge makes my skin crawl! Oh well, at the time it was OK. and the locomotive was due to be scrapped anyway, but I can't look at it now without thinking of it as the loss of a fine railroad artifact. And doing it to a Class "J" doesn't even bear thinking about! By the way, I misspoke on the "J"s tractive effort. Post- war modifications brought them up to 80,000 pounds of tractive force, making them the most powerful "Northerns" ever built. Oh, and the Norfolk and Western always called them "J"s, there was no way a Virginia road was going to call them "Northerns"! "Old times there are not forgotten...."
Firelock76 To Lars Loco: How much power could an all roller bearing axle locmotive have at the drawbar? Well, have you ever ridden on a jetliner? I rode behind Norfolk and Western's Class "J" 611 several times before the excursion program was stopped, and got that same set-back in the seat when the engineer opened the throttle! Not as much, mind you, but it was certainly there! A "J" could produce 73,300 pounds of tractive effort, can't tell you the horsepower, none of my books have the answer, but my dear God, what a magnificent machine! If General Lee had one available to him in the 1860's, along with "Seven-Elevens" and pick-up trucks, the South would have won The War!
To Lars Loco: How much power could an all roller bearing axle locmotive have at the drawbar? Well, have you ever ridden on a jetliner? I rode behind Norfolk and Western's Class "J" 611 several times before the excursion program was stopped, and got that same set-back in the seat when the engineer opened the throttle! Not as much, mind you, but it was certainly there! A "J" could produce 73,300 pounds of tractive effort, can't tell you the horsepower, none of my books have the answer, but my dear God, what a magnificent machine! If General Lee had one available to him in the 1860's, along with "Seven-Elevens" and pick-up trucks, the South would have won The War!
while reading your last lines...
do you know Charlie Chaplin´s "The General" ? It shows the most dramatic stunts ever made in movie´s history, now imagine he would have had a 611-class engine available ... phew... too though even for Charlie...
Well, all right! Juniatha's back! You go, girl!
I commend you on your work on this topic, and I offer you encouragement in the face of some of the naysayers.
What you offer is an engineering model, that is, a somewhat simplified version of a collection of much more complicated formulas and equations. The purpose of your model is 1) to predict the performance of known steam locomotives, with the view of understanding the rough contribution of various system components -- the grate, the evaporative surface area, aerodynamic resistance in the steam circuit, exhaust back pressure, and so on, and 2) armed with the ability of the model to predict known steam locomotives, to make educated guesses regarding what enhanced or improved steam locomotive designs could have done.
The fact that you get into "the ballpark" of the 5-6 percent thermal efficiency often quoted for 20th century U.S. steam, and that you get into that ballpark based on thermodynamic, fluid dynamic, and empirical relationships tells me that leaving aside the naysayers, that the quirks of individual steam engines are unknowable apart from much more complicated formulas, that you indeed have a good model of steam locomotive thermal efficiency and are to be commended for your efforts.
I am sorry I don't have data or measurements on steam locomotives to contribute. My only suggestions is that the David Wardale 5AT steam locomotive project has a Web site along with links to technical information you could check out (does his prediction of efficiency on the low to mid teens for this proposed design square with your methods?). David Wardale also has this out-of-print book The Red Devil and Other Tales from the Age of Steam -- if one could get a copy somehow, I am told it too has considerable technical detail on steam locomotive efficiency.
I commend you on your efforts and look forward to more results from your model.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
@Dreyfusshudson
Thank you all for this interesting post + data, can you tell more about this program? Is it shareable?
Kind Greetings
-lars
Juniatha Er-hm .. if you may pardon my joining your discussion, may I just add a few words? The UP Jabelmann double chimney arrangement included quadruple blast nozzles each. With that draughting both Challenger and FEF-II could and likely did exceed 100,000 lbs/h steaming rates. Regards Juniatha
Do you have the source of "100,000 lbs/" ? Sometimes, I have those "weirdo" thinking, that UP-Engines were pretty underestimated, concerning that...
