Overmod Incidentally, you might appreciate some of the implicit analysis in the data accompanying Dawson's (1975) analysis of Niagara road-testing (including discussion of 5500 that is not included in the 1947 report on motive power). Note the errata listed at the end carefully as you read. https://nycshs.files.wordpress.com/2014/07/roadtestingniagaras.pdf
Incidentally, you might appreciate some of the implicit analysis in the data accompanying Dawson's (1975) analysis of Niagara road-testing (including discussion of 5500 that is not included in the 1947 report on motive power). Note the errata listed at the end carefully as you read.
https://nycshs.files.wordpress.com/2014/07/roadtestingniagaras.pdf
The Errata do not appear to correct any of the number in Table 4 on p 21 giving indicated and drawbar hp under the states steam flow and firing rage.
The 1500 hp spread between indicated and drawbar values suggests a speed of 70 MPG. The 4000 indicated hp suggests 2/3 of maximum power at that speed. 90 lbs/sq feet of grate firing rate is rather reasonable. How Dawson got 54.7 boiler efficiency out of 82.2 % combustion efficiency (the amount of lost coal, which seems reasonable for the firing rate given that 10% of the coal can end up in the ashpan droppings) and 80.1% absorption efficiency -- should give .822 times .801 = 66 % boiler efficiency.
Where does the los number of 52,500 lbs steam through the blast pipe come from? Is the feedwater heater really drawing off that much from 15.8 times 4000 ihp = 63200 lbs steam/hr entering the cylinders?
The boiler efficiency, to the extent that the numbers could be reconciled seems reasonable. The 15.8 lbs/ihp-hr at 2/3 power seems a tad high in relation to the 16.7 lbs/ihp-hr I quoted from Alfred Bruce's book at full power.
As to you-need-to-figure-on-drawbar-efficiency values, 3 times 2000 HP for E7's to match the peak 6000 HP is about the same weight as Niagara and tender, although maybe you don't need 3 E7s to make schedule on a trains pulled by a Niagara owing to the much higher low-end tractive effort? For comparable HP/weight and frontal area giving much of the 1500 HP spread not accounted by machinery resistance in the steam locomotive, the "loss" involved in pushing the air aside and dragging the locomotive weight is comparable?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicAny info on where to get a copy of Fry?
https://books.google.com/books/download/A_Study_of_the_Locomotive_Boiler.pdf?id=Ez9MAAAAMAAJ&output=pdf&sig=ACfU3U0GfnFdKOOscRef_wT7q2Kc6UQ_4w
If that lunches for some reason, google Lawford Fry, "A Study of the Locomotive Boiler" and the Google Books link will be accessible from the first page of results.
Overmod:
Any info on where to get a copy of Fry?
sgriggsPaul, are you referencing Wardale's book, "The Red Devil and Other Tales from the Age of Steam"? I don't own a copy, but can look for one.
Yes, that is the book.
I bought it when they reprinted it a few years ago.
The book chronicles Wardales experience as a British ex patriate first in South Africa, where he was able to modify two locomotives, first, a light-duty 4-8-2 Engine Number 2644 of the South African Railways 19D class and later a heavier-duty 4-8-4 Engine Number 3450 of the 25NC class, considered the most powerful and mechanically reliable of South African steam. His changes to the 2644 were an improved exhaust system along with Porta's Gas Producer Combustion System (GPCS) firebox modification. Changes to the 3450 were that in addition to fitting a larger superheater and extensive changes to the valves, valve timing and inlet steam circuit, including a scary "surgical procedure" of cutting off the "steam chests" and fitting larger ones. The changes were significant enough that the 3450 was designated the prototype (and as it turned out only) member of a new 26-class locomotive.
The Tales from the Age of Steam are also three tales of 3 technology cultures in three different countries. In South Africa, the shop people along with the locomotive operating crews had a can-do, even gung-ho spirit about making these modified locomotives and operating them. Although South Africa had reasons for hanging on to steam, railway management let Wardale actually make these mods but was passive aggressive about doing anything more with them.
