Paul MilenkovicWhat is "pilot injection" in the context of reciprocating steam engines?
I use it in the same sense as in fuel injection.
The idea is that you have a fundamental set of valve events, which cause and then induce steam flow (through the ports and passages). Pilot injection involves a small modulation of additional steam which 'fine-tunes' conditions in the cylinder for action of the main charge. Note that much of the additional mass flow and timing change required for extreme high speed can be provided via sufficiently-capable (and electronically-timed) injection in addition to what the valves do, without requiring the valve gear itself to be able to source the necessary mass flow at high cyclic/low duration.
In fuel injection, a very small amount of fuel can be injected early in a compression-ignition engine (or a direct-injection engine) to raise the temperature of the air charge through partial combustion and lower the effective compression that has to be derived from crankshaft rotation, at the same time distributing a small amount of 'promoter' molecules within the cylinder volume to optimize subsequent combustion reactions, especially when the engine is running at high speed/short combustion duration but relatively high expected MEP.
Pilot injection of steam can be used for a variety of purposes, one of which is to in effect 'clean up' the indicated diagram of pressure, another of which is to increase retained compression slightly to give less wiredrawing upon valve opening but maintain overall effective mass flow, another of which is to enhance heat in the cylinder on short cutoff and long expansion to preclude nucleate expansion when operating outside the best 'envelope' for valve and cylinder construction.
The N&W booster valve does some of what pilot injection can accomplish, but in the intermediate receiver rather than directly in a cylinder. As I recall, Chapelon's modulated IP injection (and probably Porta's after him) is conducted in the receiver and controlled via some form of PID to be effective at the LP cylinder in phase with the HP.
A kind of 'opposite' of this can be seen in the auxiliary exhaust valves in a Uniflow locomotive, where additional accommodation for steam mass flow may be necessary under certain operating conditions. Perhaps by stretching the definition a Herdner valve could be thought of as a somewhat primitive, untimed device for 'injection' at starting.
What is "pilot injection" in the context of reciprocating steam engines?
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 MilenkovicI get that compounding hasn't lived up to its promise
It did in France, where coal was over "the equivalent of $6.60 per gallon", and engineers were trained as just that -- they didn't call them 'mecaniciens' as a euphemism. There were other factors that enforced low water rate through compounding, such as a relatively low fixed speed limit that stressed acceleration to speed and then fine speed control close to that limit more than absolute high speed potential.
There was evidence that compounds were getting pitifully small amounts of power out of their LP stages on account of nucleate or wall-effect condensation.
What is perhaps surprising is that so little practical recognition of the effect of this problem was made over the years. The issue is more significant than just 'condensation'; it's disproportional pressure over the stroke length, out of 'sync' with the HP expansion characteristics.
The effective 'cure' for this problem is some kind of proportional injection into the LP to equalize the thrust over the stroke with that practically being exerted by the HP. (There is a kind of parallel for multiple-stage systems like that on the 160 A1, but as I don't entirely understand the dynamic layout Chapelon used, I can only mention it in the abstract.) This was difficult to do with strictly analog machinery, even in the early 1950s, and by the time digital equipment was properly robust to work on steam power, the emphasis was more toward steam turbines and not simple reciprocating power. Even a slightly 'improved' version of the N&W booster valve is capable of reasonable performance in this kind of service ... at least in my humble opinion.
Chapelon's first approach was applying high levels of superheat so the steam would make it through the HP and LP stages with some superheat left so it wouldn't condense...
You see Porta advocate this, too ... with the same apparent blissful disregard of the important thing that rears its head: valve and cylinder lubrication and distortion at the higher peak superheat. I've never seen discussion of distortion of those fabricated Willoteaux valves, but I'd expect effective steam sealing and precise steam-edge admission and cutoff to suffer. Perhaps badly. See also ... very carefully ... Wardale's discussion of steam cooling for piston valves.
Tribology was a rock upon which a great many attractive-looking 'thermodynamic' improvements founder when you try to reduce them to Actual Railroad Practice.
Whereas his 242-A1 fast passenger locomotive gets the glory, his second approach came out of the 160-A1 high-tractive effort freight locomotive. A fuel-efficient freight locomotive is what the ACE project and their various iterations of proposed locomotives were all about.
Unfortunately, there are concerns of first cost and maintenance also concerned along with 'fuel efficiency', and considering that three cylinders was not embraced in this country ... even when steam locomotive performance was paramount ... you can readily guess where six doing the work of five would get you. Especially if you started jiggering it to achieve higher road speed, which you'd have to do for most North American traffic even if it were cost-effective to limit use to heavy mineral service.
The 160-A1 was set up as a test bed to try different combinations of things, and it seems the "best" setup was to use low or no superheat (helps with valve and cylinder lubrication) in the HP feed but to rely on jacketing the HP cylinders to fend of wall condensation.
Note that this was the engine that was tested with Chapelon's idea of using high superheat through and around the cylinder block to give it consistent preheat before encountering 'anything lubricated', thereby avoiding a need to use a saturated-steam jacket or supercritical-boiler-water tracer lines to heat the mass of the wall metal in the various cylinders that needed it.
Remember that only about .007" of the wall thickness actually cycles in and out of potential wall condensation (if we ignore the effects of the lube film on condensation nuclei) and therefore the effects of mean cylinder-mass temperature begin to affect the thermodynamics whereby this (relatively) small volume is heated and cooled during the effective stroke. It is my opinion that keeping the cylinders hot 'all the time' is a fundamentally good idea; in fact I go further than Wardale, who famously thinks that good insulating jacketing is enough, and think the cylinders should be maintained above condensation temperature for admitted steam at all times.