Looking at the BB-tests in 1943, the engines produced all less than that rate (but have a bigger boiler than a Chally or Northern). All evap.-rates were beyond 100.000 lbs/h. Though, they were not running fast, what is is the missing link here?
Cheers,
feltonhill While we're tossing numbers around, my estimate for a UP FEF-3 (844) would be about 5,500 IHP at 80 mph and 86,000 lbs/hr total evaporation. For the 4-6-6-4 (3985), it would be about 6,000 IHP at 70 mph and 94,000 lbs/hr total evaporation. These are relatively moderate figures, not full-flog readings.
While we're tossing numbers around, my estimate for a UP FEF-3 (844) would be about 5,500 IHP at 80 mph and 86,000 lbs/hr total evaporation. For the 4-6-6-4 (3985), it would be about 6,000 IHP at 70 mph and 94,000 lbs/hr total evaporation. These are relatively moderate figures, not full-flog readings.
talking about efficiency, how much power could modern "all axle roller-bearings based" steam-engines
produce at the tender's draw-bar, including mechanicary and air-resistance, actually?
I have never seen a "conversion table", but starting with your data, maybe ~20%?
So, 4500 DBHP for a FEF-2/3, 4800-5000 DBHP for the Chally? Just as a rule of thumb...
-edit-
Those figures in Mr. Dreyfusshudson's table talking ~10% ? Is not it awesome, from that point of view that modern diesel-electrics do not do better, regarding shaft power to drawbar.
Regarding modern US locomotive data:
Test reports for both the PRR T1 and NYC Niagara survive, but they are not published for sale. I know they exist because I've used them extensively over the years. I believe the Q2 test report also survives, but I've not seen it.A book called Santa Fe's Big 3, by S. Kip Farrington, has considerable operating data on the last classes of ATSF 4-6-4, 4-8-4 and 2-10-4. I have it and it's proved to be a good source of information. This book is usually available on line from several used book vendors.There's a very good book available in the UK called Dropping the Fire by Phil Atkins. Although this is not technically rigorous, it has exceptionally good write-ups on several US locomotive classes (Niagara, PRR T1, N&W Y6's...).Back to the original post. I notice that total evaporative surface is used. I believe this is shortsighted, particularly with US locomotives. After 1930, more locomotives had large combustion chambers, and this altered the proportion of evaporation produced between the direct heating surface and indirect heating surface.Two examples -(1) The PRR M1 4-8-2 of the mid 1920's had PRR's "standard" grate area of 70 sq. ft. ( used for the K4 4-6-2, L1 2-8-2, I1 2-10-0 and later the K5 4-6-2). However, it had a very large combustion chamber which allowed higher firing and evaporative rates. This increase in furnace volume enabled this improvement(2) A much later example can be found in N&W's modification of the interior proportions of its famous Y6 2-8-8-2 compounds in the early 1950s. Initially they had 24 ft flues and a short combustion chamber. This was later modified to 20 ft flues and a 48" extension to the combustion chamber all within the same boiler shell. This produced in increase in the direct HS and a reduction of the indirect HS. The total evap heating surface was reduced, but the overall steaming capacity was increased because most of the evaporation takes place over the direct HS rather than the indirect HS. N&W stated that this modification improved the combustion characteristics of the firebox and the evaporative capacity of the boiler substantially.Juniatha has also brought up valid points regarding the basic construction and configuration of UK locomotives vs those in the US, not to mention differences in operating philosophy. The frame design differences alone have an effect on locomotive resistance.
Based on appearances, the UP 4-8-4's, 4-6-6-4's and 4-8-8-4's all had similar exhaust designs: double stacks with double blast pipes separated into four exhaust nozzles each (a total of eight). It bears some resemblance to later European designs. This was done primarily because UP used low-quality on-line coal, which had a fair quantity of fines. This required an easier exhaust blast, so that the fire wouldn’t be lifted off the grates.
