Take your average train of a couple or three locomotives and 20 thousand tons. Visibility is poor...it is cold and snowing hard..the tracks are already covered with a dusting of snow...its windy and dark. does the train handle any differently than on a warm summer day?
The visibility, wind, and darkness have little effect on train handling, except of course for the effect such conditions have on the engineer.
A light dusting of snow will normally not affect train handling too much, but it will make the rail more slippery, reducing the speed especially on uphill grades. A heavy snow will affect train handling much more as the snow gets packed into the brake rigging and has to melt off before the braking can begin to reduce speed. After a few applications, the melted snow freezes into ice, which becomes even more problematic.
As far as cold, the colder the rail the more slippery it is.
And it's sure not easy on the crews either, like walking the train looking for problems in knee-deep snow.
We were under a winter weather advisory last night during our Polar Express trips. Mother Nature obliged with a bit of ice on the tracks. The loco slipped a bit, but it wasn't a problem in the end.
As Zardoz points out, the brakes are a major issue. It doesn't take much of a glazing to turn operative brakes into non-existant brakes. Sometimes you have to set the brakes from time to time just to make sure you've got them - or to melt off the built-up ice and snow.
Another consideration is the locomotives - especially older models. Some newer locomotives may be capable of using anti-freeze, but most only use water with some treatments. That means that in extremely cold weather, locomotives have to be left running or have some other means of keeping them warm, like an engine house or booster engine/system.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Back when I studied thermodynamics I learned that, at least in theory, a steam engine is more efficient in cold weather than in hot weather.
That would be true for a condensing steam engine where the colder air temperatures would lead to lower back pressure. On a steam locomotive, the back pressure is not related to air temperature, but heat losses do increase with lower air temperatures. The Milwaukee was estimating as much as a 30% performance drop from their steamers when air temps dropped to minus 30F, but the electrics performance improved as cooler air provided for better motor cooling. The cooler air also caused a small drop in the trolley/feeder resistance.
- Erik
I guess 20,000 tons might be a little more than 'normal'. Maybe 7,000-8,000 tons for an average train. Large unit trains typically run about 15,000 tons.
Winter - Air brakes leak air as it gets colder. Usually this results in shorter trains. BNSF has used air repeater cars or DPU to maintain air pressure in frigid weather.. I was a fireman on a train that was called at 2 AM - We pumped air for 2 solid hours and the caboose barely got the air gauge needle off of the pin. The dispatcher annulled the train at 6 AM and sent us home. Broken rail is another issue in really cold weather - speed restriction bulletins/slow orders slow down everything. Shoveling out switches, and restarting engines that have dropped loading are not fun.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
erikem That would be true for a condensing steam engine where the colder air temperatures would lead to lower back pressure. On a steam locomotive, the back pressure is not related to air temperature, but heat losses do increase with lower air temperatures. The Milwaukee was estimating as much as a 30% performance drop from their steamers when air temps dropped to minus 30F, but the electrics performance improved as cooler air provided for better motor cooling. The cooler air also caused a small drop in the trolley/feeder resistance. - Erik
Johnny
Some railroads prescribe specific speed restrictions in cases of high winds or sub-zero cold.
What I learned when I studied the Carnot cycle, Erik, is that the high temperature and the low temperature set the limits and efficiency is possible only between these limits. By operating in winter the distance between the limits increases and in theory the efficiency of a steam locomotive increases.
I also learned that thermodynamic principles were not used to design steam locomotives. Design principles emerged from trial and error. Thermodynamics came along after the engines had been designed.
Finally, I understand that condensing steam locomotives are not generally used except under special conditions such as in deserts where water is scarce.
John
35 to 40 on the negative side just sucks every way possible workin' outside with metal things that don't want to play. Can make for good photos though.
