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Why so few SD.80 MACS?
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Peter, I have the fuel consumption tables for most EMD engines in all notch settings. As you point out, efficiency isn't linear with RPM: it doesn't double between notch 4 and notch 8 on a turbocharged EMD engine, it roughly triples. <br /> <br />I don't have an operating profile, though, and I've never seen one, either. They may not exist because in a locomotive such a calculation would have such poor accuracy. The problem is knowing what the engine in a locomotive is likely to do every day; it's hard enough to figure it for one route, for one train, for one given set of ambient temperatures, etc. I presume that in a commercial marine application, engines are more likely to be either run at a constant speed or shut off; if so, your fuel consumption and maintenance costs are predictable with greater accuracy. <br /> <br />From an operating department's point of view -- they're the guys that pay for the fuel, not the mechanical department -- fuel efficiency is a big deal. Peter's comments suggest an answer to something I hadn't entirely understood: why railroads have tended toward more heavily loaded locomotives. <br /> <br />In other words, you build a power plan that tries as much as possible to work the locomotive as hard as possible. That causes you to lose some speed on the flat parts of your railroad, of course, but if your operating plan will tolerate the congestion caused by heavy trains dragging up the ruling grade at 8 mph, you're money ahead on the fuel bill. For example, consider the way UP operates the former C&NW across Iowa: 17,000-ton coal trains get two or three AC4400CWs, which have to work almost the entire way at notch 8, and on grades bog down to 10 mph. This always seemed strange to me given that the coal trains are sharing the track with high-speed Z trains, but now I see why you really, badly, do not want to put a fourth unit on the train -- because the engines will spend more time dawdling in a mid-range notch and your fuel consumption goes way up for not much more speed. If you run out of capacity doing that, you might even be cheaper adding another track rather than adding another locomotive to every heavy train.
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