I’m not sure where this discussion will go, but I’m still reading and trying to understand. Exhaust design is not my best subject by a long shot!
Er-hm .. if you may pardon my joining your discussion, may I just add a few words?
The UP Jabelmann double chimney arrangement included quadruple blast nozzles each. With that draughting both Challenger and FEF-II could and likely did exceed 100,000 lbs/h steaming rates. However may I ask how backpressure, draught vacuum and efficiency of this or any other draughting arrangement should be calculated indiscriminatingly of design specs?
In paragraph one of your original posting you correctly quote Porta’s saying – yet this must be seen in context. First, as from what I’ve had an opportunity to lend and read of his papers it appears Porta had a liking for strong expressions and exaggerations to make his point clear (he enlightened in using the word ‘exaggeration’ for some of his own improvements, sometimes meaning to provide a design margin against malign influences, at other points meaning an emphasise on going for sth full stride – very best efficiency, mostly). From what I have read of his, as much as he tended to elevate importance and effect of his own developments, he also tended to degrade earlier technical standards.
There is no denying, draughting arrangements were simple enough in most of US steam loco designs right to the end of the development line. However, they sure could have been a lot worse. In fact, within their very plain and simple layout, more often than not they came tolerably near to best proportions and performed reliably, if at rather high rates of back pressure. In those times this was not considered too harmful in view of relatively long cut offs and consequently high exhaust release pressures with engines run flat out. Of course this consideration was short sighted as high back pressure did in fact reduce mean cylinder pressure – and that did of course adversely affect gross cylinder output and efficiency. Interestingly, the relatively frequent exchange of worn blast nozzles necessary as a consequence of highly abrasive effects of extreme flow rates of steam at rather high pressures was considered forbidding to more sophisticated designs that would have been more costly to build and to install. What was lost however: such designs should have worked on much lower steam pressures, thus at much less aggressive flow rates that again would have made these designs last much longer. Clearly, lack of introduction of more advanced draughting arrangements was due to the early and precipitous end of development of the American steam locomotive.
Some years ago I had written an abstract on thoughts of my own as how indicated power output of the Niagaras could have surpassed 8000 ihp at speeds around 100 mph just by more sophisticated draughting and valve gear, including improved cylinder tribology and accordingly raised live steam temperature, all that on the same amount of net steam heat, i.e. even at slightly eased steaming rate, or in other words exclusively by improved thermo-dynamic cylinder efficiency. Since these improvements would not be reflected in data you consider for calculations by your general formulae, how then could it get correct results for different steam loco types of differing qualities of design? For sure, it should be interesting to read your explaining about >> lap, lead, clearance volume, port width etc << and >> many factors thought to be important in the steam era << .. >> tens of thousands of calculations all say that [in] view of gross efficiency .. these things are of second order << to quote from your first reply paragraph three, lower, and paragraph seven, upper. So far I had believed on the contrary these factors do make a difference – and have further believed Porta, Wardale have believed so, too, when they remarked upon how these things had been unwarrantably slovenly developed?
In paragraph three of your original posting you mention 30 % cut off c/o as something of a dividing point above which length of c/o has a decisive influence on specific steam consumption s.s.c. while below it doesn’t. I can see no theoretical basis for that assumption. The effect of improving s.s.c. by ever shorter cut off levelling out around a certain point depends entirely on imperfections of actual engine characteristics against the ideal steam cycle at the same live steam values. The more these imperfections bear on the actual working characteristics, the sooner a minimum point is reached beyond which further shortening of cut off does no more improve s.s.c.
This happened to be around 30 – 25 % c/o in German standard type two cylinder steam locomotives such as the 01 and 03 class Pacifics and their Decapod counterparts 50 and 52 classes and to an extend also the 42 class. 30 % cut off was generally used for constant speed running, often with laminated throttle and I think drivers were even told not to go below 30 % in view of mechanically hard running – which to me seems arguable at least and was proven wrong by Wardale for his improved SAR 19-D and 26 engines. Clearly it largely depends on mechanical design specs and actual engine condition as much as on valve gear characteristics. Certain poppet valve equipped simple expansion engines could advantageously run on c/o as low as some 5 %!
