This is true, the ear-tuning, Lois, although a recent edition of Classic Trains had an article about the Valve Pilot used on the NYC's Hudsons, for one example, that taught everyone who ran and designed steam locomotives how the locomotive could be made even more efficient that an experienced hogger could make it using his ear.
-Crandell
In answering your very specific question, Paul, I think you stated the answers yourself, your guesses are correct. Which is the major heat loss, I suspect Juniatha would have a more exact answer.
Incidentally, from my own observation of conversations with engineers who had steam experience, each locomotive was slightly different, even with the same class, and a good engineer would get the feel of the right combination of throttle position and Johnson Bar posiiton to make the schedule or make up time and still conserve fuel and water, for the different conditions of track speed, grade, and load.
Diesels in good condition are much more identacle, if of the same exact type.
Everyone wants magic. There's no magic. There are many infants born each day. 60 years ago the Children's World Book of Knowledge claimed that 47,000 babies were born EACH DAY in India...alone.
I don't know that any magic or technology is going to outrun our own hormones.
schlimm Fascinating stuff, Paul. Power plants are switching rapidly to natural gas, not because of the boogeyman environmentalists (although much cleaner-burning than coal at the plants, some claim large emissions at the gas well heads) you seem to have an aversion to, but because it is cheaper and they want to maximize profits.
Fascinating stuff, Paul. Power plants are switching rapidly to natural gas, not because of the boogeyman environmentalists (although much cleaner-burning than coal at the plants, some claim large emissions at the gas well heads) you seem to have an aversion to, but because it is cheaper and they want to maximize profits.
Seeming averse to bookeyman environmentalists, I'll tell you all you need to know.
You think you can build even a natural-gas fired electric plant without opposition?
Some independent power company thought it could build such a plant -- the Rockgen facility, gas-turbine "straight" cycle, peaking duty -- in exurban Dane County (outside Madison, WI). Every self-styled environmentalist in the 5-county region was protesting that one, but they did get it built.
You think at the "U" we sit here in our ivory towers on Linden, smug in the belief that we are a "soft" "post-industrial" "knowledge industry" beyond criticism from the environmental lobby? Our then-chancellor, an Electrical Engineering professor, informed our faculty senate that laboratory fume hood "make up air" alone, accounted for 60 percent of total campus heat usage. These fume hoods make it safe for lab workers to do stuff like develop stem cells as cures for human disease, come up with treatments for childhood cancers, stuff like that. Prior to the natural gas conversion of the Charter Street central heating plant, those activities accounted for as many as 3 railroad cars of coal per day. You don't think of such cutting edge lab work as a dirty, industrial activity, but it can be.
The MGE power company and the "U" partnered on displacing some of that coal usage as well as building reserve capacity by expanding the Walnut Street plant with a state-of-the-art gas-fired 150 MW electric co-generation combined electric power plant and district heating plant. I wasn't too cool about the "U" switching from coal to natural gas in the pre-fracking days when my home heating bill was tripling, but I was thinking, "Cool, let's see of the U with its ivory towers on Linden gets a pass from the environmentalists."
Well, guess again.
I went to the "town hall" held by our Chancellor and an MGE rep as part of the campaign to address the opponents. The most memorable part of the meeting was not about Walnut Street, but how the discussion digressed into the Sins of MGE for pulverized coal combustion in their other facilities. There was a fresh-faced young man who was dominating the Q&A, I christened him "Energy Boy", who was castigating the MGE rep for not building Integrated Gasification Gas-turbine Combined Cycle (IGGCC) to replace their polluting pulverized-coal combustion steam-cycle plants.
So I am told that fracked natural gas is now the magic bullet that will assuage the environmentalists, make profits for investors, and provide low-cost energy for business, academia, and consumers? Back in the day (which was only a few short years ago), pre natural gas boom, the "magic bullet" was IGGCC (or IGCC for short).
