14 Cylinder U30Cs

[CRQ5508]

I read that Union Pacific had (at least) a quartet of U30Cs that ran off a "14 cylinder" 7FDL engine. What it says is that while it did have 16 cylinders, 14 were used as actual cylinders while the other 2 were used as air-compressors. Can someone explain this more? When they say air compressors, do they mean for the engine, or for the air tanks? (The description is rather vague.) Also how successful were these? Were any more made?

[SW1500]

Were they still rated at 3000hp?

[CRQ5508]

Long story short, yes, they were still rated at 3000 Horse Power.

[zzmikezz]

I will guess that the two compressor cylinders drove into separate compressed air tanks, one for locomotive brakes and the other for train brakes.

[chucksc]

????? Anybody got any citations or links for this???? This is the 1st I've heard and I thought I had at least a middling knowledge of GE history?????

Just off the top of my head and having at least a rudimentary knowledge of mechanical engineering principles, it would seem to me to be a nightmare just because of the challenges of balancing the engine out (out of synch power strokes for openers) and would, I think< shake itself to pieces or try to any way????

[mestevet]

I don't think there's anything inherently wrong with a 14 cylinder engine, but it occurs to me that to achieve the proper balance in power strokes, etc. as Chuck mentioned, it would require a modified cam and cranks at a minimum.

Two other thoughts come to mind though:
1) To produce the same amount of power out of 14 cylinders that is otherwise produced with 16, something must be altered, such as higher boost (and matched increase in fuel) per cylinder... There should be a limit to how much is possible that's set by metallurgy and combustion chemistry. By my calculation, each cylinder in a 16 cylinder configuration should contribute, on average 187.5 hp but in a 14 cylinder configuration each would need to contribute 214.3 hp, a ~14% increase.
2) Does it make sense to employ the two cylinders as an air compressor? I don't know enough about the dynamics of a compressor, but it seems to me that those two cylinders aren't optimized as an compressor. For instance, in an ideal compressor, you'd want as large an air intake as possible, but an engine cylinder has a limited intake size (it's concern is getting a proper fuel/air mixture and combustion expansion). A compressor also might make more sense to run at a different rpm than the engine. I guess my point is, that if one tried to hypothesize that doing this increased efficiency that offset the loss of 2 cylinders, I'd be dubious of that claim in the absence of data.

I guess, my question would be why?

Steve

[zzmikezz]

No, it doesn't make sense though I will agree that my actual knowledge is negligible. The engine will have an accessory drive, why wouldn't compressors be run from that?

[chucksc]

No, it doesn't make sense though I will agree that my actual knowledge is negligible. The engine will have an accessory drive, why wouldn't compressors be run from that?

on GEs the compressor is electrically driven by a "high speed" motor... Hence the characteristic Whoop Whoop Whrrr of GE locos when the compressor starts...

EMDs on the other hand are directly driven from the accessory drive on the Prime Mover IIRC

[BNSFfan]

1st and 2nd generation EMD's are powered from the crankshaft off the main engine and are running at all times the prime mover is running. The newer EMD's from the SD70 and up use an electric compressor driven by the accessory alternator. GE's newer units Dash 8 and up use as Chuck described, an electric air compressor. The Dash 7's and U-Boat ones were either ran off the crankshaft or were belt driven.

[CRQ5508]

Anybody got any citations or links for this?

I got my information from "Centennials in Action" By: George R. Cockle © 1980; Overland Models Inc. Page 20, top photo. And I quote: "...U30C 2915... The first of 4 experimental "14-cylinder" General Electric units delivered to Union Pacific (basically a standard GE 7FDL 16-cylinder engine, using two cylinders as air pumps, but capable of delivering the rated 3000-horsepower with the remaining 14 cylinders.)"

I haven't been able to find much information on this group of locomotives myself. It sounds interesting though.

[bwbrgb]

Almost sounds like they are using the old "Jake Brake" principal and instead of adding to the exhaust , the discharge goes to the air system . The air would still come from the air cleaner for those 2 cyls but without fuel , and the "Jake" principal the discharge would still be clean air and could be directed to the air system instead of the exhaust . The other 14 cyls would operate normally and with electronic injection timings they can probably adjust out much of the stutter .
Just a thought !

[SW1500]

i suppose the 2 air compressor cylinder are just like a cross compund pump on a steam locomotive. A large cylinder compresses low pressure air and a small cylinder compresses high pressure air. in this case it is only a large cylinder for low pressure air of only a maximum of 200psi? (not sure of mximum brake pipe pressure in the states). One cylinder would be for indipendant or loco brakes. The other would be for train brakes.

[baldwin]

I still cannot see any reason for doing that. There is already an air compressor fitted, either mechanical from the prime mover, or electricallly driven.

[Keystoneaholic]

According to 'UP Motive Power Review 1968 to 1977' and 'Union Pacific 1977 to 1980' (both Overland Models), there were 5 units - 2915 to 2919 - delivered in this specification.

It suggests that this has been tried in other industries with success, but not in rail locomotives. It sounds not to have been a great success and the units were modified to standard spec.

I suppose that the attraction is to do away with the separate compressor, together with it's drive system. In theory that should cut the maintenance requirement, but in practice that sounds not to have been the case.

At the time UP had a habit of trying out different ideas (like the rebuilt SD24 with a constant speed engine).

Rob.