So, with engines of advanced cylinder tribology and valve gear short c/o does pay while with the more indifferent kind of designs it didn’t. Clearly these contrasting behaviours cannot be banged together in one common formula. Power output graph over speed is not just higher in a more advanced engine per same steaming rate but its line also evolves into a different shape: while the more indifferent type of engine shows an apex of indicated output at a certain speed above which the line starts to fall off like the flight path of a ballistic missile, the advanced engine shows incessantly increasing power output over the entire practical range of speeds, i.e. as a Niagara improved along the lines mentioned above would have shown power output increasing over the entire then legal speed range of 0 – 120 mph.
Back pressure on piston is the one that counts as for cylinder output and cylinder efficiency – not blastpipe pressure (measured at which point?); pressure in blastpipe, or actually: at blast nozzle does neither depend on speed nor cut off but on steaming rate only – logical if you come to think of fluid dynamics and the variable mass / time rate of steam passing nozzle(s) of fixed cross section and flow coefficient. Sorry, I believe your relative data on hourly steam to cylinders for your given 5000 ihp looks somewhat inconsistent, it suggests too low values for s.s.c. Also, the Challenger having a slightly lower s.s.c. at the same speed and ihp relative to the FEF-II would surprise me indeed, taking into account that it is a simple expansion Mallet type while the FEF-II is a straight two cylinder engine.
What c/o did you calculate for the FEF-II at 100 mph / 5000 ihp? In data in column four you allow >> 10 % benefit << for feed water heater – 10 % of exactly what? why don’t you use the same net steam rate to cylinders as in column three? what evaporation data does your boiler efficiency relate to? if all your data so far should be based on net steam to cylinders, then overall drawbar efficiency lacks to account for steam to auxiliaries / if not all of your previous data is based on net steam to cylinders then what data is based on what steaming?
In calculation of locomotive resistance, mechanical resistance (drive), mechanical resistance (rolling) and aerodynamical resistances should be kept separate or you get a blurred picture; I’d like to see the formula that allows for correct data of the total of all of them to be established over speed and then based on data extrapolated from British steam locomotives of, as it was, rather special mechanical characteristics with their composite plate frames, very light rodding and extremely small diameter pins, design prone to flexure under high stress, and their smooth external lines of small loading gauge. Maybe this has lead to rather high locomotive resistance hp losses in the upper speed range and somewhat low values at low speed.
To quote paragraph 5, last sentence of your first reply: >> I was only trying to illustrate the kind of calculations that can be done; what are the most relevant calculations is entirely discussable. << Well, sure there are many ways to put up calculations. Ok, likewise I’m only throwing in a few words of mine to an interesting discussion – no insult intended.
So, to quote once again from your last paragraph in your reply: >> You will need to forgive my enthusiasm! << Well, I guess there will be no problem here, we are all enthusiasts of railroading power one way or another – steam, diesel or eclectic electric.
Regards
Juniatha
In videos I have seen of UP 844, there are actually two stacks. Or, so the twin plumes emitting from the 'stack' suggest.
Didn't the late UP locomotives have Le Maitre exhausts?
Some photos of these show multiple jet nozzles arranged in a circle and the large diameter stack suggests that arrangement. That is at least part of the way towards Porta's ideas.
M636C
Dear Pete,
Thanks for the tip- unfortunately the Altoona reports on Google are the ones I have access to! Reports 1-32 were presented to the British Institute of Mechanical Engineers in two bound volumes ca 1925, personally signed by (I think) the PRR CME. These are now in the Science Museum Library in London, disintegrating rapidly. They are wonderful documents, comprehensive data, crystal clear write ups, confident without being overbearing- a model. In terms of testing the PRR was way ahead of the game at the time. I think the 1914 Bulletin 24 on the effects of superheat is one of the most influential ever written; I'm sure Chapelon digested it and in this country, Gresley immediately copied the variations in superheater set up on his own Pacifics in 1926.
