Steam & Preservation

Right on Paul,

but please consider, as you mentioned it, a steam-turbine-electric was never successful (water and electricity packed close together on a locomotive frame... ouch!). In addition, UPRR did some serious own research about designing good draft systems. In case of BB, the second run to Green River was easier and may have shown better boiler-performance. Instead of putting "fancy" gadgets on steamlocomotives, running lighter trains with them could habe been a better alternative.

Cheers

lars

Lars Loco:

Right on Paul,

but please consider, as you mentioned it, a steam-turbine-electric was never successful (water and electricity packed close together on a locomotive frame... ouch!). In addition, UPRR did some serious own research about designing good draft systems. In case of BB, the second run to Green River was easier and may have shown better boiler-performance. Instead of putting "fancy" gadgets on steamlocomotives, running lighter trains with them could habe been a better alternative.

Cheers

lars

While your statement holds true for the N&W and C&O coal fired steam turbines my understanding is that the GE and Westinghouse oil burning turbine electrics were technically successful. They were not however, economically competitive with their biggest oil burning competitor, the diesel electric locomotive..

Instead of putting "fancy" gadgets on steamlocomotives, running lighter trains with them could habe been a better alternative. Cheers lars

One thing that comes out of such experience along with the thermodynamic analysis is that for "simple expansion" locomotives, there is probably a "best match" between locomotive and operating conditions.  Work a locomotive too hard, and you operate at large cutoffs that are wasteful of steam.  Work a locomotive too lightly, there is a minimum cutoff that you can use depending on valve gear and thermal losses, and you have to throttle for the reduced power settings and also waste fuel.  There is probably some golden mean, where the locomotive is worked at large cutoffs for some hills, throttled down on some flats, but perhaps spends most of its operating time at the most economical cutoff and throttle settings.

That is probably a contributor to the proliferation of steam locomotive "types" and wheel arrangements, and by contrast, Diesels are more standardized.  My guess is that a Diesel gets more thermally efficient the more time it spends at max power settings, and as such, you can lug Diesels down until they stall and tie up the railroad line before fuel costs start increasing -- in fact, you have higher fuel costs for putting enough power on your trains.  This need to operate "at the golden mean" with steam whereas Diesels can be loaded down until you stall or burn up the traction motors may also have contributed to the need for more helper districts with steam rather than some intrinsic inability to build steam locomotives with enough powered axles (consider the "double Garratt" proposals).

One thread running through accounts of the history of steam is that the "fancy" gadgets (apart, perhaps, from Schmidt's superheater) never caught on -- even if the "gadgets" (compound expansion, higher boiler pressure) were workable, what they save in fuel never seemed to balance out what they cost in increased maintenance.

High pressure boilers are one of the "fancy gadgets that never caught on."  The C&O coal-fired steam turbine did not use a particularly high boiler pressure, but the N&W Jawn Henry used a somewhat higher boiler pressure (500 PSI?) and I thought the oil-burning condensing turbine electric tested on the UP used a 1000 PSI water tube boiler, although I believe that one was condensing so they could afford to use demineralized water to get around the scaling and foaming problem of the common quality of water used once-through in most steam locomotives. 

Lars Loco:

Right on Paul,

but please consider, as you mentioned it, a steam-turbine-electric was never successful (water and electricity packed close together on a locomotive frame... ouch!). In addition, UPRR did some serious own research about designing good draft systems. In case of BB, the second run to Green River was easier and may have shown better boiler-performance. Instead of putting "fancy" gadgets on steamlocomotives, running lighter trains with them could habe been a better alternative.

Cheers

lars

A  better alternative to what?  Are you saying the railway would have made more money if it ran its trains faster?

RWM

Railway Man:

Lars Loco:

Right on Paul,

but please consider, as you mentioned it, a steam-turbine-electric was never successful (water and electricity packed close together on a locomotive frame... ouch!). In addition, UPRR did some serious own research about designing good draft systems. In case of BB, the second run to Green River was easier and may have shown better boiler-performance. Instead of putting "fancy" gadgets on steamlocomotives, running lighter trains with them could habe been a better alternative.

Cheers

lars

A  better alternative to what?  Are you saying the railway would have made more money if it ran its trains faster?

RWM

 

 

Hello Rail-Way Man,

yes, certainly, not on all conditions but generally yes.

It could make better sence, to operate a couple of trains more per day and keep the mainline busy and fluid. 

This is, from what I understand, are showing the results of BB test runs. 

