I had to think about this for a while and run some math formulas but I think I've figured out why a steam engine has a higher tractive effort. It actually wasn't that hard to prove. For my simple comparison I used some made up numbers trying to equal things out on paper and making some 100% efficiency assumptions. The actual answer isn't what is important, it's the trend that is. The whole idea was to make a mathematical chart that would need to prove true by showing that the diesel in some way was more efficient (for lack of a better word) blow a certain point with the steam eclipsing it above. The trend in my example did hold true.
For my examples, I assumed that each engine could get the same peak power to the rails. I just for example sake used 3000 hp. I also decided on a max top speed for which to measure this power at. I used 60 mph. The weight of the locomotive(s) was actually not relevant to determine a trend. It is relevant to see where the final lines cross.
My assumption was that at all mph points on my chart, the diesel/electric engine made 3000 hp. That's what it does everywhere. Again it assumes 100% efficiency which isn't going to happen. For the steam engine, I assumed that it would make 3000 hp at 60 mph and that power would fall linearly with speed. In other words 1500 hp at 30 mph and so forth and so on.
There was one important factor that really affects the results though and I haven't seen it mentioned here. That factor is wheel (driver) diameter. A diesel/electric engine typically has a much smaller diameter wheel(s) than a steam engine does. Obviously there have been many different sizes on both accounts depending on application but the statement is true from the standpoint of generalization. I plugged in 40" drivers for the diesel/electric engine and just for giggles didn't go too crazy and just assumed 50" for the steamer.
Now that we know this, we need to figure out how many times the engine is turning over per mph. It's easy to just figure around 60 mph and then scale the rest of the numbers from there. Once you know wheel rpm, and obviously the larger drivers are turning slower for the same speed, we need to mathematically figure out how much torque is actually getting the the rails based on the amount of power each engine is producing at each rpm. It's just simple math. I will give an example of 3 different rpms that I used. Keep in mind the location that these cross in is not important. All that matters is proving the trend to exist.
My diesel/electric engine makes 3000 hp at every wheel rpm. Again don't kill me for accuracy. With a 40" wheel, and assuming the traction motor spins at the exact same rpm as the wheels, which they don't, at 25 mph, the wheel and motor rpm would be 105.12. At 40 mph at 3000 hp, you have 168.18 rpm. At 60 mph and 3000 hp, you have 252.27 rpm. Bear with me. You need to figure out torque at each rpm now. When you plug it in, you get:
25 mph, 149,885.84 ft. lbs
40 mph, 93,685.34 ft. lbs.
60 mph, 62,456.90 ft. lbs.
Again this is just an example that I shortcutted but the trend is still the same.
Now on to the steamer. With it's larger drivers at 25 mph, it's wheels are spinning at 70.07 rpm. Since I assumed that power was linear with rpm, and it's not, this gave me 1250 hp. At 40 mph we get 112.10 rpm at 2000 hp. At 60 mph we get 168.15 rpm and 3000 hp. Same hp at the same train speed. The key was the plug in the numbers and see if the torque at the rails was greater than that of the diesel/electric. If it is, we've proven it.Here's what I got:
25 mph, 93,692.02 ft. lbs.
40 mph, 93,702.05 ft. lbs.
60 mph, 93,702.05 ft. lbs.
The numbers theoretically should stay the same. They were off for me as I rounded. We also know that this is also a perfect world scenario and that not everything works in the real world as it does on paper and would in reality fall off as rpms rise. Again, this was just to prove a point and see if there is a trend at work. We can see that there is. In my example, the diesel/electric has more torque at the rails below 40 mph but the steamer has more torque at the rails above 40 mph. Now I obviously didn't take into account efficiency differences of each engine in relation to rpm but that's fine. I also didn't take into account the gear ratio between the traction motor and the wheels which would also change the results. RPM's on the motor would rise which would mean torque would go down by the same ratio in relation to the assumptions I made. Suddenly instead of the steamer making more torque at the wheels than the diesel at 40 mph, it would do it well under 20 mph.
Weight comes into play now to finalize the results. We can't have traction without weight. We can see now that after you plug in all the numbers the relevant information to figuring out tractive effort is torque generated at the wheels in accordance with the weight on the drive wheels per unit time. This means if you have less torque at the wheels, you'd need more weight to keep traction compared to the other engine that has more torque at the wheels with less weight. Obviously you hit a point where you can't get enough weight to off set the advantage and now the added weight is working against you. The whole point of this was an exercise to prove a trend and it verifies the info in the tables that have already been posted here.
I get it now. Play with some numbers and see what you get. You'll find the same trend everytime and it matches the trend that a steamer will have more tractive effort above a certain point. Basically an engine that has a flatter torque curve will have a more favorable tractive effort as speed increases. An engine with a flatter horsepower curve will have a less favorable tractive effort as speed increases. It's neat how that works. If each locomotive weighed the exact same and had the same peak horsepower as measured at the rails, the diesel would have a higher initial tractive effort and the steamer would pass it at a certain point, which wouldn't take very long, and would surpass it above that speed.
MichaelSol wrote: Bucyrus wrote:[ If you are comparing the actual performance of the two locomotives in the tables, it seems unfair that they are not matched in horsepower, size, or similar indicator.If you compare two gasoline engines and measure the hp of one at 4000 rpm and another at 6000 rpm, you don't really have much of a comparison, and the test would meet no ISO or ASTM standard of testing that I am aware of. Or, the hp of one at 4,000 rpm and the other at some other speed where it finally maxes out on the dynamometer. Are the machines "comparable"? Well, you might as well call it a random test -- you found two machines that perform differently; basically here you want to compare a small steam engine and a large Diesel-electric. Well, why not take a large Steam engine and compare it to a small Diesel-electric then? The little DE might well generate, at 19 mph, the hp of the Steam engine at 4 mph. If you set those as your metrics, you could "prove" that a Diesel-electric was more powerful that a large Steam engine. But that's false, you only prove that it is different under different metrics. It's not a comparison that shows anything useful, but that's what you are doing -- trying to compare machines by scrambling the "comparisons" so that they are not comparable at all.Well, that's the game in cherry picking differing metrics. Somewhere in between, there is a useful measure and that is either locomotives rated similarly at similar speeds, or with similar weight on drivers. "Comparable" machines are selected based on comparable metrics -- but they have to be comparable at some particular point of commonality, because only then can you compare their performance across a range.
