The plausible outlets are reporting that both 3GS21Bs and single 3GS21C have been retired and sold back to National Railway Equipment. This surprised me as I had expected the 3GS21Bs to be rebuilt into roadslugs and the 3GS21C fodder for the SD33ECO program... unless the deal is for NRE to send NS five SD40s/45s to fill out the SD33ECO program.
Editor Emeritus, This Week at Amtrak
Evidentally they're worth more intact than as parted out hulks that might be utilized as frame/running gear donors for yet another project.
They're relatively young and surely would be a good fit somewhere, where as they were oddballs and apparently somewhat unsatisfactory in the service NS utilized them in. Union Pacific and BNSF roster over 100 3GS21B's for instance, so there has to be some decent value there as an intact locomotive.
Will be interesting to see if any of the other low-emission oddballs follow shortly in being strickened. While the two RP20DB's are active, both RP14BD's and the single RP20CD are stored. And then there's the PR43C fleet that is sitting idle rusting away right now and while active, battery powered BP4 doesn't look to have been a complete success and likely isn't the prototype for an entire line of sisters.
Leo_Ames Evidentally they're worth more intact than as parted out hulks that might be utilized as frame/running gear donors for yet another project. They're relatively young and surely would be a good fit somewhere, where as they were oddballs and apparently somewhat unsatisfactory in the service NS utilized them in. Union Pacific and BNSF roster over 100 3GS21B's for instance, so there has to be some decent value there as an intact locomotive. Will be interesting to see if any of the other low-emission oddballs follow shortly in being strickened. While the two RP20DB's are active, both RP14BD's and the single RP20CD are stored. And then there's the PR43C fleet that is sitting idle rusting away right now and while active, battery powered BP4 doesn't look to have been a complete success and likely isn't the prototype for an entire line of sisters.
Having traveled far and wide across the North American rail system and having visited just about every major rail yard there is one commonality found with gensets: they were always parked.
D.CarletonHaving traveled far and wide across the North American rail system and having visited just about every major rail yard there is one commonality found with gensets: they were always parked.
Maybe NRE has a different use in mind for them then rather than reconditioning them for resale. Maybe they'll part them out and use the frame, body, and running gear for a different project that aims to improve upon some of the ailments from their earlier attempts.
Either way, they evidentally were worth more via resale than they were to NS for any potential use.
Crews hate GenSets - not enough power when you want it, by the time full power comes on line - you don't need it. A bad solution looking for a problem.
Never too old to have a happy childhood!
BaltACDA bad solution looking for a problem.
The idea's not wrong -- just the implementation.
The problem in part is that people who don't understand switching were designing the things. Switch engines aren't little underpowered Thomas clones that shuttle hither and yon with cuts of cars, any more than commuter locomotives are old hand-me-downs trailing a sorry bunch of Ping-Pongs on a slow trek in and back. And the dominant characteristic in both cases is the same: the native ability to accelerate very quickly with a load, and just as quickly scrub momentum off.
It is extremely unwise to use 'conventional' battery chemistry as the source or sink of rapidly-increasing drain or charging current. Even if you can modulate this so the battery 'lives', ther needed to be an explicit control that predictively fires up one or more of the engines in time for the equivalent of 'power mode' (best power from the effective 'sum' of engines and battery) when performing a kick, and winds the engine down to minimize emissions afterward. And, for that matter, reduces other forms of pollution by spooling the engines up in speed with reduced load, to cut down the nanoparticulates and some other undesired exhaust constituents that form if the engine has to accelerate into substantial load, but then haqs the ability to put engine horsepower quickly to work without lugging.
I was surprised that GE in particular did not take an interest in marketing its 'hybrid battery' technology to this market ... or that we haven't seen my old 'pet' technology for this, some big counterrotating flywheel storage. Perhaps the market isn't exactly there. I can't help but think, though, there's a good market especially in air-quality management districts, for a genset-style switcher that can actually switch.
I believe that the power in question are just gensets, not hybrids like the various Green Goats from Railpower Technologies.
They're powered strictly by diesels, with multiple engines that come online as needed to meet the demands at that time (Or at least that's the theory).
It's supposed to be more environmentally friendly. A NRE 3GS21B for instance can be a 700 hp, 1400 hp, or a 2100 hp switcher as needed instead of underutilizing a 2100 hp switcher in service where often only a fraction of that power is needed.
Clearly it's not yet a perfect solution and I suspect it may never be until a traditional builder tackles the concept with a product designed and built specifically for railroad use in mind, instead of repurposing major components from elsewhere like the construction equipment engines that are in the 3GS21B. Not to mention their support infrastructure and reputation backing it.
They may be easy to remove and reinstall during maintenance, but if they're breaking down frequently and don't age gracefully, it matters little.
For switching service, my take is that "ultracaps" are a better match than batteries. Capacitors provide a much higher specific power, efficiency and cycle life than batteries. Downsides are that specific energy (e.g. w-hr/lb) is lower and the voltage rises and falls with the state of charge.
Maxwell Labs makes a 48V/165F capacitor module, which weighs about 30 pounds and QTY 1 price from Digi-Key is about $1350. The module is rated for 1,000,000 cycles (most batteries do well to reach 500). Assuming an operating mode where the capacitor is cycled between 50% power (70& voltage) and full charge, each cycle would be good for 25 w-hr. 1,000,000 of such cycles works out to 25,000kwhr or about $0.05/kwhr. Caveat is that you need to do 100,000 cycles per year or about 12 cycles per hour.
25 w-hr is enough energy to accelerate a 1,000 ton train from 0 to 1 MPH, 225 of these modules would be able to accelerate that same train from 0 to 15 MPH and with regenerative braking be able to recover most of that energy in stopping said train. With that power available instantly, this seems to be ideal for switching service.
- Erik
FWIW, Eaton appears to be a second source for ultracap modules.
Nobody but an idiot sources or sinks high current through a battery -- especially not in repeated charge and discharge cycles, as the Green Goat people discovered (and in my not-so-humble opinion should have recognized from the outset)
There are additional issues of concern with ultracapacitors. One is that they are inherently very-low-voltage devices with very strict requirements about overvoltage (even short-term spike voltage), so substantial connections in series are needed to produce the necessary voltage, and very good power conditioning necessary (it can also be difficult to assure a good ground path for 'clamped' spike attenuation). There is also a concern about how the devices tolerate internal damage, or if they can be made self-healing (or self-de-shorting, to coin an ugly term) so that relatively long life and graceful degradation of capacity can be observed in practical terms. They're much better suited to be "charge buffers" for handling high transient current than storing electrons at required energy density for a couple of cycles of kicking and braking.
One of the traditional problems with gensets is that, for pollution reasons, there are various delays associated with startup and power changes. Some of these can be addressed with better design, for example keeping all the engines on a common 'cooling' circuit that maintains the general block temperature (and more particularly the liners adjacent to combustion) at full operating temperature, and reducing the necessity for glowing before admitting fuel at starting. Many concerns here are also concerns for diesels that can tolerate 'shutdown and restart' in motor-vehicle use, for example at stoplights or when coasting, so there is ongoing research into various aspects of "pollution control". Another concern (which is shared with more conventional large diesel engines) is the rate at which a diesel changes speed, especially when under load; I happen to think this is easily if somewhat unconventionally manageable.