The country is the USA, where Wardale worked as a consultant to the ACE-3000 project to build a condensing steam locomotive with sufficient thermal efficiency to compete with diesels during the early 1980s spike in oil prices. This project was characterized by pie-in-the-sky goals (Wardale explains why bringing the ACE-3000 to market would have needed much more time and money than available to the project), a lot of "marketing" and what used to be called Vu-Graph engineering in the days before Power Point presentations.
The 3rd country was China in the latter half of the 1980s, where China had its own reasons to want to power locomotives with domestic coal. This was when China was hitting its stride in engaging with the West after Nixon's diplomatic initiative and Deng's leadership but well before China was building 1000's of miles of high-speed electric rail lines.
Wardale was hired to lead the design of an improved QJ-class 2-10-2 locomotive. Longing for the good times he had in South Africa, he complains bitterly about people at the level of factory personnel and locomotive crews getting all passive aggressive by the way they slow-walked this project until he left, with a full set of design documents but no completed locomotive.
The book is replete with charts giving performance data, especially of the 3450 26-class 4-8-4. There is a section with some stats on Ross Rowlands locomotive number 614, a 4-8-4, but don't call it a Northern, which turned in notably weak performance when it served as a "test article" on the ACE project. Both Wardale and Overmod state that with a firebox leaking into the steam space, this locomotive was not in shape to test much of anything, but I am curious diving deeper into at least the "best case numbers" when the boiler maintenance person "with murder in his eyes" (Wardale's words) "caulked" these leaks (pounded the seams, rivets and staybolt heads into shape from inside the box).
Wardale does a great job explain the "why" of Porta's GPSC and gives a lot of evidence that it is not The Magic Upgrade to Bring Steam Back.
I was hoping the book would be more technical, the the charts are tantalizing in what they leave out, but it is an interesting account of a mechanical engineer (Wardale) and his career focus on keeping mainline steam and what worked and what didn't work out in three different engineering cultures.
sgriggs I don't own a copy, but can look for one.
sgriggs Paul Milenkovic And the biggest, meanest, spread between indicated and drawbar horsepower of them all is what Wardale reports about the resistance curves of the 3450 in Red Devil. Really disappointing in that the resistance of the locomotive was multiples of what is reported elsewhere, and his only explanation was that the dynamometer car was out of wack. Does a DBHP and IHP curve for the Red Devil exist?
Paul Milenkovic And the biggest, meanest, spread between indicated and drawbar horsepower of them all is what Wardale reports about the resistance curves of the 3450 in Red Devil. Really disappointing in that the resistance of the locomotive was multiples of what is reported elsewhere, and his only explanation was that the dynamometer car was out of wack.
And the biggest, meanest, spread between indicated and drawbar horsepower of them all is what Wardale reports about the resistance curves of the 3450 in Red Devil.
Really disappointing in that the resistance of the locomotive was multiples of what is reported elsewhere, and his only explanation was that the dynamometer car was out of wack.
Does a DBHP and IHP curve for the Red Devil exist?
p 266 Rolling resistance curve
p 267 Indicated tractive effort as a function of speed and steam flow
p 269 Drawbar tractive effort as a function of speed and steam flow
p 268 Indicated power as a function of speed and steam flow
p 270 Drawbar power as a function of speed and steam flow
What I want to encourage is reading data from this and other sources and making sense of it.
In my opinion 'indicated horsepower' is about the same as pro formas in a business plan. You use them to estimate the design parameters, but they are BS as far as what happens in reality.
Then you figure out the actual profitability, or actual DBHP, the only thing that matters to actual Davis-formula calculation or predicted performance, and if you want, deduce how to make the DBHP better on actual test under actual significant running or road conditions.
I came to appreciate why PRR calculated their performance curves not in 'horsepower' but in drawbar pull at speed -- it goes directly into Davis-formula calculations for practical train resistance, and then reasonably quickly into acceleration formulae.
Drifting Mallets is a special case; you will immediately understand why the bypass valve on locomotives like 1309 is such an essential component, and recognized to be so very early.
