More times than I can count, I have heard people tell those working on a restoration what they should do or how they are doing it wrong. I guess I will take this opportunity to be one of those people. I don't know much about diesels and don't have the required information available to make informed suggestions - maybe someone else here does.

Marine diesels operate at sea level (except FM 38ND 8-1/8). The elevation of Plaster City is 105'. The ALCo 251F, which comes in 6, 8, 12, 16, and 18 cylinder versions (6 is inline, the rest are V type) are rated for full power up to 1500' max in stationary generator use. White Pass & Yukon operates from sea level to about 2800'. D&S and C&TS are asking these ALCo 251D engines to perform between 6500 and 10,000'. It's difficult to imagine anyone would be very happy with the performance of these locomotives. Of course, if you're used to a GE center cab built to operate at sea level, anything would seem like an improvement.

Several turbos have been used: ALCo 131 & 165 and even GE turbos have been adapted. I don't know which the 251D was designed with. Nozzles, orfices and gears can be changed to spin the turbo faster or slower for more/less boost but I'm certain there is a safe limit. In order to achieve around 30 psi manifold pressure, it would reason that a larger volume of air must be supplied if the engine is going to get anywhere near full rated output. I heard one suggestion of introducing air off an air reservoir or aux air pump.

Are there any examples of ALCo 251-6 built for high elevation operation in a foreign country? If so, the solution may already be out there. If not, what would it take to adapt a 251-8 or 251-12 or GE turbo and adjust the orfice/gearing to achieve ~30psi? Maybe someone here on RYPN can figure it out or someone can contact Fairbanks Morse and find an engineer willing to expend brain cells helping track down solutions. Good luck.

First of all, the Alco turbochargers have NO gearing to increase their rpm's or boost.

There are Alco locomotives used in South America in the mountains, but i do not know if the turbo is any different.

I have an Alco T6 with the 6 cylinder engine and it uses a model 320 turbo.

When my dad, who lives at between 8,000'-9,000' west of Denver, was looking to replace his John Deere garden tractor with something bigger to plow snow, he ended up buying a small Komatsu diesel tractor without a turbo, mostly because of price but also because of the maintenance needs of a turbo (he was a truck driver for 40 years so he knows diesels). He was told that where lived was about the limit for an unturbocharged diesel, and it has worked acceptably up there. Durango and Silverton NG is also operating former White Pass Alcos at high altitude, and C&TS no doubt has monitored their success. I think it will end up being a smart purchase for C&TS IMHO.

The OP's on a nuclear sub (FM 38ND 8-1/8) do not operate much underwater for the same reason the FM's or Clevelands on a WWII fleet boat did not operate underwater except with a schnorkel: the Sailors needed all the air to breathe.

Remember the sight of UP's E8's pulling over Sherman Hill with black smoke? That's because an E-unit 567 has a Roots blower supercharger which is adequate to make a 2-stroke diesel work, but not do so cleanly at altitude.

An Alco 244 or 251 doesn't need boosted air to run, but to get good horsepower, it needs it. In this case if you're running at altitude, you need a bigger turbo with more boost.

As I recall, USAAF fighters and bombers in WWII used 2-stage boost to achieve very high altitude (30,000 ft).

Phil Mulligan

In my opinion, the 'ideal' solution would be to go after some kind of grant to 'electrify' the turbos with a motor/generator using something like LiFePO4 cells.

One of the classic historical problems with the 251 (or other Alco/MLW engines) is ghastly turbo lag upon loading. This can kinda-sorta be worked around by really, really retarding the generator excitation... but then you get GE-like gutless-wonder acceleration. The problem would only be worse in thin air at higher altutude, where the turbocharger rotor has to spin faster to move a proportionally equal mass flow -- keep in mind that as a centrifugal blower it isn't positive-displacement proportional like a Roots blower.

The 'compressed air' solution is basically using the air compressor as a kind of 'turbo' assist, and the reservoir as energy storage. I'd be concerned that the absolute volume of relatively high-pressure air that would have to be supplied would be very large, even if using multiple main-air reservoirs to increase source volume, and it would have to be injected pre-turbo to avoid various poor physics in the turbocharger compressor. Ideeally the air would be admitted close to the intake ports... but then you'd have the turbo spooling against more effective back pressure.

Note that the purpose of two-speed two-stage supercharging was not to make additional power, but to preserve low-altitude engine horsepower higher up.

See, I told you I didn't know anything about diesel locomotives but it sounds like you all may be onto something. I do have some experience with the 38ND8-1/8 - about 19 patrols worth, can still hear it at night and sometimes taste it! Since Fairbanks Morse is the OEM license holder for these ALCos, I thought someone who already has a relationship with them may be able to conduct a search of their records and determine if there ever was any difference with those South American high altitude units. Just a thought...

Years ago, I gave some thought to an 'electro turbo', maybe similar to what Overmod has suggested, as a way to eliminate turbo lag smoke. The problem is that there is no way to anticipate an increase in throttle position, fuel and air demand, in a way to get the turbo up to speed soon enough. I also recall reading that the.Lehigh Valley tried giving the turbo a shot of main reservoir air to speed it up faster. Again, a controls issue, no way to predict throttle changes.