Condensation in the LP cylinders was to be forestalled by use of a reheater of the IP steam.
Interesting how this was provided, too: it puts flues in the 'bottom' tubes of a conventional convection section, where effective heat transfer is usually assumed to be lower and more recapture of gas heat in 'elements' can be made to a practical degree (lower reheat temperature than for HP).
Every degree of additional IP heat that can be achieved in a Schmidt-type return-bend loop is a degree that doesn't have to be added via the modulated steam injection. This helps in a number of ways, and it imposes relatively little restriction or time-phasing concerns on LP admission timing. The 'catch' in many locomotive designs is that the path from HP exhaust to LP valve inlet is long and comparatively tortuous in many designs, vs. where 160 A1 could put it...
I am interest in other sources of technical data on steam if someone can point me to them...
Something you might use here is the published test-plant data recorded for the PRR T1, which give essentially the best water rate made for conventional reciprocating steam in this country. Note that these numbers could be improved upon with better feedwater-heat train design, with the use of combustion-air preheat (even with Snyder preheaters, which are bone simple), and with the use of Cunningham circulation from the relatively 'dead' points of convection-section downcoming into the water legs.
Nothing recorded in the 614T tests are at all representative of what a 'first-generation' 4-8-4 could achieve. At least, not in my opinion. And why bother with indicated power when you have actual wheelrim power at a variety of speeds and loads actually 'taken' for you?
... the steam fed to stoker motor, turbogenerator, vacuum brake ejector, would increase the water rate.
It does, but in large part because of the ridiculously wasteful design that has all these devices (and don't forget that the cross-compound air compressor probably uses more steam than a mere ejector) exhausting through their own pipes to atmosphere. A modern engine, even if not using an engine as a Lewty booster, would have it as a 'central' power source to use OTS or custom equipment to drive the various auxiliaries ... at proper variable speed and torque, without a bunch of expensive governors and valves and necessity for blowing down steamlines in winter and the like. And the exhaust from that engine could probably be effectively condensed, or recompressed, in a way that a bunch of disparate, expensively-recreated, suboptimal mechanical-only things wouldn't be.
A significant source of visible 'steam' loss is the vent from a typical open FWH. Another somewhat surprising but documented one is a typical chime whistle of appropriate size. Much expensively-acquired fractional percent of additional efficiency in the Rankine cycle can be blown quickly (pun intended) through steam wasted when it need not be.
Note that I take careful account of what can't effectively be recovered, one example being the steam that comes along with the droplets removed in an Elesco "Steam Dryer" at high demand rate. That water won't always drain back properly in foaming/priming conditions, and the Canadians for example learned rather quickly to route the drain over the side rather than try to route it back into the boiler, or even the FWH train somewhere. We should carefully consider this before designing paper solutions for the resulting 'water rate increase' in practice.
Water rate is fuel efficiency because the less water evaporated, the less coal to be burnt.
But be careful, because there are other considerations on fuel efficiency that don't reflect water rate at all. It's merely an index and major contributor.
... if one could get that 11 lb/hp-hr water rate, a 70% efficient boiler, figuring water savings for a feedwater heater, water usage for auxiliaries, we are talking 8.4 lb water/lb coal or a coal rate of 1.3 lbs/hp-hr. This would pretty much meet the objective of equivalency between direct burning a solid fuel in a steam locomotive or coal-to-liquids to power a diesel.
Better than that was achieved in practice. And it didn't really mean much.
North of 81% boiler efficiency was fairly frequently reported in the literature, and in today's PSR-style operating regimen, where low peak speed and 'predictable' (at least in theory!) dwell scheduling can be known reasonably well in advance, the achievable efficiency can be better still. Something you didn't mention, the 'waste' involved with firing up and blowing down, is well addressable with proper practice, too. There is little reason other than capital cost not to use a 'return' gas pass of some kind on any routes that have stack-train clearance, and the effective Rankine-cycle efficiency of such arrangements becomes high even by French standards.
And yet we don't see practical investigation by the railroads into big external-combustion power. There are, alas! reasons that go far beyond the thermodynamics of the chosen fuel cycle.
... a 2-cylinder simple is limited to operating at a .12 factor-of-adhesion ...
That's tantamount to moronic: you can implement, and use, traction control. A simple side-acting caliper on wheelrims or cheek plates does it, with the additional advantage of keeping relatively good water rate. The Wagner throttles on a LP engine help with it, too, as on the ACE 3000. All this before you even consider implementing actually proportional cutoff valves of the type that should have been used on the PRR Q2 given the relative sophistication of its controller.
You will still be limited by practical adhesion on the larger, more expensively acquired, drivers. Or need some form of booster on some of the unpowered axles. By the time you get to the point of using something like intermittent creep-control optimization on your booster axles (a consequence of having to 'watch out' for torque peakiness at the 'limit', what race drivers call 11/10ths) you are out at the very edge of the possible ... but it's still not where AC drive naturally sits, even costed-down designs of AC drive.
which ... just doesn't do it for drag service, no matter how "low" a driver you use and how much you design the locomotive for a low-speed tractive-effort peak.
