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?
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.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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?
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!
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.
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.)
locoi1saWhy were not all locomotives built with limited cutoff?
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.
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.
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.
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.)
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?
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.
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.
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.
C&NW, CA&E, MILW, CGW and IC fan
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.
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.
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.
-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.
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.
Adjusting the cutoff is the most understandable response yet. On my last cab ride, I was told "stand there" and watch in silence. Once the throttle was opened, the engineer simply worked the train with the reverse handle (cutoff). That was all he needed for to adjust for speed and gradient, etc.
Last time I paced, it seemed to take 2 miles or more for 765 to get up 30 MPH. Suddenly in less than a mile the engineer pulled away from all the traffic like shifting into overdrive. The acceleration curve "seemed" to increase in the 45 MPH range. NKP got good performance on manifests with relatively short and consistent train lengths (maybe 50 cars, lots of produce) relatively mild grades and 60 MPH operation. Efficiency was achieved by engineers who knew the territory and the individuality of the locomotives. It has been written that they could tell you which group of the 700's had the best reputation and which of that group were the favorites. Other less favorite 700s, were notoriously "consigned" to the Wheeling District in respnse to the ebb and flow of traffic.
STCALRR Adjusting the cutoff is the most understandable response yet. On my last cab ride, I was told "stand there" and watch in silence. Once the throttle was opened, the engineer simply worked the train with the reverse handle (cutoff). That was all he needed for to adjust for speed and gradient, etc. Last time I paced, it seemed to take 2 miles or more for 765 to get up 30 MPH. Suddenly in less than a mile the engineer pulled away from all the traffic like shifting into overdrive. The acceleration curve "seemed" to increase in the 45 MPH range. NKP got good performance on manifests with relatively short and consistent train lengths (maybe 50 cars, lots of produce) relatively mild grades and 60 MPH operation. Efficiency was achieved by engineers who knew the territory and the individuality of the locomotives. It has been written that they could tell you which group of the 700's had the best reputation and which of that group were the favorites. Other less favorite 700s, were notoriously "consigned" to the Wheeling District in respnse to the ebb and flow of traffic. Interesting. This confirms the graph I saw years ago between steam and diesel locomotive of 6000hp. The diesel had enormous starting tractive effort (which was electric traction to be exact) and immediate access to its horsepower. The steam locomotive starts with less tractive effort and lower horsepower but the steam locomotive generated an inverted-U horsepower curve that peaked at 60mph. It crossed the diesel curve, rising at 30mph and eventually coming down at 90mph. That explains why the steam is a slow starter and frankly poor on grades relative to electric traction whereas between 30mph and 90mph in runs away from electric traction. If you remember the Reading T-1s, they were slow starters but once above 30mph they ran like the wind. The N&W 2-6-6-4s and the Nickle Plate 2-8-4s were outrunning diesels on a regular basis before they were put to bed. Remember that it is ton/miles that earns the money. The NYC ran with an average speed of twice that of the Pennsy but required only half the physical plant. The massive mistake that most railroads made was in not electrifying its mountain divisions where electric traction and re-generative braking would categorically outperform steam. The PRR, C&O, B&O, etc electrified the wrong end of things or used 2-6-6-6s in the hills as opposed to the flatlands where they would have excelled. I've run both steam and diesel. I absolutely love steam to death but the diesel could be shut off at night like your car, without a night watchman, and a vast support infrastructure. It did not need coal (or oil) and water and to dump its ashes. And at high speeds the existing reciprocating-valve-geared direct connected engines were in trouble with steam distribution. The steam locomotive was not beaten by some novel new technology. It was beaten by electric traction as defined in the trolley car era. The trolley car ran on 600 volts DC. Guess what the ALCO-GE S series of switchers ran on? 600 volts DC, an old proven system. The 1000hp traction motors, except to the commutator, were identical on both the Lackawana 1927 3000VDC motor cars as under the ALCO-GE S series. Even some of the control panels were identical. What was new basically came WWI submarine technology: the high horsepower diesel engine as a generator set.
Oops , just saw this thread now - cats can be so incredibly slow sometimes ...
Dunno if its still waranted to sew up something , a number of points has been mentioned already ..?
As I generally say :
nothing is for free
in technology
Regards
Juniatha
View the power and torque curves of internal combustion engines - the same types of curves apply to steam engines.
Never too old to have a happy childhood!
Steam engines less efficient at low speeds? Shhhhhhhh......we don't want loose talk like that getting around, do we? Otherwise they'll never come back.
Shhhhhhhhhh..........
Right on, Baltacd! A basic characteristic of all reciprocating machinery.
