Overmod and M636C
Thanks for your comments.
On slipping, there was and still is a tremendous amount of research going into the subject of adhesion, and it will be most interesting to see what can be learned about the specific issues 5550 might face. All I was trying to say was that I don’t know how one could, other than by introducing a few arbitrary criteria, build slipping into a steam locomotive performance simulator, since so much of what actually occurred was seemingly random.
The subject of ‘crazy high’ superheat does indeed take us back to where we started, namely poppet valves. I correspond regularly with the chap who was at one time ‘minder’ of our big preserved Caprotti Pacific, Duke of Gloucester, which operates at high superheat (about 7500F at a high working rate of 30000lbs/hr- as did many of our latter day designs). Not surprisingly, he’s one of its biggest fans! He thinks that the primary benefit of poppet valves is not their supposed or actual efficiency benefit, but that they do not suffer from the high carbonisation found in high superheat PV designs, hence are less likely to suffer from the valve problems you allude to. He has first hand steam age experience of hammering out seized up PVs when locomotives came in for shopping at the local Works.
More generally on superheat, the Table below shows some calculations on the effect of varying superheat on a British Pacific- no reason to doubt the same trends would be experienced everywhere, this is very consistent with 1912 Altoona tests on a K2.
inlet steam, degF
cut off %
Speed,
MPH
steam, lbs/hr
IHP
efficiency, %
eff relative to 650 deg F
403
21
70
27673
1341
10.4
75%
450
26465
1375
10.9
79%
500
25350
1434
11.6
84%
550
23989
1482
12.3
89%
600
22890
1534
13.1
95%
650
21933
1577
13.8
100%
700
21140
1611
14.3
104%
750
20499
1627
14.6
106%
800
19934
1646
14.9
108%
Going from saturated steam to 600oF gives a 33% improvement in efficiency, this due to both the favourable thermodynamic effects of higher temperature, and gradual elimination of cylinder wall condensation- as also shown by Altoona in the same 1912 tests- also because backpressure is falling a little. Beyond that, there is only the thermodynamic benefit to be had, and decreasing returns begin to set in, so one might question a priori the wisdom of aiming for very high superheat, never mind the practical consequences associated with it. As you say, increasing superheat does not have much effect on power developed above about 650oF- the principal effect is on steam consumption.
Perhaps the 'simplest' form of slip determination is that proposed for T1 5550 on its 'roller rig'; although the contact patch is somewhat artificial (as for historical test plant operations) it still technically understates baseline adhesion conditions. The rollers are specifically suspended to allow simulation of cross-level instabilities, non-flange-bearing frog traversal, and most if not all the other issues that destabilize a four-coupled duplex.
Kiefer famously conducted high-speed rotational balance testing on a greased track, and interpreting some of his stated results made measurements relative to different degrees of induced track motion, which would be secondarily admissible in an analysis of inducing factors for high-speed slip. Although of course rotational testing at 'high speed' involving slip leaves out a great many factors involving the transients likely to induce many of the problems.
Does ANYONE have current access to the AAR movies showing driver lifting in augment?
The superheat issue is very important in North American practice (relative to British practice where much more attention was paid to consistent 'automatic action' across a wide speed range). Even the data Mr. Pawson produces shows detected excessive superheat in one of the T1 tests. Ross Rowland IIRC is the inventor of the term 'crazy high' superheat as observed on some of his trips with locomotives equipped with superheat gauges. I very strongly suspect excessive superheat to be one of the major causes of the valve seizure of N&W 610 that abruptly ended the PRR high-speed testing.
While I do think that there is an increased benefit (in retarding nucleate condensation) to "excessive" superheat, there is little doubt that it adds little relative 'elastic power' to the steam in terms of producing extra torque. But it DOES add considerable heat to parts of the valve system right at the time lubrication is most compromised by even slight additional overheating, and therefore the maintenance costs of the excessive superheat are by far the things of greatest importance. This was one of my theoretical concerns with performance of an unconjugated T1a at 'achievable high speeds' relative to a Franklin-valved B-2 alternative with correctly cast and sprung spools. (Yes, something similar to what Wardale used for valve 'cooling' might be applied to the valve stem gland surrounds if tribology there suffered, as it well might have, from high superheat...)
As a small peripheral note: the "letter" in a Franklin system refers to the valve drive, not the valve configuration itself. That is why, for instance, the RC system tried on the T1 was called "B-2"; type B was the three-valve rotary cam system, B-2 was the special modification with bridges used for B gear to correctly actuate the four valves built for the type A installation (and sketched in Kirchhof's little corporate heraldic 'shield'), which would have been much more difficult to modify to the 'more economical' setup on, say, ATSF 3752.
The former British Swiss built Brown Boveri gas turbine locomotive was rebuilt with a single powered axle replacing one of the former idler axles (it had been A1A-A1A). This axle was powered from an AC electric locomotive and was specifically taken up to wheelslip while investigating different rail surface and adhesion conditions.
Peter
Jones 1945
I wouldn’t know where to begin in setting up a ‘slip’ facility. At the most basic level, setting and adhesion factor of 4 says you are betting the coefficient of friction at the wheelrim will be at least 0.25 if you were to start at full maximum NTE i.e. longest possible cut off, full regulator. A loco with an adhesion factor of 5 could get away with 0.20. What the actual friction coefficient is is highly variable of course, e.g. in terminal areas where standing locos are dripping oil and water onto the tracks. Not least for this reason, I suspect full NTE was used on starting only when you had too e.g. when starting a heavy freight on the ruling gradient. At speed, wheel rim tractive effort (WRTE) is nothing like NTE even at full power, so things didn’t really ought to slip, but they do. Fluctuations in WRTE around the piston cycle might have something to do with it. In this country, there is a mainline stretch of 4 miles at 1.33% gradient. There are a fair number of steam specials each year, and crews like to have a go and get to the top in record time. Unfortunately there is a slight curve near the bottom (105mph restricted for modern traction) which has a flange lubricator right where you are hoping to put down maximum WRTE. Guess what happens.
