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?
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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?
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.
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.
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.
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
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.
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
Thanks to all who posted. This is a topic that has puzzled me for some time.
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 ;)
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. :P
Fun with physics!
Charles
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?
The tender, engineer, fireman and brakeman are not part of the engine???
:o
Charles
PS, I have been wondering about that very question recently...
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.
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
I agree with third rail. The boiler would be the fuel tank(steam as fuel). The piston and drivers would be simuliar to the engine of a motor vehicle. Boy, this could get deep! Stephen
Dear pgarman,
Not to get off the subject of trains, but to respond to your comment about playing sports at altitude, I have a comment.
Red blood cells (RBC) traversing the pulmonary capillaries will exchange oxygen, carbon dioxide and nitrogen across the capillary endothelium, alveolar basement membrane and capillary endothelium down a concentration gradient and restricted by the membranes' permeability. This is nicely explained by a graph called the oxyhemaglobin dissociation curve.
The partial pressure (PP) of oxygen at the alveolus is calculated at sea level at 70 degrees F as the PP of oxygen (21%) times atmospheric pressure (14.7 psi or 760 mm of mercury) minus the PP of water vapor in the inspired air (47 mmHg). Thus, (760) x (.21) - 47 = 100 mm Hg of oxygen PP at the alvelous.
The RBC will pick up its full complement of oxygen, and beome "saturated" in 1/3 the time it takes to traverse the alveolus. This leaves 2/3 the time as reserve to increase oxygenation.
How does this increase happen? With time spent living at altitude, the heart chambers enlarge and the heart rate increases to pump more blood per time, known as increasing cardiac output. The body produces more RBC's in the bone marrow, and the spleen and other storage organs release more RBC's to the blood stream. The body produces a chemical, 2,3-DPG which lowers the RBCs' affinity for oxygen and thereby increases oxygen delivery to the tissues. The lungs will expand and increase the amount of air delivery.
These are some of the adaptations that the body does, called acclimatization, to adjust for the lowered partial pressure (PP) of oxygen at altitude. There are more RBC's to move through the pulmonary capillaries at a faster rate. This maximizes the volume of oxygen that can be pumped to the tissues.
To put it in railroad terms, the RBC's, or coal hoppers move faster through the tipple, which is dumping coal as fast as it can, but at a slower rate which is analoagous to the reduced PP of oxygen at altitude. A faster train will pick up more coal than a slow train. So, as an example, 100 coal cars 90% full have more volume of oxygen than 80 cars 98% full.
That is how the cardiovascular system at altitude delivers more oxygen to the tissues.
This is not analogous to a mechanical system, but a biologic adaptation in mammals.
As I said, this is for pgarman, and is FYI for anyone else who might be interested.
I sure learn a lot from you train guys!
Best Wishes & Merry Christmas!
Jack
I have always thought that the engine of a steam locomotive consisted of the Valve chamber, piston cylender, connecting rods and drivers.
Dave
WOW!!!!!!! I'm overwhelmed, Jack, ::) that's way to techie for me,lol . My personal experience was a tendency to black out when standing suddenly from a sitting position. which dissipated over a period of three to four years. That's 50 yrs ago now....... oh well. Best wishes and a Merry Christmas to all!
Jim Banner,
Your question: "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?"
OK, what part is the engine? Or not the engine....
Thanks,
Charles
I think the question, "What is an engine?" is open for debate. In the last century Babbage created a "calculating engine," a huge, steam driven monster of an adding machine.
I was always lead to believe that the engine part was the part that did the work - frame, wheels, cylinders, rods, etc. The boiler was ancillary; it supplied the power to the "engine."
Greetings, All.
Weren't the long tunnels (with little air circulation) the main reason for using electrics in the mountains? (Cough, cough, gasp, choke.)
I think SP had cab forward steam engines to avoid asphyxiating their freight engineers and firemen in the tunnels.
Possible secondary reason: Cheap hydro-electric power nearby.
Sincerely,
Joe Satnik
Quote from: Joe Satnik on January 16, 2008, 11:12:57 AM
Greetings, All.
Weren't the long tunnels (with little air circulation) the main reason for using electrics in the mountains? (Cough, cough, gasp, choke.)
I think SP had cab forward steam engines to avoid asphyxiating their freight engineers and firemen in the tunnels.
Possible secondary reason: Cheap hydro-electric power nearby.
Sincerely,
Joe Satnik
Joe,
Both of those are very true. Another point to consider is regenerative braking. With those steep downgrades, the regenerative braking adds up to substantial amounts of energy (e.g. money) saved compared with diesels and steam.
There is a whole lot of talk on the Milwaukee Road board on the decision to de-electrify the western sections of the Milwaukee Road.
My feeling is that it was a mistake, but I don't know that much about the Western Extension.
Gene
The choice of steam vs. electric had to take in a number of factors. The primary one would be the potential savings vs. cost. The usual mantra is that electrification is very expensive to build, but very cheap to operate. Roads like the Virginian, the Great Northern, and the Milwaukee Road looked at the tunnels and grades they had to deal with, and determined that electrics could work for the operational savings. Most important would be the elimination (or at least a greatly reduced need) for helpers. In steam days, each locomotive needs a crew, and the loco needs fuel, water, servicing, etc. Electrics, with their M.U. capability, could haul the trains with one set of "motors" and one crew. Other roads, like the PRR and NYC, had very extensive commuter and passenger traffic that ran much more efficiently with electrics (and still do today in the Philly- New York region). The downside to electrics was the expense of the installation of the overhead, and perhaps the need to build a generating station to power it, since back in those early 20th century days, the availability of commercial power was a real issue, especially in the remote areas.
Diesels, of course, are simply electrics with self-contained motor-generator units. I suspect most of the reason that Conrail abandoned all of the old PRR freight-only electrified routes was to simplfy their operations. Diesels could do the same work, they didn't need a separate maintenance force for the eletrics, they didn't have to stop and change power; they didn't have to maintain all that overhead, etc.
On the Milwaukee Road Yahoo group there has been a long running discussion/argument about the de-electrification of the early 1970s. Apparently the Road was able to sell excess electricity and the de-electrification took place just as the 1973 oil embargo took place, leading to a lot of controversey.
Gene
Where is the electricity coming from? In California they are debating a bill that would put digital thermostats in houses so that the power company could raise or lower your home temperature. This is because there is not enough capacity.
Out here on Long Island Steven Spielberg (Al Gore's good buddy) put in gas fired generators because the power company can't provide him with enough power to illuminate his estate in the Hamptons.
Maybe they should bring back the Atomic Train (remember that silly TV movie made in the seventies?)