New poster

[pgarman]

Greetings & salutations from snowy Colorado.  I'm a long time reader but totaly inept on the computer.  So here goes: I'm 69 years old,modeling in HO though no layout yet, the name of the layout will be the Aimless Mountain RR, a freelance based on the Colorado Midland.  One of the reasons for this choice was that the Midland used ten wheelers as road power & the only appropriate slide valve steamers are Bachmann's excellent versions.  However, they did use consolidations as helpers.  Are you listening MR B? there's a subtle message here.  lol  I really love this site, & want to thank you all for the informative,  helpful ,& entertaining, posts.  Special thanks to Sheldon, Gene, Jim Banner, Hunt, Rich C, Lanny, & many others. I do have a question for any of you rodders, current or otherwise.  Most of you are aware, I'm sure, that reciprocating engines lose three percent of their power per thousand feet of altitude. that amounts to 15 % here in Denver & a whopping 30% on Tennessee or Hagerman passes.  My question is, how would a steam engine be affected at the same altitudes?























































  )

[AlanM]

Steam efficiency at high altitudes is a question that I have wondered about too.  Physics is not my strong suit, but to start the conversation I would speculate that the amount of work you can get out of an engine is a function of the heat energy it contains.  Since water boils at a lower temperature at higher altitudes, it would contain less heat energy.  So wouldn't it be less efficient?  Anybody out there that understands thermodynamics?

[taz-of-boyds]

Interesting.  Considering that the water is under the same pressure as the steam; it may make no difference what the atmospheric pressure is on any aspect of the locomotive operation.  Maybe there would be a difference in starting a cold locomotive since the water would boil sooner, and start building pressure faster?

Having fun,
Charles

PS, our turbo charged PT Cruiser goes up the mountains here in the east without downshifting.

[Jim Banner]

I don't know this for sure, but it strikes me that steam engines should increase output at higher altitude.  But only very slightly.  The temperature and pressure inside the boiler has nothing to do with atmospheric pressure outside the boiler, as long as you can still get the fuel to burn.  You could create the same temperature and pressure in a boiler in outer space if you used fuel plus oxygen to fire it.  Thus the pressure operating against the pressure side of the piston would be the same.  But the pressure on the exhaust side of the piston would be slightly lower as the exhaust steam would be working against a lower atmospheric pressure as it escapes to atmosphere.  The ultimate would be the steam engine in outer space where the pressure is reduced by 14.7 psi compared to sea level.  But compared to a boiler pressure of say 300 psi, this is less than 5% for the most extreme case.  Interestingly enough, this argument holds true whether you measure boiler pressure as absolute pressure or as gauge pressure.

[ebtnut]

Since the steam generation system (i.e., the boiler) is closed, atomspheric pressure should not have much effect on it.  Yes water boils at a lower temperature on your stove, but that is open to the surrounding air pressure.  What might have some effect on efficiency is the fire.  With somewhat less oxygen, the fire in the firebox may not be quite as efficient, but probably not to the extent it would effect reciprocating engines.  I doubt that the slight decrease in air pressure would have any signficant effect on the exhaust back pressure, given that it is already a forced draft. 

[SteamGene]

I've got to agree with Jim and the Nut - 300 psi is 300 psi and it doesn't make any difference if you used ten gallons of Bunker C or 100 gallons of bunker C to achieve the 300 psi.  It might well be a factor in refueling, of course. 
There is the question of why such roads as the Virginian and the Milwaukee used electrics in the mountains - the I have to admit that what the Virginian went over hardly counts as mountains compared to what the Milwaukee did.
Gene

[pgarman]

Ok, that makes sense, but would the firebox not getting as hot due to the thin air at high altitude not have an adverse effect on boiler heat/pressure?  I know that people coming to high altitude run out of breath in a hurry & often become dizzy & worse.  sports teams from the flatlands hate to play up hear & often require oxygen.

[SteamGene]

No.  It might take longer and take more fuel, bvt if you contain x amount of water in y amount of volume and heat it long enough, it will arrive at z amount of pressure.
Gene

[pgarman]

Thanks to all who posted.  This is a topic that has puzzled me for some time.

[sour rails]

     Interesting.  According to physics, molecules are constantly in motion.  The difference among ice, water, and steam is all dependent upon pressure's relationship to temperature.  Pressure holds all the water molecules together.  If the volume remains the same,  less temperature in required to give each molecule aerodynamics over the air (the amount of which causes pressure), but only if the pressure has been decreased too.  If the pressure has increased, the amount of temperature must also be increased.  This principle works not just for water but for any substance.

     I must agree that the boiler makes the pressure constant.  This then brings about regular functioning of a steam locomotive.  However, there would be a minute fraction of increase power at lower outside pressured areas, only because there would be less air pressure in the way of the exhaled steam.

     Most importantly,
     Happy modeling

[taz-of-boyds]

I would amend my post a little.  Borrowing from the original post, pgarman's addition and SteamGene.

I suppose the fire would not be cooler necessarily.  But to get the same amount of oxygen at higher altitudes as at lower altitudes, more cubic feet of atmospheric air would have to be pulled through the burning coal (for you physics fiends out there the official equation is p*v=n*r*t, the principle sour rails is referring to).  If additional air volume must be provided by forced draft from releasing steam the total available power for driving the locomotive would seem to be reduced.  So how much steam must be used to pull the draft?  I am not a steam expert, or even a novice, but I believe I have noticed that steam can be released to pull a draft through the fire box. 

Fun with physics!
Charles

[Jim Banner]

There are two sources of steam for forcing the draft.  One is the exhaust steam from the cylinders (large volume of low pressure "dead" steam) and the other is the "blower" (smaller volume of high pressure "live" steam.)  Exhaust is used when the locomotive is moving; blower is used if needed when the locomotive is sitting still.

Trivia question - what parts of a locomotive constitute the engine?  Or if you prefer, what parts of a locomotive are NOT part of the engine?

[taz-of-boyds]

The tender, engineer, fireman and brakeman are not part of the engine???

Charles

PS, I have been wondering about that very question recently...

[thirdrail]

In engineering terms as understood in the steam era, the "engine" was comprised of the frame, cylinders, rods, and drivers. The power to operate the engine was provided by the boiler, which was comprised of the boiler and firebox. A steam locomotive has an external combustion engine, that is the combustion to provide energy takes place outside the engine itself.

[SteamGene]

I think the firebox is the answer, as that is where the external combustion takes place.  The boiler is connected to the cylinders just like the thigh bone is connected to the knee bone.
Gene