IGCC is one of these concepts that look great on paper. Like "steam could have held off Dieselization if only they build Porta's metre-gauge concept for a Mallet-Garratt only on standard gauge." Or "the nuclear-thermal rocket is the answer for NASA putting a human base on Mars." Or "IGCC offers up to 60 percent thermal efficiency (it doesn't, the 60 percent figure is for a natural-gas fired gas-turbine combined cycle), and all of the pollution in coal can be scrubbed from the gas feed to the turbine instead of the much more dilute combustion exhaust."
Energy Boy had all the answers, and the MGE rep was politely trying to explain, "Hey, wait a minute." A big hey wait a minute is that the gas producer of IGCC is this really, really complicated chemical engineering undertaking, especially if you want to do all of that pollution control, and that IGCC is still in the "pilot plant" stage. I checked on Wikipedia, and these years later, it is still in the pilot plant stage -- maybe there is one operator in Holland who has gotten one to work.
As I said, IGCC was the magic bullet of 10 years ago; today, that magic bullet is fracked gas. Today, CO2 is officially a pollutant along with dangerous stuff like fly ash silicates that you breathe into your lungs and mercury that gets concentrated in aquatic life. So if anyone wanted to pursue IGCC today, they would have to add oxy-firing and carbon sequester, and yes, at today's (maybe temporary) low gas prices, it just isn't worth the bother.
So power companies are switching to natural gas, not because they are dragged there by the environmental lobby, but because gas is cheap (today, maybe not tomorrow -- there is controversy on the "depletion curves" of fracked gas)? Well I guess yes, in a very small picture, tunnel vision interpretation of modern history you are right and I am an anti-enviromentalist hysteric.
But there may have been a window to "bring back steam" with Porta and Wardale and the ACE Project in the 1980's Oil Crisis, but after this lengthy clarification of what I meant, bringing back steam to railroad traction today, you can just fuggedaboutit.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
C&NW, CA&E, MILW, CGW and IC fan
locoi1sa We can debate limited cutoff, cylinder size, and driver size forever but I believe that the steam locomotives that were built were the best that can be done with steel wheel on steel rail. Without beefing up bridges and roadbed the maximum amount of weight on drivers will always be the limiting factor.
We can debate limited cutoff, cylinder size, and driver size forever but I believe that the steam locomotives that were built were the best that can be done with steel wheel on steel rail. Without beefing up bridges and roadbed the maximum amount of weight on drivers will always be the limiting factor.
The argument has been made that the last steam locomotives were far from the best possible, that considerable improvements could have been made, even without going to "exotic" stuff like condensing cycles, steam turbines, and electric drives.
The people making that argument were Andre Chapelon in France, Livio Dante Porta in Argentina, and David Wardale, working in South Africa, the U.S. (on the ACE 3000 project), in China (on improving the QJ class) and most recently in England (on the 5AT project for a modern new-built passenger-excursion locomotive). There are others, but these are the main one's who have written about their work -- Chapelon through a book, Porta through numerous papers, Wardale also publishing a book.
If you are limited by weight on drivers to get the tractive effort, you can build a locomotive with more drivers, and the same bridge limits come into play with Diesel multiple units having a large number of axles.
It is not that the people building steam locomotives didn't know what they were doing, but stationary power plants started out with equally low thermal efficiency to steam locomotives, and power plant and steam locomotive thermal efficiency improved over time, with advances in the science of thermodynamics as well as in materials. The thing is that steam locomotive development just quit whereas power plants went on to turbines, condensing, superheat and reheat, compounding, pulverized coal combustion, stack scrubbers.
Wardale's view on why steam locomotive development "just quit" is that even when Diesel traction was just an experiment in the 20's and 30's, the whole industry, the railroads and their supplier, "bet on" the Diesel as the best mode of railroad traction. The Diesel locomotives when this decision was made were not the SD40-2 and there were still things you could do to improve steam locomotives. But contrary to what you hear about short-term profits, people in business to have to make educated guesses as to "where things are going" and "where the trend lines are pointing."