Bucyrus wrote:[ If you are comparing the actual performance of the two locomotives in the tables, it seems unfair that they are not matched in horsepower, size, or similar indicator.
If you are comparing the actual performance of the two locomotives in the tables, it seems unfair that they are not matched in horsepower, size, or similar indicator.
If you compare two gasoline engines and measure the hp of one at 4000 rpm and another at 6000 rpm, you don't really have much of a comparison, and the test would meet no ISO or ASTM standard of testing that I am aware of. Or, the hp of one at 4,000 rpm and the other at some other speed where it finally maxes out on the dynamometer. Are the machines "comparable"? Well, you might as well call it a random test -- you found two machines that perform differently; basically here you want to compare a small steam engine and a large Diesel-electric.
Well, why not take a large Steam engine and compare it to a small Diesel-electric then? The little DE might well generate, at 19 mph, the hp of the Steam engine at 4 mph. If you set those as your metrics, you could "prove" that a Diesel-electric was more powerful that a large Steam engine. But that's false, you only prove that it is different under different metrics. It's not a comparison that shows anything useful, but that's what you are doing -- trying to compare machines by scrambling the "comparisons" so that they are not comparable at all.
Well, that's the game in cherry picking differing metrics.
Somewhere in between, there is a useful measure and that is either locomotives rated similarly at similar speeds, or with similar weight on drivers. "Comparable" machines are selected based on comparable metrics -- but they have to be comparable at some particular point of commonality, because only then can you compare their performance across a range.
I think I understand what you are saying about the comparison. At first I was taken aback when you said that I want to compare a small steam engine to a larger diesel-electric. My intent was to compare equal locomotives for a fair comparison, and I assumed that equal horsepower rating would be sound criteria for determining equality between the two locomotives. To me, it seemed that what you were doing is comparing a larger steamer to a small diesel because your steamer has a considerably higher hp rating than your diesel.
But if I understand you now, you contend that a fair comparison would be between a steamer and a diesel of similar or identical weight. And inherent with these two equal weight locomotives, the steamer would have a higher horsepower rating and can produce higher tractive effort than the diesel. I see no problem with that criterion for a fair comparison. I guess that ultimately the decision of which motive power is preferable depends on how much work it does over its life cycle and at what cost.
MichaelSol wrote: Bucyrus wrote: This is the result I would expect to see:1) Both locomotives would be producing their maximum horsepower at their maximum speed. 2) The maximum speed for both locomotives would be the same. 3) The diesel would accelerate the train to its maximum speed in less time than the steamer. And that's the problem. You've defined a set of conclusions you want to reach, and designed a test ensured to reach them. But, the DE reaches its maximum hp at about 19 mph; Steam at around 40-50. The DE generates its greatest power where it can't use it (slip, etc) and where the train doesn't need it. The Steam engine power parallels the resistance increases of the train more "usefully." Nobody would buy a car based on its maximum hp rating; but rather at a standard that represents a useful measure, i.e., where is the train at in terms of speed and weight.The importance of the weight on the drivers, and using that as the standard is well established. Older annual reports reported fleet data exclusively in terms of tractive effort, and purchasing decisions were based on that. HP offers a surrogate that most -- most -- people understand more intuitively, but it is an imperfect surrogate. There is "a" correlation between weight on drivers and TE, but because these motive power types produce power so differently, it is likewise imperfect and, because the power curves themselves are not linear, but in fact, curves -- and since the hp curves are different for Steam and Diesel-electric, your approach simply chooses two end points and assumes therefore a straight line between them. That generates misinformation, not useful information, aside from the fact that the endpoints you choose -- maxiumum hp -- are located at very different points on the scale even as you "define" them to be identical for the purpose of reaching a specific conclusion.From a tractive effort standpoint, a view similar to the hp chart earlier, shows key differences for these types throughout their operating range. The column on the right is the resistance of the train at different speeds. The TE ratings of the motive power types must exceed the resistance of the train and where the TE rating does not exceed the train resistance, that represents the speed limit of the train. MPH Diesel Steam Resistance0100,00060,000 560,00059,00014,8251042,00058,00017,9391532,00056,00019,9242028,00052,00022,1942522,00048,00024,7493019,00040,00027,5883516,00033,00030,7134014,00029,00034,1234511,00024,00037,818509,00022,00041,798558,00020,00046,062607,00019,50050,612656,50018,75055,447706,00018,00060,567At 50 mph, the train would need the equivalent of five Diesel-electric units to move at the speed, but only two reciprocating Steam engines. And this is where the capitalization of the Diesel-electric weighs heavily on railroads seeking operating efficiencies by operating at higher speeds. To operate at 50 mph, the train needs five equivalent Diesel-electric units with a combined TE of 300,000 lbs. But at 5 mph, the train has therefore 300,000 lbs of TE to move 15,000 lbs of resistance! That is extremely expensive tractive effort. Maybe it looks good to you on paper, but to me it says that this is a power type that generates its power on the wrong parts of the power curve and that represents an expensive misapplication, waste, of power and capital.A Diesel-electric that can substantially outpull a Steam engine at 1 mph loses its TE advantage pretty quickly, and by 30 mph can pull only half the train that the Steam engine is pulling. And yet the Steam engine had plenty of TE to start that train; it simply has substantially greater capacity to run that train at the higher speeds. Practically speaking, if the Railroad wants to run that train at 30 mph, it can only assign half the tonnage to the Diesel-electric that it can assign to the Steam engine. The higher TE of the Diesel-electric available at very low speeds is useless, meaningless, from that standpoint because that's not where it needs the TE. It's an utter waste of a perfectly useless statistic. And at that 30 mph speed, the Steam engine will still have slightly greater TE available per pound of train resistance, notwithstanding that it is hauling twice the tonnage.And so what is it that the Steam engine missing there? They can both start their trains just fine. The train is at its lowest overall resistance at the low speeds. High available Tractive Effort at those speeds is a meaningless statistic because that's not the range in which the train is going to develop