There are complex mechanical factors involved also which may play a part in the T1’s propensity to slip. Quite beyond me.
So it often seems that slipping is a random event with no clear indication of what the cause is.
The real issue I would see is that, given the random nature of events, there is absolutely no data I’m aware of against which you can check the general validity of your model.
Dreyfusshudson Jones1945. Thanks for the info on the PRR speed limits. I believe the NYC was also generally 80mph, with similar flexibility upwards if necessary? Thanks also for the pictures of the S1, which confirm it had a double chimney with Kiesel star blastpipes. I did find another reference on the S1 here: https://oldmachinepress.com/2018/07/05/pennsylvania-railroad-6-4-4-6-s1-locomotive/
Jones1945.
Thanks for the info on the PRR speed limits. I believe the NYC was also generally 80mph, with similar flexibility upwards if necessary?
Thanks also for the pictures of the S1, which confirm it had a double chimney with Kiesel star blastpipes. I did find another reference on the S1 here:
https://oldmachinepress.com/2018/07/05/pennsylvania-railroad-6-4-4-6-s1-locomotive/
My pleasure, Dreyfusshudson! I am glad to know that you willing to keep updating the simulation of S1 and other engines!
Regarding the speed limit of NYCRR, I think this post is worth reading on this topic: http://cs.trains.com/trn/f/741/t/116632.aspx please check it out if you like.
I read the reference link you posted not long ago, and I believe you noted that many, but not all info in that article can be found in S1's Wiki page which is having a major update since last year. Tons of references were added in the Wiki Page with the help of some familiar username (wink). There are some brief data of S1’s performance in Wiki page with reliable sources and references in the “Service History” which was never published on the web before. These data might help you to decide how to adjust the parameter of S1 if necessary.
By the way, your pic doesn’t load so I can’t read your new calculation result. You could send the pic to me so that I can post it here or you can upload your pic to free photo hosting website like “imgur” and post the link in the forum! Looking forward to your new discovery!
There was a very extensive discussion in Classis Trains forum recently about PRR’s experiential steam engines. Many forum members agree that T1 was powerful enough to handle the official schedule and PRR S1 was an “overkill”. I suspect that S1 was specially built for the 1939/1940 World Fair to represent America railroad industry thus it was built unnecessarily large and powerful. But during World War II, her power and her speed did help PRR a lot to handle the wartime traffic. After the war, there was a rapid decline of passenger trains service thus S1 or even T1 didn’t have many things to play with.
By the way, I would like to know that If your simulation could simulate or show wheel slip during heavy train starting or high-speed wheel slip? Thank you very much!
Jones 3D Modeling Club https://www.youtube.com/Jones3DModelingClub
Overmod:
Well the subjects of predicting superheat and draughting behaviour are worth extensive separate threads, but after much thought on these matters over the years, I have concluded that I don’t really have much to say.
My understanding is that the first principles CFD sums to predict superheat from a given set up are very hard if not impossible. What is true is that for shorter boilers, flue gas exit temperature exceeds superheat temperature, but for boilers longer than about 15’ in the UK, it is less. For the 21’ Q2, steam temperature is always higher, for the 19’ K4 this is also true at low rates, but at higher rates, steam temperature is higher. Whether a low exit temperature of the flue gas can actually cool the steam in the elements (as I was suggesting) I do not really know. Some over here assume this to be the case, and it certainly looks like longer boilers deliver marginally less superheat than you might expect. But you would need expertise in heat transfer, Reynolds Numbers etc. to demonstrate this was a fact not a mirage- beyond me.
I stopped stressing about this some while ago however, because
a) The effect, if it does exist and small and
b) The effect of a small change in superheat on efficiency is small and
c) Having spent years trying to work out how to design for best thermodynamic efficiency- something all designers aimed for and their Boards wanted- I concluded that small efficiency differentials were completely irrelevant to the operators ( the folk who have to make things work) - they had much higher priorities. This is why I think that whilst the Franklin T1 is somewhat less efficient than it ought to be because of leakage, this would not figure at all in the operators assessment of how good the T1s were.
d) I think I can predict from number of elements and combustion rate/sqft what the superheat range of a given boiler is likely to be, within a band within which the differences do not matter in practical terms. Superheater area is not relevant. What might matter, as Altoona showed is how close the elements are taken to the firebox. Chapelon exploited this, as did Gresley, but maintenance costs persuade Gresley to back off.
On draughting, I have come to a view that designing a good draughting system from first principles is likely an intractable problem- not only are the sums on front end behaviour very hard, but what we are interested in is combustion, not draughting, and there no good data on the state of firebeds, nor models of how they work. And, the state of the firebed is usually determined by that most unpredictable of things, human behaviour. not to mention variation in the qulaity of coal. I have been meaning to argue this out logically this year, but have never got round to it, because, if I am right, it is a most unhelpful and depressing conclusion!
I don’t really understand what you are driving at in the text beginning ‘I do think that we don't care about gas conditions…..’ I’m not arguing that there is somehow a problem with S1 superheat, only that because of its low combustion rate/sqft in actual operating circumstances, it might not be as good as it could be- but as noted above, I don’t think this is likely to matter much at all.
What I do believe is that Alco, Baldwin and Lima got it as right as it matters in terms of efficiency, even though their theoretical understanding was limited- there is no golden upland of superior performance beyond what they achieved for reciprocating engiens with firetube boilers; and, they set standards for robustness and mechanical reliability that it is hard to believe. How could a steam locomotive run 25000miles/month? Or run from Kansas City to Los Angeles, arrive in the morning and set off back the same evening? An amazing triumph of human endeavour. Unfortunately, there were better solutions!