The late George Hockaday once told me that there was no way to make the PA-4s smoke, once they come back from M-K. That system used pressure switches and a modified governor, which limited the amount of fuel to the combustion air available. This may be similar to what the GEs have. Of course, the D&H was not a mountain railroad, at higher elevations. I know the PAs worked their way east on Amtrak; I wonder how they did with regard to smoke and performance at higher elevations.

I'm in about as bad a situation regarding knowledge as Adam here, probably worse, but I seem to recall reading, in a book long, long ago in a century far, far away, that a mountain railroad in South America that wanted to dieselize initially tried it with a unit that was supposed to have a rating equivalent to that of its steam engines. The problem was the thin air meant the unit was only producing about half the power it was supposed to make. The road wound up buying engines with twice the power to get the performance that "should" have been available from a unit with half the power.

Of course, the altitude had no real impact on the steam engines.

That suggests either staying with steam power if that much "oomph" is needed, or possibly electrifying the railroad. The latter might be more appropriate for the more sensitive environment and population around the Durango & Silverton. It's not unheard of to electrify narrow gauges; the Swiss have narrow gauge electric lines, some with impressive locomotives, all over the place.

What might be most appropriate, if such an approach were taken here, and considering this would likely be a custom job, would be to make the electrics look old--say a box cab with a riveted body, along the lines of what the Butte, Anaconda & Pacific had in standard gauge.

Wasn't there a narrow gauge road in South America--an ore hauler of some sort--that had such units at one time? Are they even still there?

A highly useful (imho) reference is Tromel's 1972 report on the detail-design history of the 251 engine; this likely contains at least 'entry points' to address some of the issues brought up here so far. Why this isn't as well-known as Kettering's SAE paper on development of the 567 escapes me.

http://www.turbopartsworld.com/wp-content/uploads/2018/07/Alco251DR-FC-tromel.pdf

Note the amount of careful work that went into the design of exhaust and intake manifolds to help address the smoke problems.

He mentions that an arrangement was tried on the larger 244s where a 2' pipe and noxzle was used to try and accelerate the turbine wheel. The conclusion without further comment was that it was "clumsy" and "useless".

This was before the sealing problems with the 320, which resulted at least temporarily in a brake-air connection being made to assist with sealing pressure. There were, perhaps understandably, complaints about the chronic main-reservoir bleed. The point here is that brake-air connection all the way to the turbocharger was 'already' provided, and a multiple-jet arrangement to spin up the rotor from the impeller side could easily have been implemented. I see no record of its being tried.

By the late development period of the 18-251 with 165 turbo, there was an experiment with providing "four nozzles for a 'jet assist' arrangement to improve acceleration at the turbo and load acceptance of the engine", presumably with the Alco load controller that worked off MAP. I suspect the drawings for this arrangement survive in the Alco Historical files and could be adapted to other 251 configurations with that ever-joyful imprimatur of historical fidelity.

A point that was raised, but that has not been addressed here, is the counterpart to slow turbo acceleration, which is 'surge' when the throttle is abruptly backed off from a period of high sustained boost. This is precisely a concern that a reversible electric assist drive with magnetorheological clutch synchronization could address without much control complexity.

...What Alco Historical files? Where?


If anyone is interested in building the Roots Blown 251, I have 3 reels of several hundred blueprints for it!

I'd imagine that if surge was a big enough problem, it could handled with something similar to a wastegate. It wouldn't need to be a very elaborate affair.

I'll subsidize getting them scanned.

Tromel makes note of a gear-drive version, which some of the castings were actually designed for, that was 'not proceeded with'. I always presumed this was an assisted overrunning drive to a centrifugal compressor, much like EMD's system for turbocharged 567s and 645s, but blueprints for a Roots (positive-displacement) engine tell a very different story. (Not one, however, that I'd suspect would have much of a marketing priority...)

[quote]"I'd imagine that if surge was a big enough problem, it could handled with something similar to a wastegate. It wouldn't need to be a very elaborate affair."/quote]

OK, precisely where would you put this, how would you actuate it, and what would you do with the pressurized soot it would blow out of the sizable manifold volume?

Reading through the discussion of manifold design suggests a few other potential practical issues, not least of which would be attach points on the engine structure.

Not to make an appeal to authority, particularly in light of Tromel's repeated comments about things built to a price -- but I suspect if the solution to their surge concern was as easy as wastegating, that would be an early and obvious developed solution.

Oops, wrong term. Not a wastegate, but a blowoff valve of sorts or pressure relief - on the air side. Kind of the same principle, though. It wouldn't need to be a huge thing to find space for since we're not dealing with high pressures - it could be teed off the pressurized air side of the turbo and vent to the atmosphere at a predetermined overpressure to prevent surge. It wouldn't help very much with turbo lag, though. Unless you immediately throttle back up.

Maybe it would be considered a maintenance issue or won't scale up effectively - I don't know. They're not complicated devices. Just a thought...