its need for high Tractive Effort. It's the Diesel-electric that fails to carry its burden at the higher speeds, not the reciprocating Steam engine. And that is a fundamentally different characteristic of the motive power types.In this instance, even if these TE curves are adjusted in the fashion you desire -- maximum hp reached by each motive power type -- the adjustment still presumes, even by the standards of steam locomotives extant 60 years ago, a relatively small steam locomotive even by comparison with the average hp Diesel-electric road locomotive today.Is there a point in comparing a relatively large Diesel-electric locomotive with a relatively small reciprocating Steam engine? Yes, it is the only way to get the results you want because, ironically, the Steam engine at the identical "maximum" hp as the Diesel-electric has a substantially lighter footprint than the Diesel-electric at that horsepower, which limits its tractive effort to that of the Diesel-electric. But, that offers the "unfair" advantage to the Diesel-electric by limiting the Steam engine to the Diesel-electric's inherent limitations, by carefully setting the "maximum" hp at completely different points: 19 mph for the Diesel, 50 for the Steam, and calling them "equal" which yield's Steam's advantages of substantially higher hp, single units with greater TE per pound of locomotive on the driving wheels. In other words, your test is carefully calibrated to produce exactly the results you want, by eliminating all of the advantages of Steam power, and testing only on the advantages of the Diesel-electric. While that may be satisfying, it will not translate accurately nor usefully into meaningful economic data, and will in fact give false and misleading results. Testing both motive power types against genuinely common metrics yields completely different results. What that illuminates is that the reciprocating Steam engine, pound for pound on the driving wheels, delivers more power than the equivalent hp Diesel-electric. That is why, when the weight on the driving wheels is comparable, the Steam engine can generate a substantially greater hp and TE -- it is more efficient at producing power at the speeds where the power is needed and through the means that the power is applied: through the driving wheels at the rail.And of course, this underscores the point of the thread -- no matter how you slice and dice the data, the capital cost of reciprocating Steam likely remains substantially lower than equivalent Diesel-electric hp, and the operating costs of the Diesel-electric are now so high that it represents, by a substantial margin, the most expensive operating alternative for railroad motive power.
Bucyrus wrote: This is the result I would expect to see:1) Both locomotives would be producing their maximum horsepower at their maximum speed. 2) The maximum speed for both locomotives would be the same. 3) The diesel would accelerate the train to its maximum speed in less time than the steamer.
This is the result I would expect to see:
1) Both locomotives would be producing their maximum horsepower at their maximum speed.
2) The maximum speed for both locomotives would be the same.
3) The diesel would accelerate the train to its maximum speed in less time than the steamer.
And that's the problem. You've defined a set of conclusions you want to reach, and designed a test ensured to reach them. But, the DE reaches its maximum hp at about 19 mph; Steam at around 40-50. The DE generates its greatest power where it can't use it (slip, etc) and where the train doesn't need it. The Steam engine power parallels the resistance increases of the train more "usefully." Nobody would buy a car based on its maximum hp rating; but rather at a standard that represents a useful measure, i.e., where is the train at in terms of speed and weight.
The importance of the weight on the drivers, and using that as the standard is well established. Older annual reports reported fleet data exclusively in terms of tractive effort, and purchasing decisions were based on that. HP offers a surrogate that most -- most -- people understand more intuitively, but it is an imperfect surrogate. There is "a" correlation between weight on drivers and TE, but because these motive power types produce power so differently, it is likewise imperfect and, because the power curves themselves are not linear, but in fact, curves -- and since the hp curves are different for Steam and Diesel-electric, your approach simply chooses two end points and assumes therefore a straight line between them. That generates misinformation, not useful information, aside from the fact that the endpoints you choose -- maxiumum hp -- are located at very different points on the scale even as you "define" them to be identical for the purpose of reaching a specific conclusion.
From a tractive effort standpoint, a view similar to the hp chart earlier, shows key differences for these types throughout their operating range. The column on the right is the resistance of the train at different speeds. The TE ratings of the motive power types must exceed the resistance of the train and where the TE rating does not exceed the train resistance, that represents the speed limit of the train.
At 50 mph, the train would need the equivalent of five Diesel-electric units to move at the speed, but only two reciprocating Steam engines. And this is where the capitalization of the Diesel-electric weighs heavily on railroads seeking operating efficiencies by operating at higher speeds. To operate at 50 mph, the train needs five equivalent Diesel-electric units with a combined TE of 300,000 lbs. But at 5 mph, the train has therefore 300,000 lbs of TE to move 15,000 lbs of resistance! That is extremely expensive tractive effort. Maybe it looks good to you on paper, but to me it says that this is a power type that generates its power on the wrong parts of the power curve and that represents an expensive misapplication, waste, of power and capital.
A Diesel-electric that can substantially outpull a Steam engine at 1 mph loses its TE advantage pretty quickly, and by 30 mph can pull only half the train that the Steam engine is pulling. And yet the Steam engine had plenty of TE to start that train; it simply has substantially greater capacity to run that train at the higher speeds. Practically speaking, if the Railroad wants to run that train at 30 mph, it can only assign half the tonnage to the Diesel-electric that it can assign to the Steam engine. The higher TE of the Diesel-electric available at very low speeds is useless, meaningless, from that standpoint because that's not where it needs the TE. It's an utter waste of a perfectly useless statistic. And at that 30 mph speed, the Steam engine will still have slightly greater TE available per pound of train resistance, notwithstanding that it is hauling twice the tonnage.
And so what is it that the Steam engine missing there? They can both start their trains just fine. The train is at its lowest overall resistance at the low speeds. High available Tractive Effort at those speeds is a meaningless statistic because that's not the range in which the train is going to develop its need for high Tractive Effort. It's the Diesel-electric that fails to carry its burden at the higher speeds, not the reciprocating Steam engine. And that is a fundamentally different characteristic of the motive power types.