It cites Reed, and I suspect leans heavily on him. It does not give blastpipe dimensions, but it does say that the chimney exits are 21” in diameter, 4.8 sqft in total. Now the Altoona report on the Q2 says that, with a similar set up, the chimney exits are 5.33 sqft, or 22” in diameter. The Q2 blastpipes had an area equivalent to 8.5” diameter, so I am thinking that the S1 blastpipes probably had somewhat more restricted area (no rigorous logic for this, just a hunch).
So, I have recomputed the power map for the S1 based on a blastpipe area equal to 8” diameter, allowing for the reduction in backpressure given by feedwater recycle in the manner described earlier. i.e. actually computing on the basis of 8.5"
This shows lines of power at different cut offs and speeds, and also the power developed at three different steam rates vs speed (the more horizontal lines). The lowest rate of 78000lbs/hr is 550lbs/sqft evaporation, the two higher rates 675 and 800lbs/sqft/hr.
What you can see ( or could if I could figure out how to insert the imaage!) from this is that at what is probably something like the maximum rate of steaming, 113000lbs/hr, you get about 7200ihp with this more restricted blastpipe configuration, which aligns with the quoted maximum power. At the low rate of steaming, well inside the boiler’s comfort zone, you are getting about 5500IHP. At what I suspect were service maximum needs of 3500-4000HP, you require but 15-20% cut off at speed- if the loco could be driven that way.
Now on the spreadsheet I am about to send you, I have analysed the running of a log with T1 5501+1060 US tons working from Crestline to Chicago, culled from the pages of the Journal of Made Up Data.
From Crestline to Fort Wayne, the T1 observes the 80mph speed limit, and slows to 70 mph restrictions across a number of diamonds and round the sharper bends. It gets to Fort Wayne in 102 minutes without exceeding 4000IHP, often less on easier stretches. The Broadway was allowed just over 2 hours, including the Fort Wayne stop.
From Fort Wayne onwards, the crew threw caution to the wind, and worked at 5000 IHP, (a still comfortable 60000lbs/hr) and left quite a few diamonds in worse shape than they were. The stretch from Larwill on is slightly downhill, and the 68.7 miles from Winona Lake to Valparaiso were covered in in 42.5 minutes, an average of 99 mph. After easy running in from Gary, they got to Englewood in 102 minutes vs the Broadway schedule of ca. 130mins.
The point of this fable is that a T1 was more than powerful enough to beat the Broadway schedule with a heavier train – hence the S1 was grossly overpowered!
You can see the Kiesel star nozzle and blastpipe height in one of the pictures. I am presuming there are two of these (one for each engine) exhausting into the two stacks, as this was common practice in that general era. At minimum this gives a check on the cross-sectional area and effective entrainment coefficient that would be applicable, even if we don't have hard data on the flow streamlining of the upper front end.
I would confidently predict you will not find any superheater damper arrangements on this locomotive, and for any high mass flow through the front end the effective superheat on at least some of the elements would become dramatically higher than 'expected' -- that has certainly been the observation on some lesser locomotives, notably Greenbrier 614. Consider the subatmospheric TOF difference relative to effective gas-to-tube heat transfer for that 'extra' 2' or so of tube over 'correct' 40.6x ratio and tell me if you think heat transfer would result in measurably reduced gas temps in the front end at high speed.
I still cling to the 'entrainment' theory of complex nozzle geometry (including the practical effect of things like Goodfellow tips) vs. the theory that Jos. Koopmans has come to develop regarding multiple nozzles (the most efficient being multiple circular nozzles at appropriate angle and spacing to produce the effect of x long, thin conventionally-scaled chimneys). I don't think we will resolve this for Kiesel nozzles until multiphysics simulation is backed up with empirical observation ... with steam, in situ, not using some assumed approximation like blowing with straight air. I do think that we don't care about gas conditions at any particularly high 'economy' cutoff in terms of the present discussion, which implies operation at 'best power' at high cyclic, almost certainly within shouting distance of 40%, with corresponding mass flow and incident gas-plume kinetics (and relying on the very large boiler and its presumed high radiant heat uptake to source that mass flow ... there should be little difficulty assuring adequate superheat for it given the comparatively restricted expansion past significant initiation of nucleate condensation that would characterize very short cutoff operation. I am tempted to say we need to concentrate on the gas generation and physical coupling into steam generation (and then superheat) from the physical boiler, rather than doing theoretical calculations of ihp that inherently assume steam-chest pressure derating, even as slight as the ~30# mentioned.
Thank you very much, Dreyfusshudson.
From my understanding, there was not even one article about PRR S1 #6100 on Keystone, not even one! This was one of the reasons why I joined this forum. I already gathered all the books and articles recommended by forum members on Classic Trains forum, except this one, recommended by Reed:
Redwards Some years ago Feltonhill had recommended the following article on the S1: "The S1's history was covered in a 7-page article by the late Charlie Meyer in the Jan 1992 (Vo.10, N0.1) issue of Milepost, a magazine published by Friends of the Railroad Museum of Pennsylvania. I believe they're still in existence, maybe out of Strasburg, and this is available as a back issue. It's well worth trying to get. It's probably the only detailed account written at this point." I managed to find a copy on eBay and as he states, it's the most detailed account I've seen on the S1. --Reed
Some years ago Feltonhill had recommended the following article on the S1:
"The S1's history was covered in a 7-page article by the late Charlie Meyer in the Jan 1992 (Vo.10, N0.1) issue of Milepost, a magazine published by Friends of the Railroad Museum of Pennsylvania. I believe they're still in existence, maybe out of Strasburg, and this is available as a back issue. It's well worth trying to get. It's probably the only detailed account written at this point."
I managed to find a copy on eBay and as he states, it's the most detailed account I've seen on the S1.
--Reed
On the other hand, in "HAGLEY DIGITAL ARCHIVES" ( https://digital.hagley.org/ ), you could find some non-copyrighted photos of S1 during its construction, showing its smokebox, boiler and firebox, I hope this will help!