Of course, designing any direct reciprocating locomotive for 'drag service' in these times is silly to begin with, simple or compound, two-cylinder or three or four. It's even silly to design a motor locomotive for such a service, although that would be enormously more practical to operate (and solves much of the speed problem that direct reciprocating power has) and modern control makes synchronizing the motors more sensible.
A .15 cutoff in a simple engine is equivalent to a .39 cutoff in each of HP and LP stages of a compound, which combined with a multi-cylinder arrangement to make the torque less peaky at about a 40% cutoff, such allows use of enough cylinder volume to operate much closer to a factor-of-adhesion up around .3 ...
This is a valid observation, but there are much better ways to remove the effect of torque peakiness, and of severe short cutoff, than by compounding. Pilot injection alone solves much of the MEP-vs-thrust-angle concern on a 2-cylinder DA (nominally simple) engine; you'll need good insulated reversible compression control ... but what sensible 2-cylinder simple would run without it?
And nobody but a fool would run drag service at limited cutoff anyway; you'd have better controls ... or better training ... or a better bunch of employees ... who would know the right tradeoff of throttle vs. reverser for any situation they found themselves in, and know how to use their instrumentation to decide quickly, and implement equally quickly and correctly, how to optimize steam admission (and drifting) moment by moment over the road.
OK, everything has to break the right way in terms of balancing HP and LP stages to realize smoother torque to achieve a high factor-of-adhesion, it assumes good control of condensation in a compound setup and all the things mentioned earlier.
That is, if you haven't been listening to why IP injection works. Let alone proportional injection with the possible degree of superheat that modern valve materials would permit.
Maybe I am missing something -- for an advanced 2-cylinder simple, what factor-of-adhesion, cutoff, water rate and coal combustion efficiency can one target, and is the resulting efficiency good enough to compete with coal-to-liquids or biomass-to-liquids, which was what Porta and others were targeting?
Keep in mind that the world has moved well on from the 'state of the art' in liquid fuel synthesis since Carter's rush program (that didn't work well) in the 1970s. Likewise, an increased understanding of the use of liquid fuels as 'carrier fuels' (rather than insisting they stand or fall strictly on overall thermodynamic well-to-wheel least cost) is valuable to recognize. If we take biodiesel as an example: a lower-refined product with less optimization to pass through fine injectors is a useful potential fuel for external combustion, and its infrastructure and much of the necessary delivery infrastructure is at least nominally available for that purpose. But is it more efficient, net of all development and capital, to divert some biodiesel feedstock to that purpose, rather than fully refine and treat it and provide additives for use in existing diesel-electric power with several times the thermal efficiency and far fewer support requirements? Similar arguments apply to any cycle from Fischer-Tropsch on up that would either produce liquefied or slurry fuel from coal or gasify and then hydrogenate it. That, not the arrangement on the locomotives, is where the sticking point really is.
Just as major catenary projects presuppose the existence of a grid to source and sink power at minimum marginal cost, any 'steam' equipment would presuppose enough volume to justify the special support equipment and techniques to keep it running ... and to generate the alternatives like torrefied-wood fuel in sufficient delivered quantity, and with the correct additives and quality control, etc. It is not impossible that some sort of 'diversion' of some coal transported for electric-station or even metallurgical use could be arranged for some locomotive needs -- but there will still be the need to provide water, treatment for that water, and ash handling.
Interesting that in this whole response, I haven't mentioned water-tube boilers explicitly even once, until now.
I get that compounding hasn't lived up to its promise. That is basically what Chapelon was working on because France was all about compounds, and those locomotives weren't performing as well as they could.
There was evidence that compounds were getting pitifully small amounts of power out of their LP stages on account of nucleate or wall-effect condensation. Apart from his work on lower back-pressure exhaust, streamlining the steam passages, lower-restriction superheaters, increasing direct heating area in the firebox with syphons, although the potential for quenching the luminous flame giving radiative heat transfer has been mentioned, Chapelon's first approach was applying high levels of superheat so the steam would make it through the HP and LP stages with some superheat left so it wouldn't condense.
Whereas his 242-A1 fast passenger locomotive gets the glory, his second approach came out of the 160-A1 high-tractive effort freight locomotive. A fuel-efficient freight locomotive is what the ACE project and their various iterations of proposed locomotives were all about. The 160-A1 was set up as a test bed to try different combinations of things, and it seems the "best" setup was to use low or no superheat (helps with valve and cylinder lubrication) in the HP feed but to rely on jacketing the HP cylinders to fend of wall condensation. Condensation in the LP cylinders was to be forestalled by use of a reheater of the IP steam.
I am interest in other sources of technical data on steam if someone can point me to them, but Wardale's Red Devil book has numbers for limited sets of speed and cutoff. I have converted speed to MPH, the indicated HP at that speed to a factor of adhesion assuming 82 metric tons on drivers for Locomotive 3450, and converted to water rate form kg/kW to lbs/hp.
Page in "Red Devil" Speed Cutoff Factor-of-adhesion Water rate (lbs/hp)
p 261 37.5 MPH 15% .12 11.0
p 258 42.8 MPH 24% .15 12.8
p 261 22.2 MPH 33% .19 15.9
p 257 34.0 MPH 32.5% .16 14.7
p 257 34.0 MPH 41% .19 15.7
p 257 35.0 MPH 49% .19 17.0
p 260 25.6 MPH 65% .24 22.4
The numbers are for indicated power giving indicated adhesion factor on 82 metric tons on drivers and for "cylinder steam flow" -- the feedwater heater should reduce the water rate from that number whereas the steam fed to stoker motor, turbogenerator, vacuum brake ejector, would increase the water rate.