Still hoping someone has access to details of the final flowering of US steam from ca 1926-1949
Google books has tests of locomotives from the Pennsylvania RR done on the test plant. These are very interesting reads. The PRR testing department tested everything. Even the coal is broken down to its BTU and ash content.
Here is a test on an E2s Atlantic loco from 1910.
http://books.google.com/
Pete
[Edited to shorten URL]
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Thanks very much for your response. You are correct to pick me up on the loose use of the word 'Superheat'; I do of course mean inlet steam temperature not the level of superheat in the steam.
The use of constant IHP in my calculations was just for illustrative purposes. If you use constant steam rate as the basis, then you do indeed get IHP values that asymptote as speed increases. There is a possibility that IHP will decrease if you go above a certain speed at constant steam rate, i.e. efficiency decreases despite the fact the cut off is shortening and expansion ratio improving. UK test plant work was normally not above 80mph, so with your diameter +10% rule, you would not expect to see this, and you don't except for some hints thereof on older GW railway designs with low clearance volume, where there is serious overcompression at high speeds.
You can use the computer programme to establish when this would occur; it depends on the operating condition. With late UK designs, e.g. the streamlined A4, (80" drivers) it says that at constant steam rate in the normal working range, efficiency begins to plateau around 100mph and shows positive decreases about 120mph. The point is that where this turnover point is can be now be calculated, if you have the detail of the engine dimensions (Lap, lead, clearance volume, port width etc). This is the next layer of detail that I would need to understand about US types, but tens of thousands of calculations all say that from the point of view of gross efficiency, the point in question, these things are second order.
Now in practice locomotives were worked neither at constant steam rate nor constant power of course, and my argument justifying the 5-6% overall thermal efficiency is indeed a bit simplistic. However, I have done lots of work simulating logs of reported steam performance on various main lines (the only US one on which I have sufficent data is the Milwaukee from Chicago to La Crosse), and you can use equations derived from the outputs above to work out fuel consumption on a trip, and average DHP. It is really this experience of translating predicted performance into practical estimates of drawbar efficiency that leads me to believe that my conclusion about drawbar efficencies is sound- but that's another huge discussion! Incidentally, the MILW calculations surprised me in showing how little power relative to the 96.5 sqft grate was needed to do what the F7s did when cruising at speed; the secrets of fast schedules were barnstorming starts and super slick braking. O to have witnessed them.
I would be very surprised, like you, if a 4-8-4 with a 100sqft grate was ever steamed at 100000lbs/hr, even a Challenger, so I do understand this point; in the UK outputs above about 750lbs/sqft/hr were rare, even though they are surely possible. Bear in mind again I was only trying to illustrate the kind of calculations that can be done; what are the most relevant calculations is entirely discussable.
The calculations are very easy to do- as long as it takes you to input 3-4 numbers and press. In the 1950s, UK test plant results were reduced to a 'power map' which had IHP on the ordinate, speed on the abscissa, and lines of IHP at constant cut off, and constant steam rate, together with the coaling rate at each steam rate- a one stop shop that tells you everything you need to know about power and efficiency of both boiler and engine. If equivalents for US designs exist, I haven't seen them, but it is these power maps that I would like to create.
The calculation of engine efficiency is by no means simplistic, as you seem to fear; it is standard fluid mechanics, with cylinder heat transfer built in, plus steam tables, and requires simultaneous integration of 5 separate partial differentials. The big surprise is the simplicity of the headline conclusions that it leads you to, perhaps the most important of which is that many factors thought to be important in the steam era aren't. And once you start to think about it, it all makes sense. In the UK at least, the data available in steam days was simply not good enough to work out all the subtleties; whilst people knew what might be important, they coudn't be precise about how important; this is what the computational model helps you establish, and it is quite revealing. So I believe there are indeed simple conclusions, but this does not mean the process used to achieve them is simplistic, far from it. You will need to forgive my enthusiasm! Having said this, having compared the computer predictions to about 1500 fully instrumented test plant runs, it is clear there are things that are not so clear, and you do need to be aware of this, but these uncertainties are factored into my enthusiasm.