Even drifting them with 'snifting' to atmosphere results in dramatic compression from the very large LP cylinders out there on a two-axis pivot to slop around... and then the hunting from overbalance starts. Very few of them were set up to modulate the intercepting valve for pure drifting (at 15psi or so as on simple engines).
And no Mallet of 1910 had Franklin wedges, roller bearings, modern rings or crossheads, good rod bearing construction, etc. etc. etc.
timz Railway Age Gazette for 11 March 1910 p513 says a Mallet "will not drift down a 1 per cent grade." Then in the 15 Apr issue p997 it says GN towed some 2-6+6-2s with electrics and found the Mallet rolling resistance (speed unspecified) averaged 11885 lb. (Engine plus tender weighed 250 tons.)
Railway Age Gazette for 11 March 1910 p513 says a Mallet "will not drift down a 1 per cent grade." Then in the 15 Apr issue p997 it says GN towed some 2-6+6-2s with electrics and found the Mallet rolling resistance (speed unspecified) averaged 11885 lb. (Engine plus tender weighed 250 tons.)
Drifting probably depends on reverser and throttle settings (Wardale has a favorite mode of drifting with neutral reversal and a little throttle of steam to keep from aspirating smokebox gases). This in turn may involve compression and other effects Overmod mentioned?
In all these cases, it obviously isn't "machine friction" of the usual kinds or, as you say, you'd be seeing it as heat.
Meanwhile, remember Chapelon noting that the only reason roller-bearing rods can possibly work is if they are laterally bending dramatically. (That is inherently in the "correct" alloy and fabrication procedure for modern lightweight rods, e.g. with cerium steel...)
It would be relatively very easy to assess most true 'machine friction' on something like the PRR test plant as improved, if you can motor the rollers and measure any slippage or 'jump' between wheeltread and roller (the contact patch being imho fairly dramatically smaller). I remember seeing estimates or figures for the T1 being somewhere in the 96 to 98% range, which implies that a very small amount of interference or 'stiction' or whatever would be producing higher overall machine resistance if it is coming from 'mechanism' somewhere. Which leaves steam-cycle issues as the place the 'cylinder horsepower' is going -- and when you look at compression alone, I think you're finding effects of sufficient magnitude to account for the 'missing power', with flow between port and exhaust tract after release being the 'next' source of lower actual expansion thrust.
I argued that proper calorimetry would reveal if the valves were actually bouncing or leaking to any significant degree; we now have test procedures using several different disciplines that could actually visualize the effects at high cyclic, as well as flow patterns at unshrouding, and in the non-flow-optimized tracts close to the ports, in the Franklin A and B-2 systems. But I'm not really expecting to find showstopping issues, either leakage or shock stall, at properly debounced valves, and there are methods (including those proposed to be tried in 1948) that should cure most of the issues for any high-speed cutoff that produces the necessary cylinder thrust for high speed. (I'm predicting that will be a duration corresponding to just over 40% but with timing and careful reversible-compression management for 5550)
There is another potential issue, related to high mass flow and excessive superheat at high cyclic. I would not be surprised to find that the actual mass flow of steam at very high demand but short cutoff induces substantial shocks in the starting-and-stopping flow, and these shocks might easily either throttle or wire-draw the actual steam getting into the cylinders under 'assumed steady-state' steam-supply conditions. This is one of the reasons I went to very large effective steam-chest 'reserve' volume combined with valves that rotated and reciprocated to increase the effect of long-lap long-travel fast port opening and closing -- but I have not modeled the result at all exhaustively.
IHP is not, and never will be, more than a theoretical estimate -- and not a particularly good one considering the non-ideal-gas nature of that female dog-goddess steam. The catch is to get rid of all the places you can where the steam gets to act out ... and then see where your losses are actually coming from, and which of them are cost-effectively addressable.
