I was wondering if there were any fast and easy answers to efficiency comps for the largest, and the most successful of the super power steam locos. In my mind, the best of the best considerations must include efficiency, for, after all, the cost of fuel is the single most expensive consummable commodity on any railroad, even today.
Since there are no easy answers to this question, and since a scientific study is at best an arduous, time-consuming task resulting in exceptions, controversy and conflicting data, I propose that the very best solution is to look at how the designers had the tenders built after years of operating experience was able to provide them with all the answers they needed to hook up a properly defined tender(s) to the beasties.
Bottom line, gents: It ain't rocket science. How much coal each loco typically carried vs how much water, and what were they able to do with it on average in terms of tonnage, speed, and hill climbing was well-defined by experience and design resultants. We need look no further than the tenders.
Big Boy final 5 production loco tenders carried 25,000 gal water and the same amount of coal as the first 20 did - 28 tons, or 56,000 lbs. I've never seen a photo with an auxiliary tender behind a Big Boy, so I am going to say the rate of water boiled off as steam per pound of coal burned must then be 2.24 lbs coal per each gallon of water boiled off.
Next, lets look at, say a class A N&W since it is also a simple articulated, and pulls 125,000 lbs, just 10k lbs less at the drawbar than the BB, and runs at comparable speeds. That auxiliary tenders were commonly used behind these "A" locos is well-documented fact, and it is my understanding that they often steamed off another 10-15,000 gallons minimum before exhausting their fuel supply.
Let's first look at use with only a primary tender situation.
2-6-6-4 A carried 22,000 gal water primary & 26 tons or 52,000 lbs. coal so we're looking at 2.32 lbs coal/gal water. Somehow the A is already appearing to be more efficient than BB, but we need to add some auxiliary tender capacity to get a more realistic view of the actually road use numbers. If you add an extremely conservative 5,000 gallons that makes it work out to 1.92 lbs coal/ gal water. I understand that the numbers are more like 38,000 gal water steamed per tender load of coal, which actually makes it just 1.37 lbs coal / gal water, approaching an amazing increase in efficiency I was not expecting to see when compared to BB. hmm.
We know that the Y6's were far more efficient than that, but it is not fair to compare the two, since they were really built for very different kinds of running, pulling, and speeds. The Y6b, and all the earlier Y's that were upgarded to use the famous high pressure diverting valves so that they could run as simple engines as well as compounds at the will of the driver pulled an incredible 156,206 lbs at the drawbar (BB was ~ 135,000lbs)!! but never ran faster than 40, maybe 50 MPH tops downhill with a good tail wind and fresh running gear - and usually ran at 25mph where they made their best power, whereas the A's and the BB's ran at 40-50 routinely.
I still love them Big Boys, though. By far they win the "Most Coolest Locomotive Ever" award. OK, OK, N&W gets 5 points to Griffindor for "The Best Pair of Locomotives ever Built" award.
I'm not a snob. I am not proud. I have no problem collecting Challengers alongside Class A's, N&W Chesapeakes alongside UP Big Boys, C&O Alleghenies alngside SP Cab Forwards, 2-6-6-2's alongside Yellowstones.
I love articulateds. In all shapes and sizes! HahA! I run one wi-i-i-i-ld and c-ah-ra-a-a-a-zy kinda layout, folks! Hm...I still need to find a Clinchfield caboose for that one 4-6-6-4 though...