Wardale publishes a lot of numbers, but to get a consistent narrative, 614 was operated at 40% cutoff (p 393), and taking into account its less efficient exhaust system, let's say its water rate was in the low 20's (on a good day when the firebox stay leaks were caulked shut), with the 45% efficient boiler giving a coal rate of 5.4 pounds (of a good, high BTU coal) per pound of water, giving about 4.1 lbs coal/hp-hr or about 4.4% wheel-rim efficiency, in the ballpark of the 3.65+.65 = 4.3% value given on p 397.
Water rate is fuel efficiency because the less water evaporated, the less coal to be burnt. The numbers on the ACE test of Locomotive 614 are on pp 396-398.
I know that a coal-burning freight steam locomotive is not going to happen -- coal to synthetic diesel fuel is not going to happen either -- because of international initiatives to limit CO2, and biomass-burning freight steam may have limited applications to countries that may favor that. But if one could get that 11 lb/hp-hr water rate, a 70% efficient boiler, figuring water savings for a feedwater heater, water usage for auxiliaries, we are talking 8.4 lb water/lb coal or a coal rate of 1.3 lbs/hp-hr. This would pretty much meet the objective of equivalency between direct burning a solid fuel in a steam locomotive or coal-to-liquids to power a diesel.
Where the multi-cylinder compound comes in is that a 2-cylinder simple is limited to operating at a .12 factor-of-adhesion, which is fine for a high-speed passenger locomotive, but it just doesn't do it for drag service, no matter how "low" a driver you use and how much you design the locomotive for a low-speed tractive-effort peak.
A .15 cutoff in a simple engine is equivalent to a .39 cutoff in each of HP and LP stages of a compound, which combined with a multi-cylinder arrangement to make the torque less peaky at about a 40% cutoff, such allows use of enough cylinder volume to operate much closer to a factor-of-adhesion up around .3. This was also the concept behind Chapelon's 6-cylinder (!) 160-A1 testbed locomotive.
But there is no way that I know of to get anywhere near that water rate in a 2-cylinder simple at a drag-freight factor-of-adhesion, and a low water rate is efficiency. Maybe I am missing something -- for an advanced 2-cylinder simple, what factor-of-adhesion, cutoff, water rate and coal combustion efficiency can one target, and is the resulting efficiency good enough to compete with coal-to-liquids or biomass-to-liquids, which was what Porta and others were targeting?
One major 'take-home' point about the 1980s steam research was that it implicitly involved two things: "energy independence" in the immediate post-Carter years, and perceived cheap fuel translating into cheaper running costs. As those became 'deprioritized' all the disadvantages of external combustion at the required large, cheap scale became just as insurmountable as they were historically. You may have observed it hasn't shut down development of higher-efficiency steam locomotives; you may also have observed that even the more likely applications of it in practice haven't occurred (the suburban service in Switzerland being a comparatively recent example).
That is not entirely because the technology is unworkable; it's more because the effective barriers to re-entry, political and economic, are too high, and the risks intolerable to modern institutions. There are other factors waiting should those be overcomable in a particular context, but those are sufficient enough so far, and predictably into the futures we currently predict.
Paul MilenkovicWhat had Wardale so glum about the Locomotive Number 614 tests is that the 614 was running 12 BTUs to carry the same tonnage as 1 BTU in a diesel locomotive. The necessary 4-fold boost in steam locomotive thermal efficiency was in Wardale's eyes (not just mine) just too much ground to cover.
Wardale apparently made the mistake of emphasizing this point to Ross et al. at the wrong time. To this day, bring it up and Ross will strongly react that Porta was the critical design 'genius' and Wardale unable to accord with that, or uncomfortable in a "subordinate" position -- rather than that he was noting where all the shortcomings were.
To this day, obtaining the results of the 614T testing is a difficult (and, in my case, fruitless) exercise. In no small part this is likely because they are far from representative even of what 614 could achieve if properly lagged and jacketed, rebuilt in certain common-sense ways, and given proper thermodynamic enhancement (in at least one case, of a type actually tested and acclaimed as valuable on the C&O itself.)
Apply the achievable thermodynamics of a 'perfected' J-3a (and yes, Tom Blasingame has working drawings) and even with "1940s technology" you may come close enough to being able to burn coal cost-effectively for transportation purposes -- which was the 'other half' of the design exercise.
... operating the 614, however, generated in Wardale's view substantial negative publicity for the ACE 3000 project with the public and especially with CSX and the other partner railroads. The enormous appetite for fuel, the columns of dark smoke from the stack, and yes, the stresses placed on the track were reminders as to why the railroads gave up on steam in the first place.
This is a bit reductionist and one-sided, and I think flavored with a little sour grape. The stresses were recognized at the time as being essentially less than those of contemporary large diesel-electrics with Flexicoils (a point brought up from time to time, and as fact as recently as earlier this year in a different forum); the tests were conducted in winter where most of the exhaust plumes would have been white, and proper firing of a J-3a is of course easily made 'non-black' when railfans paying for smoke shows are absent; the appetite for fuel has been addressed above but in any case was accepted during the tests, and presumably was addressed intelligently in the ACE 3000 and whatever the ACE 2-10-2 project would have been called, as a start. As noted, it was certainly not 'large fuel burn' that killed railroad interest in American Coal Enterprises.
