Why a V-18 251 ?

Discussion of products from the American Locomotive Company. A web site with current Alco 251 information can be found here: Fairbanks-Morse/Alco 251.

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Ol' Loco Guy

Why a V-18 251 ?

Post by Ol' Loco Guy » Fri Aug 26, 2005 10:47 pm

As the V-18 251 was developed in the mid to late 60's, there has to be someone out there who can comment as to why the engine was developed. However, having done some of the math, I've come up with a point that may be significant.

With 9 throws on the 18 cylinder crank, it appears that a pair of cylinders will fire at 40 degree intervals. Note that this figure is less than the bank angle of 45 degrees. So, without the benefit of a 'proper' textbook that would refresh my memory on the mechanics of IC engines, something tells me that the 18-251 would tend to be 'smooth.'

In contrast, a V-8 engine crank having 4 throws, this would would make for firing pulses every 90 degrees. Note that the 90 degree figure is twice the bank angle of 45 degrees. Hmmm....

As for the V-10 configuration, the only V-10 IC engine that comes to mind is the example created for certain Dodge trucks and the Viper automobile.
In this case, the reason for the V-10 was to utilize an existing V-8 engien transfer (production) line and the need to meet certain hp/torque requirements.

Allen Hazen
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Post by Allen Hazen » Sun Aug 28, 2005 1:00 am

Didn't one of the European auto makers (??Mercedes??) have a five cylinder in-line diesel? This would have the same number of throws as a V-10...
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There is a (built? proposed?) British V-18 of slightly less than standard locomotive-diesel size: Paxman V-something (V-185 sticks in memory). The twelve cylinder version has been used in re-engining some HST power cars (replacing an earlier Paxman type, the Valenta), and Roger Ford in a column in the British "Modern Railways" once back-of-an-enveloped some specs for a light weight high horsepower CC diesel locomotive to be used on passenger trains. As I recall, the V-12 is basically designed as a double V-6 (with a turbocharger at each end?), and the V-18 would be a trio of such "modules" driving a common crankshaft (with, I think, three turbos). I probably still have the relevant issue of the magazine, but won't search for it unless you are REALLY interested...
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As to other unusual cylinder numbers, didn't U.P. have a few (one? two?) U30C that got their full power from 14 cylinders, with one crankshaft throw being used to power an air compressor built integrally with the engine frame? ((Since the loading on that throw would be in the opposite directin to the powered ones, I would think that the idea would have given someone in GE's engineering department nightmares, but I suppose it appealed to the same sense of elegance that decided that the dynamic brake grids on the U and most Dash-7 series would be cooled by the radiator fan.))

mxdata
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Post by mxdata » Sun Aug 28, 2005 6:35 am

I always thought the 18 cylinder 251 project seemed like a great deal of effort for a rather small incremental increase in power output. If I was going to put this kind of effort into a project I would want an outcome that put me farther ahead of the competition.
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deezlfan
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18 cylinders .....

Post by deezlfan » Sun Aug 28, 2005 9:38 am

The design philosophy may have something to do with the Hot Rodders adage: There is no replacement for displacement. ?
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N. Todd
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Post by N. Todd » Mon Aug 29, 2005 10:15 pm

As for the V-10 configuration, the only V-10 IC engine that comes to mind is the example created for certain Dodge trucks and the Viper automobile.
Ford and Wolkswagen use V10s in their Expedition and Touareg models, respectively; the latter has two turbos.

Now a 14 cylinder vee would be quite interesting. But given that two pistons shoot at a little over 51*, that doesn't appear to be quite stable.

oibu
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Post by oibu » Tue Sep 06, 2005 2:59 pm

I would say it's simply a matter of "no replacement for displacement" as mentioned above, plus getting the HP while keeping the RPM's low (16 Cyl 251F was already pretty well maxed out RPM-wise just get 3600 hp), you wouldn't want to push that same already-maxed 16 cyl. engine up another 100 RPM or whatever). Plus just in general lower RPM=less wear=less downtime and fewer parts replacements.

As for the previous comment about a lot of effort for minimal advantage over the competition- well, at that point the competition was 3600 HP out of 20 cylinders (EMD) so 4000 HP out of 18 cylinders is actually pretty good. Perhaps better than asking why Alco needed 18 cylinders for 400 hp would be to ask why EMD needed 20 cylinders for 3600 which Alco and GE got out of a 16-cyl. engine running at lower RPM! (the answer of course in part is 2cycle vs. 4). Again, bear in mind, fewer cylinder=less moving parts= less aprts to wear or fail or otherwise require maintenance/replacement.

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RPM

Post by Allen Hazen » Wed Sep 07, 2005 12:44 am

minor nitpick, oibu: EMD's 645 engine was actually lower RPM (900, I think) than the Alco and GE prime movers (in the 1000 to 1050 range). Though, as you remark, they are 4-cycle: so a lot fewer POWER strokes p.m. than the EMD engine.

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Post by N. Todd » Thu Sep 08, 2005 9:59 pm

minor nitpick, oibu: EMD's 645 engine was actually lower RPM (900, I think) than the Alco and GE prime movers (in the 1000 to 1050 range)
Actually, we are talking 1100 RPM.

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