GT MillsI was wondering if there were any fast and easy answers to efficiency comps for the largest, and the most successful of the super power steam locos. In my mind, the best of the best considerations must include efficiency, for, after all, the cost of fuel is the single most expensive consummable commodity on any railroad, even today. Since there are no easy answers to this question, and since a scientific study is at best an arduous, time-consuming task resulting in exceptions, controversy and conflicting data, I propose that the very best solution is to look at how the designers had the tenders built after years of operating experience was able to provide them with all the answers they needed to hook up a properly defined tender(s) to the beasties. Bottom line, gents: It ain't rocket science. How much coal each loco typically carried vs how much water, and what were they able to do with it on average in terms of tonnage, speed, and hill climbing was well-defined by experience and design resultants. We need look no further than the tenders. Big Boy final 5 production loco tenders carried 25,000 gal water and the same amount of coal as the first 20 did - 28 tons, or 56,000 lbs. I've never seen a photo with an auxiliary tender behind a Big Boy, so I am going to say the rate of water boiled off as steam per pound of coal burned must then be 2.24 lbs coal per each gallon of water boiled off. Next, lets look at, say a class A N&W since it is also a simple articulated, and pulls 125,000 lbs, just 10k lbs less at the drawbar than the BB, and runs at comparable speeds. That auxiliary tenders were commonly used behind these "A" locos is well-documented fact, and it is my understanding that they often steamed off another 10-15,000 gallons minimum before exhausting their fuel supply. Let's first look at use with only a primary tender situation. 2-6-6-4 A carried 22,000 gal water primary & 26 tons or 52,000 lbs. coal so we're looking at 2.32 lbs coal/gal water. Somehow the A is already appearing to be more efficient than BB, but we need to add some auxiliary tender capacity to get a more realistic view of the actually road use numbers. If you add an extremely conservative 5,000 gallons that makes it work out to 1.92 lbs coal/ gal water. I understand that the numbers are more like 38,000 gal water steamed per tender load of coal, which actually makes it just 1.37 lbs coal / gal water, approaching an amazing increase in efficiency I was not expecting to see when compared to BB. hmm. We know that the Y6's were far more efficient than that, but it is not fair to compare the two, since they were really built for very different kinds of running, pulling, and speeds. The Y6b, and all the earlier Y's that were upgarded to use the famous high pressure diverting valves so that they could run as simple engines as well as compounds at the will of the driver pulled an incredible 156,206 lbs at the drawbar (BB was ~ 135,000lbs)!! but never ran faster than 40, maybe 50 MPH tops downhill with a good tail wind and fresh running gear - and usually ran at 25mph where they made their best power, whereas the A's and the BB's ran at 40-50 routinely. I still love them Big Boys, though. By far they win the "Most Coolest Locomotive Ever" award. OK, OK, N&W gets 5 points to Griffindor for "The Best Pair of Locomotives ever Built" award. I'm not a snob. I am not proud. I have no problem collecting Challengers alongside Class A's, N&W Chesapeakes alongside UP Big Boys, C&O Alleghenies alngside SP Cab Forwards, 2-6-6-2's alongside Yellowstones. I love articulateds. In all shapes and sizes! HahA! I run one wi-i-i-i-ld and c-ah-ra-a-a-a-zy kinda layout, folks! Hm...I still need to find a Clinchfield caboose for that one 4-6-6-4 though...
The unknown in your calculations is the heat value of the coal burned by the UP in the Big Boys vs the coal burned by the N&W. I don't have the values!
My understanding over the years has been that coal used by the western carriers was seriously substandard when compared to coal that was used by eastern carriers. The grade of coal has a very large effect on the efficiency of steam engines.
Never too old to have a happy childhood!
The point is quite valid. NP locomotives had large fireboxes to compensate for the low-grade coal they burned.
Coal BTUs is very important. One of our group was on a steam excursion that performed well until the replacement coal started into the engine and then it became a struggle !
CSSHEGEWISCH The point is quite valid. NP locomotives had large fireboxes to compensate for the low-grade coal they burned.
Northern Pacific, for example, used very low grade (sub-bituminous/lignite) from on-line deposits, and so bought steam locomotives with bigger grates/fireboxes than average.
Many railroads designed their locomotives specifically to burn local, available coal; from deposits convienient to the end user railroad. 'Mine-run' coal could range anywhere from smaller sizes, to sizes approaching small boulder sizes (ie: basketball sized(?). coal for stoker-fired engines could be in the range of pieces the size of ballast (2" (?), or smaller pieces.