The reason I keep coming back to compounding is the situation where simple-expansion steam does not operate efficiently when running a locomotive anywhere near its adhesion limit for mile after mile, which is what CSX was doing with their diesel locomotives dragging coal.
Single-expansion steam does just fine in that situation; it just doesn't do it with the same admirable water rate you could achieve with a higher-speed (more pulses per minute) operating rate. Tuplin was a tireless proponent of lower boiler pressures on locomotives, long after the world of engineering thought it had left him behind, but he was right to note that relatively long cutoff gives a combination of high effective MEP over a 'long enough' percentage of the stroke that the torque peaks are both long-sustained and come close to overlapping: isn't there a diagram in the Red Devil book itself that shows the relative situation with a good 2-cylinder single vs. three-cylinder Swiss drive?
In fact, slogging at long cutoff makes for an intolerable water rate on a locomotive that throws away nearly the entire latent heat of vaporization; you'd think there would be more realization that this needed to be recouped in the Rankine cycle, and there were some fairly heroic attempts at this, including Holcroft-Anderson 'recompression', the whole checkered history and lies of the Franco-Crosti preheater saga, the happy eggheaded world of exhaust-steam injectors (including on Big Boys!) and Snyder combustion-air preheaters (or their equivalents applicable at least in theory to overfire or other 'secondary-air' admission)
It has to do with you just cannot operate 2-cylinder single-expansion engine sets, whether on a rigid frame or a simple-expansion articulated locomotive, near the adhesion limit required of drag service and get enough steam expansion to get anywhere near peak thermal efficiency.
What it really means is that you can't operate a 2-cylinder single-expansion engine in the wrong service, or outside its effective mechanical range. An important note about the Allegheny that people keep missing is that it could pull a heavier train at the higher speed than it could when restricted, at the cost of inefficient 'action' during the acceleration to that range around the horsepower peak -- to 'overload' it was less a concern than an operating issue. As on D&H, the "correct" thing was to raise the prospective 'one-speed' fundamental operating rate (which they did with the adoption of 4-8-4s and Challengers) and make up the additional fuel and water over your hyperefficient slow engines with increased utilization, less net congestion of trains working over the road, and better perceived service time. But there was also an alternative, and it, too, pointed at D&H: if you do not want higher one-speed operation, design power to peak at the lower anticipated speed and then optimize what you do around that, instead of buying an inherent high-speed engine you can't use.
On C&O the thing is a bit complicated by the prior (and very successful) designs of the AMC for inherently higher-horsepower 2-8-4s and 2-10-4s for appropriate services. I think the AMC assumption going to Lima was that the Alleghenies were the larger extension of the successful T-1 formula, as I like to call it a 'Berk-and-a-half' (or more appropriate on C&) a Kanawha-and-a-half) without giving much thought to the idea that the railroad might misinterpret what such a locomotive could or would be used for, or recognize the working conditions under which such a locomotive might be expected to work.
As mentioned in the prior thread I think C&O would have been much better served with a lower-wheeled 2-8-8-2 along the general lines of the N&W Y-7, if coal trains with peak speeds in the high 20s were the anticipated thing. Modern balance and valve improvements would make these capable of operation with 'acceptable' augment and track forces up to reasonable fast-freight speed, and modern truck guiding and lateral-motion provision would keep track forces 'at least in line' with much of the peak load from primitive old unshocked Flexicoils...
... or increased the speed of what they used Alleghenies on to get best use from the capital, the coal, and the water that 'had to be' used.
The diesel locomotive doesn't have this problem, that is, if you are not running the locomotive so slow that all of your diesel HP is heating up and burning up the traction motors.
Problem is that you could say the same thing of an STE, which was not exactly what was observed in practice either on C&O or N&W with them.
The 'real' potential of the diesel is that you can (in theory, more than 'as governed' in first and second-generation electric MU) run the engine at a speed corresponding to its best efficiency, with only the fuel feed necessary to make demanded HP for instant speed and load conditions, and let the electric transmission handle the acceleration and speed-change conditions -- which even a DC modified Ward-Leonard system can do quite nicely over a wide range. AC drive, of course, improves on this still further, most particularly decoupling slow and even locked-rotor torque from catastrophic motor overheat while pulling at low speed (including low speed by intent, as when traversing certain kinds of bulk unloading).
Wardale's discouragement was that you cannot operate the type of two-cylinder simple-expansion locomotive at any kind of efficiency near the adhesion limit -- as you shortened the cutoff to get more expansion, you made the average torque fall off substantially.
You need to qualify this, initially, by noting it is a slow-rotational-speed adhesion limit, in the range where torque peakiness and absence of meaningful compression effects worst affects you. And that you see in this a different tradeoff, between the Scylla of increased tendency to slip and the Charybdis of stalling -- both of which are characteristics of direct reciprocating drive. As noted in the Australian discussions on starting technique, the better answer to low-speed slip control is to modulate throttle admission pressure, not variable cutoff approximating 'bang-bang' control of fixed high pressure (especially when you coincidentally jigger the valves and steam circuit to source more and more steam at high effective superheat quickly and smoothly into the cylinder promptly, and without the 'dreaded wire-drawing', starting right at the moment of steam-edge crossing for admission).