Let's have a look, the lightest train with engine 4004 and 3539tons took Wasatch with a good clip of 21,2 mph, and needed 20min less than the other two runs (approx 4hours for 75miles). And as written, this time "the 4004 really rolled them that evening, because the high iron was loaded with many trains..."

In all cases, the minimum continuous speed was 13-14mph from milepost 942 eastward to 928 at a continuous grade of 1,14%, keeping the train one hour working there.

That performance is OK in my eyes,

Otherwise, just put some more hundred tons on the train, it than maybe working two hours on the grade with 7-8mph and wasting fuel and low economical performance.

Cheers

lars

 

 

 

 

 

carnej1:

Lars Loco:

Right on Paul,

but please consider, as you mentioned it, a steam-turbine-electric was never successful (water and electricity packed close together on a locomotive frame... ouch!). In addition, UPRR did some serious own research about designing good draft systems. In case of BB, the second run to Green River was easier and may have shown better boiler-performance. Instead of putting "fancy" gadgets on steamlocomotives, running lighter trains with them could habe been a better alternative.

Cheers

lars

While your statement holds true for the N&W and C&O coal fired steam turbines my understanding is that the GE and Westinghouse oil burning turbine electrics were technically successful. They were not however, economically competitive with their biggest oil burning competitor, the diesel electric locomotive..

 

From a theoretical standpoint, UPRR steam turbine 1+2 from 1939 were successful, too and could have been further improved, but they never made real money on the road (maybe some bucks for the GN, though)

Lars

Paul, as you started this thread about thermal efficiency about feedwater-heaters, 

I would like to ask everbody interested, following:

is it true that in post '40 era. the Railroads tendencies were using commonly more simple parts like Type A super-heaters and Worthington feed-waters without hardly notable performance decrease?

Paul, have you already googled for baldwin's 60000 test results, if not this may interest you.

Cheers

lars

 

Paul Milenkovic:

I remember some time in the late 1960's living in Boulder, Colorado and hanging out with the local model railroaders and railfans, and hearing something about a "steam ejector" that "could have saved steam."  Not to get the "should have kept steam longer" debate going again, but you have to remember that 1969 was just 10 years after Norfolk and Western dropped the fire on their last Y-class, and Colorado narrowgauge steam was a going concern until the mid 60's?   

Years later I think they were talking about Kylchap or Giesel or whatever kind of improved exhaust drafting nozzle, and I always wondered how what I considered to be minor modifications to the boiler draft could make that big a difference for what was inherently a low boiler pressure, non-condensing, inefficient steam cycle.

 

The trains article was on the Giesel ejector. The advantage was not so much how much more draft it could produce, but how much less back pressure was needed for the draft. Think advantages of using a condenser on a steam turbine versus exhausting at atmospheric pressure.

Paul Milenkovic:

So 115,000 lb tractive effort at 14 MPH works out to about 4300 HP -- somewhat less than the max 6000 HP, but to be expected at "grade climbing speed."

 This relates to La Massena's thesis in his article "The Big Engines". The UP could have made up their trains to make use of the Big Boy's peak tractive effort of a bit over 120,000 lb, but the train would have been slugging up the hill at less than 10 MPH. By dropping the tonnage by 5%, the UP got 50% more speed and were less likely to stall on the hill.

10 tons of 10,000 BTU/lb coal at 4300 HP works out to about 5.5% coal-to-tractive-effort efficiency -- about in the ballpark of those mentions of efficiency in the mid 4% range.

 

I was also getting a figure of a bit over 4% for thermal efficiency from the Big Boys from the data in Kratville's book. I wonder what tractive effort and speed combination would give the best thermal efficiency? A WAG on my part would be say 40,000 lb at say 30 MPH, where the throttle would be wide open, the reverser hooked up as tight as can be to get maximum expansion.  The locomotive would be running at less than maximum power which "should" help improve both combustion efficiency and heat transfer efficiency.

- Erik

erikem:

 This relates to La Massena's thesis in his article "The Big Engines". The UP could have made up their trains to make use of the Big Boy's peak tractive effort of a bit over 120,000 lb, but the train would have been slugging up the hill at less than 10 MPH. By dropping the tonnage by 5%, the UP got 50% more speed and were less likely to stall on the hill.