Much of the value of a 'hybrid' transmission with energy storage is associated with this concern about rapid start and shutdown of diesel prime movers. The 'standard' alternative is to provide some sort of 'whackable' controls that fire up various combinations of motor and excitation on demand, with idiot lights and gauges/displays that indicate when the system is 'up to speed' (net of all pollution-abating actions) and ready to accelerate a cut properly. It is also possible, but with 'issues', to provide controls for 'predictive shutdown' (which can be actuated when a crew is 'about' to decrease power). Without these functionalities, gensets are principally good only for adjusting power to average load (see the Essl design for a modular 'Centipede' for a good discussion of the idea) and not for switching.
I always thought gen-sets had an awful lot of moving parts for what they did. One 12 cylinder EMD turbo has the same output as those three engine gen-sets.
I also thought the benefits of a gen-set would be marginal. That 12 cylinder EMD's fuel efficiency is nearly the same in any notch (once the idle fuel burden is paid for). So, maybe the gen-sets save you some idle fuel? Let you shutdown in cold weather? That's not much.... For a yard/local locomotive, I'd take the wayside plug- heater solution over a gen-set.
Maybe NS has reached the same conclusion?
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
You take a Vapor-Clarkson automatically controlled oil fired 300-psi steam generator and connect it to a heavily insulated water tank with a steam space on top. You feed steam to an eight coupled wheel engine set.
Besides providing good insulation blankets over everything, you provide steam jackets to the cylinders to reduce condensation losses, especially for operating after the thing is parked awhile. The steam jackets don't have to be complicated cylinder castings. Rather, they can be pipe traces welded to the cylinders and then covered with the fiberglass or other rock wool insulating blankets.
Bam!
Tractive effort on demand and low standby losses . . .
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicYou take a Vapor-Clarkson automatically controlled oil fired 300-psi steam generator and connect it to a heavily insulated water tank with a steam space on top. You feed steam to an eight coupled wheel engine set.
Actually, what you do is charge the device from an external overcritical-water source, like a power or utility boiler, and use the on-board heat source mostly for for 'makeup' and superheating. I think there are better onboard steam-generator designs than Vapor-Clarksons (although, with modern controls and implementation, they are a reasonably evolved and efficient design) -- see the Cyclone Engine for one alternative design that also generates some topping shp.
I also wouldn't do typical reciprocating drive -- I'd do something like Steins' oil-fired switcher, the poster child for Franklin type D if the patent drawings are accurate, or a modernized Heisler arrangement with closed gearcases to 'diesel' wheelsets. I won't rehash all the arguments unless someone wants to get into them. Yes, you could use modulated independent braking on driver cheek plates to do practical slip/traction control for high acceleration at low effective FA, so I'm certainly not going to agitate against the principle of relatively-simple recip engines in this service, and yes, there is some advantage in using modern materials like cerium steel in reducing augment in the running gear ("high speed" here being taken as, properly I think in this context, high rotational speed) BUT it needs to be remembered that this service is one of the worst for rapid deceleration with large trailing load, so buckling or deflection of the rods is a much more likely and severe issue than in most forms of road service -- designer beware!
Besides providing good insulation blankets over everything ...
And that has improved, radically, in the past decade with aerogel, nanoshield, and other technologies. It is now easy to provide removable/reinstallable formed lagging panels less than 1/4" thick, steam and water tolerant and very light, that have very low heat transfer by conduction, convection, or radiation.
... you provide steam jackets to the cylinders to reduce condensation losses, especially for operating after the thing is parked awhile.
Just to be clear: BOTH good insulation and 'heat' jackets. They do different things. Remember that most of the actual heating of the cylinder block is only of concern for alignment, expansion and sealing reasons, and to minimize absolute condensation when steam is first admitted to 'cold' cylinders: the only concern in "condensation" is in the .007" or so of wall metal that cycles back and forth between admission and exhaust temperature, and so you want the metal of the cylinder block at a high enough temperature to keep the 'condensate' that tries to adhere to the oil film and bushing metal in "enough" of a vapor phase not to start coalescing, and to serve to minimize the loss of effective superheat in the steam, of which more in a moment. For repeated idling, you want to maintain the cylinder block very hot, and for that there is no better solution in my opinion than -- not steam jacketing, but overcritical water 'jacketing' of the sort that would be driven from the Cunningham jet pump on a locomotive with a conventional steam boiler. Here you would recirculate water from the 'fireless cooker' reservoir with enough heat makeup, entirely in the liquid phase, to achieve desired block-temperature equilibrium.
(As a peripheral note: You want to minimize the heat transfer loss OUT of the cylinder block along the piston rod(s) in a reciprocating engine, and you do this several places: at the piston rings, at the junction of the piston and the piston rod, and at the crosshead, as there is heat gain at each of these locations that is unavoidable, but you want to keep your gland tribology AND sealing good at the same time)
The steam jackets ... can be pipe traces welded to the cylinders and then covered with the ... insulating blankets.
Note how very much better this approach works with overcritical water circulating through those pipes, and with molded nanoinsulation in the blankets.
Yes, without a jet pump, you will need some means of assuring circulation, and of draining the tracers to prevent freezing if the engine is laid up dead for any extended period. The amount of power to run the circulation is trivial, as the pressure head is probably less than that involved in a Lamont boiler, somewhere below 3psi, and I do not think it is difficult to spec either a 'sealed' pump or a shaft-coupling or seal arrangement that can handle the overpressure in the circuit.
Now, the reason for superheat is that even after eliminating the wall condensation losses, there is still the nucleate condensation in the steam to address. This is not only for the usual 'thermodynamic' reasons, but because the nuclei can tend to coalesce and induce heat transfer from the walls when it isn't wanted (close to exhaust where the heat transfer really only increases evolving exhaust volume precisely at the time that is least wanted!
So you want some controllable superheat in the steam, sufficient to overcome the effects of nucleate conversion depending on the near-instantaneous steam demand or mass flow. A separately-fired design on a fireless locomotive, using the same fuel as the 'make-up' generator, is likely the best way to go; you could use lithium elements or some of the other exotic 'main line fireless locomotive' technologies to extend the intervals between superheater 'firing' but that's just economically-driven detail design.
RME Nobody but an idiot sources or sinks high current through a battery -- especially not in repeated charge and discharge cycles, as the Green Goat people discovered (and in my not-so-humble opinion should have recognized from the outset)
Li-ion batteris are more than capable of sourcing or sinking high currents - state of the art ten years ago were that Li-in batteries had about the same specific power as ultracaps. Cycle life for batteries is an issue though.
Part of the reason for using the Maxwell modules is that the modules take care of the voltage balancing, monitoring OV condictions and over temp. These modules are designed to be connected in series, with the proviso that the string voltage does not exceed 750V. A string of 15 of these modules in series would have an normal max voltage of 720V, with 765V being the Do Not Exceed limit. For a single series string, going from 720V to 765V would require over 20,000J of energy. My proposal was to use on the order of 15 these strings in parallel to get a useful energy storage for a switcher (i.e. storing enough to accelerate 1,000 tons from 0 to 15 MPH with a 30% voltage drop).
Power conditioning would be made a bit easier by using a PWM inverter, which need a fairly substantial local capacitances to stabilize the DC link voltage. A dump resistor would be a necessity.
Another design concern is temperature regulation of the capacitors as their lifetime shortens at temperatures much above 40C.
Keep in mind that the maximum reccommended charge/discharge rate for ultracaps is on the order of 5 to 10 seconds to go from discharged to full charged or vice versa. The rates I'm proposing for switcher services would be slower than this.
