Steam

[NW Mailing List]

Pete,

On Thu, May 29, 2008 at 5:21 PM, NW Mailing List <nw-mailing-list at nwhs.org>
wrote:


> Sounds about right.  However, below that speed point, the drawbar HP of the

> 1.6 SDs will begin to exceed that of the A because the A's engines can't

> absorb all the HP that the boiler is producing,

>


The old saw about the engines not being able to handle the steam that the
boiler is producing is irrelevant.  The tractive effort produced is what
matters.  Until the SD70 no diesel could make as much tractive effort on a
per axle basis as an N&W Y6.



> whereas the traction motors of the SDs will be able to absorb all the

> electric energy that the Diesel engines can produce down to a pretty low

> speed.

>


If under 10 mph the maximum boiler output is not required to produce the
maximum TE then that is an advantage over the diesel which requires the
maximum prime mover output and fuel consumption to produce the maximum TE.



> (At starting, 1.6 SDs will exert well over 160,000 lbs tractive effort v.

> the 115,000 of the A.)  The modern 6-axle Diesel, particularly, with AC

> drive, is the ultimate "drag" engine ever.  (I've heard that AC loco powered

> coal drags in Wyoming sometimes climb grades at three mph!)

>


The Modern Steam Locomotive has no restriction on continuous TE versus
starting TE. No traction motors to burn out and produces just as much TE at
10 mph as it does at 0 mph,  a diesel cant do that.



> The modern steam loco is a good speedster - whatever it can start, it can

> move at a pretty good clip.  I read somewhere that it took 3 GP 7s(?) to

> replace one NKP Berkshire in fast freight service on a relatively flat RR,

> which makes sense because the HP is about the same for both set-ups.

>

> Since a steam engine is a constant torque engine (within limits), the

> drawbar HP will drop as the loco speed drops below the maximum HP speed

> (where the engine is converting to tractive effort all the steam that the

> boiler can produce).  Due to "breathing" constraints, the steam engine will

> also be unable to absorb all the HP that the boiler can produce above a

> certain speed.

>


On poorly designed locomotives like most all American late steam ones.



> I've read somewhere that TE begins to drop when steam engine piston speed

> exceeds 400 feet per minute, but I'd have to think that's empirical.

>  Improved valving and steam pipe design would obviously make a difference

> here.  (cf, Chapelon and Porta.)

>


Piston speed can hit 2,000 feet per minute or higher.



>

> Note that a steam loco produces its maximum horsepower at one speed.  An

> electric loco or a loco with an electric (or hydraulic) transmission can

> deliver its maximum HP to the rail over a fairly broad speed range.  In

> automotive terms, a steam loco is like a car with a single gear; a Diesel

> loco is like a car with an automatic tranny.

>


Not hardly.  The max DBHP on a Diesel-Electric is 20 MPH and it falls at
around 150 DBHP for each 10 MPH till it gets close to the max speed for the
locomotive.



>

> Nevertheless, I still fantasize about a double 2-10-2 Beyer-Garratt with a

> boiler based on that of a VGN AG, with all modern conveniences, such as

> computer-controlled poppet valves, etc., maybe 1 HP and 2 LP compound

> cylinders on each engine.

>

> Finally, I'm more impressed by the performance of the late Ys.  The A is a

> good textbook design, but who could have imagined the performance

> improvements that N&W was able to make over the years in the USRA 2-8-8-2??

>

>


The Y6 was a good locomotive.  It good have gone even farther in development
if Chapelon had worked for the N&W.

John Rhodes
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://six.pairlist.net/pipermail/nw-mailing-list/attachments/20080530/c4d1c995/attachment.htm>