In this instance, even if these TE curves are adjusted in the fashion you desire -- maximum hp reached by each motive power type -- the adjustment still presumes, even by the standards of steam locomotives extant 60 years ago, a relatively small steam locomotive even by comparison with the average hp Diesel-electric road locomotive today.
Is there a point in comparing a relatively large Diesel-electric locomotive with a relatively small reciprocating Steam engine? Yes, it is the only way to get the results you want because, ironically, the Steam engine at the identical "maximum" hp as the Diesel-electric has a substantially lighter footprint than the Diesel-electric at that horsepower, which limits its tractive effort to that of the Diesel-electric. But, that offers the "unfair" advantage to the Diesel-electric by limiting the Steam engine to the Diesel-electric's inherent limitations, by carefully setting the "maximum" hp at completely different points: 19 mph for the Diesel, 50 for the Steam, and calling them "equal" which yield's Steam's advantages of substantially higher hp, single units with greater TE per pound of locomotive on the driving wheels.
In other words, your test is carefully calibrated to produce exactly the results you want, by eliminating all of the advantages of Steam power, and testing only on the advantages of the Diesel-electric. While that may be satisfying, it will not translate accurately nor usefully into meaningful economic data, and will in fact give false and misleading results. Testing both motive power types against genuinely common metrics yields completely different results.
What that illuminates is that the reciprocating Steam engine, pound for pound on the driving wheels, delivers more power than the equivalent hp Diesel-electric. That is why, when the weight on the driving wheels is comparable, the Steam engine can generate a substantially greater hp and TE -- it is more efficient at producing power at the speeds where the power is needed and through the means that the power is applied: through the driving wheels at the rail.
And of course, this underscores the point of the thread -- no matter how you slice and dice the data, the capital cost of reciprocating Steam likely remains substantially lower than equivalent Diesel-electric hp, and the operating costs of the Diesel-electric are now so high that it represents, by a substantial margin, the most expensive operating alternative for railroad motive power.
To reinforce what has been stated here, please go back to the previous page and look at the performance of the 48 Ton steam locomotive that I listed some of the stats for. Any serious consideration of this little engine shows the stark difference in the performance characteristics of the two types of power.
How can a 48 ton steam locomotive pull 2000 tons at 50 MPH? It has the capacity of a standard gauge diesel that weighs more than 4 times more than it which has the supposed advantage of all of its weight on the drivers.
The diesel or set of diesels that have the same ability will certainly cost a lot more to produce the same results than the $2 per horsepower per hour that the narrow gauge steam power costs to produce this output.
Bucyrus wrote: So, setting aside the high TE of the diesel at very low speed, the two locomotives develop similar shaped TE curves. The steamer shows a higher TE overall, but we are not comparing these actual amounts because there is no stipulation that the two locomotives are identical in power, size, or capability.
So, setting aside the high TE of the diesel at very low speed, the two locomotives develop similar shaped TE curves. The steamer shows a higher TE overall, but we are not comparing these actual amounts because there is no stipulation that the two locomotives are identical in power, size, or capability.
One of the key facts, and it is absolutely the key, is that the reciprocating Steam locomotive could, in fact, develop vastly greater horsepower and Tractive Effort in a single unit. That is part of the explanation for the significantly lower cost per horsepower, and is part of the explanation for the lower maintenance costs.
That is, in a machine of similar size and lower cost, you were in fact, getting a locomotive that WAS NOT identical in power or capability -- AND THAT'S THE WHOLE POINT! -- but rather you were getting a machine significantly more powerful and with much greater capability in delivering power to a train at speeds where the train needed more power -- higher speeds.
For the one single metric which is, in fact, comparable -- weight on the drivers -- with identical weight the Steam engine far outperforms the Diesel-electric. Indeed, that is the only metric that remains constant throughout the operating range, and is the single metric that does, in fact, offer a comprehensive comparability throughout that range.
It is true if you take away the advantages specific to Steam -- its high horsepower, high TE output -- and force it to resemble a Diesel-electric, it will in fact resemble a Diesel-electric. But, if you reverse the exercise, and try and force the Diesel-electric to resemble the high performance characteristics of the Steam engine, it doesn't happen because the Diesel-electric can't do it. It maxes out at 19 mph on hp, with a more rapidly declining TE capability throughout. A Steam engine delivering that same hp at 19 mph has plenty of hp left to develop and plenty more TE to deliver to the train.
And yet, you are taking the Diesel-electric's max hp -- at 19 mph, and comparing it with Steam's at 50 mph. To do that, the Steam engine has to put considerably less weight on the drivers than the Diesel-electric -- all in order to force the Steam engine to "look like" the Diesel-electric, from which you then conclude that it looks like a Diesel-electric.
But if you are serious, then you compare a Steam engine and a Diesel-electric using similar metrics -- identical horsepower at the same speed metric and at the same weight on drivers metric -- because that's what "comparisons" mean -- not cherry picked metrics that are all over the place and different for each given machine.
When you do that, at 19 mph and with the same weight on the drivers and you do in fact compare a 4,000 hp output of each at that speed, you will find that the Steam engine outperforms that Diesel-electric at higher speeds, provides more TE, has a higher range of operation than the D-E, and yet offers no disadvantage at low speed operations because the hp and TE requirements of the train remain substantially lower than the capabilities of the locomotive.
Their use of the word continuous would seem to imply everywhere. It's interesting that it's only at a paltry 13.7 mph.
Using car analogies is something I definitely understand as I've written many technical articles on engine design and power.
fredswain wrote: I was just browsing GE's website and looking at the specs for the Evolution series engines. They mention starting tractive effort but also continuous tractive effort and give a number for each. If tractive effort decreases with speed, how can they state a continuous number?They also have a chart that shows a % of adhesion. How does this relate to tractive effort and horsepower?
I was just browsing GE's website and looking at the specs for the Evolution series engines. They mention starting tractive effort but also continuous tractive effort and give a number for each. If tractive effort decreases with speed, how can they state a continuous number?
They also have a chart that shows a % of adhesion. How does this relate to tractive effort and horsepower?