>> the same types of curves apply to steam engines. <<
Same type of , Balt ACD , yet not same curve :
IC engines usually do not feature something equivalent to a variable cut-off , for instance , and thus have no means of significantly increasing torque in the low rpm speed range . If you point to compressors or turbo chargers they are basically used to increase filling in *upper* to *highest* rpm speed ranges ; especially turbo chargers couldn't easily be profiled to boost low rpm filling pressure because they rely on exhaust gas flow - and that's low at low rpm ; a compressor at least theoretically could be adapted to boost low rpm filling pressure , however that would tend to produce undesirable level of stress loads on cylinder walls , crank shaft and even the motor block and head(s) - not to speak of problems involved with cam and valves ..
Further , IC engines - low torque at low rpm or not - cannot start away from standstill and that's a principal difference from the steam engine deeply rooted in their different fundamental functioning .
On the other hand , lately variable profile valve operation by means of adjustable phase cam shaft or by variable combination of valve operation from two differentially profiled cam shafts have helped to significantly widen the range of best output and / or efficiency of IC engines . Apart from mentioned adjustable cut-off , this is something that has - afaik - never been done with steam engines , at least not of locomotives , yet would be perfectly possible and reasonable .
The variable timing of the iginition spark is very analogus to the variable cut off of steam engines. As the RPM of a IC engine increases the timing of the spark is advanced to occur more degrees before top dead center.
BMW, I believe, has been 'playing around' with starting IC engines from a standstill. With computer controls, the computer knows when to stop the engine so that the next cylinder to fire is stopped at a position in it's cycle where the only thing necessary to start the IC engine is the spark from the spark plug. Turning the engine 'ON' fire the appropriate plug and away the engine goes.
Both Steam and IC engines are 'powered' by the rapid expansion of gas pressure. In the steam engine, high pressure steam is admitted to the cylinder and acts against the piston in the cylinder in a timed fashion. In the IC engine atomized fuel is entered into the cylinder and expanded against the piston in the cylinder by a timed spark. The fuel is different, the mechanical actions are the same and generation of horsepower and torque follow similar curves and are basically defined by both the bore and stroke of the engines. Needless to say, the bore and stroke of steam locomotives is massively larger than those of IC engine we are most familiar with, however, the large marine diesels that have their bore and stroke measured in units of steam locomotive size and even larger produce astounding horsepower and torque values - on a similar curve.
BaltACDBMW, I believe, has been 'playing around' with starting IC engines from a standstill. With computer controls, the computer knows when to stop the engine so that the next cylinder to fire is stopped at a position in it's cycle where the only thing necessary to start the IC engine is the spark from the spark plug. Turning the engine 'ON' fire the appropriate plug and away the engine goes.
All things made new, I suppose. My Silver Ghost would do that, reliably. A bit of an artifact, but still a well-recognized phenomenon. And that's with now-century-old tech...
(of course, it's more of a technical effort to do with an overhead-valve engine, but less difficult when you have full modulated direct injection. Much more interesting to keep the engine within pollution specs for the 20 or so revolutions it will take to get to sustained idle speed. But there is little perceived 'sizzle' in those engineering points...)
>> The variable timing of the ignition spark is very analogues to the variable cut off of steam engines. As the RPM of a IC engine increases the timing of the spark is advanced to occur more degrees before top dead center. <<
No , actually it isn't .The analogue to variable timing of ignition being variable advance which I have remarked upon .
The fundamental difference between IC engine ignition and steam engine cut-off being that in the former invariably but the volume of gas being inside a closed cylinder chamber can be ignited while in the latter case cut-off can be deferred so as to allow for continued *filling* of the cylinder chamber and thus - ideally - constant pressure before cutting off . The *volume* of media used in the cylinder can thus be vastly increased over a filling comparable to that of an IC engine - which would rather be in the vicinity of - 10 % ( to quote corresponding notes by L.D. Porta ) .
You have thus not realized the fundamental difference between a concept of piston engine having to realize pressurizing of its media by combustion of a filling limited by the small volume round upper dead center and a concept of piston engine being charged by pressurized media from a large volume external source: in the latter , working pressure is being kept up as long as intake is open - and it generally is open for the larger part of piston stroke at starting - while in the former , pressure in closed cylinder chamber rapidly drops as high combustion gas temperature gets discharged through cylinder walls , head and piston . That's basically why - besides other aspects - the IC engine cannot effectively start from standstill under a load .
Kick-starting while presenting some tricky points to deal with all by itself is something quite different from starting under load , mind you !
>> My Silver Ghost would do that , reliably <<
Oh , sure , Overmod - *gee* - no one wouldn't expect nothing less , even if it became a Silver Worst in the event .
Bye , now ! on that controversial nonproductive IC stomping alley .
= J =
Edited for continued same sequence of IC and steam
Juniatha >> My Silver Cloud would do that , reliably << Oh , sure , Overmod - *gee* - no one wouldn't expect nothing less , even if it became a Silver Crowd in the event .
>> My Silver Cloud would do that , reliably <<
Oh , sure , Overmod - *gee* - no one wouldn't expect nothing less , even if it became a Silver Crowd in the event .
