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.
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 Ni
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% fo
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…
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.
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 quar
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.
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…
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.)
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 calculati
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 prod
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?
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.
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.
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.
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 g