Your car engine is given a rating -- a specific horsepower at a specific number of rpms under ideal conditions.
Is that the hp your car will actually generate backing out of your driveway? Is that the horsepower that you will use when you are in passing gear going around a long truck? No, it is simply a "rating" designed to offer a comparative metric to other engines in similar applications at the same rpm. It doesn't even suggest, nor is it designed to suggest, that the engines being compared will have similar horsepower at different rpms. Indeed, it is unlikely that your engine actually puts out that "rated" hp at that rpm because it is a "lab" measure on a dynamometer which itself is somewhat artificial.
At best, it is simply "a" rating from which the analysis does not end, but rather, begins.
"Continous tractive effort" generally has a specific speed assigned to it, 13.7 mph in this case, which means it is "continuous" -- only at that speed.
I am somewhat bemused that people want to take superficial ratings and make very strong conclusions about them across the board without acknowledging that not only is that a fool's errand even with something as straightforward as comparing light duty gasoline engines, but useless when comparing entirely different technologies without a careful examination of the relevant power curves across the expected range of operations.
It was not my intention to design a test that will show the conclusions I want to reach. I do not advocate one type of motive power over the other, but rather, I am only interested in the comparison as it relates to the question that titles this thread. And I see that question as being primarily related to the quickly shifting economics of fuel. So I am not trying to reach any conclusion. I have no preference or stake in the matter whatsoever.
My only objective in proposing the test that I did was to provide what seemed to me to be the fairest apples-to-apples comparison. My prediction of the results is not a wish for those results. It is only to test my understanding of the comparison by stating what I expect before the test is performed.
It seems to me that the test I proposed is basically the same as the comparison that you have offered in the combination of the above table showing tractive effort and your earlier one showing horsepower. However my test includes the stipulation that both locomotives are rated at the same horsepower. I know that horsepower is not the whole story of performance, but it seems like the most comprehensive characteristic for a fair comparison. I keep thinking that a fair test must pit locomotives of identical power ratings, or some fair measure of capability, but maybe that is not the case for the point you are making. If you are only trying to show the shape of the TE curve during acceleration of steam compared to diesel, the power or size of the two locomotives need not match.
But still, both locomotives exhibit a similar rate of TE fall-off as speed increases. The only difference is that the diesel TE falls off faster and is higher in the beginning. As you point out, the diesel's high TE at the beginning is not useful, but is it really a penalty? It seems to me that it is a consequence of the electric transmission that may or may not be useful, but is not a penalty assuming that the transmission is a necessary attribute for overall performance.
So, setting aside the high TE of the diesel at very low speed, the two locomotives develop similar shaped TE curves. The steamer shows a higher TE overall, but we are not comparing these actual amounts because there is no stipulation that the two locomotives are identical in power, size, or capability. Indeed, the steamer, according to your first table of horsepower is considerably more powerful than the diesel, so I would expect it to produce higher TE where it is indicated by the second table.
So I am still a bit confused by your conclusions from the tables, and my confusion boils down to this:
If you are not comparing the actual performance of the two locomotives in the tables, I don't see how you can draw any conclusions about which one provided more tractive effort at any given speed.
In re-reading all that you have said about this issue, it seems that you are indeed comparing the actual performance of the two locomotives and concluding that the steamer's TE performance is superior to a comparable diesel even though the steamer has at least 2800 more horsepower than the diesel going into the comparison test.
So it seems that the biggest issue is that on a power for power basis (all else being equal), the diesel locomotives biggest disadvantage compared to a steam engine is although it has plenty of power, it can't get it to the ground nearly as efficiently. Power means nothing without traction and traction means nothing without power. Power and traction are meaningless if you don't have the load behind you putting enough resistance to justify using it all. It's like using a body builder to open a coke can as opposed to a child. Both can do it so all the extra power there isn't necessary.
It would seem the diesel engine's biggest advantage over a steam engine is as a slow speed yard slug.
fredswain wrote: The steam engine would seem to have the advantage after the train gets moving whereas the diesel would seem to only have the advantage of initially getting the train moving. Tractive effort again comes into play which effects this.
The steam engine would seem to have the advantage after the train gets moving whereas the diesel would seem to only have the advantage of initially getting the train moving. Tractive effort again comes into play which effects this.
Having ten times more TE than you need at 1 mph still doesn't mean you need it, or can use it.
Having half the TE that you need at 30 mph, however, means that you don't go 30 mph because that's where you do need it, and can use it, but it's not there.
Here's what I am gathering from all of this. Please forgive me for any ignorance that I may type after this point. This is all interesting and something I have never thought about before. I am going to assume a few things too so please correct me if I'm wrong.
I assume that the horsepower rating of a diesel engine is based on it's generator and not what actually gets to the wheels. An electric motor is a pretty efficient device but as with anything has areas of higher efficiency and lower efficiency. Let's say it's 90% efficient max. That would mean a 4000 hp generator would only be able to theoretically put 3600 hp to the ground. I would also assume that as rpm's rise, efficiency goes down on an electric motor somewhat due to a number of things such as added heat, etc. Because of this it would seem logical that it's max available power would be at the lowest speeds. However it doesn't have the adhesion to the rail to take advantage of all this power. An electric motor's horsepower curve theoretically on paper is flat with rpm. Efficiency differences change this. From what I gather, by the time you get moving at a speed that allows you to go to full throttle without spinning your wheels, you are no longer at your max rated horsepower are in fact much lower. Let's say your motor lost 5% efficiency by full speed. This would mean you'd be at 3400 hp or so at the rails. Is this correct? Then it would seem to make matters worse your tractive effort on a diesel at speed is significantly lower than at lower rpms. It seems diesels run into some interesting problems. Where they make the most power, they can't use it all as they'll just spin the wheels. Where they can use their highest power setting, they are now down on peak power but more importantly at a very low tractive effort in addition to this. Is this correct?