I'm not quite done with infernal combustion, thank you very much! ;-}
Ghost, not Cloud. There's a very important difference between those two.
This is the old original Ghost, as built in Springfield in the early '20s for the American market. The engine can 'self-start' when the ignition is switched back on after a start. Anyone interested can PM me for the details.
The original digressions I made in this post have been removed; they were off-topic for this thread. If I am going to argue about the thread drifting, the least I can do is not contribute drift in a different direction. I leave this point in because it addresses BaltACD's comment about self-starting BMW engines.
Something that is potentially interesting in a discussion of slow-speed steam efficiency is the behavior of small, double-acting automobile engines that are directly connected to the final drive, as in Stanleys. I have seen some discussions of low vs. high-speed efficiency over on the SACA 'phorums', and it might be valuable to ask this question over there to get a response from that very different community.
The analogue to VVT is still timing and duration; but the interval (and duration) are different for EC vs. IC, and the piston thrust is determined by the pressure in the medium for EC (and tapered off via wire-drawing effects, etc.) rather than by the combustion-event's characteristics and spark/injection advance. The intake valve or port in an IC engine uaually being WELL closed by the time ignition (and consequent piston thrust) is to be considered.
"Normal' steam can develop high torque at zero rpm if the 'expander' is designed so that admission is always occurring 'somewhere' (or, of course, if the valve or equivalent is open to steam for admission when the throttle is opened). In a double-acting and quartered piston engine, you can always have one valve open and admitting steam to its piston face at suitably long cutoff. (On steam engines with fixed limited cutoff, it is possible to have to put in a clutch to turn the engine off an effective dead center; there were some steam automobiles somewhat misguidedly designed that way -- another story; we can take up how to warm car and stoker engines and the like in a different thread.) To add a detail, starting ports ("Weiss ports" in the ACE 3000 design) can be provided to supply a little more mass flow early in the stroke; you can compare the operation of the Herdner valves Wardale installed on the Red Devil.
Most of the USC motors, though, will stall very much like an IC engine as their steam admission is 'metered' similar to fuel injection (and, in fact, in at least two prototypes I know of, using modified fuel-injector technology.) Here you start the engine with some sort of motor and Bendix drive, and keep the engine 'turning over' at the analogue of idling when you anticipate using it.
(Part of the reason the gas pressure drops so sharply after 'cutoff' in an IC motor is that the combustion gas is just that, a gas. Steam has very substantial latent heat of condensation, so it exerts pressure in a cylinder longer even after admission is cut off.)
Juniatha That's basically why - besides other aspects - the IC engine cannot effectively start from standstill under a load . Kick-starting while presenting some tricky points to deal with all by itself is something quite different from starting under load , mind you !
That's basically why - besides other aspects - the IC engine cannot effectively start from standstill under a load .
It's the starting under load scenario that we're talking about here, isn't it? I think this would have significant bearing on any kind of kick start which then impacts some of the following poster's mechanical and theoretical observations which appear to me to be being made about starting an engine which is not under load.
As an old diesel and hydro powerhouse operator, I think your point is well taken and I can assure you that any machine being kick started under load conditions such as I worked in power generation would be something else as far as design goes. I have to say also if you did start under load (hot cold or otherwise) the Chief or the Super would have you up on the carpet for improper operating practice, if not being fired for the resulting damage to the engine and other gear. In power generation the customers would have been howling. The combustion/expansion and mechanical observations are obvious to any experienced and qualified engineer or operator. The under load discussion is quite likely somewhat different.
The view from here.
Charlie
Chilliwack, BC
lenzfamily It's the starting under load scenario that we're talking about here, isn't it? I
It's the starting under load scenario that we're talking about here, isn't it? I
That is not at all what the original thread is about.
The issue is why steam locomotives are less efficient at low speeds. The original poster distinguished this from 'developing less power or uneven torque at low speeds'. And it is certainly different from conditions at starting, which are interesting from an operating standpoint but fairly meaningless in terms of gauging practical operating efficiency. While a discussion of starting is certainly interesting, and would deserve its own thread and discussion, it's only a distraction here.
I apologize for my part in contributing anecdotes to a discussion without paying sufficient attention to the topic. And confess that I am still watching for more discussion on the actual topic.
OvermodI apologize for my part in contributing anecdotes to a discussion without paying sufficient attention to the topic. And confess that I am still watching for more discussion on the actual topic.
Sir,
And that is precisely what I did recognize.....given your previous response to Juniatha, duly quoted above in this thread. I most certainly understand the 'issue' as you put it, and commented as I did in response to Juniatha, re starting under load, based on my experience and qualifications in both stationary and traction settings. You most certainly did provide an unnecessary and rather more than an anecdotal distraction in this instance. I thought Juniatha deserved better treatment.
If your apology is intended for me also, I accept your apology, this time.
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