I was also getting a figure of a bit over 4% for thermal efficiency from the Big Boys from the data in Kratville's book. I wonder what tractive effort and speed combination would give the best thermal efficiency? A WAG on my part would be say 40,000 lb at say 30 MPH, where the throttle would be wide open, the reverser hooked up as tight as can be to get maximum expansion.  The locomotive would be running at less than maximum power which "should" help improve both combustion efficiency and heat transfer efficiency.

- Erik

Thank you Erik,

as you mentioned it, does somebody know what peak tractive effort BB could excert? With a 4000tons train it was 115.000lbs, final ratings were 4450tons, 10percent more, so 126.500lbs? I could never figure it out, my guess that would lug BB down to 5-10mph.

Kratville stated, "later, they performed so well... in the final years of steam they were given 4450 tons". The 4450 tons rating occured 1948, btw. However the book leaves us railfans pretty alone about that.

Cheers

lars

 

erikem:

By dropping the tonnage by 5%, the UP got 50% more speed and were less likely to stall on the hill.

If you're talking about the Wahsatch climb, 5% less tonnage would mean something like 5% more speed. It's not clear just what Le Massena was trying to say in that paragraph, but it we can't accuse him of saying 5% less tonnage means 50% more speed.

timz:

erikem:

By dropping the tonnage by 5%, the UP got 50% more speed and were less likely to stall on the hill.

If you're talking about the Wahsatch climb, 5% less tonnage would mean something like 5% more speed. It's not clear just what Le Massena was trying to say in that paragraph, but it we can't accuse him of saying 5% less tonnage means 50% more speed.

 

let us compare it with those test-data:

I made a mistake by writing min. speeds of all runs was 13-mph.

Actual  with run no. 4004 it was 15.9mph (the lightest one with 3539tons).

The heaviest of this trio was 3883tons with engine 4016. Here the occasionally min. speed was 13mph, regularly 14mph on 1.14% grade (~4300hp).

Engine 4004 produced ~14% more speed with ~9% tonnage, Echo to Evanston: Water/Evap. per Coal 4.72%  against  4.15%  of engine 4016.

It is a difference, but not as big as the propagated 5% less tons and 50% more speed.

 

Cheers

lars

 

Paul,

I came back to Baldwin`s 60000 web-page and had some fun with the numbers:

though, it had a  Worthington feed-water, it contained some modern boiler aspects and achieved during tests coal/to water ratios of 6-7% and boiler efficiency of 50-70%.

The fun is, however, taken from the test on the ATSF

PERFORMANCE OF LOCOMOTIVE NUMBER 60,000, AND 3800 CLASS LOCOMOTIVES, BELEN TO MOUNTAINAIR

tests results show, BB (and other BIG articulates ) would produce more than double of HP in the speed of 10-14mph.

OK, blame me for this unfair comparison, but Baldwin 60000 is not a small loco at all, but BB is not double big either.

But nothing from the Baldwin was adapted to later built engines.

-edit- 

Anyway, do locomotive compatible boiler-based steam-turbines exist? 

Any propagation to put it on a locomotive frame?

Cheers

lars 

Steam locomotives (and other steam engines both reciprocating and turbine type) operate on the Rankine cycle. As with other thermodymanic cycles, there are four parts, compression, addition of heat energy at the high temperature, expansion, and extraction of heat energy at the low temperature. All can be modeled as either closed cycle, where the working fluid is used repeatedly, or open cycle, where the working fluid is used once and then must be replenished. A non-condensing steam engine is an open cycle machine.

The reason that the Rankine cycle was the first to be commercialized was due to several factors. First, the Rankine cycle involves a phase change in the working fluid. The fluid is condensed at the low temperature point from a gas to a liquid, and then the compression is done by means of a pump of some sort, either an injector or a conventional pump of some kind. Because the volume of the condensed water is so small compared to the volume of the evaporated steam, and because liquids are non-compressible for all practical purposes, the energy required for the compression part of the cycle is small compared to other cycles where the compression takes place with the working fluid in a gaseous state.

Second, a practical engine generating useful amounts of power could be made with simple materials and machinery that were available early in the history of the industrial age. There was no requirement for high speed parts or rapidly turning precision bearing types.

Thus the simpler open cycle machine was quite practical to build and the cycle itself is conceptually simple, simple enough to understand even before anything was really known about thermodynamics or modern physics. The use of water allowed the open cycle to easily dump the waste heat at the end of the cycle into the atmosphere, an inexhaustable heat sink, unlike some other machines such as the Stirling cycle, which needed a heat exchanger of some kind to dump waste heat into the atmosphere or a cooling jacket of some kind.