How is horsepower measured on a steam engine? Is it at the wheels? It can't be in the boiler! Is it figured out in theory based on known working boilder pressure in relation to the cylinder bore and stroke? With a steam engine, in theory instead of your horsepower curve theoretically being flat with rpm as an electric engine's theoretically is, your torque instead is theoretically flat with rpm which means horsepower rises as rpms rise. Again, efficiency changes the rules a bit. Is this correct? If so this would mean that a steam engine's max power is available at high speeds where it can be used. They don't develop as much initial power for starting but since you can't put much down to the ground, this doesn't matter anyways. They seem to still be able to provide enough power to spin the wheels so it seems they have enough power. Since power would appear to be rated basically at the wheel, this would make a much smaller rated power steam engine equal to a larger rated power diesel.
If my above assumptions are correct this would mean that the same "rated" horsepower engines, 1 steam and 1 diesel, wouldn't be the same when put into actual practice. They 'd be quite different and not consistent with what the numbers imply. The steam engine would seem to have the advantage after the train gets moving since this is where it develops the most power and since it still has good tractive effort to utilize the power whereas the diesel would seem to only have the advantage of initially getting the train moving as it's max tractive effort is right off of a standstill. I hope I'm getting this right.
Is this all correct? What am I missing? I might still be a bit confused. This is fascinating to me.
http://www.cf.missouri.edu/energy/em_renewable/tdf.html
Dave
Lackawanna Route of the Phoebe Snow
Phoebe Vet wrote: Guys:I have been casually watching this seemingly endless argument (it ceased being a debate 200 posts ago) and have a couple of questions for either team, but probably more for the coal team.I am not a mechanical engineer, or a railroader, so I do not understand "draw bar horse power" or "tractive effort".A steam engine makes it's power by varying the speed of the pistons. A diesel makes it's power by varying the RPM. Since the prime mover is just driving a generator, it can move into it's best power range early in it's speed range. It can therefore make it's maximum power throughout the entire speed chart. I don't understand why that is a disadvantage.Now to address the original question: "Could steam make a comeback?" If steam was better, SOMEBODY would still be using it, so my guess is no.If it is really coal, not steam, that you are trying to push, I would think that it would make more sense to recommend electrification, and coal fired power stations. Many advances have been made in coal generated electricity, including mixing coal with shredded tires which makes it burn hotter and solves the tire disposal problem. Win/Win. The technology used to make coal burn cleaner is easier to do on a large scale than it would be at the locomotive level.Just a thought.
Guys:
I have been casually watching this seemingly endless argument (it ceased being a debate 200 posts ago) and have a couple of questions for either team, but probably more for the coal team.
I am not a mechanical engineer, or a railroader, so I do not understand "draw bar horse power" or "tractive effort".
A steam engine makes it's power by varying the speed of the pistons. A diesel makes it's power by varying the RPM. Since the prime mover is just driving a generator, it can move into it's best power range early in it's speed range. It can therefore make it's maximum power throughout the entire speed chart. I don't understand why that is a disadvantage.
Now to address the original question: "Could steam make a comeback?" If steam was better, SOMEBODY would still be using it, so my guess is no.
If it is really coal, not steam, that you are trying to push, I would think that it would make more sense to recommend electrification, and coal fired power stations. Many advances have been made in coal generated electricity, including mixing coal with shredded tires which makes it burn hotter and solves the tire disposal problem. Win/Win. The technology used to make coal burn cleaner is easier to do on a large scale than it would be at the locomotive level.
Just a thought.
Chuck
I would need to see a graph that compares a diesel and conventional steam locomotive of the same maximum horsepower rating, pulling the same train on the same level and straight track. Each locomotive would accelerate the train to the balance speed (max. speed at full throttle). During the acceleration, the horsepower and tractive effort produced would be recorded along with the rate of acceleration. Maybe the comparison would be conducted several times with a heavier or lighter train to yield a range of balance speeds, but in each case, the comparison would be apples-to-apples.
MichaelSol wrote: AnthonyV wrote: I am not saying that the weight on drivers is irrelevant to locomotive performance. What I am saying is that comparing steam and Diesel on the basis of equal weight on drivers is irrelevant. Steam locomotives only had a fraction of their total weight on drivers while Diesels had all their(with some exceptions) on drivers. Using equivalent weight on drivers as a basis for comparison artificially penalizes the Diesel.Anthony V. This is a gem. The weight on the drivers is the weight on the drivers. That's how the power gets to the rail. Ninety per cent of the train is weight "not on the drivers" and doesn't "penalize" the Diesel-electric any more or less than the fact penalizes a Steam engine.
AnthonyV wrote: I am not saying that the weight on drivers is irrelevant to locomotive performance. What I am saying is that comparing steam and Diesel on the basis of equal weight on drivers is irrelevant. Steam locomotives only had a fraction of their total weight on drivers while Diesels had all their(with some exceptions) on drivers. Using equivalent weight on drivers as a basis for comparison artificially penalizes the Diesel.Anthony V.
I am not saying that the weight on drivers is irrelevant to locomotive performance. What I am saying is that comparing steam and Diesel on the basis of equal weight on drivers is irrelevant. Steam locomotives only had a fraction of their total weight on drivers while Diesels had all their(with some exceptions) on drivers. Using equivalent weight on drivers as a basis for comparison artificially penalizes the Diesel.
Anthony V.
This is a gem. The weight on the drivers is the weight on the drivers. That's how the power gets to the rail. Ninety per cent of the train is weight "not on the drivers" and doesn't "penalize" the Diesel-electric any more or less than the fact penalizes a Steam engine.
ah but with a steam engine 90% of that weight is not on the drivers it's on the wheels the drivers are simply there to connect the wheels to gether and connect them to the piston in the cylinder. It's up to the cylinder and piston to move the locomotive not support it
I may just be a freshamn in High School, but I know a thing or two about running a steam loco.
For one: Yes it is hard work in a hot and dirty enviornment, but if you love doing that kind of work then that's not an issue. The labor involved is not for the faint of heart and if you have been a fireman on a real steam loco like I have then you would know what if would be like for the people who would be opperating the engines.
