Horsepower output

I'm looking for rough performance figures for relatively late steam.
I know:
4-8-4 or 2-10-4: 5000 to 6000+ HP
4-6-2 or 2-8-2: up to 3000+ HP.
I want a reasonable range for a
4-8-2 or 2-10-2
4-6-4 or 2-8-4
I would also like values for many smaller/older wheel arrangements, but I expect there's a problem: because of having been built earlier, they aren't fair to compare.

Triplex wrote:I'm looking for rough performance figures for relatively late steam.
I know:
4-8-4 or 2-10-4: 5000 to 6000+ HP
4-6-2 or 2-8-2: up to 3000+ HP.
I want a reasonable range for a
4-8-2 or 2-10-2
4-6-4 or 2-8-4
I would also like values for many smaller/older wheel arrangements, but I expect there's a problem: because of having been built earlier, they aren't fair to compare.

This site is a good source for Steam technical specs:
http://www.steamlocomotive.com/

Here is some data from a Westinghouse Electric Corporation sales book published post-war which discusses all types of railroad motive power built or being considered at the time. There are two large data tables in the back discussing passenger locomotives and freight locomotives; many of the figures are familiar and the sharp reader might guess which each quoted average figure is for; no railroads or classes are given in these representative tables. I'll only give the steam engines. I will give wheel arrangements, and then "Nominal HP / Maximum Rail HP" as given in the book. I'm sure that their 'nominal' is indicated HP otherwise known as cylinder HP.

PASSENGER LOCOMOTIVES

4-6-2 4200/3700 HP
4-6-4 4700/4200 HP (probably NYC J3a)
4-8-2 4600/4100 HP
4-8-4 6500/5800 HP (probably NYC Niagara)
4-4-4-4 6600/6000 HP (obviously PRR T1)

FREIGHT LOCOMOTIVES

4-8-2 5400/4800 HP (probably NYC Mohawk)
4-8-4 6500/5800 HP
2-10-4 7000/6200 HP (probably C&O T class and PRR J class)
4-4-6-4 7900/6800 HP (obviously PRR Q2)
2-6-6-4 7100/6300 HP

Again note that this Westinghouse book, printed in November 1948 is quoting figures for very modern examples of all wheel arrangements.

We can get another quick look here in John Kirkland's book on Baldwin diesel locomotives, considering his use of PRR locomotive test data in discussion of the "Centipede" locomotives. PRR test data from the 1934 Claymont tests is given; keep in mind that all the steam locomotives here are PRR locomotives, and not all of them were modern at the time. I will give the class, the wheel arrangement, and the given HP figure which I feel sure is indicated HP (cylinder HP.)

D16sb 4-4-0 1200 HP
E3sd 4-4-2 1958 HP
K4s 4-6-2 3184 HP
M1a 4-8-2 4662 HP

Many things can be extrapolated from even this rudimentary collection of data. Hope it helps!

-Will Davis

I've been using an estimate of 4500hp at the rail for a late 4-8-2, and these figures show that to be reasonable. Considering the overall size of a 4-6-2, I had wondered if my figures were low, and they are. Or is that an abnormally high value for a 4-6-2?

I also found http://www.internationalsteam.co.uk/trains/russia09.htm
In Russia, they built old wheel arrangements longer. Note that these engines are only about 2/3 the weight of US engines of the same wheel arrangements. Their 2-6-2 has ~1600hp, their late 2-10-2 3000+hp (though so does their 4-8-4), and an older 2-10-0 (the class used in the US and known as "Russian Decapods") has 2000+hp.

Any more information you can supply would still be appreciated, though what I already have is useful.

If you have the principal dimensions of a particular engine, you can approximate the indicated horsepower theoretically by the formula
PLAN/33,000
where P is the mean effective pressure - you can take this to be 40% of boiler pressure, in psi
L is the length of the stroke in feet
A is the area of the pistons in square inches
N is the number of power strokes per minute - rpm x4 for a two cylinder locomotive
and 33,000 is the definition of the horse power, in ft-lbs/min

PRR E6s 4-4-2 2500 hp.