Practical machines could be built that didn't even require high pressure steam at all. The first machines such as Newcomen's design that was used to pump out coal mines, used steam at atmospheric pressure and operated by condensing the steam in the cylinder and using the resulting vacuum to operate the large diameter cylinder and lift water out of the mine. Efficiency was low, but it worked. Even the genius of James Watt, who used the steam expansively on a double acting piston, didn't like high pressure as the likelihood of boiler explosions was high with the primitive materials avaliable before 1800.

With the advent of high pressure steam, locomotive construction became practical. Pressures were low by modern steam standards, being no more than 100 pounds per square inch even by the late 1800s, but the increased pressure did two things. It increased the amount of expansive work that could be done by the steam and it also increased the upper temperature at which heat was added from the firebox. Both served to increase efficiency. Superheating allowed still higher temperatures to be achieved, reducing condensation losses in dry pipes, valves and cylinders and improving efficiency still further. With superheating, the next limit became the lubrication of valves and cylinders. Slide valves especially couldn't stand higher temperatures and pressures, so they were replaced with cylindrical valves.  Compounding had the potential for improving efficiency as well, but except in the Mallet type it was mostly abandoned as presenting too much mechanical complexity for the rewards to be gained.

All of this depends largely on the benefits inherent with the Rankine cycle operating open loop. Attempts to operate railroad locomotives closed loop were limited, confined to places where water supply or quality were such to make prohibitively expensive open loop operation. The condensing locomotives used in South Africa were the most well known examples, but though quite successful, they required rather immense tenders to accomodate the large condensing surfaces to dispose of the waste heat into the atmosphere.

Brayton cycle engines (gas turbines being the best known example) operate open loop in railroad service, the Union Pacific gas turbines being the best example. They are capable of achieving very high horsepower in a relatively compact and lightweight package. However, they have a big disadvantage in that their efficiency drops off rapidly as they throttle down. This has to do with the reduction of pressure ratio (roughly equivalent to compression ratio in an internal combustion engine) as the engine speed spools down at part throttle, the only way to reduce the power output of an open cycle gas turbine. (Note that a Rankine cycle engine operates at approximately the same temperatures and pressures, and thus approximately the same efficiencies, no matter what the throttle setting.) This, as much as anything doomed the UP's turbines to retirement. By the way, it is a characteristic of the Brayton cycle that they have a large amount of "backwork", meaning that the work required to operate the compressor is a large fraction (typically about 2/3) of the work produced by the turbine. Clearly compressor and turbine efficiencies plays a large part in the overall efficiency of such a machine. Even the addition of regenerators (adding a lot of weight, space and mechanical complexity) do not overcome this fuel consumption problem and they are hard to incorporate in the limited space of a locomotive.

Diesels (Otto cycle) have many advantages for rail service. High compression ratios produce relatively high efficiencies and the required heavy construction necessary to cope with the high internal pressures are no disadvantage in railroad service. They maintain good efficiency except when they are heavily overloaded. As excess fuel is fed to a diesel, it produces very little additional power for the additional fuel. Thus, these engines really are horsepower limited, unlike a steam locomotive that can be overloaded quite heavily with comparatively smaller reductions in efficiency.

Stirling engines have never been very attractive for railway service as they are large for the horsepower produced and they require a low temperature heat sink to discard the waste heat. For high horsepower the required high and low temperature heat exchangers would become rather cumbersome.

The Carnot cycle is not a practical cycle for a real engine as it is incapable or producing power at a rate that would be useful for much of anything. It is incorrect to assume that any practical engine approximates the Carot cycle. None of the practical engines come anywhere near approaching reversible conditions. Isentropic operation would require more than no thermal or mechanical friction losses. It requires that the changing conditions in the working fluid (expansion, for example) occur in a manner that the flow has no internal losses, no internal friction, no swirls or turbulence. The flow must be perfectly smooth and laminar in nature. Normally this requires extremely low velocities, no sharp corners in passages, perfectly smooth walls, etc. This is simply not achieveable in a practical engine. It isn't even approximated. Thus, where a simple analysis of the theoretical efficiency of an engine (taken from an evaluation of the high and low temperature sinks) might show 50%, the actual efficiency due to the non-reversibilities would be less than 20%.

By the way, the idea that steam engines can only operate in the low single digit efficiencies is a fallacy. The best Rankine cycle engines (large stationary plants used to generate electricity) operate at 35 to 40% and supercritical plants do even better.

