Someone on the narrow gauge board said these units may be the difference between continuing to operate or becoming the D&S hiking and bike trail, due to nimby opposition to operating steam during fire season, and I think we can all accept that short-term compromise. I would have gone in a different direction though, with EMD 710s such as EMD is using in the GP22eco units and overbuilt cooling systems such as on the old D&RGW tunnel motors.

Personally, I think these locomotives will be a complete failure. I like the fact that they purchased the WP&Y Alco locomotives and I would like to ride behind one of them all the way to Silverton on one day and steam on another day.

Much of the issue I've heard of with the larger Cats in locomotive service (which are not high-speed engines like the C175 series) has been certain aspects of maintenance. Specifically very expensive crankcase explosions if you don't stick rigorously to the expen$ive Cat maintenance regimen ... something railroads that "invest" in Cat repowers are probably not noted for. This of course is not helped by extortionate parts prices.

The C175 is a large-displacement engine rated for railroad service at 1800rpm (it was allowed 2000 in some stationary genset applications). There was a certain amount of fun associated with one of the early high-speed PRIIA-compatible 125mph contracts, I believe with Illinois DOT, where EMD had specified power at 1800rpm and Cummins tried to stick with lower rpm on their QSK, and EMD filed suit with detailed calculations showing the Cummins-powered locomotive could not quite reach the contractual 125mph under certain conditions. (Apparently Cummins had some kind of short-term overpower allowance that it thought covered acceleration to 125, the details of which to date I have not seen fully documented.) From what I gather from later production, Cummins overclocked the QSK to 1800rpm after testing, which produced ample power, and while I doubt most of the locomotives equipped with QSKs don't see peak-horsepower operation regularly, there is a marked absence of horror stories about them. (Interestingly, most of the well-documented horror about the F125 has to do with the detail design of the NOx-reduction system, notoriously a government-'inspired' feature that "derates the prime mover to zero" if the DEF injection system has a problem -- this caused a high-profile early failure on a publicity run when the locomotive stalled in view of the dignitaries and could not be timely revived...

Keep in mind that New Jersey Transit has been operating dual-modes with a pair of Caterpillar engines in them for many years now, with relatively little public exposure of either immediate or chronic problems. I'd be highly interested to hear from anyone with specific knowledge of NJT maintenance as to what their maintenance regimen on these is, and whether there are special features that facilitate their 'care and feeding'.

I am sure anyone who works with semi trucks nodded in grim recognition, the DEF system is the part of a truck most likely to prevent you from completing a run, and 99% of the time it is from a faulty/clogged sensor. I've never received the countdown, but a temp driver I was meeting had it happen to him when he was on a road without shoulders and nowhere to pull over.

How are modern GE/EMD units meeting T4?

My understanding is that both builders use the "exhaust gas recirculation" method. I will spare everyone my layman's interpretation, but a page on wikipedia lays out the idea behind it. I believe the 710 won't meet tier 4 except in marine service, so it must be part of a rebuild which maintains part of an old unit, e.g. the frame, to qualify under tier 2.

The builder is Motive Power and Equipment Solutions in Greenville, SC. Their website:
https://railequipmentsolutions.com/

Here is the D&S page on these units:
https://www.historictrain.com/introduci ... fall-2020/

Altoona has rebuilt a GP59 into a GP34ECO, upgrading the 12-710G3A engine to meet Tier 4 with catalytic converters and diesel exhaust fluid injection.

Interesting, Republic Locomotive was/is in Greenville too, and they also use Caterpillar engines. I guess D&S is still waiting for the trucks to arrive from Brazil.

If I recall correctly, the EMD attempt at non-SCR Tier 4 final failed to make spec by something like 0.3% (yes, that's a fractional percent) on a comparatively small part of the test duty cycle. Considering the absolute number of pounds of NO this would represent, and the relative lack of HC for this to cause photochemical smog, you'd wonder as I did why the spec (which AFAIK was arbitrarily set to a round number for both parts of Tier 4) could not have been revised to permit this very expensive development to be built during a very expensive time for Caterpillar/Progress to be unable to sell new locomotives. I have been advised that one of the hidden purposes of Tier 4 final was to 'force the freight railroads to accept SCR and DEF' and, to be honest, that's consistent with the way the matter seems to have been handled.

Ironically, DEF properly applied can be a godsend -- since it is capable of knocking down even small proportions of nitrogen oxide, there is no reason to keep idiot EGR on the engine, since you can arbitrarily run any CR and MEP the engine will take and 'not have any more NOx after SCR'. Meanwhile the particulates will form less with the higher temperatures and permissible boost oxygenation, and in particular the dangerous nanoparticulates, the ones that breeze through nitwit DPFs or other traps, are more likely oxidized away before quench -- perhaps even more certainly at 645/710 peak rotational speed.

So break out those EB pins and compatible rods, and start increasing the firing pressure -- and stop wasting fuel on regens...

From what I can tell https://ww2.arb.ca.gov/sites/default/fi ... nal_v1.pdf the CA/EMD/UP attempt worked, the only complaint from UP is that it would require a crane to lift the center hood section off the frame to change out a power assembly in the field. From a non-expert's analysis it looks like it used a ceramic section lined with catalyst (e.g. platinum) without using DEF. I have no doubt the railroads are aware of the horror stories from trucking and have just decided not to use DEF-equipped units.

The expense of using DEF probably isn't an issue, the ratio of diesel fuel to DEF used is around 18 to 1 in my experience and DEF is about half the price per gallon. But the regulators have been unrealistic in its application to trucks, i.e. favoring 100% compliance over the ability to complete a run. I am sure it would be the same with rail service (just like I think they were unrealistic in pushing gensets as a way to cut down on units idling).

Well the railroads are about to find out what happens with EGR only systems about 3-5 years after they hit the system. Even with the ULSD that is burned by all diesel engines these days a certain little problematic acid is created by burning anything with that has S in the mix. The acid is sulphiraic acid or SO4 that will pretty much eat thru anything there is metal wise including stainless steel. Yes there are compounds you can put into the metal to prevent it but one of the other problems with diesel exhaust is particulate matter. So your sandblasting components at the same time they are being sprayed with a hot acid mix. The OTR industry calls it the Mayo maker as when it does eat thru the EGR coolers sooner rather than later you end up with an engine full of MAYO from the oil water mixing. To say it is next to impossible to catch short of regular changing of parts is next to impossible.

EGR on locomotives need not be the same disaster it is on trucks -- for one thing, there is ample splittable cooling available, for another the amount of crap building up in the cooler and valves from the gook in the bypassed gas can be handled, or filtered, more easily with the larger packaging size. Note that the diesel-engine catalyst is a different animal -- the EGR is an analogue of FGR, to reduce the oxygen in a given cylinder charge's worth of expanding gas mass so that firing temperature doesn't get up into the magic NO region even at higher firing pressure (e.g. on engines with 16:1 CR)

That catalyst is likely for the HC emissions, particularly important on GM 2-strokes as I understand it's difficult to optimize precise scavenge across the full range of loads and speeds, particularly during power changes. Now, it is HC in conjunction with NOx that produces the photochemical smog, so we might give the twentysomething regulators a little slack in requiring DEC ... but only as much slack as fits the real-world chemistry. Important for locations where many locomotives might be idling or periodically revving, in California, but not so much the other 98.x% of the time.