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 .
Regards
Juniatha
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.
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
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 torq
Juniatha
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
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.
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.
Charlie
Chilliwack, BC
Well, no. The subject wasn’t the ‘starting under load’ scenario. And that, indeed, was the point I intended to be making, and did make, I think, regarding the off-topic drift…
Unlike some, I apologize when mistaken. I see no reason to defend, or change, my behavior in that respect, or for that matter to comment on certain other aspects of your response that do not address the thread topic.
I am quite certain that Juniatha recognizes the spirit in which I commented – on topic or otherwise – and would expect to hear from her directly regarding any details of my comments. Your intrusion is condescending to her, at best, in my opinion.
If you have experience and qualifications concerning the topic of low-speed steam efficiency (which you may well have), as I said, I look forward to further discussion. (Perhaps including, even though not strictly on topic, how you think reciprocating steam locomotives are regularly started without being under load.) But this is neither the place nor the subject for any further discussion of other matters; it belongs off-list.
Sir
Your opinion is yours to hold. Mine is mine to hold. That’s how i see the thread progression here.
I do indeed know when and how to apologize on this forum as I have done on a number of occasions previously.
I will not continue further discussion with you.
Charlie
Chilliwack, BC
To return to the original question, I think the lowly pedal bicycle provides a reasonable analogy that may help understanding. The steam locomotive is like a bicycle in a tall gear ratio. How tall a ratio is the equivalent of the driver diameter. It is a struggle to start from a standstill if in top gear, but once on a good roll the pedaling becomes easier.
The diesel equivalent is a bicycle fixed in the bottom gear. Starting is easy, but soon you are going too fast for your legs to apply much pressure on the pedals…
The analogy is highly oversimplified since the mechanisms are very different. But there are some surprising equivalencies.
John
[8D]in m. baldwins day there were no answers, only questions that were only proven or disproven by trial and error. some engineering department guidelines were those of one mans decisions. the camelbacks a case in point.The FEC/flagler systems chief engineers need the most powerful fastest engines money could buy? were they lees efficient than there heavy 0-8-0 switch engines? it all is a matter of your perspective on the historic facts?[8-|]
Juniatha, See emdiesels.com. EMD turbochargers are gear driven at lower speeds. See Products, Power Products for torque curve info. This gives it a much fatter torque curve at low speeds. gap920
It’s not a matter of perspective, it’s a matter of how the locomotives were designed and built. An FEC 4-8-2 would be quite efficient on the head end of a fruit block or the “Havana Special”, it would be decidedly inefficient if it was used to kick cars in Bowden Yard. An FEC 0-8-0 would be reasonably efficient in low-speed yard or transfer duty, it would incur the wrath of the M/W department if it was assigned to a local freight.
That is not a good analogy. The diesel engine doesn’t directly turn the wheels. The electric traction motors do, and electric motors are an infinitely variable rate transmission.
The notion that diesel-electrics somehow lose lots of power at speed that I have seen mentioned in this thread is not only amusing, but it is completely wrong.
If you look at the power curve of a modern diesel-electric, it is almost flat as a pancake over its entire operating speed range. For example, the 6,250 HP GEVO CSX AC6000 is a constant force, rising HP machine from 0 to 11 mph. This is due to the adhesion software maintaining a constant TE as the speed increases. Above 11 mph, it becomes a constant HP machine to its software limited speed of 75 mph. The only losses to drawbar HP as speed increases is from air drag and rolling resistance. This isn’t much, it only takes around 300 HP to move an AC6000 at 75 mph on level track.
The bottom line is an AC6000 is a 5,600 to 5,700 drawbar HP locomotive from 11 to 75 mph. That is about as far from a fixed gear bike analogy as you can get.
[8D]during the sugar harvest what ever was available was going to be used as long as it did not excide the gross weight limits?[8-|]
To quote Overmod :
Well, no. The subject wasn’t the ‘starting under load’ scenario. <<
Well , yes , that’s at least how I saw it , too . Idle starting mode wouldn’t point out such a significant difference between steam and IC reciprocating engines .
Unlike some, I apologize when mistaken. <<
Well , I take your word for it …
I am quite certain that Juniatha recognizes the spirit in which I commented <<
I’m not sure at all …
and would expect to hear from her directly regarding any details of my comments. <<
?? Dunno what makes you expect that ?
Your intrusion is condescending to her, at best, in my opinion.<<
Ho-ho-ho , strong medicine … intrusion … condescending … and that from one who has been quite self-righteous at times .
No insult intended , yet I think this had to be clarified .
J__uniatha
Likewise for clarification only:
This was the salient point, and its response.
All the rest … you can put your popcorn away. Digression ends here.
(Except to note that a far better pun would have been “Sliver Cloud”… ;-} )