You should find the discussions (most of them, weirdly enough, on a narrow-gauge forum) about how we determined how Franklin type D was supposed to work. There, the idea of what was effectively wire-drawn cutoff control was used to simplify operation of Army locomotives under battlefield operating conditions by what might be relatively untrained personnel, but the approach works as well if, for example, 'filling in' between fixed cam profiles in a RC valve-gear system. You will want 'excessive' superheat in the admission tract, but that is not too difficult to achieve...
Norfolk and Western was running compound articulateds up to the end of their use of steam at the end of the 1950s? There was nothing said that the Y6b locomotives were too expensive to maintain for what they did?
But it was also true that actual proportional LP 'contribution' was lousy on any Y class up to the introduction of the booster valve, and I think there was enough 'refinement' going on with the device that N&W was at least considering ramping it up from a 'full reheat' device to full proportional admission (as Chapelon proposed for articulated or duplex compounds). And it is also true that most of the points of compounding affect reduced water rate (and the factors that depend upon and from it) in the absence of very good jacketing (or insulation) and the presence of sufficient resuperheat to preclude nucleate condensation in the LP cylinders until reasonably well after the period smooth and predictable pressure (and hence derived wheelrim torque) is expected.
Proportional injection is just as important for high speed out of articulated compounds as it is for smooth operation of a von Borries or other 2-cylinder compound. (You can, I think, readily recognize why having as near 'identical' indicator-diagram pressure equivalents on both cylinders of a conventional DA 2-cylinder high-speed engine is desirable ... and just how suboptimal this can be at a given (high) road speed where guiding and suspension become significant performance elements.)
These are not particularly difficult refinements to make in an otherwise good 2-8-8-2 or 2-6-6-4/2-8-8-4 configuration; the point is to recognize and make them before starting to implement long expansion from the higher boiler pressures that watertube boxes begin to facilitate.
And, in many cases, some of the weirder design features of the ACE 3000 will begin to make much better sense in that 'world'. Particularly the use of drivers nearly as low as those on a Y6 with adequate construction to accommodate proper balance ... or use a different way of reducing augment for the expected range of cyclic rpm in the service speed range you want.
Wardale suggested that whereas a steam locomotive may never be better than some small multiple of a diesel locomotive's fuel consumption in BTUs, it could be equal to or better than the process of making synthetic fuel out of coal to run a diesel locomotive. If the synthetic fuel plant took 3 BTUs of coal to produce 1 BTU of #2 diesel fuel and an advanced steam locomotive took 3 BTUs of coal to haul what 1 BTU could in a diesel locomotive, you were breaking even, and you didn't need the expense of the synthetic fuel plant.
The thought was that late-era steam needed 6 times the BTUs of diesels and a doubling of steam thermal efficiency to 3 times diesel was in the realm of what the Chapelon-Porta-Wardale improvements could achieve.
Of course all of this was in the era before emission of CO2 came under regulatory stricture with Kyoto and Paris agreements on forestalling CO2-induced climate change. Whatever you think about the seriousness, urgency or perhaps lack of such of this problem, you are just plain not going to get any government support or even regulatory approval for a scheme that replaces a petroleum-derived energy course with a coal-derived energy source with a 3:1 increase in CO2 emissions. It is just not going to happen.
On the other hand, the US Federal government was contemplating just such a thing of using massive coal reserves to substitute for scarce imported oil in the era of the ACE project. Even Porta and especially the Project 130 people caught wise to an emerging new reality with the idea that, "we will be burning carbon-neutral biofuel, not coal, and the same formula applies to biofuel-to-liquids conversion being equivalent to combusting solid biofuel directly in a steam locomotive of perhaps double the thermal efficiency as late-era US steam.
What had Wardale so glum about the Locomotive Number 614 tests is that the 614 was running 12 BTUs to carry the same tonnage as 1 BTU in a diesel locomotive. The necessary 4-fold boost in steam locomotive thermal efficiency was in Wardale's eyes (not just mine) just too much ground to cover.
OK, so the "real purpose" of the 614 trials was to give the Foster Wheeler engineers "hands on" experience with a large mobile boiler and the operating environment for such a boiler. Purposed as such, operating the 614, however, generated in Wardale's view substantial negative publicity for the ACE 3000 project with the public and especially with CSX and the other partner railroads. The enormous appetite for fuel, the columns of dark smoke from the stack, and yes, the stresses placed on the track were reminders as to why the railroads gave up on steam in the first place.
The reason I keep coming back to compounding is the situation where simple-expansion steam does not operate efficiently when running a locomotive anywhere near its adhesion limit for mile after mile, which is what CSX was doing with their diesel locomotives dragging coal. This has nothing to do with operating the H8s well below their peak horsepower speed. It has to do with you just cannot operate 2-cylinder single-expansion engine sets, whether on a rigid frame or a simple-expansion articulated locomotive, near the adhesion limit required of drag service and get enough steam expansion to get anywhere near peak thermal efficiency. The diesel locomotive doesn't have this problem, that is, if you are not running the locomotive so slow that all of your diesel HP is heating up and burning up the tractions motors.
charlie hebdoWhy? Building coal-fired or oil-burning steamers, other than nostalgia replicas, is not going to happen for obvious reasons.
Not necessarily in this country, but there are ample markets even in Europe for external-combustion power, and in a number of contexts for 'renewable' or clean versions of locomotives technically using those kinds of fuel, for example those burning biodiesel or the kind of highly-torrefied wood proposed Project 130. While the 5AT project has fallen on hard times, there are just as many potential uses for that size and character of engine as there were 20 years ago.