Timz
Thanks for these additional data; from another source (book by UK author Reed) I now have valve events as lap 1.875” (Cf RME), lead 0.32”, exhaust clearance 0.25” valve diameter 12 in. Unfortunately, this source does not give the exhaust dimensions, which are absolutely critical, and if he doesn't have them, it will be a long search!. It also says that the tube plate distance was 22’- very long indeed, which will I fear tend to reduce superheat (exhaust gases at exit below the superheated steam temperature). I suspect that at what I suppose were normal maximum steam rates of less than 60000lbs/hr superheat would already be compromised, because the specific combustion rate/sqft grate would be quite low, leading to low gas temperatures.
In my initial stab at the S1, as I wrote, I gave it the equivalent of a 9” diameter blastpipe, and assumed a discharge coefficient of 0.99 (i.e. a plain blastpipe), for no better reason than if the PRR wanted to exploit the full potential of the boiler, it would need something like this! The C&O H8, which had a similar grate size, had a blastpipe area equivalent to a 9.9” plain blastpipe, but its cross pieces would reduce to the discharge coefficient- maybe to 0.9 which would make it in effect equivalent to a 9.5” plain blastpipe, this allowing to produce the 8000+IHP needed for its reported peak DBHP of 7500; the Q2 had Kiesel star nozzles with an area equivalent to a plain blastpipe of 8.55”, which also allowed 8000IHP.
However, the first thing the exhaust system has to do is produce enough draught to produce steam, and it may well be that to do this, the S1 blastpipe would need to be less than 9”. As I wrote, this would have pretty dramatic consequences at high steam rates. The first line in the Table below shows the power estimate on the original assumption. The second shows what would happen at a more realistic 280 psi steam chest pressure, a blastpipe diameter equivalent to 8.5”, with a discharge coefficient of 0.9 (typical of PRR set ups of that era). There is a significant reduction in steam rate, power and efficiency. The third line shows that you can get back to the original steam rate by lengthening the cut off to 37.5%, but under these new assumptions power is 900HP lower at 7200. The third and fourth lines show the same exercise with an 8” blastpipe- now 1250 less HP.
So, knowing what the blastpipe dimensions were is absolutely crucial at these high steam rates- it wouldn’t matter that much at what I imagine would be the normal maximum steam rate of 60000lbs/hr. An additional complication is that the programme used for these calculations assumes that the blastpipe flow is the same as the cylinder flow. However, with a feedwater heater, around 10% of the steam gets recycled, meaning that back pressure will be significantly lower than the programme estimates. To get round this and calculate at the correct back pressure, you have to icheat and input a blastpipe diameter that is 0.5” larger than actual.
So, the third line in the Table gives a fair estimate of what the performance would be if the true blastpipe diameter was 8”.
Cut-off
Speed
St.cons
BackP
Effy
bp diam
discharge
SCP
%
mph
lb/hr
Psi
ins
coeff
psi
35
120
118182
8092
22.05
12.6
9
0.99
290
108363
6888
27.54
11.7
8.5
0.9
280
37.5
117988
7215
31.65
11.3
104401
6310
31.7
11.1
8
38.8
117777
6843
38.03
10.7
It seems that there is no data on the S1 in the Locomotive Cyclopedia, and if there is nothing on the exhaust system in RME, then the only hope is that someone has unearthed this for the PRRHS in Keystone. I do not have access to this.
In summary, I think we can estimate power reasonably accurately, but the figures I posted need updating with the new info, and crucially, the blastpipe dimensions if they can be located.
Overmod If you have a better package for analyzing reciprocating steam locomotives...
OvermodCan you scan and post the corresponding Zeuner diagram
Percent of cutoff in full gear is DH divided by DE
To get DH you need the cosine of angle DOP
Angle DOP is angle DOY plus angle YOP
Cosine of angle DOY = (lap + lead) divided by half the valve travel
Cosine of angle YOP = lap divided by half the valve travel.
For the 6-4-4-6, angle DOY is 54.315 degrees, YOP is 60 degrees, and DH/DE is 0.706.
If you assume the piston and the valve are each moving with a sine-wave motion, the Zeuner diagram is the result (or the equivalent Reuleaux diagram) and the above is mathematically the same.
Dreyfusshudson I have two answers to your question about how long it would take 6100 to accelerate 1065 tons to 100mph on level track. The first is, if we assume that flat out working is 7200HP (I don’t know how this reported figure was arrived at), and that when starting you can put down about 70% of the rated TE without slipping (Pure guess, about the maximum normally applied ion the UK), then you reach 100mph in 11 miles, about 9¾ minutes. After that you can maintain 100mph with about 5400HP. During the acceleration, steam rate is in excess of 100000lbs/hr, and you are burning about 17000lb/hr top quality coal. This kind of time is what you might claim for PR purposes. However, my sense of the way locomotives were actually expected to perform is somewhat different. Starting is about TE, sustained performance is about how hard you are prepared to steam the boiler. As far as I can tell, it was unusual for US boilers to be steamed much above about 600lbs steam/sqft/ grate/hr, sometimes less. (This figure refers to top quality Coal of about 13500BtU/lb; it would be less for lower calorific values). Above this specific evaporation rate, unburned coal losses rise sharply, and it may be that this was a prudent level to avoid high boiler maintenance costs, e.g. due to cinder cutting, by not asking too much of them- the draughting usually allowed up to at least 900lbs/sqft/hr- a whopping 120000lbs/hr for the S1. Looked at this way, the Table below shows how a number of different locomotives might be expected to perform with a 1065 ton train on level track, again working at 70% maximum TE up to 20mph, maximum steam rate about 600lbs/sqft/hr beyond that. All numbers are just indicative of relative potential, not precise.
timzYou think 8092 IHP at 120 mph is "reasonably accurate"? Why?