RME Paul Milenkovic You take a Vapor-Clarkson automatically controlled oil fired 300-psi steam generator and connect it to a heavily insulated water tank with a steam space on top. You feed steam to an eight coupled wheel engine set. Actually, what you do is charge the device from an external overcritical-water source, like a power or utility boiler, and use the on-board heat source mostly for for 'makeup' and superheating. I think there are better onboard steam-generator designs than Vapor-Clarksons (although, with modern controls and implementation, they are a reasonably evolved and efficient design) -- see the Cyclone Engine for one alternative design that also generates some topping shp. I also wouldn't do typical reciprocating drive -- I'd do something like Steins' oil-fired switcher, the poster child for Franklin type D if the patent drawings are accurate, or a modernized Heisler arrangement with closed gearcases to 'diesel' wheelsets. I won't rehash all the arguments unless someone wants to get into them. Yes, you could use modulated independent braking on driver cheek plates to do practical slip/traction control for high acceleration at low effective FA, so I'm certainly not going to agitate against the principle of relatively-simple recip engines in this service, and yes, there is some advantage in using modern materials like cerium steel in reducing augment in the running gear ("high speed" here being taken as, properly I think in this context, high rotational speed) BUT it needs to be remembered that this service is one of the worst for rapid deceleration with large trailing load, so buckling or deflection of the rods is a much more likely and severe issue than in most forms of road service -- designer beware! Besides providing good insulation blankets over everything ... And that has improved, radically, in the past decade with aerogel, nanoshield, and other technologies. It is now easy to provide removable/reinstallable formed lagging panels less than 1/4" thick, steam and water tolerant and very light, that have very low heat transfer by conduction, convection, or radiation. ... you provide steam jackets to the cylinders to reduce condensation losses, especially for operating after the thing is parked awhile. Just to be clear: BOTH good insulation and 'heat' jackets. They do different things. Remember that most of the actual heating of the cylinder block is only of concern for alignment, expansion and sealing reasons, and to minimize absolute condensation when steam is first admitted to 'cold' cylinders: the only concern in "condensation" is in the .007" or so of wall metal that cycles back and forth between admission and exhaust temperature, and so you want the metal of the cylinder block at a high enough temperature to keep the 'condensate' that tries to adhere to the oil film and bushing metal in "enough" of a vapor phase not to start coalescing, and to serve to minimize the loss of effective superheat in the steam, of which more in a moment. For repeated idling, you want to maintain the cylinder block very hot, and for that there is no better solution in my opinion than -- not steam jacketing, but overcritical water 'jacketing' of the sort that would be driven from the Cunningham jet pump on a locomotive with a conventional steam boiler. Here you would recirculate water from the 'fireless cooker' reservoir with enough heat makeup, entirely in the liquid phase, to achieve desired block-temperature equilibrium. (As a peripheral note: You want to minimize the heat transfer loss OUT of the cylinder block along the piston rod(s) in a reciprocating engine, and you do this several places: at the piston rings, at the junction of the piston and the piston rod, and at the crosshead, as there is heat gain at each of these locations that is unavoidable, but you want to keep your gland tribology AND sealing good at the same time) The steam jackets ... can be pipe traces welded to the cylinders and then covered with the ... insulating blankets. Note how very much better this approach works with overcritical water circulating through those pipes, and with molded nanoinsulation in the blankets. Yes, without a jet pump, you will need some means of assuring circulation, and of draining the tracers to prevent freezing if the engine is laid up dead for any extended period. The amount of power to run the circulation is trivial, as the pressure head is probably less than that involved in a Lamont boiler, somewhere below 3psi, and I do not think it is difficult to spec either a 'sealed' pump or a shaft-coupling or seal arrangement that can handle the overpressure in the circuit. Now, the reason for superheat is that even after eliminating the wall condensation losses, there is still the nucleate condensation in the steam to address. This is not only for the usual 'thermodynamic' reasons, but because the nuclei can tend to coalesce and induce heat transfer from the walls when it isn't wanted (close to exhaust where the heat transfer really only increases evolving exhaust volume precisely at the time that is least wanted! So you want some controllable superheat in the steam, sufficient to overcome the effects of nucleate conversion depending on the near-instantaneous steam demand or mass flow. A separately-fired design on a fireless locomotive, using the same fuel as the 'make-up' generator, is likely the best way to go; you could use lithium elements or some of the other exotic 'main line fireless locomotive' technologies to extend the intervals between superheater 'firing' but that's just economically-driven detail design.
Paul Milenkovic You take a Vapor-Clarkson automatically controlled oil fired 300-psi steam generator and connect it to a heavily insulated water tank with a steam space on top. You feed steam to an eight coupled wheel engine set.
Or you rebuild any spare GP38/40's you have as 8 cylinder ECOs and save the millions of dollars of development money (though railfans may be dissapointed)..:)
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
RME BaltACD A bad solution looking for a problem. The idea's not wrong -- just the implementation. The problem in part is that people who don't understand switching were designing the things. Switch engines aren't little underpowered Thomas clones that shuttle hither and yon with cuts of cars, any more than commuter locomotives are old hand-me-downs trailing a sorry bunch of Ping-Pongs on a slow trek in and back. And the dominant characteristic in both cases is the same: the native ability to accelerate very quickly with a load, and just as quickly scrub momentum off. It is extremely unwise to use 'conventional' battery chemistry as the source or sink of rapidly-increasing drain or charging current. Even if you can modulate this so the battery 'lives', ther needed to be an explicit control that predictively fires up one or more of the engines in time for the equivalent of 'power mode' (best power from the effective 'sum' of engines and battery) when performing a kick, and winds the engine down to minimize emissions afterward. And, for that matter, reduces other forms of pollution by spooling the engines up in speed with reduced load, to cut down the nanoparticulates and some other undesired exhaust constituents that form if the engine has to accelerate into substantial load, but then haqs the ability to put engine horsepower quickly to work without lugging. I was surprised that GE in particular did not take an interest in marketing its 'hybrid battery' technology to this market ... or that we haven't seen my old 'pet' technology for this, some big counterrotating flywheel storage. Perhaps the market isn't exactly there. I can't help but think, though, there's a good market especially in air-quality management districts, for a genset-style switcher that can actually switch.
BaltACD A bad solution looking for a problem.
The Durathon battery you are referring to was designed specifically for the Hybrid Evolution series locomotive GE was promoting but I don't think any railroad was really interested in buying them. The company then marketed them as standy power for stationary installations. There were few orders and GE has discontinued the product and shuttered the plant...
RME Actually, what you do is charge the device from an external overcritical-water source, like a power or utility boiler, and use the on-board heat source mostly for for 'makeup' and superheating. I think there are better onboard steam-generator designs than Vapor-Clarksons (although, with modern controls and implementation, they are a reasonably evolved and efficient design) -- see the Cyclone Engine for one alternative design that also generates some topping shp.
Well yeah, superheat has two functions. One, it increased the thermodynamic cycle efficiency somewhat by expanding the specific volume of steam at a given pressure. Two, it keeps everything hotter so there is less of all modes of power-robbing condensation.
I have read enough to realize that a wall jacket, whether steam or as suggest pressurized water for this application, does something that a high degree of insulation doesn't quite provide. I have been told and I have also read of a "poor man's" wall jacketing in the form of training crews to set the brakes, open the throttle, and cycle the reverser so as to heat the cylinders up before starting up.
The evidence from Chapelon's 160 heavy tractive effort locomotive experiment is that if you keep the steam hot, from wall jacketing and compound-expansion reheat (a kind of superheater between HP and LP cylinders), the thermodynamic advantage of superheat is only about 7 percent compared to 30-40 percent when you rely on superheat to keep the walls hot.