If only we'd had high speed computing in 1910, things might have been different. Unfortunately, we needed the steam locomotive to do its job, and pass on, to put things in place that allowed us to invent computers!
I believe we need to clarify some terms first. The steam temperatures you mention are not superheat but total steam temperature. Big difference. 250 degrees superheat was considered conservative for modern steam locomotives. Tests of the NYC Niagara and PRR T1 showed superheat temps of well over 300 degrees at their respective boiler pressures (275 and 300 psi).
Another item is the constant IHP as speed increases. Test data indicates that this is not how things work. Most estimating methods compute theoretical IHP as being asymptotic as speed increases. However, actual IHP tends to increase up to about driver diameter plus 10% then starts to decrease.
I'm also suspicious of the very high steaming rates at low speeds for both examples above. Whereas both boilers could probably produce over 100,000 lbs of steam an hour, neither would be particularly efficient at such high rates.
Be very cautious about simplistic ratios when trying to estimate locomotive performance. I've seen a bunch of them and almost always they produce only a meaningless average. Worse, they tend to overlook various components that are important to consider in the overall scheme of things. Steam locos are not easy to predict. I've used generally accepted industry methods and tweaked them a bit for modern construction and some other items. There are abut 20 equations involved, none of which I would call simplistic. Careful with this.... I'm interested but skeptical.
It is generally accepted that American steam locomotives achieved thermal efficiencies of around 6% at the drawbar, and there are claims that with not too radical technology, this could have been significantly improved. Porta said American draughting systems (including blastpipe dimensions) ‘could not have been worse’. I am lacking some key bits of data I need for this, and am wondering if anyone in these forums might have access to the data.
The calculation of drawbar efficiencies requires knowledge of three things- engine efficiency (how much steam needed to produce 1 horsepower for an hour), boiler efficiency (how much coal to produce a given amount of steam) and the amount of power that needs to be expended to move the locomotive as a vehicle, which must be subtracted from the cylinder power to get drawbar power.
With regard to engine efficiency, I have a computer programme developed by a very distinguished UK Professor, which calculates engine efficiency from first principles. I have validated this against UK and Altoona test data, and with some caveats that I can share with those interested, it works just fine. What it says is engine efficiency is dominated by the beneficial effect of higher superheat, which generally gets higher at higher steam rates; the next most important factors are blastpipe pressure, which increases detrimentally at high exhaust rates, and cut off. When locomotives are operating in less than 30% cut off, cut off is not such a big deal, but higher values, as required at low speeds and when climbing mountains become quite detrimental. A final component on which I am still working is leakage of steam e.g. within the engine past valves and piston rings, but basically, if you know superheat, and how it varies with steam rate, and blastpipe area, which determines back pressure, you can very easily get a pretty good estimate of engine efficiency at any cut off or speed, hence power developed.
Boiler efficiency is similar for all hand fired locomotives at the same coal rate, or evaporation rate/sqft of grate; for hand fired locomotives it is about 70% at an evaporation rate of 600lbs/sqft/hr, falling to about 60% at the higher 800lbs/sqft/hr- not far from a probable practical upper sustained limit. For stoker fired locomotives these figures are about 59% and 50%. (UK and US data agree on this). If you think about the underlying theory, the reasons for this similarity are not surprising. There are two basic factors, the efficiency of heat transfer from flue gases to steam, which is pretty good, around 80%, not changing much with steam rate, and unburned coal loss, which basically depends on the combustion rate/sqft of grate, increasingly very dramatically at high rates; it is this component that is worse for mechanically fired coal. These figures can be improved by feedwater heaters and exhaust injectors.