I believe he is using Bill Hall's Perform software (and has discussed how to use it with Prof. Hall). If you have a better package for analyzing reciprocating steam locomotives, or advice in using it or setting initial conditions, please provide it.
I think he is indeed using 'engine' to mean 'locomotive', as 8092ihp to just four wheels is patently nonsensical. Yes, technically the S1 has two 'engines' and the results are a slightly weighted sum of the two as indicated -- I suspect more adjustment of duplex performance from an 'equivalent' conjugated equivalent might be warranted but much of this would likely involve empirical factors...
Rwy Mech Engr 8/39 says 6-4-4-6 valve travel was 7-1/2, lap was 1-7/8, lead was 5/16. Don't think the article gave the exhaust lap/clearance. A Zeuner calculation says that's 70.6% maximum cutoff.
Can you scan and post the corresponding Zeuner diagram, as it would be useful in a number of ways here? There are a number of comparable ones in the steam_tech Files section (calculated and drawn by Mick Duncan) but I can't link them here as it's a closed group. Maximum cutoff in his table is well shy of the built-in limited cutoff, I think.
DreyfusshudsonI think we can estimate the power the engine will deliver reasonably accurately.
(Maybe when you say "engine" you don't mean "locomotive"?)
Timz;
Well I think we can estimate the power the engine will deliver reasonably accurately. The Table below shows part of my first pass attempt at modelling the S1 engine output.
lb
25
60
65218
4689
5.47
30
76585
5447
8.12
13.5
88571
6129
11.74
13
40
101686
6740
16.12
12.4
45
113822
7343
20.71
12
50
128126
7874
25.81
11.4
15
46258
3283
2.47
13.9
70290
5126
6.48
82604
5958
9.68
13.6
95618
6688
14.1
110247
7369
19.08
124914
8025
24.44
11.9
80
48887
3530
2.77
74331
5496
7.37
14
87744
6357
11.21
101796
7138
16.18
117330
7883
21.71
90
51024
3732
3.03
14.2
77941
5785
8.24
90607
6741
11.98
107158
7492
18.04
124637
8268
24.08
100
52816
3892
3.27
80859
6009
8.99
95911
6887
13.95
13.4
111581
7762
19.61
12.9
130779
8560
26.11
12.1
110
83185
6179
9.65
98641
7064
14.91
115239
7961
20.92
12.7
84934
6300
10.17
100794
7193
15.66
13.3
Two things need to be said;
· This is a first attempt. I do not have lap, lead, exhaust lap, clearance and volume nor superheat vs steam rate for the S1- I have estimated them; these will have some modest impact on the efficiencies I calculate. I also assumed steam chest pressure was 290 psi across the board which is decidedly optimistic. Crucially however, I set the blastpipe nozzle area as 64 sq ins. This is very generous and allows low back pressure at high rates. If it is significantly less than this, back pressure will rocket at high outputs and the very high powers shown at 100000lbs/hr+ will be curtailed significantly. If anyone can supply further details on these dimensions, most especially the blastpipe design, that would be helpful to improve matters.
· It can be seen nonetheless that the engine is capable of delivering enormous power. You are therefore right to imply that these figures don’t tell you a great deal- the limiting power is all about the boiler output that can be achieved, which can only be established by trying!.
Thanks Jones 1945.
As tim z points out below, it’s not quite as you think- the resistance of the locomotive would not change, only the coach resistance would fall in proportion to the weight, and the figures themselves are not directly useful.
I have two answers to your question about how long it would take 6100 to accelerate 1065 tons to 100mph on level track.
The first is, if we assume that flat out working is 7200HP (I don’t know how this reported figure was arrived at), and that when starting you can put down about 70% of the rated TE without slipping (Pure guess, about the maximum normally applied ion the UK), then you reach 100mph in 11 miles, about 9¾ minutes. After that you can maintain 100mph with about 5400HP. During the acceleration, steam rate is in excess of 100000lbs/hr, and you are burning about 17000lb/hr top quality coal. This kind of time is what you might claim for PR purposes.
However, my sense of the way locomotives were actually expected to perform is somewhat different. Starting is about TE, sustained performance is about how hard you are prepared to steam the boiler. As far as I can tell, it was unusual for US boilers to be steamed much above about 600lbs steam/sqft/ grate/hr, sometimes less. (This figure refers to top quality Coal of about 13500BtU/lb; it would be less for lower calorific values). Above this specific evaporation rate, unburned coal losses rise sharply, and it may be that this was a prudent level to avoid high boiler maintenance costs, e.g. due to cinder cutting, by not asking too much of them- the draughting usually allowed up to at least 900lbs/sqft/hr- a whopping 120000lbs/hr for the S1.
Looked at this way, the Table below shows how a number of different locomotives might be expected to perform with a 1065 ton train on level track, again working at 70% maximum TE up to 20mph, maximum steam rate about 600lbs/sqft/hr beyond that. All numbers are just indicative of relative potential, not precise.
Speed after 20 miles and elapsed time
final speed, mph
elapsed time, mins
sustained HP
PRR S1
96.8
16.50
5500
NYC J3a
84.6
18.75
3750
Niagara
90.4
17.25
4500
T1 Franklin
86.9
18.00
4100
T1Walschaerts
86.2
K4
71.2
24.50
2400
Not even the S1 can reach 100mph, though all are still accelerating slowly, and the S1 would eventually get there. The Niagara comes out better than the T1 versions, because the PRR banked the supposed engine efficiency advantages of the Franklin valve and reduced their grate size from 100 to 92 sqft, thus, according to my criteria, reducing the maximum sensible steam rate.
Of course, on any real line there will be gradient fluctuations, which might enhance acceleration. On the Water Level Route and PRR Crestline to Chicago the gradients are gentle, but the eight coupled designs would all get up to 100mph after a while, and cruise in the low 90s. And, if a train is overloaded or running late, there is likely plenty of upward power reserve to knock a hole in these figures.