So, in place of superheat, which is difficult to achieve in the sort of steam generator fed accumulator locomotive I have in mind, you could do compound expansion and then reheat the steam between HP exhaust and LP inlet? Or you could apply heat to the cylinder jacket, or do both.
"Advanced" steam cycles in stationary powerplants indeed use superheat followed by (in some cases) more than one reheats between stages of expansion, and this is all thermodynamically advantageous. You can think of cylinder jacketing capable of transfering a lot of heat to the steam in the cylinders as a limiting case of an infinite number of partial expansions followed by reheat before the next partial expansion.
I haven't done the cycle calculations, but I am not certain I agree that adding heat late in the expansion is really wasted when this is balanced against rigorously preventing wall condensation. This is like Chapelon countering the (mainly British) objection to high levels of superheat leaving exhaust steam above the saturation temperature, regarded as "wasted heat."
Paul MilenkovicSo, in place of superheat, which is difficult to achieve in the sort of steam generator fed accumulator locomotive I have in mind, you could do compound expansion and then reheat the steam between HP exhaust and LP inlet? Or you could apply heat to the cylinder jacket, or do both.
Chapelon did both in the 160A (he had a little Schmidt-type 'resuperheater' in the lower part of the boiler). I also recall his proposing using superheated steam injection as a means of achieving better equalization of cylinder effort between HP and LP (for example to simplify some aspects of dynamic engine balance)
"Advanced" steam cycles in stationary powerplants indeed use superheat followed by (in some cases) more than one reheats between stages of expansion, and this is all thermodynamically advantageous.
Actually, what you see more often for 'thermodynamic advantage' are more than one bleed in between turbine stages, to optimize the feedwater heating part of the Rankine cycle. There is usually very little advantage in passing turbine flow out of the rotating machine to anything that can impart the necessary fast heat transfer with concomitantly minimal flow restriction and then pass the flow back into the turbomachinery without having a blind section of shafting in the middle...
(Now, that gets done for turbines in some PWR nuke plants (where the steam is not really 'superheated' but there is LOTS of cheap thermal energy for the taking. Nobody likes to talk about 'thermal efficiency' too much when discussing those things...). One of the first full-scale reactor setups (at Indian Point) was specified and I think built with separate oil-fired superheaters to get the steam quality where the coal-plant engineers thought it should be for best efficiency. Turned out there were other ways to optimize a fuel source sometimes ...
You can think of cylinder jacketing capable of transfering a lot of heat to the steam in the cylinders as a limiting case of an infinite number of partial expansions followed by reheat before the next partial expansion.
I read that over and over until I got a migraine, and still haven't quite figured out what it means. The jacketing can't and doesn't transfer heat to any kind of steam in the cylinders; it heats up the cylinder block metal from the outside until the very small volume of bushing metal adjacent to the cylinder bore (the about .007" or so I keep referring to) that experiences actual thermal cycling between admitted steam and exhaust steam exposure 'sees' a temperature on the block-metal side that is higher than the temperature corresponding to the start of phase-change wall condensation. In practice it should probably be multiple degrees higher as I suspect there are other mechanisms that cause water molecules to coalesce on the cylinder walls and reduce some of the available pressure that does the work (the molecules will 'de-coalesce' happily and go back into the vapor phase when the exhaust valve comes open, choking some of the flow out the ports and through the exhaust tract.
But what this has to do with partial expansions and reheat, especially taken as the limit of an infinite series, is ... well, please tell me you're not going to invoke quaternions. Please...
... I am not certain I agree that adding heat late in the expansion is really wasted when this is balanced against rigorously preventing wall condensation.
This is like Chapelon countering the (mainly British) objection to high levels of superheat leaving exhaust steam above the saturation temperature, regarded as "wasted heat."
The British are notable for the counterpart of this argument: not optimizing their brake systems for fast and repeated applications because 'brakes waste momentum' that was so elaborately and expensively accomplished with Rankine-cycle-driven expansion work. The added heat 'above saturation' at initial exhaust pressure is to speed up the exhaust, something necessary to get the engine to work effectively at higher cyclic rpm if you can't separate the exhaust tract from the intake tract (cue Kirchhof and the explanations about Franklin System of steam distribution...) and probably desirable to an extent even if you can.
At least some of the "problem" with high exhaust temperatures is that, historically, it was difficult to recover the heat in the exhaust effectively (for the Rankine cycle). First you're mixing it with the comparatively hot combustion gas (which reheats the steam again in the entrainment zone, making it billow in a great many directions that don't facilitate ejecting motion of the entrained jet!) and then you can't take it down to, say, the dew point of sulfuric acid in an 'exhaust system' of the necessary length and complexity to accomplish heat recovery at the required mass and flow combination corresponding to high horsepower at high speed. Much of this has been solved (or at least we know that technical solutions exist for the problems) with modern materials and analytic design. But -- returning to the original proposal, which was not something necessarily benefiting from heat recovery late in the exhaust that is not connected with substantial percentage of condensation -- there might not be enough economic rationale to build these exhaust-heat recovery systems. (My personal opinion 'says' there is, but don't make me pay for it with my own after-tax money!)
There is also a question of how hot you can get the exhaust-steam preheater for your coil monotube boiler -- perhaps this is quite hot indeed but in a comparatively small volume in a contorted sort of space, and not proportional to demanded power (the exhaust heat may take some time during the early stages of a kick to 'get all the way to' the point where the fuel is encountered and the combustion plume begins for it, and then you have some amount of heat running around when you close the throttle that then has to be dissipated...
I got lost. Are we talking about steam gensets?
_____________
"A stranger's just a friend you ain't met yet." --- Dave Gardner
We've gone from the science of gensets to invoking the name of Andre Chapelon. I love it.
Paul of CovingtonI got lost. Are we talking about steam gensets?
Not quite. We're talking about a steam locomotive that does a specific job -- switching where cars are frequently kicked -- better and with the same sort of economy as genset locomotives are supposed to provide.
First: As Ed and some others can tell us, a large range of practical switching jobs involve high acceleration and rapid braking. This requires -- for very short periods of time -- very high power, while 'the rest of the time' the powerplant of the switch engine is essentially idling (or shut down) when not needed.
The premise of the genset locomotive was to use multiple small engines that could be started and run in combination, to select the amount of power needed at a particular time. This was great for limiting emissions in air quality management districts, but not so great when the amount of power developed by the locomotive has to go from low to full quickly, without more than a few seconds' actual warning, and then as quickly be reduced to 'coasting' level. Diesel engines don't like accelerating into a load, and they (and their turbochargers) don't like being chopped back to idle or, worse yet, shut off as soon as they aren't needed.
This issue can be partly overcome by providing an energy-storage transmission -- what in cars is called a hybrid -- which can store energy over time from a comparatively small or lightly-loaded powerplant (running steadily at the peak of its torque curve where efficiency is highest and emissions at a minimum per hp/hr), release the stored energy quickly to aid acceleration, and then use regeneration to provide both braking and energy recapture. To this, we add the ability to fire up additional engines 'when needed' just to help accelerate cuts of cars a bit quicker.
What Paul was proposing is to use a fireless cooker locomotive with a comparatively small, efficient steam generator (like a glorified boiler) to keep it charged and hot. This accomplishes the same thing with steam pressure and mass flow that the hybrid genset does with stored and moving electrons. The difference is that steam used in a simple circuit involves much less cost and complexity for equivalent drawbar power, and even as high-density energy storage in advanced battery chemistry and supercapacitors becomes expensive and prone to damaging and even 'runaway' thermal effects, overcritical-water storage and onboard 'steam charging' become much more efficient as thermal insulation technologies and barrier coatings become better and cheaper.