Adrianspeeder
USAF TSgt C-17 Aircraft Maintenance Flying Crew Chief & Flightline Avionics Craftsman
John WR What I learned when I studied the Carnot cycle, Erik, is that the high temperature and the low temperature set the limits and efficiency is possible only between these limits. By operating in winter the distance between the limits increases and in theory the efficiency of a steam locomotive increases. I also learned that thermodynamic principles were not used to design steam locomotives. Design principles emerged from trial and error. Thermodynamics came along after the engines had been designed. Finally, I understand that condensing steam locomotives are not generally used except under special conditions such as in deserts where water is scarce. John
I think Erik's point is that if it's not a condensing engine, it's not a closed system cycle. On a normal steam engine, at the cold side of the cycle, the temperature will be cooler because of the colder ambient temperature, however, I would not assume the hot side wouldn't also be cooler. A typical steam engine would take on water from a cold water tank into a cold tender. Also the combustion air would be colder. This is why they must burn more coal in the winter as noted by another poster. Otherwise the hot-cold differential might not be any different.
The advantage of cooler temperatures with condensing cycles is that lower condensing temperatures lead to lower exhaust pressures. For example, lowering the condensate temperature from 120F to 100F, will drop the condenser pressure from 1.7 psia to 0.95 psia, where psia is Pounds per Square Inch Absolute. Note that normal sea level pressure is 14.7 psia. This difference in exhaust pressure would allow more energy to be extracted from a given pound of steam, hence better efficiency.
In an open cycle steam locomotive, the exhaust pressure (back pressure) is pretty much the same regardless of temperature, so cooler air does not improve performance. Note with a back pressure of say 10 psi with respect to ambient will equate to about 25 psia (24.7 if at sea level and exactly 10 psi of back pressure). FWIW, 25 psia is equivalent to condensing steam at 240F.
Making use of a good exhaust vacuum with a steam engine would require multiple stages of expansion (compounding). Conversely, to make compounding successful, effort must be put into keeping back pressure as low as possible. One reason why N&W stuck with Mallets long after other US roads dropped them was that N&W paid close attention to the back pressure problem.
HMMMM, Remind's me of summers in Moscow.
MidlandMike John WR What I learned when I studied the Carnot cycle, Erik, is that the high temperature and the low temperature set the limits and efficiency is possible only between these limits. By operating in winter the distance between the limits increases and in theory the efficiency of a steam locomotive increases. I also learned that thermodynamic principles were not used to design steam locomotives. Design principles emerged from trial and error. Thermodynamics came along after the engines had been designed. Finally, I understand that condensing steam locomotives are not generally used except under special conditions such as in deserts where water is scarce. John I think Erik's point is that if it's not a condensing engine, it's not a closed system cycle. On a normal steam engine, at the cold side of the cycle, the temperature will be cooler because of the colder ambient temperature, however, I would not assume the hot side wouldn't also be cooler. A typical steam engine would take on water from a cold water tank into a cold tender. Also the combustion air would be colder. This is why they must burn more coal in the winter as noted by another poster. Otherwise the hot-cold differential might not be any different.
The water in the tender might be cold, although in colde climes there may be steam coils in the tender to keep the water from freezing. Heck, out here you gotta do something to keep diesel fuel from freezing.
On a steam engine, there are steam injectors that heat the feed water before it reaches the boiler. It will not do to dump cold water into a hot kettle.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Lion,
You give a lot of good reasons for why steam locomotives were developed by trial and error rather than by theoretical considerations.
BroadwayLion The water in the tender might be cold, although in colde climes there may be steam coils in the tender to keep the water from freezing. Heck, out here you gotta do something to keep diesel fuel from freezing. On a steam engine, there are steam injectors that heat the feed water before it reaches the boiler. It will not do to dump cold water into a hot kettle. ROAR
Sometimes even the water towers are heated and insulated (external to the engines Carnot cycle). The heating coils in the tender will remove heat from the engine and reduce efficiency. The feedwater heaters and injectors will only raise the water temperature a certain amount above the starting temperature. The point I was trying to make is that cold weather does not increase a steam engines efficiency, and judging by the fact that it takes more coal, efficiency appears to go down.
John WR Finally, I understand that condensing steam locomotives are not generally used except under special conditions such as in deserts where water is scarce.
I just remembered that two condensing steam locomotives were built in the U.S. circa 1939, the GE Turbomotives which were first used on the UP. These had a high pressure watertube boiler, steam turbine electric dream and air-cooled condensers. The condensers were used for both reducing the amount of high purity water lost and to reduce the back pressure on the turbine. Lower air temperatures would have lowered the back pressure, though too low might have led to water freezing inside the condensers.
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