The problems that I see with using steam locomotives would be their range (how far they can go on a full load of fuel) and the always present danger of a boiler explosion. Eniornmentalists would probably have a fit about the steam engines but they drive hummers, SUVs, ect just like the rest of us.
We have the technology to build them, fine examples of the finished product, all the fuel for them can be found here in the states, the only thing we are missing is the will to do so. Not to menchion that coal is not the only thing that steam engines can run off of.
A steam engine cam be run off of anything that can be burned.
Not to menchion the fan fair supporting a live steam loco. In all I think that now steam engiens arn't going to see any main line service or even branch line service anytime soon, but there is always the posibility. If steam locos do make a come back then I die a happy man, if not then I kepp volinteering to see live steam in action.
GP40-2,
What NS data re: 611 are you referring to? I don't doubt the figures because 611 was never challenged very much in excursion service, but where did you find this information? I'd like to get a copy of these figures. I'll be in Roanoke next week so if I know what to look for and/or when it was written, that would help.
jmlaboda wrote: AnthonyV wrote: Steam locomotives only had a fraction of their total weight on drivers while Diesels had all their(with some exceptions) on drivers. Using equivalent weight on drivers as a basis for comparison artificially penalizes the Diesel.Its a tractive effort thing... since diesel-electrics these days have all their weight on their drivers, be they 4- or 6-axle it seems to me that it would penalize steam more than diesel, since not all the combined weight is ever applied to a steamer, except it be a steam storage or tank locomotive.
AnthonyV wrote: Steam locomotives only had a fraction of their total weight on drivers while Diesels had all their(with some exceptions) on drivers. Using equivalent weight on drivers as a basis for comparison artificially penalizes the Diesel.
Its a tractive effort thing... since diesel-electrics these days have all their weight on their drivers, be they 4- or 6-axle it seems to me that it would penalize steam more than diesel, since not all the combined weight is ever applied to a steamer, except it be a steam storage or tank locomotive.
Here's where experience can verify or disprove theory. I run locomotives everyday-it's in my job description.
A diesel locomotive is a constant horsepower machine at a wide range of speeds in theory, on paper and in sales brochures, not in practice. Why is that?
The weight on the drivers has a direct correlation to how much any locomotive can use it's potiential horsepower. If the locomotive produces more horspower than the factor of adhesion can take, it will slip helplessly.
Diesels can not produce their full horsepower until they are in notch 8. If today when I climb in the cab and start the train with the throttle pulled out to notch 8 the engine will sit there and spin until it burns through the rail down to the road bed or burns out its poor little traction motors.
Tractive effort is what allows the engine to take advantage of its available horsepower at any given speed. If you ever looked at the tractive effort curves of a diesel, I don't care what kind it is or how old it is. The available tractive effort falls like a rock after about 4 miles an hour. I believe there have been several graphs on this thread expressing this fact.
The tractive effort of a steam locomotive increases as the speed increases, along with its horsepower curve until it is limited by the boiler's ability to make steam or the valves and pistons reach their capacity to use steam or the engine tears itself apart.
The above characteristic of a steam locomotive allows it to take advantage of its horsepower potential at greater speeds than the diesel.
I will tell you a story about a particular trip I made with the 4501 when I was working with the Southern Steam Program.
We had a trip scheduled with the 4501, a diesel helper and 25 coaches, most were heavyweight steel cars. On this run the 4501 was normally limited to 17 cars due to the grades along the way. That day we had 25 so we had the diesel helper along. On the return trip the diesel broke down on one of the grades and we had no choice but to pull everything plus the dead diesel back to to our destination. We were originally scheduled to wait in several places along the way for hotshot freights, but as the extra engine was dead this was more tonnage than the 4501 (a light weight mikado built in 1911) could start on an ascending grade, so after much radio communication and order changes we were allowed to occupy the main line all the way back.
That mikado pulled the 25 cars and the dead diesel over those grades at 30 MPH and on the level parts of the route was easily able to maintain the current track speed of 55 MPH. We got back on time without any problems. If this had been another diesel of equivalent weight on the drivers (I think a GP 38 is closest in comparison) we would have never made it back at all.
AnthonyV wrote:I'm not making anything up. Each locomotive type can be characterized by its nominal horsepower rating. The Big Boy can be characterized as a 6000 hp machine even though this occurs over a very small portion of its operating range. Diesels rated 6000 dbhp (either single or in multiples) produce this power over almost their entire operating range except at low speeds, a subject that has been discussed previously.Therefore, steam locomotive performance can equal the Diesel's only at a single point for equivalent nominal horsepower.
I'm not making anything up. Each locomotive type can be characterized by its nominal horsepower rating. The Big Boy can be characterized as a 6000 hp machine even though this occurs over a very small portion of its operating range. Diesels rated 6000 dbhp (either single or in multiples) produce this power over almost their entire operating range except at low speeds, a subject that has been discussed previously.
Therefore, steam locomotive performance can equal the Diesel's only at a single point for equivalent nominal horsepower.
The 6000hp (prime mover HP, not dbhp) diesels with AC transmissions will produce that power over most of the operating speeds, but earlier generations of diesels may not be capable of producing constant power over the operating range. One big difference is that the alternator in the AC transmission pretty much runs at a constant voltage output, where the alternator or generator in the DC transmission the terminal voltage varies inversely with the output current (Lemp control).
Since I don't have a voltage vs current plots (VI curves) for any traction generator or alternator, I'll be making an educated guess on what's going on. The goal for an ideal Lemp control is to produce a voltage that is exactly inversely proportional to the current (i.e. constant power) for a given prime mover speed. The reality is that the voltage isn't exactly inversely proportional to current and in the low current limit, the terminal voltage may end up being substantially less than the ideal case (a likely cause would be saturation of the field steel (i.e. the frame on a generator or rotor on an alternator). The upshot is that the locomotive power will drop off at high track speeds (and I haven't brought up the issue of the maximum voltage rating for a generator).