There are things you can do to improve coal-fired steam power plants from the standpoint of pollution, efficiency, and yes, even CO2 emissions through CO2 capture and storage in rock formations. But I think the utility industry no longer "has their heart in it" because coal gets so much disrespect these days, maybe from self-appointed guardians of the environment who think nothing of flipping a switch to use electricity when they want, but who regard the whole cycle of coal mining, coal combustion, and ash disposal as a moral evil. Trains have switched to Diesel and they may switch to natural gas, large cargo ships pretty much the same, the last holdouts of coal-fired steam-cycle power are the generating plants, and maybe their days are numbered.
daveklepper 3. All locomotives have limited cutoff to some extent. But a locomotive designed for greater efficiency at higher speeds, with boiler size, cylinder size, and driving wheel size, needs to have steam in the cylinders for a longer period of time on each stroke to have the needed tractive effort to start the train. This means reduced efficiency at low speeds and starting, but all possible tractive effort and power at those low speeds . (But still less than rated power, which is obtained only at higher speeds, but with reduced tractivfe effort.)
3. All locomotives have limited cutoff to some extent. But a locomotive designed for greater efficiency at higher speeds, with boiler size, cylinder size, and driving wheel size, needs to have steam in the cylinders for a longer period of time on each stroke to have the needed tractive effort to start the train. This means reduced efficiency at low speeds and starting, but all possible tractive effort and power at those low speeds . (But still less than rated power, which is obtained only at higher speeds, but with reduced tractivfe effort.)
I "get" the part about a high-speed locomotive operated at steam-saving short cutoff at high speed, at a somewhat steam-wasting long cutoff at low speed to get enough tractive effort out of the comparatively small cylinders, short stroke, and large wheels so as to start the train.
I noticed, however, in Wardale's charts that cutoff being equal, efficiency appears to drop off at lower speeds. That is, "cruising" at a moderate level of tractive effort at 20 MPH is less efficient than at a similar level of tractive effort and hence cutoff percentage at 40 MPH. What gives?
Is this a heat loss effect? That is, the steam sits in the cylinder long with each stroke and more heat is lost? Is this a boiler "turn-down ratio" effect? That at the same cutoff, at slower speeds you are drawing less steam from the boiler, and the boiler is less efficient at low rates of evaporation?
The last revenue mile pulled by a steam locomotive on the PRR was pulled by an I1sa. Remember that these were built in the drag freight era. Long and slow was the rule of the day and trains pushed and pulled by multiple locomotives. The fast freight era was just starting out when diesels were coming on the scene. The J1 and the oil burning leased locos were better on the flat lands that ran shorter but faster freights. The taller drivers were better at faster speeds but needed much more power to get them started, thus used more steam to start.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
The reasons for short cutoff, at least as applied to the I1, were explained in my post, and so were the reasons for not applying short cutoff. Limited cutoff reduces the flexibility of the engineer's judgement. If engnineers are well trained, they will have the Johnson Bar in the corner only when maximum tractive effort is needed (and conditions are such as remove slipping possibities, sanders working, or dry rail, etc.), and move it to shorten cutoff rapidly as speed bills up to conserve steam and improve efficiency. In the case of the I1, the PRR found it could start heavier trains and increase tractive effort, without always spinning wheels, by lengthening cutoff from 50% to 65% (still fairly short for maximum cutoff), and that its engineers would use this flexibility intelligently. Also.a few I1's may have outlasted the last J in service, but only because so many I1's were built.
locoi1saWhy were not all locomotives built with limited cutoff?
1. The 2-10-4 J's lasted as long as the I1's. In fact, PRR leased AT&SF Ripley 2-10-4's to work along side its J's on coal traffic while scrapping any I1's that needed work. And all this while total dieselization had already been set as a goal.
2. The I1 was designed as a low-speed locomotive with high efficiency at low speeds. This mean very large cylinders and small driving wheels as compared to boiler size. Wihtout limited cutoff, it would have been very easy to use full throttle, Johnson Bar in the corner, and simply spin the wheels by tryihg to obtain tractive effort beyond the capabilities provided by the factor of adhesion, and a the same time rapidly deplete boiler steam.