To explore all these factors, I have spreadsheets with a simple flat test track, also the PRR main from Crestline to Chicago and back. I can send you these if you wish, together with the equations which will allow you to drive any of the above locomotives to see how all this works for yourself- there is an enormous range of possibilities.
An important input in all this is what the speed limit on the PRR main was on this stretch. 1940s and 1950s schedules from Crestline to Englewood only require average speeds in the mid to low 60s, I suppose after the 1946 Naperville disaster, speed limit was 80mph- is this so?- What was it before then? The answer to the second question determines what the maximum power you need from you locomotives is. If it was 90 to 100mph, then faster schedules would seem possible with T1s and diesels.
To summarise, the answer you are looking for depends on exactly what question you are asking. Are you are asking ‘What would happen if an S1 was pushed to its limit? The Niagara, T1, Mallard and French Compounds were all thrashed to find out the answer to this question for them. You really would have had to do the experiment to find out the true limit of the S1. But, I would argue that the results obtained with the four types mentioned when tested this way tell you very little indeed about what their in service potential is. Steam fans quote these efforts as indications of their relative prowess. Chapelon used his results to try to convince his bosses that steam was a viable answer. But in all cases, these feats do not represent what they did in service.
If you are asking what kind of performance an S1 might reasonably deliver in service, then I think my second estimate is more realistic. The S1 is the only type that could realistically whizz 1065 tons along the level at 100mph, thanks to its massive fire grate. This would however only be possible if the line was fettled up to handle that, and other trains are making similar speeds. Until that happened, the S1 would have been constrained by other traffic.
I am no professional, by the way, just an amateur with no axes to grind, at least I hope so!
Some more thoughts in a follow on a note to timz.
Thanks a lot for the link, timz. I think I could figure it out myself. : )
Move from other post:
His table estimates the power needed to pull the train at a given speed. He doesn't claim to have a good idea of the engine's power -- we're all guessing at that. You can guess as well as anyone, and you can calculate the result of your guesses. You'll assume the engine has so many pounds of drawbar pull at 1 mph, and the train has so much resistance, so you can calculate the rate of acceleration from 0 to 2 mph, and the time and distance for that. Do the same for 2 to 4 mph, and 4 to 6 mph...
An example
http://cs.trains.com/trn/f/740/t/242844.aspx
Dreyfusshudson Thanks for this- I haven't paid much attention to the S1 in the past, but have had a quick attempt to simulate its performance. My simulations are on Excel, using equations for resistances of coaches and loco, and the power developed by a loco in a given cut off and speed. The coach resistances are taken from standard sources (US trains are a nightmare because of the variety of coach types and the power needs for air con), loco resistance from equations of my own devising based on UK data (the US data I have seen on this subject is not entirely reliable, but the ball park is clear), and the power equations are computed from first principles- I get good agreement with a wide variety of locos on both UK and US test plants, and I think the extrapolations to types that weren't tested will be pretty good. For the S1 I have had to make a few guesses because I don’t have all the data, but these will be second order effects that won’t change the big picture much I think. We do know what the resistance of PRR P70 stock on PRR track is from the AAR tests (a bit less than the Davis formula), and using this I get the following powers needed for an S1 with loads of a) 1460 tons and b) 730 tons to sustain various speeds on level track -indicative rather than precise figures. S1 plus 730 US tons speed mph IHP EDHP Loco Res 80 2656 1326 1331 90 3478 1729 1751 100 4465 2214 2253 110 5633 2790 2846 120 7000 3467 3537 130 8583 4253 4334 140 10404 5157 5246 S1 plus 1460 US tons 80 4016 2652 1365 90 5250 3458 1795 100 6734 4428 2310 110 8493 5581 2917 120 10554 6935 3626 130 12943 8507 4443 140 15684 10315 5379 The sources I have give the maximum cylinder power (IHP) as 7200 at 100mph, which in my hands needs about 32% cut of and 100000lbs/hr steam- should be well within the capacity of the 132 sqft grate. The above says that an S1 could cruise at 100mph on level track with 1460 tons, but it would take quite a time to get there. The most favourable stretch of track on the PRR from Crestline to Chicago is perhaps from Bucyrus down to Upper Sandusky, 15 miles at 1/470 worth about 2000HP at 90mph with a 1460 ton train, 1300HP with the lighter one. You will be able to work out from the above Table what the prospects for the claimed speeds of 130+mph are! Using my equations, I can get 1460 tons up to 90mph on the level in 9 miles working flat out, but the acceleration to 100mph is painfully slow and takes another 10 miles. So there would seem to be some disparity between your calculations and mine. Happy to try to work this through off line if that would be of interest- it’s tedious stuff! Depends if you know the provenance of the equations in the TRAINZ simulator?- I am completely unfamiliar with it. In my computer, locos neither slip nor derail by the way- my tracks are all arrow straight, but do go up and downhill according to gradient profiles.
Thanks for this- I haven't paid much attention to the S1 in the past, but have had a quick attempt to simulate its performance.
My simulations are on Excel, using equations for resistances of coaches and loco, and the power developed by a loco in a given cut off and speed. The coach resistances are taken from standard sources (US trains are a nightmare because of the variety of coach types and the power needs for air con), loco resistance from equations of my own devising based on UK data (the US data I have seen on this subject is not entirely reliable, but the ball park is clear), and the power equations are computed from first principles- I get good agreement with a wide variety of locos on both UK and US test plants, and I think the extrapolations to types that weren't tested will be pretty good. For the S1 I have had to make a few guesses because I don’t have all the data, but these will be second order effects that won’t change the big picture much I think.
We do know what the resistance of PRR P70 stock on PRR track is from the AAR tests (a bit less than the Davis formula), and using this I get the following powers needed for an S1 with loads of a) 1460 tons and b) 730 tons to sustain various speeds on level track -indicative rather than precise figures.
