does steam get affected by power at altitude much like a car does when it is a at altitude like a loss of poweror steam pressure or temp? thanks
actually water boils at a lower temp at altitude. Someone know the boiling point of water at 10000 ft?.
Altitude doesn’t make a difference. Yes water boils at lower temperatures at the lower pressure of high altitude, but the water in the boiler is still at operating pressure. The steam pressure gauge actual measures the difference between external pressure and internal boiler pressure - but the needle reading is corrected for atmospheric pressure at sea-level. So if the guage reads 200 psi at 10,000 feet - you still have about 200 psi working pressure.
One would have to be above about 14,000 or 15,000 feet elevation for the lower oxygen content to start impacting the flame temperature. Even then, increasing the blower setting a bit should compensate.
dd
Yes altitude does make a difference. If the grate area is big enough to burn the fuel at say 90% efficiency less heat is needed to boil water and the steam pressure is the same. That is why feed water heaters were so important. Got the water closer to boiling so heat from boiler did not have to raise temp. So there may be better steaming at altitude.
The engines I saw many times when I lived at 14,400’ AMSL in the Peruvian Andes in the late 50’s did not have feedwater heaters.
This is how I see it. I hope an engineer or physicist can help us out with this. While less heat is needed to get the water to boil, that only works where the boiler starts cold and equalized to the outer atmosphere. If it has more than five or six PSI above that, then more heat is needed. That same water will boil none the less, but it will take longer since the firebox of a given size will not produce the BTU’s that it can being fired well at sea level. So the equation works as long as the boiler is producing the psi that gets to the piston surface area. The expansion coefficient of the steam, even when relatively cool, is still going to do the work necessary, although not quite as efficiently as at sea level because the steam won’t have the latent energy in it in the way of heat.
Similarly, the safeties have a nearly negligible sensitivity to the pressure at sea level because they are purely mechanical. They only respond effectively to the absolute pressure working on their springs. If less heat makes the water turn to steam, the pressure in the boiler will rise only until it is sufficient to lift the safeties. That may be a predetermined 180 psi, 200, 250, 500… That is the beauty of the steam engine and any pressure vessel…it works everywhere, even in outer space if you build it right. If you can get the pressure to the cylinders, even with ice-cubes, you will get the work that 200 psi will do for you.
Speaking of Peru, I remember something from the BBC that was shown on PBS in the eighties, “Great Railway Journeys” or something like that. They said that when the South American railroads went to diesels, they hadn’t counted on the diesels needing oxygen more than steam, so they ended up having to buy much larger diesels with more horsepower than the horsepower of the steam engines they were replacing. Think they even bought some FM Trainmasters to replace relatively small steam power.
I was present as a nearly 11-year-old when the first diesel ever to make it up to the altitude made its maiden voyage. I can recall what surely were 120 or more “gringo” staff and families at the Cerro Golf Course overlooking a very shallow horseshoe curve that crosse part of what used to be in Ripley’s Believe it or not as the highest golf course on the planet. We knew the engine’s arrival was imminent and hurried from our various home to watch it come around a bluff and wind across the golf course, a distance of perhaps 400 meters only.
I may well have been an FM, come to think of it. In any event, the train was typically short for the road and the altitude, perhaps 15-20 cars or so, but the point is while the diesel led the consist, it was assisted by one of the trusty Consolidations at the rear. The diesel was incapable on its own. That changed not much later with an addition or some form of improvement/augmentation that the engineers performed on it.
-Crandell
Trainmasters used a a non boosting roots blower to scavenge the cylinders. Engines that operate on atmospheric pressure do suffer a loss of power at altitude. A properly designed turbocharged engine reduces or negates the elevation effect. For example, the latest turbocharged GE’s built for China operate at their designed HP output, even on the 15,000-18,000 foot Tibetan Plateau.