"Overcritical water" is essentially steam that is being held in the liquid phase by pressurizing it. For short-term power it can be thought of as a reservoir 1000 times the physical volume of the tank, initially charged by transferring liquid from a pressurized boiler system (like a power boiler) rather than the familiar fireless cooker method of bubbling and condensing live steam into colder water. The novelty here is in providing a comparatively small machine that, on average, puts the heat back into that tank of water at 'enough rate' that the developed steam pressure does not fall beyond a working limit during the engine's assigned 'shift'. And, as the last part of the discussion was adding, the small machine is also arranged to provide working superheat for the steam going from the storage reservoir to the working cylinders, for the reasons the last few posts were discussing. (It probably bears noting that the reasons for 'failure' of historical reheated fireless locomotives (Fowler's Ghost and the Sentinel 'Receiver' locomotives being a couple of examples that come to mind) may not involve the current emphasis on very high short-term efficient power excursions for acceleration...)
Theoretically, at least, an engine built this way can have the thermal efficiency usually associated with battery-electric 'plug-in' hybrids -- it is charged with the same water used to generate electrical power, so it shares the efficiency of modern Rankine-cycle electrical generation without the actual generation, switching, and transmission losses, and it is 'recharged' thermally with heat that need not be even roughly synchronized with physical acceleration rate, for even comparatively small storage-reservoir mass (and for adhesion, there is little point in not providing a large reservoir if the insulation methods are good...)
The reason I use 'overcritical' rather than the more typical term 'supercritical' for steam kept liquid by pressure is that I reserve 'supercritical' for steam that is over its 'critical pressure' (between 3206 and 3208psi) -- above that pressure it is ALWAYS liquid no matter how much superheat is put into it. Engines can be designed to take advantage of this (the enginion AG 'zero emission engine' being a good example, and the Cyclone Technologies powerplant another) but many details of their construction and operation are very different from conventional steam power even when they use apparently-similar piston engines (a fancy euphemism for that being 'positive-displacement expanders'). These make an interesting alternative in locomotive service, too ... one which I've described in other posts ... but in very different ways, and at probably much higher initial implementation costs, than a 'normal' fireless system even of Gilli pressure.
RME "Overcritical water" is essentially steam that is being held in the liquid phase by pressurizing it.
"Overcritical water" is essentially steam that is being held in the liquid phase by pressurizing it.
I never heard of this term before. Water held under pressure at a temperature below the saturation temperature (i.e., the boiling point) is generally referred to as subcooled liquid or compressed liquid.
Edit: These terms do not necessarily refer only to high pressures and temperatures. A glass of water at 70F is a compressed liquid since because it is at 1 atmosphere pressure and at only 70F rather than 212F. It is the pressure of the atmosphere that prevents the water from boiling. If the pressure dropped below about 0.36 psia some of the water would flash into steam.
RME ... The reason I use 'overcritical' rather than the more typical term 'supercritical' for steam kept liquid by pressure is that I reserve 'supercritical' for steam that is over its 'critical pressure' (between 3206 and 3208psi) -- above that pressure it is ALWAYS liquid no matter how much superheat is put into it. ...
...
The reason I use 'overcritical' rather than the more typical term 'supercritical' for steam kept liquid by pressure is that I reserve 'supercritical' for steam that is over its 'critical pressure' (between 3206 and 3208psi) -- above that pressure it is ALWAYS liquid no matter how much superheat is put into it. ...
As I remember from thermodynamics, Supercritical is a fluid that is neither liquid nor gas phase, but has some of the properties of both, such as high density and fills its volume.
RME "Advanced" steam cycles in stationary powerplants indeed use superheat followed by (in some cases) more than one reheats between stages of expansion, and this is all thermodynamically advantageous. Actually, what you see more often for 'thermodynamic advantage' are more than one bleed in between turbine stages, to optimize the feedwater heating part of the Rankine cycle. There is usually very little advantage in passing turbine flow out of the rotating machine to anything that can impart the necessary fast heat transfer with concomitantly minimal flow restriction and then pass the flow back into the turbomachinery without having a blind section of shafting in the middle... (Now, that gets done for turbines in some PWR nuke plants (where the steam is not really 'superheated' but there is LOTS of cheap thermal energy for the taking. Nobody likes to talk about 'thermal efficiency' too much when discussing those things...). One of the first full-scale reactor setups (at Indian Point) was specified and I think built with separate oil-fired superheaters to get the steam quality where the coal-plant engineers thought it should be for best efficiency. Turned out there were other ways to optimize a fuel source sometimes ... You can think of cylinder jacketing capable of transfering a lot of heat to the steam in the cylinders as a limiting case of an infinite number of partial expansions followed by reheat before the next partial expansion. I read that over and over until I got a migraine, and still haven't quite figured out what it means. But what this has to do with partial expansions and reheat, especially taken as the limit of an infinite series, is ... well, please tell me you're not going to invoke quaternions. Please...
I read that over and over until I got a migraine, and still haven't quite figured out what it means.
This business of rereading my prose and getting a migraine. You sure you weren't one of the anonymous reviewers of my last journal article submission?
Seriously, folks. The objection was raised some comments back that the heat applied to the cylinder jacket was wasted because it heated the steam during the entire expansion stroke, including late in the stroke where the heat-expanded steam is about to be discharged through the opening of the cylinder to the exhaust.
Well, either the steam or pressurized-water heated cylinder transfers significant heat to the expanding steam or it doesn't. If it doesn't transfer significant heat to the expanding steam, the worry that heat is wasted in the exhaust is moot. If it does transfer significant heat to the expanding steam, one expansion stage with heat added during that expansion should be thermodynamically equivalent to having many compounded expansion stages with reheat between each stage.
You tell me that no one applies reheat between turbine stages in a conventional turbine power plant because of all of the tubing pressure losses, and I take your word for it. Where I have seen cycle diagrams with reheat between multiply compounded expansion stages is in thermodynamics textbooks, where such books are written by ivory-tower academics who may have never seen the turbine gallery of an actual power plant.
If you are still worried about too much heat in the steam remaining during exhaust, you can always recover (some) of that heat by either A) using it to help heat the feedwater or B) using it to preheat the combustion air. Both of these have been done or proposed.
As to having too much heat remaining in the flue gases on account of the need for high superheat, yes, that Franco-Crosti gizmo cooled the gases too much and was wrecked by acid dewing, but I believe it was (again!) Chapelon who proposed a flue-gas economizer in the form of simply restricting the water flow with the front part of the boiler with a baffle. Wardale proposed this system for his 5AT design more recently.
But in my proposed steam-accumulator switch engine, you are only providing a small supplemental "steam generator" to top off the steam accumulator (not my original idea -- there are descriptions of this concept on the Web). Envisioning the cylinder steam as drawn from the accumulator, I am accepting that this is a saturated-steam cycle, and as such, you need some what to counteract cylinder wall condensation. This could be done with some combination of reheat between compounded expansion stages, the reheat being drawn from the accumulator instead of messing with extra coils in the steam generator, or in cylinder jacketing. This jacketing may or may not transfer substantial heat to the expanding steam in the cylinder. If it does, this is not thermodynamically disadvantageous, at least not according the Chapelon (argument by authority) or according the thermodynamic calculations (argument by a simplified mathematical model).