Overmod sgriggs I can't get my head around that much power being consumed in machine friction. Seems insanely high, as if some components would have to be glowing cherry red to dissipate that much power Personally, I think some of it is in compression; at least one person thinks it is related to steam leakage at the poppet valves, perhaps partly related to uncontrolled valve bounce (I disagree in principle but can't prove it; it may take full-scale experience on 5550 to confirm or deny sufficiently). I look forward to seeing how effectively reversible active compression control (following what Jay Carter did with steam automobiles) might relieve the practical effects of insanely high spot compression near FDC/BDC. To my knowledge there is no accounting for nucleate condensation (as opposed to wall condensation) in the ihp calculations, despite the fact that work extracted from cylinder contents has to result in cooling through the steam mass -- this is one of the important purposes of sufficient late superheat, but that promptly rises to bite your butt at exhaust release if you don't have really, really good exhaust arrangements...
sgriggs I can't get my head around that much power being consumed in machine friction. Seems insanely high, as if some components would have to be glowing cherry red to dissipate that much power
Personally, I think some of it is in compression; at least one person thinks it is related to steam leakage at the poppet valves, perhaps partly related to uncontrolled valve bounce (I disagree in principle but can't prove it; it may take full-scale experience on 5550 to confirm or deny sufficiently).
I look forward to seeing how effectively reversible active compression control (following what Jay Carter did with steam automobiles) might relieve the practical effects of insanely high spot compression near FDC/BDC. To my knowledge there is no accounting for nucleate condensation (as opposed to wall condensation) in the ihp calculations, despite the fact that work extracted from cylinder contents has to result in cooling through the steam mass -- this is one of the important purposes of sufficient late superheat, but that promptly rises to bite your butt at exhaust release if you don't have really, really good exhaust arrangements...
The high apparent MR in the T1 example is not an anomaly specific to poppet valve locomotives. There is a large difference between IHP and DBHP on the NYC Niagara (6600 IHP - 4600 DBHP) at 85mph. Obviously, much of this can be attributed to air resistance and rolling resistance of the tender and locomotive non-drive wheels, but those can be estimated from Davis and accepted aero formulas and what's left over (Machine Resistance) still seems quite high (836 HP, by my calculation). The Johnson MR formula predicts 623 HP at 85mph for the Niagara.
The same can be said of the PRR Q2 duplex, which recorded 7987 IHP (highest ever measured, to my knowledge) and 6782 HP at the drivers on the Altoona plant. That is a whopping 1205 HP of just Machine Resistance at 57mph! Johnson's MR for this locomotive is 587 HP at 57mph. Maybe the drivers were slipping?
My conclusion has been that quoted IHP readings may not be accurate measures. R.P. Johnson discusses difficulties measuring IHP on page 353 of his book, and table XLVII shows that the excess of IHP could be as much as 14-17% at higher engine speeds (269 - 296 RPM). Such overstatement of IHP would appear as high machine friction when the difference between IHP and Drawbar or wheel rim HP is resolved into its components.
Scott Griggs
Louisville, KY
sgriggsI can't get my head around that much power being consumed in machine friction. Seems insanely high, as if some components would have to be glowing cherry red to dissipate that much power
Overmod Meanwhile, in my opinion and observation, the machine resistance of a modern roller-bearing locomotive, particularly one with poppet valves, was much smaller than the numbers being bruited about here. This is particularly true of a locomotive like the T1 with Franklin wedges and roller-bearing boxes and rods. Do not conflate the machine resistance with the mass of the engine and tender being added to the Davis formula.
Meanwhile, in my opinion and observation, the machine resistance of a modern roller-bearing locomotive, particularly one with poppet valves, was much smaller than the numbers being bruited about here. This is particularly true of a locomotive like the T1 with Franklin wedges and roller-bearing boxes and rods. Do not conflate the machine resistance with the mass of the engine and tender being added to the Davis formula.
