Steam

[NW Mailing List]

Robb,

On Fri, May 30, 2008 at 10:39 PM, NW Mailing List <nw-mailing-list at nwhs.org>
wrote:


>

>  A: Until the SD70 no diesel could make as much tractive effort on a

>  per axle basis as an N&W Y6.

>

>  B: 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.

>

>  C: 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.

>

>  D: 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.

>

>  John Rhodes

>

>

>

> A:  Not really a fair comparison though, given that the Y6 had some 25%

> more weight on it's drivers, by virtue of having more axles and larger

> bearings and wheels.  Max TE is ultimately determined by weight on driven

> axles * adhesion factor.  Adhesion factor is ultimately determined by mu sub

> k, the static coefficient of friction of steel on steel.  Truck and motor

> design also affect adhesion factor, but it can never be higher than mu sub

> k.



I think it is a fair comparison.  No diesel was given the weight and I dont
believe the earlier Traction motors could have handled it.



>

>

> The Y6s' had 522,850lbs on the driven axles, with a max TE of 152,206lbs

> simple, or a 29% adhesion factor...  an SD70 has 396,800lbs on driven axles

> with a max TE of 163,142lbs, or a 41% adhesion factor... both of those are

> at max optimal conditions, so you can reduce each by 3% or so, if not more,

> to get a more realisitc max TE number in everyday operations.

>

> B:  Max TE is not determined by power output (a diesel, nor any other

> locomotive type, does not require full power output to get max TE... )...

> continuous max TE is.  At continuous max TE, a diesel does require its full

> power output.



I didnt say max TE was determinied by power output of the prime mover.  I
said a DE needed more primemover output to get max TE than a steam loco.



>

>

> C: Not only can a diesel not produce as much TE at x speed as it does at

> start, nor can any other locomotive of any type ever built... I'm curious as

> to the physics equatinos you used to arrive at your hypothesis, as the ME in

> me says it's not possible to do so.  Are they in your paper?



Maybe I should have been more in depth.  In terms of cylinder TE it remains
the same till the cutoff has to be reduced when the boiler can't provide
enough steam to allow full cutoff.  TE at the rail is limited by adhesion.
 So if the cylinder size is set to allow the maximum desired TE to be
produced at the max speed in which the boiler can supply enough steam to
allow full cutoff then all of the preceding speed range will have the same
rail TE limited by adhesion.  The cylinder TE could be hire but is limited
by adhesion.  The drawbar pull however would be less at say 10 mph due to
locomotive resistance which must be subtracted from te to get Drawbar pull.
 The locomotive resistance at 10 mph would only be a few thousand pounds
though.



>

>

> D: While drawbar horsepower will fall as speed increases (darn that

> physics), the diesel is applying full power to the rail throughout it's

> speed range.



Irrelevant a diesels DBHP at 0mph is still 0



>  A mechanical steam locomotive has the advantage of being able to increase

> horspower as speed increases, however, becuase of this mechanical system, it

> simply cannot create that rated power at lower speeds.  No mechanical engine

> in the world is capable of a constant hp curve...






> this inabilty to start or move trains at lower speeds that it can move at

> higher speeds is the greatest pitfall for a steam locomtive.



This doesnt have to be don't have so high a max DBHP and keep the starting
TE inline with a diesel.  Imagine a lower horsepower Yellowstone or A John
Rhodes



>

>

> Robb Fisher

> RFDI

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