Locomotive Resistance was not, in the UK at least, experimentally well defined in steam days. New analyses of old data have given a formula which is consistent with the best of that data. US locomotives are much larger, but the since the overall formula is based on realistic formulae for the basic components- aerodynamic resistance, the resistance of the machinery between the pistons and the wheel rims, and resistance of the locomotive as a vehicle, it should extrapolate reasonably well and at least get into the right ball park for US locomotives.
So, to estimate US locomotive efficiencies all one really needs to know superheat and blastpipe dimensions. The US data I have is basically for the period from the 1890s to 1920s from Altoona. The PRR K4 had a maximum superheat of about 610 degrees at high steam rates, and a blastpipe of 7” in diameter, but things did move on, I suppose, after the K4! Tests on the 1926 Baldwin High pressure compound 60000 show its superheat was 680 degrees, but had something like a 6.5” blastpipe- the backpressure was about 20 psi at an exhaust rate of 60000lbs/hr- 730lbs/sqft/hr- . What I lack is any data for the final essays in US steam, apart from 1984 tests on C&O 614 which showed superheat of around 800oF, as high as anything I am aware of.
Some illustrative sample calculations on a UP Challenger, and UP 4-8-4 are shown below at a constant cylinder power of 5000HP. Please note that these use entirely made up estimates of superheat (680oF) and blastpipe dimensions (two times 5 5/8” diameter)!
UP Challenger
Cut off %
Speed Mph
Cyl steam, lbs/hr
Lb Evap/ sqft grate*
IHP
Back press psi
Cyl eff %
Loco Res HP
Equiv DHP
Cyl eff ref to drawbar %
Boil Eff, %
Overall DB eff, %
75
21.2
112769
769
5002
30.8
8.4
234
4768
8.01
53
4.24
34.5
40
74868
510
4998
13.29
12.7
473
4525
11.50
7.13
60
70044
478
11.06
13.5
899
4099
11.07
63
6.98
24.4
80
69619
475
4997
10.87
13.6
1584
3413
9.29
64
5.94
UP 4-8-4
32.9
105273
947
27.31
9
290
4707
8.48
50
56.8
86621
780
18.71
11
371
4631
10.18
5.40
39.7
73418
661
5004
12.57
12.9
687
4317
11.13
56
6.23
33.7
69785
628
5001
10.91
1188
3813
10.37
5.91
31.1
100
68622
618
10.41
13.8
1920
3077
8.50
58
4.93
*Allowing 10% benefit for feedwater heater
Despite the uncertainties in the inputs, the basic messages are clear. Note that as speed increases, cylinder efficiency increases, as the cut off required for 5000IHP decreases. (For each locomotive the minimum speed at which 5000IHP can be developed is shown, assuming 75% maximum cut off). As the amount of steam needed to produce 5000IHP decreases, so the boiler efficiency increases; counteracting these two positive benefits however, is the increase in locomotive resistance, which means drawbar efficiency peaks at about 50-60mph, and then declines. Given US freight locomotives spent a lot of time working at low speed, the quoted 5-6% thermal efficiency at the drawbar is not surprising. Under the (unsupported) assumption I have made about blastpipe diameters back pressures are high, especially at low speeds. Note also that the Challenger is more efficient than the 4-8-4 up to 80mph, because of its larger grate and lower cut off- the comparison is unfair to the smaller 4-8-4 which, whilst it clearly can develop 5000IHP, would be more efficient working at 4000-4500IHP.
What I would like to be able to do is produce comparative calculations on the last and best coal fired US steam designs NYC, PRR, C&O, NW, UP etc. As a basic minimum, I would need superheat vs steam rate and blastpipe dimensions (free nozzle area, i.e. basic diameter, less any protuberances into steam flow) for these types (I have basic engine and boiler dimensions). If anyone has access to these data (or even better full test reports), and would like to assist in this venture, I would be more than interested to receive them.
I realise there are a number of sweeping assertions in what is written here - some of this is due to the need to keep this input simple, and would be happy to discuss any detailed objections people might have.
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