Picking one test point from the PRR T1 test report (400 RPM/20% Cutoff), the locomotive produced 6442 IHP and 5829 HP at the drivers. So, 613 HP due to machine resistance alone at 95 mph. Johnson's MR estimate (20 lbs/ton of driver weight), would work out to 679 HP. So, a 10% savings in MR over Johnson's rule-of-thumb figure. I can't get my head around that much power being consumed in machine friction. Seems insanely high, as if some components would have to be glowing cherry red to dissipate that much power (457,300 watts!) continuously. I've always wondered if IHP figures were significantly overstated. Doesn't seem hard to believe when you look at how squirelly indicator diagrams look at high test speeds. Johnson himself speaks to indicated horsepower measurements having increasing excess error as speed increases. IHP was a sales tool, I think, so errors probably didn't really matter.
Do not be fooled by the broken-image picture. Click on it and the actual picture will likely open legibly; it did for me on a very ancient browser.
Watch what happens when you enter the correct modern factor costs of coal, water, and ash handling into the numbers for the steam locomotive.
Then add the cost for maintenance as practiced, say, by NYC to give the standby performance of 'contemporary' diesels ... hot suits, anyone? Bet that would cost more today if you could get permission to implement it as needed...
The added 'friction' of the carrying wheels was comparatively slight, and of course with the roller bearings the high starting resistance to establish the hydrodynamic film was much, much less -- as you can imagine from the girls being able to start those locomotives moving.
The real 'ringer' in those pictures is the effective friction between the piston rings and the bore; presumably these were designed to exert far less force without steam pressure 'behind' them and, in fact, I suspect a little promotional hanky-panky in adapting clearances in the glands and piston/valve rings to reduce friction which, had actual 265psi or whatever steam been present, would likely have allowed a veil of white and the sound of considerable blow...
The actual frontal resistance of a locomotive is important at the higher speed ranges, but it does not matter the way, say Cd of an automobile does. Very few locomotives appear to have been designed with quartering streamlining particularly in mind ... or with actual, functional drag reduction rather than its Art Moderne semantic representation being the design factor of importance. The cube-of-the-speed drag rising meets the functional cyclic steam circuit mass-flow and timing and compression issues falling at some speed, and if the valves in particular are not designed correctly, you're faced with the painful spectacle of, say, a C&NW E-4 or ATSF 3460 class, which probably gets up near 100mph reasonably well but by only a trivial additional number of mph more is clapped out -- the former couldn't even crack 100mph with the AAR test train; the latter probably couldn't get above 105mph unless it reached terminal velocity falling off a bridge. It would be interesting to see the effect of proper streamlining ... but other parts of the design have to be made right first.
Paul Milenkovic On the topic of mechanical efficiency, the go-to reference I would offer as the John Knowles blog posting. I am told Mr. Knowles is still active on some railroad enthusiast sites but his lengthy blog posting is not longer available. The next best source is the Ralph Johnson of Baldwin and his steam-locomotive book, offering a rule-of-thumb "20 lbs resistance for each ton of weight on drivers." As I mention above, Withuhn claims a J3 Hudson achieved, under unspecified operating conditions, 2 lb coal/hp-hr putting it at 9% indicated (cylinder level) efficiency. Do you a link or a reference to Altoona T1 data? I would think the test plant gives efficiency at the wheel rim (rollers) without deduction for the Davis formula terms for rolling resistance, especially of the "carrying" wheels and those on the tender. But what I am most interest is the breakdown into the indicator diagram-derived lbs steam/hp-hr and the test-plant pounds coal/pounds of steam.
On the topic of mechanical efficiency, the go-to reference I would offer as the John Knowles blog posting. I am told Mr. Knowles is still active on some railroad enthusiast sites but his lengthy blog posting is not longer available.
The next best source is the Ralph Johnson of Baldwin and his steam-locomotive book, offering a rule-of-thumb "20 lbs resistance for each ton of weight on drivers."
As I mention above, Withuhn claims a J3 Hudson achieved, under unspecified operating conditions, 2 lb coal/hp-hr putting it at 9% indicated (cylinder level) efficiency.
Do you a link or a reference to Altoona T1 data? I would think the test plant gives efficiency at the wheel rim (rollers) without deduction for the Davis formula terms for rolling resistance, especially of the "carrying" wheels and those on the tender. But what I am most interest is the breakdown into the indicator diagram-derived lbs steam/hp-hr and the test-plant pounds coal/pounds of steam.