However heat is added to the steam after it leaves the boiler, whether in one go with a high degree of superheat up front or in multiple passes of reheat, it is at least my experience with solving the exercises from the thermo textbooks that none of this heat is wasted, even if the exhaust is a lot hotter than you think it should be. The exhaust is hotter (higher temperature where heat is removed in the cycle) but the superheated (or reheated) steam is also hotter (higher temperature at which heat is added to the cycle), and calculations show, on balance, that thermal efficiency improves.
And this is backed up by what Chapelon was saying in defense of going for as high a superheat temperature as your pipes and cylinder oil can stand. It was the British who held to high superheat being wasted heat as evidenced by their pitifully small superheater areas on their locomotives, which Chapelon regarded as a thermodynamic error.
MidlandMike RME ... The reason I use 'overcritical' rather than the more typical term 'supercritical' for steam kept liquid by pressure is that I reserve 'supercritical' for steam that is over its 'critical pressure' (between 3206 and 3208psi) -- above that pressure it is ALWAYS liquid no matter how much superheat is put into it. ... As I remember from thermodynamics, Supercritical is a fluid that is neither liquid nor gas phase, but has some of the properties of both, such as high density and fills its volume.
My recollection from thermo was that supercritical meant no phase change during heating. Below supercritical pressure, heating a fluid at constant pressure would involve a region where heat could be added but there would be no increase in temperature. The added heat would be consumed by converting liquid to gas.
One advantage of running a boiler at supercritical pressures is that the fluid being heated would be homogenous as opposed to the mixture of liquid and gas phases in two phase flow.
CAUTION -- this is a long post. Very long. Much worse than the usual 'yes-but' sort of production. Be advised that I couldn't find a TL;DR solution for you all. Don't read it if you don't like this sort of thing or tolerate Aspergers sufferers well...
Paul MilenkovicSeriously, folks. The objection was raised some comments back that the heat applied to the cylinder jacket was wasted because it heated the steam during the entire expansion stroke, including late in the stroke where the heat-expanded steam is about to be discharged through the opening of the cylinder to the exhaust. Well, either the steam or pressurized-water heated cylinder transfers significant heat to the expanding steam or it doesn't.
The principal purpose of the 'jacketing' (at least at locomotive scale) isn't intended to 'transfer significant heat to the steam'; it's to reduce the temperature differential across the small diameter of wall metal that necessarily cycles between admission and exhaust temperature. There are surprisingly few references that discuss 'proactive' steam jacketing, and the ones I've found tend to be from the nineteenth century on smaller engines (not that this necessarily indicates the idea is wrong). The great exception is Chapelon's experiment on 160 A1, where he uses enormous "free" superheat passed around the HP cylinders (to heat them before the superheated steam comes anywhere near something needing tribology) -- I have not seen the precise ducting patterns he used for this, especially around the cylinder ends, but it should be possible with judicious use of heat pipes to get good coverage where needed without significant differential thermal-expansion problems, and I believe good ring design would make up for overall higher expansion of the cylinder inside wall at any high degree of 'wall-condensation eliminating' heat.
Some reasons for my proposing to use 'boiler' (here, accumulator) water instead of steam is that, while it is not superheated, it does inherently provide "liquid" rate of heat transfer combined with a temperature significantly higher than equilibrium temperature of late-expansion or exhaust steam -- this is essentially quite a good amount of 'superheat' relative to the temperature of steam 'tending' to condense on the cylinder walls and reduce late expansion pressure (and hence extractable work on the piston, the point of the "thermodynamics" there). In addition, Chapelon's method, to my knowledge, did not allow circulation of highly-superheated steam 'bypassed' through the jackets with the throttle restricted or closed; all the steam necessarily went through the ports and passages, and among other things this would still require cylnder cock opening at starting, overpressure relief discs or equicalent in the heads, etc. Furthermore in the absence of separately-fired superheaters (superheater dampers being a kind of primitive approximation) there is what I at least suspect would be the possibility of severe element damage with that level of superheat from a Schmidt type setup, if the mass flow suddenly decreases but the combustion flow does not do so synchronously. Again I'm cheating a bit by proposing that the locomotive be 'practical' for service outside of what Chapelon was proposing for 160 A1 (or the sort of service that was typical of runs like the ones on the Rio Turbio line, where long stretches of continuous working at reasonable cyclic speed were a major constituent of ordinary daily practice). This is almost completely the opposite of the current situation under discussion - use of a locomotive for sudden bursts of speed at high required power, followed by uncertain periods of near-total idleness.
If it doesn't transfer significant heat to the expanding steam, the worry that heat is wasted in the exhaust is moot.
You keep coming back to the thermodynamics, when it is the pressure effects (and concomitant flow effects) that are the real issue and concern in locomotive cylinders and tracting. In many cases -- apparently including your own discussion further down -- it's better to eliminate the exhaust at a higher temperature in order to reduce effective back pressure (especially when issues of practical compression management can be handled separately from having to approximate things with the steam volume and quality 'remaining locked in the cylinder' at the conclusion of exhaust-valve closure). This is the situation I'm discussing when I point out that the condensations -- wall and nucleate -- that are reversed only as exhaust pressure falls contribute negatively to the engine's ability to produce extractable work.
A good example of how this applies to locomotive practice can be seen in a somewhat unorthodox place: the exhaust-plenum arrangements on the GE high-pressure steam-turbine-electrics of the late 1930s (which I think can indeed be thought of as a series of intermediate expansions from very high initial pressure to 'as low as possible' final temperature, complicated by the need to use air-cooled condensers in a presumably often very hot environment. At any point that there is choked flow in the steam circuit, it becomes the limiting factor in extractable work, and that (not thermodynamic efficiency overall) is both the concern I was addressing and one of the critical reasons for the 'great increase in economy' produced by Schmidt superheating in practice.
If it does transfer significant heat to the expanding steam, one expansion stage with heat added during that expansion should be thermodynamically equivalent to having many compounded expansion stages with reheat between each stage.
Where I get the migraine here is that the 'heat added during the expansion' has nothing to do with 'expansion stage'; it's just keeping the phase change from reducing the effective steam volume. It isn't intended to 'resuperheat' the steam (as some huge defective attempt to reduce nucleate condensation in the steam volume via a relatively small temperature differential from a polished metal surface) - only to preclude as much wall condensation as economically justified.
You tell me that no one applies reheat between turbine stages in a conventional turbine power plant because of all of the tubing pressure losses, and I take your word for it.
There are plenty of places there is reheat between powerplant turbine sections (what you refer to as 'multiply-compounded expansion stages') -- what you don't see is reheat between stages in a particular section (this is not just semantics) as if you were doing a feedwater-heater bleed in reverse to keep the interstage losses minimized (for example to reduce erosion due to nucleate condensation). Naturally there are points where steam quality in the exhaust from a given turbine section -- of a large enough plant, with enough packaging room to support the arrangements -- will benefit from reheating before going into another section, and in some cases the reheat is dictated in part by the size and maintenance of a turbine that would otherwise deal with 'unreheated' steam quality. My experience with powerplant turbines is restricted, but I don't think I remember more than three external reheat stages (exclusive of supercritical) in most practical powerplant use.
This is comparable, I think, to compounding in positive-displacement expanders, where the reheat is done entirely between cylinders (for example as in the 160 A1 between HP and intermediate pressure) with a separate little combustion-gas 'superheater element' arrangement).