I do think that the Project 130 claims regarding Amtrak-capable power were, shall we say, a little overstated (and I notice that Ward's approaches have considerably backpedaled from the original claims). For a variety of reasons we have discussed, the original impetus for 'clean coal' power that drove the research involving 614T and 'American Coal Enterprises' didn't have much of a renaissance after the artificially-induced fall in oil prices around the Iran-Iraq War torpedoed it in the mid-80s, and it is almost unthinkable now, although some competent organizations known to me continue to advocate and work for that technology as an alternative.
Why? Building coal-fired or oil-burning steamers, other than nostalgia replicas, is not going to happen for obvious reasons.
Keep in mind that the 614T testing was not 'done' to determine the thermodynamic efficiency possible out of the C&O J-3a design: there was no air preheat, no feedwater heat, no enhanced firebox-leg circulation, and no feedwater heat. And bad uncorrected leaks in the firebox staybolting, poissibly other places. The purpose of the testing was to develop characteristic curves for Stephenson-style boilers for the Foster-Wheeler people, ASME for example long having had no applicable boiler code for that construction in mobile power boilers.
Even assuming overall-Rankine-cycle efficiency as high as Porta thought possible for "Gen 1" steam, between 9 and 10%, you are still multiples of fuel cost away from diesel, even before you have to incorporate the water consumption, carriage, and handling costs. This was supposedly 'made up for' by the cost of the fuel used (which is why the ACE 3000 was somewhat suicidally designed to run on "mine run" coal) but you should not expect any large conventional reciprocating locomotive to be particularly efficient overall, and to this we add the ghastly slow-speed performance characteristics (as commonly ascribed to the 'misuse' of the H-8 Alleghenies with substantial consists held to top speeds well below the locomotive's horsepower peak).
Remember that the effective feature of 'compounding' on locomotives is the longer possible expansion from inlet to exhaust. Good modern 2-cylinder engines had an admission pressure essentially limited not by boiler technology but maintenance cost, and an exhaust pressure (with suitable front end) equivalent to that the LP engine of a compound could produce; the only real 'price' of saving the complexity and extra cost/maintenance of a compound is that the valve gear needs to be effective at assuring effective 'long expansion' regardless of speed and applied load. Enough thermodynamic advantage to overcome the first-cost and maintenance advantage of 'fewer cylinders' comes only with relatively high boiler pressure, where practical single expansion is not mechanically workable, and some very different detail design and construction of a waterleg staybolted firebox is necessary to give reliability even a few psi above around 300psi gauge pressure. Hence much of the attractiveness of a good watertube box.
Modern techniques of robot positioning and welding have removed much of the cost associated with complex shapes and fabrication, but much practical work and testing is probably still needed to determine what will 'work' and what is not advisable for working locomotives.
Keep in mind that the 614T testing was not 'done' to determine the thermodynamic efficiency possible out of the J-3 design: there was no air preheat, no feedwater heat, no enhanced firebox-leg circulation, and no feedwater heat. And bad uncorrected leaks in the firebox staybolting, poissibly other places. The purpose of the testing was to develop characteristic curves for Stephenson-style boilers for the Foster-Wheeler people, ASME for example long having had no applicable boiler code for that construction in mobile power boilers.
OK, more than 2 cylinders and compounding superceded by improved 2-cylinder locomotives?
I keep coming back to Wardale's account of the C&O 614 tests by the ACE people that he relates in The Red Devil. On a BTU basis, he rates the 614 as using 12 times the energy of the SD60 diesels used for coal drags on the same route.
Mind you, Wardale speaks of the host railroad's attitude towards thrashing the diesels (they were for it), but when I say coal drags, they were really underpowering their trains and averaging 20 MPH whereas the 614 was averagin about 30 MPH. Yes, the faster speed works somewhat against energy efficiency.
Wardale also blames "the poor exhaust system" and "the leaking firebox", but they were operating a 614 at high loads and low speeds far from where it would get its peak thermal efficiency. Compounding along with multi-cylinder could have gone a long way to producing tractive effort close to the adhesion limit mile after mile, what the CSX was doing with the diesels they were comparing against, with a reasonably efficient degree of expansive working for efficiency. A two-cylinder single-expansion locomotive is just not going to do it in that service.
Schmidt as in smoketube superheaters, not Schmidt as in terminally high pressure in purified water. Roughly a decade and a half apart.
The thermodynamic craze for extreme pressure on locomotive boilers seems to have started roughly in step with improved metallurgy for power-station boilers, without precisely realizing that the situation on board the locomotives of the day would not be comparable in a great number of respects.
Mind you that high pressure in and of itself did not necessarily hold terrors - Jacob Perkins, building on the work of Oliver Evans, was working with 2000psi pressure (in small-flattened-bore thick-wall tubes) by the 1840s, and his grandson built a yacht (the Anthracite) with a boiler hydro'ed to 4000psi, proofed to 2000psi, tested at 750psi and running reliably at 350psi across the Atlantic in 1880. The generation of engineers who were expected to run the Schmidt-system 4-8-4 on NYC, however, were faced with a very large steam gauge normally reading 850psi, and never did come to like it -- this not being surprising after very similar high-pressure tube failures.
Anything higher than 300psi was recognized in the 1920s to involve compounding. This went hand-in-hand with the perceived advantages of three cylinders ... in the 1920s. The practical effect of the changes that would make large 2-cylinder engines so good 'later on' didn't really start happening until near the end of that decade.