Hi Paul,
I figured out how to post the graphic from the N&W: Giant of Steam.
Note that N&W estimated its steam locomotives to have a thermodynamic efficiency of 6%, when measured at the rail (i.e. not based in Indicated HP).
Here is a summary page from the NYC Niagara test report. Note that the NYC determined thermodynamic efficiencies for this locomotive at 4000 IHP/2500 DBHP (not 6600 IHP/4500 DBHP). The Dry Coal/IHP is given with and without accounting for appliances and is 2.29 lb/IHP-hr with appliances and 2.10 lb/IHP-hr without appliances. Thermal efficiency based on 2500 DBHP was "only" 4.77% for the 6023 (baker valve gear S1b) and 5.51% for the 5500 (poppet valve S2a). As I said in the earlier post, the NYC test report suggests it was not possible to run the Niagara at low enough cutoffs to maximize thermal efficiency (riding qualities of the locomotive were unsatisfactory if operated with too-short a cutoff). Consequently, the locomotives were operated at a higher cutoff and at part throttle to avoid exceeding division speed limits.
The NYC was considering a duplex-drive 4-4-4-4 with poppet valves of its own (C-1 class, I think?). Maybe they were thinking having twice as many smaller cylinders with poppet valves would allow them to run at more efficient short cutoffs without the unacceptable riding qualities?
The 2000 HP difference between indicated and drawbar values at 86 MPH is also found in Alfred Bruce's chart in his book.
By the HP = drag * mph/375 formula, the 2000 HP amounts to 8721 pounds of tractive effort to be supplied.
The Ralph Johnson formula for a constant mechanical friction as 1 part in 100 of the adhesive weight works out to 2750 lbs or about 631 hp at that speed. Interestingly enough, this is roughly 10% of the indicated HP giving the 10% "mechanical efficiency" that Wardale writes about, but from the John Knowles essay, it does not seem this loss decreases at a lower output of hp output?
This locomotive plus tender weigh in at 400 tons -- 800,000 lb, giving a rough Davis formula resistance of 1600 lb consuming 367 hp.
It is also interesting that the sum of 1600 lb from the Davis formula rolling resistance and 2570 for the mechanical resistance of pistons-to-wheels adds up to 4350 lbs, close to what I read at the low end of Bruce's chart for the difference between cylinder and drawbar tractive effort when air resistance vanishes.
This suggests that the aerodynamic drag was a full 4750 lbs consuming at least 1000 hp. The Niagara appeared to be quite unstreamlined, but this 1000 hp is pushing aside the air in which the train cars "draft", so I don't know if you could assign its full value as an inefficiency of the locomotive apart from arguing passenger locomotives need to have effective aerodynamic treatment.
A diesel also has a drive offering less than 100% efficiency, but its Davis rolling resistance is much less owing to many fewer axles -- let's say you are saving about 250 out of the 2000 hp.
This business of know-where-the-power-is-going ties into the Chapelon-Porta-Wardale-others claims of what could-have-been and what should-have-been.
Wardale talks about increasing the locomotive power-to-weight ratio. Even if you have a 4-8-4 wheel arrangement for guiding reasons, the Niagara and many late-era high-power locomotives have proportionately more weight on the carrying wheels as earlier designs -- Bruce's photo section gives stats on locomotives from the early 20th century to the end of steam. If you could Chapelon-ize or Porta-ize a locomotive to consume less coal and water, the smaller tender would also reduce the Davis rolling resistance cost, not to mention climbing even a modest grade, of a tender that a diesel doesn't need to drag around.
Of all the loss factors, I am most curious about the mechanical loss from cylinder to wheel rim and whether as Johson claims, this stays constant, even at reduced power output, if for any other reason than understanding those photos of the Timken Four Aces being towed by four women of slight build.