S1 plus 730 US tons
speed mph
EDHP
Loco Res
2656
1326
1331
3478
1729
1751
4465
2214
2253
5633
2790
2846
7000
3467
3537
130
8583
4253
4334
140
10404
5157
5246
S1 plus 1460 US tons
4016
2652
1365
5250
3458
1795
6734
4428
2310
8493
5581
2917
10554
6935
3626
12943
8507
4443
15684
10315
5379
The sources I have give the maximum cylinder power (IHP) as 7200 at 100mph, which in my hands needs about 32% cut of and 100000lbs/hr steam- should be well within the capacity of the 132 sqft grate. The above says that an S1 could cruise at 100mph on level track with 1460 tons, but it would take quite a time to get there. The most favourable stretch of track on the PRR from Crestline to Chicago is perhaps from Bucyrus down to Upper Sandusky, 15 miles at 1/470 worth about 2000HP at 90mph with a 1460 ton train, 1300HP with the lighter one. You will be able to work out from the above Table what the prospects for the claimed speeds of 130+mph are!
Using my equations, I can get 1460 tons up to 90mph on the level in 9 miles working flat out, but the acceleration to 100mph is painfully slow and takes another 10 miles.
So there would seem to be some disparity between your calculations and mine. Happy to try to work this through off line if that would be of interest- it’s tedious stuff! Depends if you know the provenance of the equations in the TRAINZ simulator?- I am completely unfamiliar with it.
In my computer, locos neither slip nor derail by the way- my tracks are all arrow straight, but do go up and downhill according to gradient profiles.
Thank you very much, Dreyfusshudson! I have been waiting for a professional calculation to simulate the performance of S1 for so long and I finally got one! This means a lot to me! Thanks a lot! TRAINZ simulator is not a professional software so I could only get a brief and inaccurate result from it.
Under normal circumstances, the PRR S1 #6100; the preferred engine for the prewar premier overnight all-coach train the Trail Blazer ( Standard consist was 14 cars), was needed to haul a PB70ER passenger baggage car (154500 lbs), Ten P70kr or P70gsr betterment coaches ( 146100 lbs ), a twin unit dining car consisted of a D70dR Kitchen Dormitory (191400 lbs) and a D70cR Full dining car (169700 lbs), a POC70R - Parlor-Observation Car (149500 lbs), thus the whole consist of the Trail Blazer was weighed 2126100 lbs (1063.05 US tons). The reason I used the 1460 tons figure was that I tried to test the limit of PRR S1.
Base on your professional calculation result, can I just simply adjust the figure of IHP (as well as EDHP and Loco Res) by multiplying them by 0.728 (1063/1460) from the figures you provided like the following table?
S1 plus 1063 US tons
EDHP(unedited)
Loco Res(unedited)
2924
3822
4902
6183
7683
9423
11418
I would be really grateful if you could help me to calculate the time and miles of PRR S1 needed to reach 100mph (or above) with 1063 tons behind her! Thank you very much! It seems that PRR S1 was capable to reach at least 110mph hauling 1063 tons, this is compelling for me!
Wiki
Jones 1945,
We do know what the resistance of PRR P70 stock on PRR track is from the AAR tests (a bit less than the Davis formula), and using this I get the following powers needed for an S1 with loads of a) 1460 tons and b) 730 tons to sustain various speeds on level track -indicative rather than precise figures, not least becasue all the data on resistance runs out at 80-90mph, and so the high speed estimates are based on a big extrapolation. We do know that resistances tend to increase with the square of speed, so that 140mph should be roughly twice 100mph is not unreasonable.
erikem
Passenger comfort before what I believe is the tried and tested way of dealing with this situation? interesting!
Dreyfusshudson Jones 1945 -thanks for the tip off- a great set of postings that it will take me some time to digest. I think there are a couple of points i would like to add, but need time to engage brain fully on these rather different topics.
Jones 1945 -thanks for the tip off- a great set of postings that it will take me some time to digest. I think there are a couple of points i would like to add, but need time to engage brain fully on these rather different topics.
You are welcome, Dreyfusshudson. Take your time, It's not urgent.
I am a user of Trainz simulator, I understand that it is not a professional mechanical or automobile engineering program but it is the most realistic simulator available for trains simulation. I believe many of our forum members using this software like me. One of my projects is to simulate PRR S1 6-4-4-6 #6100 by using all actual figures of the real engines specification I gathered from books, forums, and internet.
Starting the engine (*1460 tons passenger stock behind ) with a maximum cut-off at full throttle caused the engine wheel slipping endlessly and stuck in the same spot. The only way to get the train moving forward is to adjust the cut-off to 26%-32%, full throttle, the S1 (in the computer) will start moving gradually and reach 60mph by increasing the cut-off from 26% to maximum cut-off. The engine can reach 105mph or above after 12-15 mins on level track by gradually decreasing the cut-off to 41% or less, depending on the gradient of the track.
In the realistic mode which allows derailment, my S1 derailed at every single sharp curve and it is not easy to restart the train once she stopped in random places; sometimes I have to spend 5 mins to get her moving forward again by adjusting the throttle and % of cut-off.
I remember a Trains "Second Section" piece about a cab ride on the 20th Century Limited, where the locomotive got into a high speed slip and the correspondent was "guest engineer". The correspondents first impulse was to back off on the throttle, but the engineer said "no" because it would cause slack action. The engineer cured the slip by spinning valve gear wheel to lengthen cut-off. One explanation was this would soften the impulses and thus relieve the slip.
I agree that, for the reasons you give, full gear and part regulator is the way to start.
My only point was ( apologies if I wasn't clear) that if you drove a T1 in this fashion, in the way you would drive a K4, the wheel rim horsepower on an individual wheel would be much greater than on a K4. The load on the drivers is not that different, so other things being equal (they are not) you might expect more slippage. Also, because of the different characteristics of the valve gear, and the presence of four cylinders, you would also get more HP at each wheelrim than on a Niagara driven in identical fashion.
