Steam power at high altitude (again)

[AlanM]

Since the original thread on this subject (labeled "new poster") has drifted off this subject, I would like to get back to it with a new and more informative title.  I have enjoyed the postings that addressed the physics of whether or not a steam locomotive would be more efficient, less efficient, on unaffected by high altitude.  However, it seems to me that there must be a good deal of folk wisdom on the subject.  Firemen and engineers who actually ran the locomotives must have had some opinions, whether or not they might be scientifically correct.  Anybody know where such lore might be found?
     Alan Miller
     Bainbridge Island, WA

[Tim]

Alan

The only effect altitude will have on a steam loco is in the burning
of it's fuel.  a greater (stronger) draft is needed to supply oxygen
to the combustion, as compared to sea level.

The engine exaust provides more than enough draft in a steam loco.

Therefore altitude has no effect on a steam loco.

Altitude has a great effect on internal combustion loco's.
That is why road diesels on mountainous railroads are turbo or super
charged, the difference is how they are driven.

Tim Anders
Souderton, PA

[jsmvmd]

Dear Alan,

I would respectfully suggest you check with Union Pacific, who have or had a VP who ran a steamer on a long round trip in the mid west.  I got a video from Sam's Club Christmas 2006 who showed this guy running a Challenger on the Clinchfield RR in TN.  Perhaps he could help you.  I will try to view video and get you his name. He is rather young, perhaps not 50.

Too, how about calling the Strasburg RR and talking to one of their mechanics who restore steam locos?  Similarly, you could call Steamtown.

My inclination would be to call a physics department and try to get an answer from a physicist.

Good luck and Best Wishes!

Jack

[Jim Banner]

Alan, the main difference between your question and the one pgarman asked on 11 Dec. is that his question was about the efficiency of a steam engine at high altitude whereas your question is about the efficiency of a steam locomotive at high altitude.  His question ignores the loss of efficiency of the boiler (not part of the steam engine) while your question includes the boiler (part of the locomotive.)  The boiler definitely loses efficiency at high altitudes.  In order to get enough oxygen to produce enough heat, greater volumes of air must be sucked through the firebox.  This takes energy, particularly if becomes necessary to use the blower while running.  Note that while the volume of air increases, the mass of the air does not.  So the cooling of the boiler by the 80% of the air that is not oxygen remains virtually unchanged.  But the velocity of the combustion products through the tubes increases so that there is less time for them to transfer heat to the water, reducing efficiency.  I am sure there are other effects as well.

[Atlantic Central]

This question is complex and can only truely be answered on a loco by loco basis. The real question is how well designed was the locomotive?

Since modern steam locomotives generally had boilers capable of producing more steam than the pistons could consume at average speeds/loads, it would be safe to say altitude effected efficiency (amount of fuel and water consumed) but had little or no effect on power. The boilers ability to keep up may have effected top sustainable speed. This would include most post WWI stoker equiped or oil fired locos.

But many 19th century locos had boilers just barely able to supply the needed steam, so rates of heat transfer, rates of fuel consumption, how fast can you shovel?, could be serious factors at high altitudes with older/simpler designs.

Sheldon

[Guilford Guy]

I am not sure how relevant this is... In physics we learned that at a greater altitude, Water's boiling point is lower. Would this mean that you could get the same volume of steam, which is cooler than at sea level, by using the same amount of coal?

[Tim]

Alex

That is true of an open vessel in ambient air pressure.

A locomotive boiler is a closed system, the water in the boiler is at
the same pressure as the steam.  This makes the boiling point much
higher.

The boiling point in a given boiler at the same pressure would be the
same at sea level as at 10,000 ft.

Tim Anders
Souderton, PA

[CHUG]

Your scientists working for the railroad have charts on this because you need to figure out before you go up a mountain if your going to crap out half way up. Before charts it was all on feel by engineers and thats how the top of mountains got called peeks because some engineers wouldnt look until the felt the engine get to the top. But basically the science equations your talking about here are more less the ones used.