Paul Milenkovic Let me leave it for discussion right now as to where the 6% thermal efficiency for modern steam in US practice comes from and consider later on how the lbs steam/lbs coal ratio (coal ratio? Cole ratio?) along with the lbs steam/hp-hr can vary under different designs and operating conditions.
Let me leave it for discussion right now as to where the 6% thermal efficiency for modern steam in US practice comes from and consider later on how the lbs steam/lbs coal ratio (coal ratio? Cole ratio?) along with the lbs steam/hp-hr can vary under different designs and operating conditions.
Paul,
I think you left a layer of mechanical conversion efficiency out of your calculation. I think the 6% rule of thumb applies to overall thermal efficiency of a typical late steam era locomotive, possibly operating under steady state conditions. There is a figure in Jeffries book, "Norfolk & Western: Giant of Steam" on page 62 that sheds some light on the assumptions of this 6% rule of thumb. Hopefully, you have this book and can reference, but it is a comparison of the operating cost between a diesel-electric locomotive and a steam locomotive on the basis of "work at the rail per dollar". It shows 400,000 BTU of work being done at the rail for 6,666,666 BTU/$1 of coal at the then-current cost of 13,666 BTU/lb coal. This works out to 6% thermal efficiency (400,000/6,666,666). I tried to post a scan of this figure, but apparently the Trains forum requires an image to exist somewhere on the internet to link. It is important to note that this is work at the rail (tractive force), and not work in the cylinders.
If we adjust your 6% number (derived from figures roughly applicable to the maximum indicated horsepower output levels of fthe NYC Niagara) for the rather jaw-dropping mechanical and resistance efficiency loss factor (4600 DBHP/6600 IHP @86mph)= 69.6%, we get an overall estimate of thermal efficiency of only about 4.2%. Of course, that would be at the very inefficient operating condition of maximum IHP and presumably very high (and inefficient) firing rate. And it should also be pointed out that we're being a little sloppy in mixing tractive force developed at the driver rim with drawbar pull (which is reduced by the rolling resistance of engine and tender and air resistance), but for discussion purposes requiring rough numbers, I think we can make some informed simplifications.
I was fortunate enough to be able to purchase a digital copy of the July 1948 NYC Niagara test report from the NYC Historical Society a few years ago, and it includes calculations of overall (drawbar) thermal efficiency for the road tests. Here are some of the comments from the report relevant to that testing:
"Full throttle operation with locomotives 5500 and 6023 throughout the entire working time was not practical with the train loadings used on account of their high power output and the speed limit of the division. Therefore, an arbitrary minimum cutoff for each locomotive had to be established on the basis of the riding qualities of the locomotive. Upon reaching this minimum cutoff, power output was controlled by throttle manipulation. Such operation naturally varied the average pressure at the steam chest. For the purpose of obtaining some information to establish a relationship between locomotive operation and economy, several tests were conducted with comparatively short average cutoffs with the necessary high average steam chest pressures. Operation of this type was not considered normal or practical."
"Locomotive 5500 (S2a equipped with poppet valves) had an economic advantage over locomotive 6024 (S1b equipped with Baker valve gear) as shown by the average curves for the thermal efficiency based on dynamometer horsepower (Figure 46). This amounts to from 0.60 to 0.80 percent thermal efficiency. The maximum thermal efficiency of locomotive 5500 was 5.86 percent obtained on test No. 141 and the minimum was 4.93 percent obtained on test No. 115. The maximum and minimum thermal efficiencies for locomotive 6023 were 4.94 and 4.22 percent obtained on test No. 111 and No. 137 respectively. For tests conducted with comparably short cutoffs the maximum thermal efficiencies were 6.57 and 5.58 percent for locomotives 5500 and 6023 respectively."
I suspect these tests involved stopping and starting the trains, rather than steady state operation (after all, these are passenger locomotives). The report makes the following comments that seem to relate to these operational effects on efficiency:
"During stationary testing (NYC 6000 had been tested for boiler capacity on the Selkirk test plant), the firing rates are consistent with evaporation, steam used, temperatures, and pressures. Coal rates in road operation, especially during periods of acceleration, usually are much heavier than the average temperatures, pressures, and steam requirements indicate. This is a result of the necessity to build up the fire or even force the fire in preparation for capacity operation. Evaporation and superheat temperatures naturally lag during these periods."