As to whether Duplexes, by their nature, slip more, I am quite unable to comment
The data I have are times- to the nearest minute only-at Vandale, Warsaw, Plymouth (these two the stretch in question), with an overall elapsed time of 91 minutes for the 118 miles from Fort Wayne to Liverpool- an exceptional effort after a slow start to Vandale.
The first point is that you cannot make any meaningful claim to average speed when times are only to the nearest minute- there could easily be an error of a minute between two points, which has a big impact on the average speed.
The second point is that if you work out the power needed to achieve what was claimed, it works out at about 4500 cylinder horsepower for a quarter of an hour. This is way in excess of what they were able to achieve on the test plant with a much improved version of 5399- and then only for a short period. Steam rate would be in excess of 80000lbs/hr. So, we are in dreamland.
The log, such as it is, analyses more sensibly if you assume maximum power was around 3500HP- as on the earlier tests with the 1000ton test train when they were trying to push the loco to its limits. The average speed then works out at about 91mph on this stretch- remember it is ever so slightly up hill, so this is a great effort. It could be a bit better than this, but nowhere near 100mph.
I suspect a bit of judicious rounding up of the Warsaw and Plymouth times was made to support the claim. Franklin were clearly in 'sales' mode and this was great publicity. As I read the papers, the PRR folk were equally keen to believe and support the claim. Times had been very tough and they needed something to cheer.
DreyfusshudsonBy time course I mean the passing times at all points along the route.
DreyfusshudsonIt is also interesting that they say maximum cut off should be used on starting and then 'gradually' reduced. This would lead to very high wheelrim powers when accelerating, more so than on a PV 4-8-4 because of the enhanced steam flow from the Franklin gear and four cylinders at a given cut off, and if driven this way, it is perhaps not surprising they tended to slip.
This actually means something a bit different, which is well-established wisdom in some parts of the world like Australia. That it's wisdom developed after the recognition of low- and high-speed slipping (and adjustment of things like FA and equalization to overcome the problem) on T1 locomotives should tell you there's more to it.
Typical "thermodynamic expert" revealed wisdom is to get the throttle fully open as fast as possible and then 'drive on the reverse' -- this produces theoretical minimum throttling loss/wiredrawing in the admission steam and micrometric cutoff control of developed power. The 'advocated' strategy is saying just the opposite: keep the reverse 'down in the corner' in the desired direction for a while, and drive on the throttle (which is the thing I think you're missing in the criticism here).
The problem with early advance of the cutoff is the problem you note: much peakier torque (with conventional valve cutoff methods) resulting in more propensity to slip under any given adhesion conditions at a given developed horsepower (or average demanded torque, to use a different physical metric). Keeping the cutoff 'long' does two things: it keeps the average torque more normalized over the stroke, and it provides a vast sink of steam (at a given throttle opening) so that any slip once it starts to propagate becomes quickly self-limiting (in the same sort of way that the LP of a Mallet is self-limiting).
Problem #1 with Franklin-modified Lentz gear is that the gear can have, and usually does have, inherent limited cutoff, and problem #2 is that the gear can, and usually does, have very positive and precise action up to comparatively high rotational speed (one of the salient tested advantages observed for the T1 over the T1a). This means that even with the cutoff as long as it can be 'wound' there may still be sufficient steam to keep a slipping engine out of re-establishing static friction ... until the aggregate throttle is closed enough that the non-slipping engine loses power or stalls.
Now, the T1 is fitted with Franklin Precision air throttle, so very fine modulation of the throttle at any point is technically easy, regardless of how the multiple cams are set or if the effective throttle opening is smoothly progressive with physical throttle opening (which we won't know until 5550 is actively tested under steam; my guess is that some fun empirical calibration will be needed to get this effect). So driving the engine right at adhesion limit becomes fully practical once you have reasonable slip indicators, a thing we have covered in other posts here... that is, it becomes fully practical with appropriate haptic feedback IN the physical throttle.
That is not something likely to be easy in the grapevine setup as applied to the T1, which I think needs appreciable 'augmented force' (as applied to the F107 controls) in both servo directions to be particularly good. That right there is the antithesis of a typical K4 throttle, which despite postdating the practical implementation of Wagner-throttle servo action required quite an amount of banging open and closed at small opening. (I never had the chance to run one, but I suspect there are some here who have, and can confirm this.)
One approach that I can NOT advocate is something Neil Burnell mentioned as a 'coping mechanism' some engineers tried -- letting the throttle pressure fall off approaching and at a stop, so the locomotive would start with, say, 185psi gauge during the critical runup to 35mph or so (in the process mirroring some of Tuplin's observations on sliding-pressure firing Niagaras). As you get to the critical speed where the T1 has rapid acceleration, the increased draft etc. will have developed fire and hence steam pressure up to where desirable... and off you go.
I trust you see (1) that this perfectly mirrors the idea of simply keeping the throttle part closed until up to reasonable speed, and (2) what delightful effect this will have on things like staybolts in parts of your boiler, with the pressure and necessarily concomitant thermal cycling at each start. As people accuse Livio Dante Porta of finding out, sometimes thermodynamic expediency leads to substantial maintenance despair, wiping out any 'where's my big savings' on the coal and water bill perhaps many times over...
Dear forum members,
There is a post in Classic Trains forum "PRR Duplexes and Experimental Engines Discussion ( S1, S2, T1 etc.)" http://cs.trains.com/ctr/f/3/t/271182.aspx discussing different experimental steam engines, including Pennsy's duplexes. Please feel free to check it out if you like. Your input and participation are always welcomed! Thank you for your attention.
You are correct on the lack of training. After reading seveal articals in the Keystone Mag. on T1, this consensus came out. Unlike how management views training of new equipment (think flight simulators for a Boeing 777), back then you learned on the job and because you can run a K4 you go run a T1. Some Engineers learned as they went and where very good handeling a T1, while other's just run them hard and the rest be darned.
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