The responders are correct but the question remains. Why was the Johnson bar shoved to the corner? It was up to the engineer to limit the cutoff. The PRR built 598 I1s 2-10-0 locomotives with 50% cutoff as full throttle and later increased to 65%. They lasted until the end of steam when newer and more modern locos were being cut up for scrap. With 90,000 lbs of tractive effort at 20 revolutions there were very few 2 cylinder locos more powerful. Tractive effort fell off as speed increased so in essence they were more efficient at slower speeds.
Some steam locomotives were built to be efficient at slow speeds over faster speeds such as the I1s. The question should be. Why were not all locomotives built with limited cutoff?
I was just thinking about the same question.
Generally speaking, a steam locomotive is most efficient when 1) steam is supplied to the cylinders at a very low cutoff to provide maximum expansion of the steam, and 2) the boiler is operating at its rated capacity for steam generation. These conditions are met at the upper end of the speed range of the locomotive, where the boiler is about able to keep up with the steam demand, that is, when the driver RPMs are high and the cutoff is low (say, at 25% in contrast with 80% at starting).
The locomotive is least efficient when starting and operated at high cutoffs (say, steam is admitted for fully 80% of the piston stroke). This gives the maximum tractive effort, but it sure uses a lot of steam and hence energy, and since this is at low speed, it doesn't represent much horsepower.
The thing puzzling me relates to Fig. 82 on p 267 of David Wardale's The Red Devil and Other Tales of the Age of Steam. Yes, an incredibly hard-to-find book, but there was a recent reprinting and there were posts on the Trains forum regarding where to order a copy.
That chart shows tractive effort on the vertical or y-axis as a function of locomotive speed on the horizontal or x-axis. The "islands" of constant thermal efficiency are plotted on that x-y scale. This chart is much like the torque-RPM "map" of an automobile engine also showing islands of constant thermal efficiency.
Having worked a long time ago for a major auto company, I can tell you that the auto engine map is measured in an engine dynamometer test cell. Race car teams use such a "dyno" to tune their race engines. Such a test appliance is called an "engine test plant" when it is applied to a whole locomotive, and the Pennsylvania Railroad, back in the day, famously had such a facility in Altoona. Wardale didn't have such a "steam locomotive dyno", and he shows results in Table 37 on p 215 of road tests using electric locomotives with dynamic brakes as "braking sleds" to do the same thing out in the field.
The thing I haven't figured out is that Table 37 shows a great deal of variability in measured fuel economy between tests whereas Fig. 82 shows these smooth efficiency islands. I will need to study the book carefully to see if I can find out how Wardale really got his "engine maps" without access to a test plant to more carefully control the operating conditions.
However these maps were determined, you would think that if you drew a horizontal line at constant torque, corresponding to a fixed cutoff setting, you would get the same efficience that didn't change with speed. Instead, the "islands" show a drop in efficiency at the same torque but with a drop in speed.
Can any of our steam engine experts -- Overmod, Juniatha, others -- weigh in why that may be?
I suspect it might have to do with heat losses. As you drop in speed, even at the same torque and hence expansion ratio and theoretical thermodynamic efficiency, each charge of steam admitted by the valves stays in the cylinder longer, allowing it to give up heat to the wall, robbing power and efficiency. Also, as you drop in speed at the same cutoff and nominal torque, you are drawing less steam from the boiler.
Steam engine boilers famously become inefficient at very high draft and evaporation rates because they start lifting the firebed out the chimney. A wheel slip can also do that by spinning the wheels and greatly increasing the draft from all that steam sent up the stack, and on pp. 105-106, Wardale tells a story about "why the locomotive number is painted on the tender" that will have you rolling on the floor. But maybe boilers become inefficient as the evaporation rate trails off, again because of thermal losses.
In L. D. Porta's "bucket list" of what you need to do to a steam engine that never got around to being tried was putting "excessive insulation" around everything -- add to boiler lagging, all steam pipes, and certainly the cylinder jackets. Porta claimed with such treatment, a steam "shunting engine" (switch engine in U.S.-speak) could have the same fuel consumption as a Diesel, and switch engines were the first ones you wanted to replace by Diesels because of high coal consumption just sitting there.
I've read that steam locomotives are less efficient when running at low speeds, why would that be? And how does steam locomotive efficiency correlate with speed in general?
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