I would think well-designed superpower freight locomotives with large combustions spaces that are operated at efficient firing rates (<100 lb/sq ft/hr) with a minimum of stopping and starting could approach the 6% thermal efficiency.
A quick review of the PRR Altoona Test Plant report for T1 locomotive 6110 shows overall thermal efficiencies generally between 6 and 7%, with some as high as 7.5-8.0% (with cutoffs less than 25%). Of course, these are steady state tests under test plant conditions without losses due to standby periods, acceleration, or obviously rolling and air resistance.
timz Paul Milenkovic Whereas I am offering speculation, I am indeed suggesting that a Niagara could be run that efficiently at part-power The numbers again: 7400 lb/hr of 14000 BTU/lb coal = 103600000 BTUs per hour = 80600800000 ft-lb per hour = 40707 horsepower So 4000 hp is 9.8% thermal efficiency. Offhand guess: no Niagara did better than 7% on any test. NY Central didn't care enough about efficiency to find out the 4-8-4 was actually that much better? Other US engines could hope for 9% anyway? But tests never revealed their efficiency either?
Paul Milenkovic Whereas I am offering speculation, I am indeed suggesting that a Niagara could be run that efficiently at part-power
The numbers again:
7400 lb/hr of 14000 BTU/lb coal = 103600000 BTUs per hour
= 80600800000 ft-lb per hour
= 40707 horsepower
So 4000 hp is 9.8% thermal efficiency. Offhand guess: no Niagara did better than 7% on any test. NY Central didn't care enough about efficiency to find out the 4-8-4 was actually that much better?
Other US engines could hope for 9% anyway? But tests never revealed their efficiency either?
William Withuhn (2019) American Steam Locomotives, p 253 gives the coal rate of the J3 Hudson as 2.03 lbs/indicated (cylinder) hp or 8.7 percent.
So performance under some operating condition of late-era American steam better than the well-quoted 3 lb/hp-hr or 6% thermal efficiency is not unheard of. The question is, under what operating condition are people talking about because boiler efficiency charts (lb water/lb coal) and Wardale's indicator diagrams (lb water/hp-hr) show that these supporting elements of efficiency can vary widely.
Again, efficiency percentages above 6% are widely quoted for French, German and British late-era steam, but did they have some "special sauce" that US designers ignored, or is it a question of how these locomotives were operated?
Paul MilenkovicWhereas I am offering speculation, I am indeed suggesting that a Niagara could be run that efficiently at part-power
Another approximation useful for calculating locomotive efficiency is:
TE (lbf) X Speed (mph) X 1.99 = power in Watts ("2" is a good approximation for 1.99)
Kratville's book on the Big Boys had dynamometer data from eastbound runs from Ogden, recall coming up with a figure of 4 to 4.5% for efficiency converting energy in coal to DBHP.
Paul MilenkovicI think that is pretty much what I am saying. The 3000 HP rating of an SD40-2 is "before the traction generator" but "after the auxiliary loads." I was contrasting this with my figures for a steam locomotive, also "before the mechanical rod transmission of power" but without taking deductions for auxiliary loads.
Oops. I misread it.... Sorry!
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Paul MilenkovicThere is a narrative that especially the French and to some extent the Germans and the British were building much more efficient steam locomotives than the ham-fisted Americans.
There are equally clear explanations on the American side why cheap, robust construction and cheap maintenance concerns 'win the day' over expensive and often fragile or illusory thermodynamic improvements.
I will not make exhaustive (and ever more boring) lists or citations of the various issues. But one fairly dramatic one might serve. You may remember the 614T testing, 'supposedly' providing data for modern boiler design. Not only were some of those tests conducted with leaking staybolts, NONE of them was conducted with a working feedwater heater.
Our community is FREE to join. To participate you must either login or register for an account.