Stuart

I built a little calculator and looked at some 4-6-4s ,
design data courtesy of http://steamlocomotive.com/

Assumptions
40% MEP most economical cutoff , presumably locomotive is specified to match load to optimum economy, not max instantaneous,
40MPH avg speed,
unlimited steam supply,
hp is at the crank, not the drawbar.
Here are a range of three light-medium 4-6-4s

now here is a big 4-6-4 the C&NW class E4
first at the above conditions, then going a bit faster and with the cutoff somewhat longer as when accelerating,
then cranking upgrade at speed.

The calculator you've developed is very interesting - although I would like to point out that, as one example, the boiler on the C&NW E-4 class would almost certainly not have been capable of producing the horsepower at maximum your calculator gives (over 6000 ihp) and I'd also add that your equation ignores limits of adhesion. While the calculation is decent for reciprocating equipment it's important to remember the whole picture; this is why I usually only try to quote test data. It's also hard to simply (or arbitrarily) pick an MEP for a given speed without knowing something about a locomotive's valve events and other flow characteristics. BROAD generalizations can be made about MEP, but only very broad- and you have to remember boiler capacity and load.

Again, while the calculator is a good and useful approximate tool, it seems to stand out that the figures it produces allow a locomotive like a C&NW E-4 (powerful though it was) to make the 6000+ ihp range that is usually only attributed to locomotives like the NYC Niagaras, the PRR T-1's, the C&O 2-10-4's and perhaps a few others. We must thus be careful when applying purely calculational, analytical tools this far after the fact in estimating locomotive performance.

-Will & Dave Davis

agreed, theoretical values are of limitted practical value, and assuming unlimitted steaming capacity is of course absurd.
you are absolutely right that this calculator estimates indicated horsepower only, not drawbar power.

by including the last figure, I hoped to demonstrate that just naming a hp figure for a particular engine leaves much to be desired.
the rate of work goes up with speed obviously, and cut off is another critical variable, so at the very least
a set of standard conditions must be established.

Actually, I'm not 100% certain that a smaller engine couldn't produce a temporary indication of much higher power output in certain conditions.

While I know the comparison is bad, I have noticed that even under heavy acceleration a diesel will not show its rated horsepower all the time. As a locomotive engineer on a class one railroad, I have the opportunity to frequently see the computer "screen-outs" of engines under load. When on the flat or slight grades, even heavy acceleration usually only shows... 70-80% of the engine's rated horsepower. It isn't until the engine is slugging it out upgrade with a massive train, dropping to 13-14mph in 8-throttle that you see the diesel/generator put out the horsepower its rated for.

Is it POSSIBLE that a steam engine might not do the same? With the horsepower output being a function of the engine's speed, boilerpressure, steam capacity, it seems to me that "steam capacity" would be a function of backpressure as well as vacuum formed in the smokebox as a result of draft. With a wider-open throttle (less cutoff) the steam being exhausted would have more energy to entrain the exhaust gasses. The caveat would be also higher backpressure, which could be partially relieved through the application of an exhaust ejector such as the Klypor, Lempor or Lemprex (if Porta ever got around to finishing the calculations for it).

Another factor, in addition to the F.A. which limits the ability to put crank HP to the railhead, would also be the passages in the steam circuit and how much turbulance resulting in pressure drop the circuit between the throttle and cylinders.

jgalloway, you bring up some interesting "end points of design" issues as well as limits to actual hp output. Increasing volume of exhaust steam creating both rising back pressure on the cylinder exhausts, but also potentially reducing furnace draft by choking in the chimney, is an interesting convergence. The whole smoke box apparatus must be designed to accomodate a particular maximum steamflow+gasflow and must eventually put an upper stop on that runaway indicated power !
The proportions of the exhaust are much more likely to be limiting than the live steam passages, as really enormous velocities are normal in high pressure steam piping and a few pounds of pressure drop at very high rates would hardly be noticeable.

A few pounds might not be noticable, but it was standard to assume an average of 85% boiler pressure available in the cyulinders due to pressure drops in the steam circuits.

jgallaway81 wrote:A few pounds might not be noticable, but it was standard to assume an average of 85% boiler pressure available in the cyulinders due to pressure drops in the steam circuits.

the vast majority of that 15% figure occurs in the superheater, which is typical of stationary practice also, and that varies with load of course.