Bucyrus wrote: MichaelSol wrote: Bucyrus wrote: I think the relevance of weight on drivers in this thread depends on its relevance to what we are discussing at any particular point. Certainly it is relevant to locomotive performance in general. So is the number of drivers, maximum horsepower available, and transmission ability to vary torque versus RPM. However, in these last couple pages, I thought we were comparing how steam compares to diesel in terms of developing horsepower at various speeds. I don't see what the weight on drivers has to do with that. The horsepower requirements are developed from tractive effort, which is, in fact, directly related to the weight on the drivers. Ultimately, it has everything to do with performing the calculations regarding horsepower, which is why I "marked" the earlier comment that thinks the whole idea of "weight on the drivers" is "just made up" or 'irrelevant". The forumula is: HP=TE*Speed/375I understand what you are saying and how tractive effort relates to horsepower and speed. But what I have been focusing on is your table about horsepower. I don't see that the table indicates any relationships about tractive effort even though tractive effort has a relationship to horsepower in locomotive performance.
MichaelSol wrote: Bucyrus wrote: I think the relevance of weight on drivers in this thread depends on its relevance to what we are discussing at any particular point. Certainly it is relevant to locomotive performance in general. So is the number of drivers, maximum horsepower available, and transmission ability to vary torque versus RPM. However, in these last couple pages, I thought we were comparing how steam compares to diesel in terms of developing horsepower at various speeds. I don't see what the weight on drivers has to do with that. The horsepower requirements are developed from tractive effort, which is, in fact, directly related to the weight on the drivers. Ultimately, it has everything to do with performing the calculations regarding horsepower, which is why I "marked" the earlier comment that thinks the whole idea of "weight on the drivers" is "just made up" or 'irrelevant". The forumula is: HP=TE*Speed/375
Bucyrus wrote: I think the relevance of weight on drivers in this thread depends on its relevance to what we are discussing at any particular point. Certainly it is relevant to locomotive performance in general. So is the number of drivers, maximum horsepower available, and transmission ability to vary torque versus RPM. However, in these last couple pages, I thought we were comparing how steam compares to diesel in terms of developing horsepower at various speeds. I don't see what the weight on drivers has to do with that.
I think the relevance of weight on drivers in this thread depends on its relevance to what we are discussing at any particular point. Certainly it is relevant to locomotive performance in general. So is the number of drivers, maximum horsepower available, and transmission ability to vary torque versus RPM. However, in these last couple pages, I thought we were comparing how steam compares to diesel in terms of developing horsepower at various speeds. I don't see what the weight on drivers has to do with that.
The horsepower requirements are developed from tractive effort, which is, in fact, directly related to the weight on the drivers. Ultimately, it has everything to do with performing the calculations regarding horsepower, which is why I "marked" the earlier comment that thinks the whole idea of "weight on the drivers" is "just made up" or 'irrelevant".
The forumula is: HP=TE*Speed/375
I understand what you are saying and how tractive effort relates to horsepower and speed. But what I have been focusing on is your table about horsepower. I don't see that the table indicates any relationships about tractive effort even though tractive effort has a relationship to horsepower in locomotive performance.
The Diesel-electric and Steam outputs were generated from published HP tables. The "HP necessary" -- the far right hand column --was generated directly from a TE table, using the equation to generate equivalent horsepower for the simple expedient that the conversation was about Steam's ability to generate horsepower at higher speeds and horsepower and speed seems to offer a more intuitive presentation regarding what the motive power types confront as they attempt to increase the speed of the train.
A similar table showing only TE would show both motive power types declining in TE; the Diesel-electric declining in output more rapidly than a Steam engine of the same weight on the drivers, and generally with considerably greater TE output at the higher speed, which is consistent with the higher HP output of the Steam engine at the higher speed.
selector wrote: Okay, fellas, I'm just trying to make sense of this, and please don't take my statements as implying that I am absolute in my understanding. I suppose my next approach to making sense of all this for Crandell's sake is the following series of questions: is a comparable diesel doing 20 mph while generating 6000 hp (do they?) going to have the tractive effort to apply to a given tonnage hauled that an H-8 would be capable of doing at 20 mph? Maybe my terms are muddled. Should I be asking about adhesion and not tractive effort? Is adhesion good enough in either case that we need only deal with tractive effort? Will three SD-40's pulling 10,000 tons apply more of their effort to the rails than a single H-8 would at speeds between 5 and 50 mph? What does Michael's chart suggest and how would any of you counter it with theory expressed in a credible source?Be gentle. I bruise easily.
Okay, fellas, I'm just trying to make sense of this, and please don't take my statements as implying that I am absolute in my understanding. I suppose my next approach to making sense of all this for Crandell's sake is the following series of questions: is a comparable diesel doing 20 mph while generating 6000 hp (do they?) going to have the tractive effort to apply to a given tonnage hauled that an H-8 would be capable of doing at 20 mph? Maybe my terms are muddled. Should I be asking about adhesion and not tractive effort? Is adhesion good enough in either case that we need only deal with tractive effort? Will three SD-40's pulling 10,000 tons apply more of their effort to the rails than a single H-8 would at speeds between 5 and 50 mph? What does Michael's chart suggest and how would any of you counter it with theory expressed in a credible source?
Be gentle. I bruise easily.
I would explain it this way: Tractive effort depends on adhesion, which in turn depends on weight on drivers, number of drivers, and the condition of the rails. Tractive effort also depends on the ability of the locomotive to produce force (in the form of torque) at the drive wheels. Turning the wheels against the load by the application of torque is called work. Work performed per unit of time is called horsepower. Moving the train is the work. The faster you move it, the more work you accomplish in a given time. Theoretically a windup clock could develop enough torque to pull a 10,000 ton train, but just not very fast. I say theoretically because, from a practical standpoint, there would be so much friction in the massive speed reduction that the clock would not be able to overcome it.
selector wrote:How can it be irrelevant when it is so highly contributory to the over tractive effort? And how do you account for the disparity in absolute performance characteristics at any given speed, except for where they cross? One's a horse and the other's a mule. Both good at what they do. But the steam engine, even now, gets the hearty nod because it is so cheap to run by comparison. One crew riding 6000 hp can do what two or three MU'd units do now with one crew. Cleaner, cheaper to run, even though the crewing is identical.
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