Note that the practical versions of (a) on locomotives are almost always achieved by bleeding the exhaust steam, not using it directly, and very few of the attempts to do (b) have worked out in practice. It is interesting, by the way, to consider what both these systems would consist of on the proposed switch engine, which presumably uses a blower and monotube (I suspect all the necessary work has been done over the years since Doble by the enthusiasts over at SACA). Once again, there may be, and historically often has been, a big distinction between 'best thermodynamic efficiency' and the most practical working locomotive that accomplishes what a railroad needs, is built to an acceptable price and size, and can be maintained economically by 'available resources'.
[quote]As to having too much heat remaining in the flue gases on account of the need for high superheat, yes, that Franco-Crosti gizmo cooled the gases too much and was wrecked by acid dewing, but I believe it was (again!) Chapelon who proposed a flue-gas economizer in the form of simply restricting the water flow with the front part of the boiler with a baffle.[quote]
That's not Chapelon as much as it's part of Baldwin's sectional-boiler idea, as seen on the hinged-boiler Santa Fe Mallets and similar thermodynamic tours de force of the early 20th Century. If you look at why that didn't work so well then, you'll realize why it won't work so well now, and in any case how is that relevant to practical recovery of combustion heat from a monotube steam generator with no defined 'convection section' with lolog heat uptake?
The point with the Franco-Crosti isn't that it 'cooled the gases too much' as that it was made too 'thermodynamically effective' at trying to squeeze out the last possible traces of useful heat from high combustion-gas mass flow with a single installation that would often have to see reduced flow in practical service. In any case the acid-dewing issue is better addressed in other ways (some of which we have already described) IF we have decided to make use of the residual heat in the exhaust. (And yes, I am a believer in recovering as much of that heat as can be justified by economics.)
But in my proposed steam-accumulator switch engine, you are only providing a small supplemental "steam generator" to top off the steam accumulator (not my original idea -- there are descriptions of this concept on the Web).
At least a couple of which I've contributed to. You're the one who raised the idea in this context, and therefore it's fully appropriate to consider you the 'proposer' here.
Envisioning the cylinder steam as drawn from the accumulator, I am accepting that this is a saturated-steam cycle, and as such, you need some what to counteract cylinder wall condensation.
I assume you mean 'heat', as that makes best sense in the context of this discussion. Part of the conceptual 'detail design' is the inherent 'steam quality' that is maintained in the accumulator by the maintaining action of the 'makeup generator' -- if this, for example, is held at the level used for a Gilli-cycle engine, the available superheat as throttled to the valves may be sufficient in the absence of some form of separately-fired superheat. Quite a few designs of small boiler are designed to support high pressure economically, and with good insulation there is relatively little additional loss involved in 'keeping' the accumulator charged to 1000psi or higher as maintenance instead of operating 'makeup' only as steam quality at lower pressure begins to drop below conventional acceptable limits (for ordinary 'fireless cooker' industrial locomotives and the like).
Now, part of the thing that favors a monotube here (as I think you've already covered) is that the makeup load for a locomotive like this may be highly intermittent, unpredictable, and involving little advantage from any 'residual heat' after periods of high firing. So I am tempted to accept that a 'makeup system' with high proportional output, perhaps even capable of supporting a considerable proportion of 'full output' steam flow "by itself" (as if, for example, in a Sentinel engine) would make sense even in a pure thermodynamic-optimizing design here.
This could be done with some combination of reheat between compounded expansion stages, the reheat being drawn from the accumulator instead of messing with extra coils in the steam generator, or in cylinder jacketing.
This is an interesting point, and would best be considered by doing the equivalent of heat-balance diagrams for the different configurations. In this particular application we wouldn't be greatly concerned with augment in a compound engine, so considerations of IP injection, etc. to adjust torque moments and the like in a compound direct-acting engine might be of less concern, and the relatively long steam path including that through heat exchangers to get effective reheat from the accumulator water might be worthwhile.
The 'extra coils in the steam generator' is only workable if the makeup SG has come up to efficient firing conditions when the additional superheat is desirable. It seems to me that this is precisely what is called for in this design, as most of the additional 'superheat' required in the engine follows very closely after acceleration begins, and of course terminates when the acceleration does; it would certainly seem to be a better use of 'capital' to fire the SG instead of providing and maintaining a whole separately-fired superheater arrangement (admittedly of much less sophistication than a monotube and its control systems) or a long system of intermediate interstage reheat in the accumulator.
I'd at least look into whether some combination of accumulator and 'combustion' reheat would produce the best steam quality for required acceleration 'net' of all other costs.
This jacketing may or may not transfer substantial heat to the expanding steam in the cylinder. If it does, this is not thermodynamically disadvantageous, at least not according the Chapelon (argument by authority) or according the thermodynamic calculations (argument by a simplified mathematical model).
How did we get back on the subject of jacketing? This is superheat applied to the steam entirely outside the cylinder, and acting in the conventional ways within it. To recap the previous discussion, "substantial heat" is not what the jacketing (vs. better insulation) is intended to provide to the steam itself, and wall condensation is not the only consideration that additional superheat is designed to overcome.
I thoroughly agree that unconventional methods of 'heating' the steam may be practically as well as thermodynamically advantageous; that's one reason I was so interested in the detail design of the approach used on 160 A1. We do need to be careful in applying 'argument by authority' in this particular case, as Chapelon himself appears to have taken considerable pains to explain 160 A1's design as applying to a very restricted set of circumstances. and we must fall back more on the 'authority' of his design principles and desiderata. (Which I am usually in agreement with, not that that's an important fact in itself...)
However heat is added to the steam after it leaves the boiler, whether in one go with a high degree of superheat up front or in multiple passes of reheat, it is at least my experience with solving the exercises from the thermo textbooks that none of this heat is wasted, even if the exhaust is a lot hotter than you think it should be.
We can cut to the chase, without textbooks: the heat is "wasted" in a Rankine cycle if it is not practically returned to the cycle so that extraction of work from the cycle is facilitated. Any superheat in steam exhausted to atmosphere is wasted if its energy does not produce a corresponding amount of additional draft or ejection efficiency. Heat remaining in the combustion gas is wasted if it is used for nothing other than evolution of the smoke plume above the cab windows on a locomotive.
But heat can also be 'wasted' if it is applied in the wrong part of an expansion cycle. "Heat" doesn't do anything per se in an engine; one of the reasons for the use of that mysterious metric "entropy" is to do a transform from heat transfer to pressure (would that the French experiments on ether compounding in the 1850s had understood the point of this!) This is a different point from the usual overreliance on maximizing "thermodynamic efficiency" at the cost of having a usable locomotive. Almost right up to the end of the 'steam era' the reason for benefits from a 'free exhaust' were debated and, I think, often misunderstood. One of them is surely reduction of the losses from evolved exhaust volume due to internal condensations (of both types). And part of our attention should be focused on the methods best suited to eliminate those condensations without introducing more difficulties than they practically solve.
The exhaust is hotter (higher temperature where heat is removed in the cycle) but the superheated (or reheated) steam is also hotter (higher temperature at which heat is added to the cycle), and calculations show, on balance, that thermal efficiency improves.
Again, I assume that the 'on balance' includes an accounting for the increased losses of all types where the cycle occurs at higher temperatures, including those related to differential thermal expansion (as in the original Stumpf uniflow) or mechanical systems (I'm thinking particularly of the valve troubles in the Paget locomotive).
You will not hear me complaining about using a higher starting temperature for a Rankine cycle in this application -- you will note that I predicated part of my design on initial charge from a powerplant boiler, inherently at high pressure and starting temperature, although I confess I had not thought far enough ahead to realize that the ending temperature in the accumulator also needed to remain high (and presumably 'recovered' by transfer back to the powerplant boiler in the appropriate place(s) in its feedwater train at the end of the service day).