Boiler pressure isn't everything when it comes to efficiency. The temperature at which heat is transferred to the working fluid is what matters. This is why superheating gave such a boost to steam locomotive efficiency. The working fluid (steam) could be heated far above the temperature at which water in the boiler would change from liquid to gas. Stationary steam plants send the superheated steam through the high pressure turbine stage, and then back into the boiler combustion chamber where it is reheated again to the same superheat temperature but at a lower pressure. It is then sent to the medium pressure turbine stage. This same technique was tried in some compound locomotives with something called a smokebox reheater where the exhaust steam from the high pressure cylinders was reheated by sending the medium pressure steam through a reheater in the smokebox where it could pick up additional heat. Eventually, such reheaters were replaced with an additional set of superheater tubes that allowed for higher reheat temperatures and subsequent higher efficiencies. This is an analogous concept to reheating in a stationary steam plant between the high pressure stage and the medium pressure stage.

Why, then, couldn't a steam locomotive achieve the same high efficiency of a stationary steam plant? One issue is that a stationary steam plant really does operate at higher temperatures and pressures. A watertube boiler such as that used in a stationary steam plant has the high pressure water and steam on the inside of the tubes and drums. The expansive forces tend to keep the tubes round and intact. In a firetube boiler, the pressure of the steam within the boiler wants to collapse the tubes, and thus the boiler pressure is limited to what the tubes and flues can withstand.  Another is that a stationary steam plant has room for large pipes with optimized dimensions for good flow conditions that simply aren't possible in the limited loading gauge of a steam engine. Remember, every, restriction in a passageway causes a pressure loss with a subsequent drop in temperature and thus efficiency. This is why your analysis of the exhaust temperature at the blast pipe is not a good approximation. A steam locomotive, with its losses in the many feet of pipe between the steam dome and the blast pipe, would have had much higher losses than you surmise. (Surprisingly, the efficiency of the fire tube boiler used in steam locomotives was very good. They could achieve efficiencies and steaming rates very rarely obtained in stationary boilers operating at the same temperatures and pressures.)

Yes, there were several types of feedwater heaters to capture some waste heat and preheat the water before it was injected into the boiler. This was to prevent "quenching" the evaporation of the water in the boiler as much as anything. A standard steam injector did heat the feedwater to some extent and was thus superior to the crosshead pump used previously. The exhaust steam injector could use exhaust steam for the same purpose, and was something of a "poor man's feedwater heater", but it had to be started using live steam first before shifting to exhaust steam. One disadvantage of this type of injector is that oil from the valves and cylinders would be injected into the boiler along with the feedwater where it could cause problems. This was also a potential problem with the "open type of feedwater heater where exhaust steam would come into contact with the supply water, as opposed to closed type feedwater heaters where the exhaust steam would not come into contact with the boiler feedwater. The closed types were preferred in the early days of feedwater heater use, but later, as methods of separating out the oil from the feedwater got better, the open types started to be preferred because of simpler construction and maintenance.

The best examples of steam locomotive efficiency were probably not achieved in any North American locomotive, or even in any production locomotive. The locomotives of Chapelon, the French railway engineer, were marvels of efficiency and power by anyone's standards. A 4-8-0 type achieved 40 indicated horsepower per ton in the 1930s, a number perhaps never exceeded. His 4-8-4 constructed in 1946 (a rebuild of an unsuccessful 4-8-2 simple type) achieved efficiencies of 12% (early diesels probably operated at a lower efficiency than this) and a cylinder power output of 5,300 horsepower. In operation it could make 4,000 drawbar horsepower at 62.4 miles per hour from an engine weighing just 146 metric tons. Coal consumption at this speed and power level were 2.641 lbs/hour/horsepower and water consumption was 14.31 lbs/hour/horsepower. He did this by paying careful attention to the configuration of all the steam passages in the machine including the exhaust system and the valving as well, and by using a three cylinder compound design. This locomotive was designed for fast heavy express passenger service and from these numbers it is clear that all design objectives were met. Though only one was built, it was perhaps the greatest steam locomotive ever constructed and was the pinnacle of steam design.

My sources indicate that the UP 4000 class could exert a starting tractive effort of 135,000 pounds. Of course, at speed the tractive effort would decrease. Best horsepower was obtained in the 35 to 40 mile per hour range. Slower than this, the engines were not using all the steam the boiler was capable of producing.