Horsepower and Notch Setting

[Denver Dude]

I searched for this but couldn't find the answer. Does each notch setting represent 1/8th of the HP that the engine can produce, or is it scaled in someway?

[Allen Hazen]

Quick answer: 1/8 of maximum power is FAR too simple. I don't think all diesel locomotives have been set up in exactly the same way, but the notches are usually if not always "scaled." I may be able to find a detailed answer somewhere in my "library" for at least one model of locomotive...
The first notch, "Run 1," is, I think, the same engine r.p.m. as idle, but with the motors connected to the generator. A branch line of a now defunct railroad I used to watch back in the early 1970s had (i) lousy track and (ii) short trains, with the result that there was no throttle setting that would result in a speed low enough for safety: the engineer, I was told, would cycle between Run 2 and Idle: suggesting that Run 2 was the lowest notch that actually produced tractive effort.

[Allen Hazen]

Slightly more informative reply.
I found a table (in "How Diesel-Electric Locomotives Operate," by W.J. White (1997; publisher identified entitle page as "Peat"), page 3-10) of the engine horsepower of a General Electric B36-7 locomotive at the different throttle notches. The B36-7 was "officially" a 3600 h.p. locomotive, on the American rating convention (rated power is what the engine delivers to the main generator): actual engine power is a bit higher to cover power needs of auxiliaries.
Notch : h.p : (fuel consumption, gallons/hour)
1 : 125 : (7.83)
2 : 370 : (20)
3 : 770 : (40.2)
4 : 1245 : (61.3)
5 : 1875 : (89.1)
6 : 2465 : (114.5)
7 : 3190 : (144.2)
8 : 3845 : (174.4)
Remarks:
1) All the horsepowers are divisible by 5, suggesting that these are slightly rounded off estimates/measurements.
2) The power increment is less for low notches than for higher. I don't know for certain why this should be so, but I can think of a possible reason ("just-so story"): the low notches are what you use in starting a train, and there is more of a worry about wheel-slip then than there is when running at speed. So it would be reasonable to "scale" th power increments to give finer control at low notches.
3) My guess is that figures for other locomotive models would give a broadly similar picture, but I suspect there would be differences, even between locomotives from the same builder.

[Denver Dude]

Many thanks for all the info. I appreciate it. I never knew that idle and run weren't the same thing!

[Allen Hazen]

Another factoid, from a few pages earlier in the same book. With the turbocharged EMD 645 engine (as on GP-40, SD-40 types), the turbocharger usually doesn't act as a TURBOcharger until notch 6. (At lower notches, it functions as a gear-driven blower, functionally analogous to the Roots blower on the non-turbo engines on GP-38 and SD-38 types. Which is why fuel economy isn't very good at low throttle notches on 40 series locomotives.) And, as a result, the biggest one-notch-to-the-next power jump is between Notch 5 and Notch 6.
Moral: don't assume things are simple.
Problem: this sort of information isn't all that easy to find!

[Pneudyne]

Allen has provided a good summary. This GE chart from the mid-1950s provides an illustration:

GE Power Curves mid-1950s.gif

With just 8 notches, there needs to be judicious allocation of the increments, and typically notch 5 is at or near the half-power point. As may be seen, as well as graduating running power, the same 8 control notches are also used to graduate starting and low-speed accelerating tractive effort. Also, the designated power for each notch is delivered only over the hyperbolic section of each notch curve; above and below this, the power taken from the engine decreases.

Where larger number of notches are used, as found to some extent in European and Japanese practice, it is possible to have some separation between the two functions. For example, the 1950s Sulzer viewpoint was to use the initial notches to graduate out to maximum starting tractive effort with the engine remaining at minimum speed, with the remaining notches then graduating running power with steadily increasing engine speed.

The GE case illustrated appears to be that of a 1600 hp (tractive) Alco 12-244 engine fitted with the GE 17MG electro-hydraulic governor. That allowed pretty much an independent choice of each of the 8 engine speeds. With the Woodward PG governor fitted with electro-hydraulic speed control, it was customary to use 8 equally-spaced engine speeds. This was not mandated by the governor speed control system, although the speeds were necessarily interrelated in some way. That patented Woodward speed control system arrived, I think, with the 1945 new version of the SI governor, and was segued to the PG in 1948. It could provide up to 15 engine speeds, and was also configured to replicate (using the same trainwire protocol) the 8-speed control provided by the 4-unit variant of the GE 7MK3 throttle operator (and its EMD derivative), as used with the UG8 and earlier SI governors fitted with rod shutdown.

As Allen says, this kind of information is not easy to find, and at best one usually has, to use an analogy, an incomplete jigsaw puzzle from which interpolations and extrapolations are needed to construct an estimate of reality. There are different ways of approaching the whole subject; my preference is to use Lemp load control as the foundation for study.


Cheers,

[Denver Dude]

Great post - thanks!