Here in Kansas the Katy(MKT), and AT&SF used local mined coal that was of a poor grade, almost a 'culm' [ie: waste] grade because of the way it was found in shallow pockets mixed with soils.
There is a LOT more to this 'comparison' than just the comparative heat content, but to start there, the Big Boys burned a particularly woeful kind of subbituminous, whereas the As were getting, if not Pocahontas coal, something reasonably close in BTU, one of the better run-of-mine steam coals.
As an immediate secondary observation, the Big Boys were fired in a manner that in some ways better approximates oil firing than conventional "coal" firing: much of the fuel was friable and burned 'better' when suspended in a current of hot air, so much of the actual 'combustion' in that large firebox and chamber space was conducted with the fuel actually levitated, as if in pulverized-fuel firing, and releasing radiant heat for fourth-power uptake in much more of the general 'firebox' heating surface than locomotives with more typical heat release from the combustion-gas plume.
As you might expect, firing this way was a highly inaccurate "science" in the 1940s, and likely would remain so in any real-world locomotive today, so you'd be getting quite a bit of unburned carryover in the exhaust, which might fool the casual armchair railfan to think that the locomotive is being worked 'too hard' and the fire's being "lifted off the grates" -- it is, but not unintentionally...
Meanwhile, unlike any Challenger, the class A has a deep firebox with an arch and circulation, which provides multiple-pass plume length from a typical good coal fire on the grate, and (as with the Allegheny, for example) has a very large radiant absorptive surface in the firebox and chamber for the wavelengths from evolved carbon and hot gas in the plume. (Radiant combustion of carbon will more or less completely cease by the time the gas is no more than about 6" into the tubes and flues, at which point only convection and conduction work for heat transfer (in the absence of Besler tubes, which have a decidedly different effect -- but were not used on any large steam locomotive to my knowledge) and you have the typical Wagner ratio of 1:406 or so for the useful tube length -- which regardless of locomotive size works out at somewhere in the vicinity of 20', with the rest of the boiler "best" optimized to use something other than convective heating in firetubes and flues, and the elements in the flues (and their configuration) 'rightsized' for the kind of firing and the purpose the elements serve.
This represents perhaps a record for oldest resurrected zombie thread on the forums. Do any of the current participants remember what was discussed back in 2005?
Didn't steam engines stop more often for water between coaling. Does tender water capacity depend more on water tank spacing?
All this certainly make the job of a fireman very inportant. Cannot imagine how busy one would be firing a steamer on hog back country. Maybe it is time to get some insight from firemen before they all expire ?
MidlandMike Didn't steam engines stop more often for water between coaling. Does tender water capacity depend more on water tank spacing?
CSSHEGEWISCH MidlandMike Didn't steam engines stop more often for water between coaling. Does tender water capacity depend more on water tank spacing? They didn't necessarily have to stop for water. Tenders on NYC passenger power tended to have high coal capacity and smaller water capacity. The tenders had water scoops and depended on track pans to refill the water tank while in motion.
...and this was true for many tenders on the Pennsy as well. They tended to have large coal bunkers, but their cisterns were replenished via track pan and scoop. You wouldn't want to be a distracted engineman when your scoop was nearing the end of the pan at 40-70 mph. Or dropped early.
selector CSSHEGEWISCH MidlandMike Didn't steam engines stop more often for water between coaling. Does tender water capacity depend more on water tank spacing? They didn't necessarily have to stop for water. Tenders on NYC passenger power tended to have high coal capacity and smaller water capacity. The tenders had water scoops and depended on track pans to refill the water tank while in motion. ...and this was true for many tenders on the Pennsy as well. They tended to have large coal bunkers, but their cisterns were replenished via track pan and scoop. You wouldn't want to be a distracted engineman when your scoop was nearing the end of the pan at 40-70 mph. Or dropped early.
And I doubt you would want to be a car or two behind the engine with the windows open as the train went over the track pan!
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