[quote ... this is backed up by what Chapelon was saying in defense of going for as high a superheat temperature as your pipes and cylinder oil can stand. It was the British who held to high superheat being wasted heat as evidenced by their pitifully small superheater areas on their locomotives, which Chapelon regarded as a thermodynamic error.[/quote]
There is an additional British 'error' in the placement of the superheater on the far side of the throttle, making a number of practical difficulties for what I consider very little gain in effectiveness. In this context, I would note that neither you nor Chapelon seem to consider the practical problems involved with throttling very highly superheated steam (perhaps reverting to the idea of having some or all the additional superheating after the throttle), but I think those problems can be overcome on locomotives.
How you can have 'wasted heat' from higher net superheat with the typical combustion-gas temperatures observed at superheater headers in normal locomotive boilers is a mystery to me. The issue is, and I think always was, much more involved with getting elements to 'live' an acceptably long time in practice, and accommodating the cycling and damage that occurs when high peak superheating and the high effective 'turndown' in efficient normal railroad operation occur in the same passive design (and you don't have a fancy 'mecanicien'-controlled system of combustion-gas flow management to protect the elements at all times).
Yes, you have to design the engine correctly to make best use of higher superheat. I am tempted to note that almost certainly locomotives need to make use of compound expansion (not just internal approximations in a single long expansion) to achieve the best gains from very high superheat, once the effective limits of 'jacket-induced superheat' have been achieved.
We may need to 'agree to disagree' in principle on a couple of thermodynamic points related to elevating cylinder-block temperature, and the reasons for doing so, until a few good heat-balance diagrams have been generated to show all the flows and losses in the different arrangements. I'm going to stick to the idea that only the amount of block heat that stops effective heat transfer OUT of the steam as it 'tries' to condense or coalesce on the walls is the 'best use' of Rankine-available heat.
(There is another potential approach to reducing wall condensation that involves dielectrics and electric charge, but that's a discussion for a decidedly other day!)
BTW: my use of a coined distinguishing term is only because in historical steam-power discussions the use of the word 'supercritical' is applied in two very different contexts as two essentially different terms. In power generation it means steam well above 3206psi, with the effects erikem described; in analyses of things like boiler explosions it means water superheated to the point where, at reduced or atmospheric pressure, it will suffer nucleate boiling 'everywhere' leading to very high rates of peripheral acceleration and potential shock effects on boiler cladding. Since 'supercritical' and its big sister 'ultrasupercritical' (which useta be around 4200psi but is now apparently edging higher) are so well established in contemporary steam engineering, I chose to address the 'other' effect with a distinctive term that would be familiar to someone using the older one in context. A term like 'subcooled liquid' is more applicable to the sort of phenomenon where water stays in liquid phase as it is heated well above 'boiling' temperature (at a given equilibrium pressure), then flashes when nuclei are introduced -- this is a different effect from what happens when pressure is relieved suddenly from a mass of water actively evolving steam at the time, even though the physical principles may be understood as common.
OK, OK, alright already!
In keeping "stuff" (the cylinder walls, the steam, the whatever) hot enough that you don't start condensing steam on the walls (and then flashing the condensate back to steam when the exhaust valve cracks open, losing whatever heat you added to the walls), you are going to end up with steam entering the blast pipe hotter than the saturation temperature, where it can start condensing into liquid.
I don't care how that heat got into the exhaust steam, whether from a high superheat at the steam chest feeding the valve or from heat transfered from the proposed cylinder jacketing to the expanding steam, there are those who claim this wastes heat (an earlier comment on this thread complaining about excess heat in the steam just before the exhaust valve opens, Chapelon's British critics).
What I tried to say was "were" (subjunctive tense of "is", that is a conditional or provisional state of affairs), were heat transfered from the cylinder jacket to the expanding steam, even if this heat transfer took place late in the expansion where it doesn't do any good according to the wasted heat worriers, and I am not even saying this heat transfer takes place because that would have to be determined by experiments and careful measurements and indicator diagrams an all of that, were heat transfer to take place, this would not be a bad thing.
It can be proven to not be bad, in the eventuality that such a thing takes place, because you can solve the efficiency of theoretical multiple-reheat Rankine cycles from thermo textbooks that show it to not be a bad thing, were (again, subjunctive verb) such a thing to be a concern.
And yes, I have evidence that such a thing could take place, in fact did take place (the heat transfer in question) and it was not a bad thing. It is claimed, by a French Web site, that not only did the Chapelon 160 12-coupled locomotive (the French count axles, not wheels) not lose efficiency at slow piston speeds (see Wardales efficiency charts in The Red Devil for this effect), it actually gained (a little bit) in efficiency the slower it went.
So who am I around here, Gallileo before the Inquisition trial? The cylinder jacket can and did transfer heat to the expanding steam, and Chapelon, no less an authority, proved it.
RME A term like 'subcooled liquid' is more applicable to the sort of phenomenon where water stays in liquid phase as it is heated well above 'boiling' temperature (at a given equilibrium pressure), then flashes when nuclei are introduced
A term like 'subcooled liquid' is more applicable to the sort of phenomenon where water stays in liquid phase as it is heated well above 'boiling' temperature (at a given equilibrium pressure), then flashes when nuclei are introduced
RME -- this is a different effect from what happens when pressure is relieved suddenly from a mass of water actively evolving steam at the time, even though the physical principles may be understood as common.
-- this is a different effect from what happens when pressure is relieved suddenly from a mass of water actively evolving steam at the time, even though the physical principles may be understood as common.
I know that the crews on the Capr Fear Railway at Ft. Bragg, NC were none to impressed with them. "They load too slow," was the quote to me. CF is a hilly little shortline. I can understand their frustration.
One major issue with Class 1's ordering more genset units is that, for the most part, the smaller engines used in that locomotive type rely on SCR/DEF (i.e urea) to meet Tier IV emissions levels, a technology the big railroads want to avoid. The only exception to this that I am aware of is some of MTU's genset size engines which use exhaust gas circulation.
This may not be as big an issue with industrial operators whose locomotives stay captive within their plant trackage..
carnej1 This may not be as big an issue with industrial operators whose locomotives stay captive within their plant trackage..
Where I have the most interest is in the Class II use of reliable small high-speed engines to replace "cheap old GP7s" and the like as bottom-line cost-effective solutions for the size and nature of the trains they run. An interesting current thread in LocoNotes indicates that a couple of SW1000-size engines are going to have their frames lengthened, a pair of 750-hp [edited; was 900] Cat gensets installed, and the brake gear updated and modernized ... presumably for this type of service, and with the 'modularity' of the power such that loading and unloading issues due to engines having to be cut on and off to meet transient grades and other causes of train resistance will be effectively minimized.
These are said to be dual-fuel capable C18s, probably (at 750hp) not very different from the 'small' engine in a PR43c. Does this engine need SCR, or could it use alternative technologies like EGR effectively -- there certainly seems to be room for the necessary equipment for non-DEF NOx reduction for two engines this size.
Not sure I have seen a project quite like this before from one of the 'alternative locomotive' builders (the concentration seems to have been on repowers with larger high-speed engines, penny-pinching minimum-power gensets or battery hybrids, or 'environmental-centric' builds for use in air-quality-management districts perhaps without regard to actual operating flexibility as a required parameter.) I'll be watching out to see where this project goes, how successful it is, and whether it justifies its modification costs in service.
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