The engines I fire at 5500 ft do not have feedwater heaters. We do have lifting injectors which also preheat but we also use crosshead pumps which don’t preheat. I repeat - altitude does not make a difference because the water in the boiler is not boiling at atmospheric pressure and the difference between 200 psig at sealevel and at 10,000 ft is negligable.
dd
I don’t see how altitude could effect the pressure inside a closed and pressure regulated boiler. It should boil at the exact same temperature internally. What would be affected would be the pressure on the boiler from a metallurgical stress standpoint as the outside pressure is less at altitude than at sea level. However the difference in pressure is only a few psi and from the standpoint of a couple hundred psi working pressure it’s basically nothing and would know no difference. If steam engine boilers were open containers at atmospheric pressure, the boiling temperature would change. It would go down. We wouldn’t be able to harness it though! I see no way from a boiling point perspective that altitude could change anything. The same would still be true in the vacuum of space.
What I could see happening is that the fire takes more effort to get hot as it directly relates to the amount of oxygen present in the air but since I’ve never fired a steam engine, I couldn’t tell you how this translates into real world operation.
The Central Railway of Peru, until recently the highest railway in the world, ran for decades with steam-engines. Summit was at roughly three miles high near Oroya in the Altiplano.
Martin, this is the railway system I was mentioning in my posts above. The Ferrocaril Central Del Peru was state owned, while the Cerro Mining Corporation based out of New York owned a good portion of it, and all of it beyond La Oroya. The highest pass we drove over was called Ticlio (TEEK-leoh), but I am unsure the railway got that high (15,000). It probably used a nearby valley.
La Oroya, if my memory is correct, sits a roughly 12,000 feet, but Cerro de Pasco, where I witnessed the arrival of the first diesel, was at 14,300 feet. The Golf Clubhouse that served as our vantage point was at 14,400’.
No, no, no - altitude makes no difference. The same amount of heat is required to make steam whether the loco is at sea level or topping over Mt Everest. The water in the boiler is not at atmospheric pressure once there is a fire on. The whole point of a boiler is that it is a sealed pressure vessel - it is not open to the atmosphere.
And there is no connection between operating altitude and the provision of a feedwater heater. There were as many railways in the world that operated at high altitudes and did not use feedwater heaters, as there were sea-level railways that did.
Mark.
Crandell, somewhere or other I have a diesel roster for the Central, and as far as I recall they never had any FMs. IIRC the only “export” Trainmasters were those in Canada. The CdP had both Alco DL535s and DL560s, which is what I suspect you recall seeing. Again, IIRC the Alcos didn’t perform well until they were fitted with barometric governors.
All the best,
Mark.
Thanks, Mark, I’ll try to find an image on the www and see if it flashes a memory or two. It was so long ago, and I certainly would not recall what the diesel was.
Nice to have you back “on the job”, BTW. [:D]
-Crandell
It doesn’t make much difference, but–
You remember that a given safety-valve setting (and a given reading on the steam gauge) gives a constant difference in pressure between the inside of the boiler and the outside. So at the top of Everest the absolute pressure inside the boiler is less than it would be at sea level-- which means saturated steam in the boiler will be slightly cooler, with slightly less energy/enthalpy per pound.
Thanks, Crandell! If I can find the book there are some photos I can scan and post to jog your memory.
Cheers,
Mark.
No, it doesn’t make any difference. The pressure gauge simply shows the pressure inside the boiler, nothing more. It does not compare or give a reading relative to outside air pressure. If you’ve ever used one, or taken one apart for calibration or maintenance, you’d know this. Same for the safeties - they’re mechanically set to lift at a given boiler pressure, without any reference to the outside air pressure.
No, it isn’t, and I’m buggered if I can understand why you’d think otherwise. The boiler pressure is an absolute value, and is the same at sea level or at 15,000 feet. 200psi is the same pressure at any altitude.
I have to ask, what practical experience do you have on steam locos?
Mark.
Mark, I found this site that does bring back some memories. Although I don’t seem to recall the nose on the diesel they show, the rest of it is right on the money.
Good site! I think the Alco’s shown were delivered with high short hoods, and got the “chop” later on. I’m not at home at the moment, otherwise I’d find that bloody Peruvian book!
Incidentally, that same website has a page featuring my old loco:
http://www.railwayinternational.com/Australia/3801/3801.html
Not only was I working on this trip - I 'm in one of the photos! LOL! It’s funny seeing all of my mates posted up on the web…
Cheers,
Mark.