The Schmidt system? One-offs were seen in England, France, Germany and on the NYC.
Keep in mind that there were successful watertube designs, not necessarily involving higher pressures. The Brotan design in Europe was probably the most utilized of these; to my knowledge it was not used in North America.
In almost all cases in North America, the design is not for a watertube boiler per se (like a Yarrow); it's a watertube firebox (to replace staybolted-plate construction with a vulnerable crown sheet and high maintenance requirements including differential thermal issues) which is appended to a 'normal' shell-and-tube/flue convection section. These had their own thermal-expansion issues, some of which were solved with improvements in welding technology and inspection, involved considerably more fabrication than conventional 'Stephenson' construction, and had sometimes extreme problems with circulation at different levels of turndown (which becomes critical at the high peak firing rates found in large locomotive boilers).
In my opinion, the critical thing that 'killed' the adoption of watertube boxes was cleaning and maintenance. When you combine a high evaporative capacity per foot with indifferent feedwater quality (and, later, the presence of chemicals to treat the feedwater, some of which produce solids that have to be frequently or continuously blown down) you wind up with sludge and deposits which have to be carefully turbined down lest they form hot spots with resulting DNB and stress-corrosion acceleration (and more!) There is also an amazing amount of quench in many of these designs, as they aren't limited to 'waterwall' structure but may have rows of tubes in the combustion plume, like syphons, that stop much of the luminous radiation literally cold.
Perhaps most notable among American designs were the Emerson fireboxes applied to B&O power. An interesting approach to economical construction was used on Baldwin 61000 (still available for study in the Franklin Institute) where a combination of those 1920s power panaceas, three-cylinder drive and Smith compounding, were facilitated by a nominal achievable boiler pressure of 350psi. (Most of the service difficulties with nominal pressure 300psi or above is in the staybolted firebox construction.) Baldwin made a point in their testing discussion that this firebox was equally capable of operation on coal or oil fuel without significant modification.
The Yarrow (as best exemplified for railroad service in the boiler actually purpose-built for rail service and applied to the 'hush-hush' LNER 10000) is almost fiendishly complex in its tube construction -- all of which tubes will require periodic turbining most if not all of their length -- and has difficulty with its circulation when fired far off its steady design operation (as would for example be found in shipborne use, where the Yarrow design was very successful ... using purified feedwater in a closed condensing system).
Much of the fun with a boiler like a Yarrow, though, concerns not the water circuit but the combustion gas, which is external to the tube-nest structure and requires gastight external jacketing. In the case of the LNER engine trouble was experienced over time assuring this, with the expected sorts of result. (This does not include the circumferential 'duct' between the gas jacketing and the outer boiler 'cleading' which was intended as a kind of combustion-air preheater but which provoked weird periodic rippling in the outer visible aspect of the boiler at speed!)
There was at least one reasonably successful pure watertube design: the chain-grate 600psi unit installed on the N&W TE-1. A problem here is that, according to a reliable source, the design couldn't be scaled even to 6000hp equivalent (from 4500), let alone the power density that a steam-turbine electric of output proportional to its size and complexity would need to match modern combustion-engine designs.
My own opinion is that a good waterwall firebox with high forced circulation and perhaps high gas speed is the 'right' answer if the drawbacks of a comparable staybolted box cannot be overcome. Of the designs that have been developed over the years, the LaMont principle has been the most recognized as effective for transportation use; this continually circulates feedwater at high speed through the waterwall tubes, then passes the flow through cyclonic steam separators for very effective removal of priming/foaming effect -- this incidentally enabling a simplified form of Porta-McMahon boiler treatment, less most of the consumable antifoaming agent, to be used. The circulating pump runs entirely pressurized, so it need not involve more than a few hp (the head is only about 3-5psi even at peak steam demand) unlike the BFP for a once-through boiler) although I don't think a jet pump (like the type on a Cunningham circulator) has the right characteristics for the necessary assured flow volume per unit time.
Also in my opinion, there is no relative benefit to a watertube convection section (compared to a firetube/flue construction with one end welded and the other properly prossered and then seal-welded) either in construction or maintenance. Turbining firetubes is a simple matter, and turbining flues only a bit more complicated (the elements have to be accommodated) and a leaking firetube can be easily wooden-plugged with only slight loss of availability -- the equivalent on a watertube boiler is a prompt road failure. Superheating in most watertube designs is a difficult thing to proportion, whereas Schmidt-style elements in larger diameter tubes are more suitable for locomotive service.
"Watertube" construction begins to look attractive again in bottoming where it may be a little easier to construct shell-and-tube with the gas outside tubes fabricated in a removable 'nest'. Here the thermal gradient is no more than a few hundred degrees F, though.
I am aware of several attempts to build locomotives with high-pressure water-tube boilers spanning from late 1920s to early 30s, often either using the Schmidt system or a water-tube firebox combined with a fire-tube boiler.
Something I've wondered is why more locomotives were never tried with a marine three-drum Yarrow or Admiral boiler. The LNER 10000 used a modified back-to-back Yarrow boiler that from what I know seemed to work well enough but the locomotive with otherwise plaqued with issues such as superheating troubles and feedpipe troubles before the whole thing was given up.
It's interesting the Yarrow boiler was never tried on another locomotive. I would think in the United States it would have been tried at least once due to a more lenient loading gauge and maybe someone dedicated could have made it work. Why do you guys think it was never even attempted? Was it considered economically unsound as superpower steam reached its peak?
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