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
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.
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
selector wrote: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
blue streak 1 wrote: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 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.
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.
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'.
selector wrote:It may well have been an FM, come to think of it.
It may well have been an FM, come to think of it.
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.
marknewton wrote: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.
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.
selector wrote: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. -Crandell
timz wrote: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.
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.
timz wrote:So at the top of Everest the absolute pressure inside the boiler is less than it would be at sea level...
So at the top of Everest the absolute pressure inside the boiler is less than it would be at sea level...
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.
http://www.kellstransportmuseum.com/Peru/FCCA/FCCA.html
marknewton wrote: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.
When we're at sea level (with the outside air pressure at 14.7 psi) and the locomotive pressure gauge reads zero, what is the pressure inside the boiler?
marknewton wrote:I have to ask, what practical experience do you have on steam locos?
None.
Oh, oh, oh..! I know this one! It would be whatever pressure the gauge is calibrated to read at its "zero" point. If it is PSIAMSL, it should be very close to the pressure at sea level. If it is some other arbitrary value, then it will read zero when the pressure inside the boiler reaches that point. The pressure in the boiler, practically, will eventually match the outside pressure based on the altitude at the place where the neutralizing takes place. If at sea level, the pressure in the boiler, via leaks here and there, will eventually reach the pressure of sea level. But the gauge may say something entirely different...a non"zero" value depending on its calibration.
I do think the safeties are marginally sensitive to outside pressure at whatever altitude we find ourselves, but it is very small compared to the pressure working on the springs at full working pressure.
It would seem to me that altidude does not affect the heat energy of the steam if it is in a contained vessel. Thermodynamically a steam engine is a heat engine and they work by flowing heat through a device to harnese it. The energy stored in the water molecules rapid movement is used to push a piston. Steam is a hot expanding gas. The hotter it is the more energy it contains. The cooler the steam is once its out of the engine the more efficent the engine is. At high altitudes there is less back pressure on the exhaust stroke so the engine is more efficent. This is the same principle as the seperate condenser James Watt invented!
Think about a steam turbine in a power station. the large low pressure stage uses steam that is basically 1 psi and by the time its hit the end its pulling a vacuum! This in effect "pulls" more steam through at the high pressure side, again increasing thermal efficency.
Turbocharged engines also follow the same principle- turbos work very well at high altidude because the pressure upstream of the turbo in the manifold is immense and full of hot expanding gases. The lowered atmosheric pressure allows the turbo to spin more freely and use more of the waste exhaust. (superchargers , mechanical and turbo alike have what is known as a "critical altitude" this is the maximum altidude at which the engine will develop its rated sea level power and manifold pressure. The GE B series turbochargers used on WWII aircraft such as the B-17 and B-24 bombers and the P-38 and P-47 fighters had a critical altitude of 25,000 feet. beyond that the engine has to be throttled down to prevent the turbo from overspeeding and being destroyed by centrifugal forces.
As far as the actual combustion in the firebox the effects of altidude are quite small. at high altitude there is not enough air to flow into the cylinders of a reciprocating naturally aspiratied IC engine to burn the fuel. Air is taken in parcel by parcel and if the air is less dence the engine simply cant breath. A firebox however is a very large area that pulls air constantly through very large openings. There is no shortage of air.
In short steam engines improve their performance as altitude increases (to a point where the air is so rarified that even the massive grate area cannot supply enough, pretty darn high) and IC engines lose their performance respectivly. (unless some means of forced induction is incorperated, even then the critical altitude is lower because of mechanical limitations on turbo RPM)
I have seen a proposal for generating energy on the moon that involves steam and a turbine. Now that is high altitude.
timz wrote: marknewton wrote: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.When we're at sea level (with the outside air pressure at 14.7 psi) and the locomotive pressure gauge reads zero, what is the pressure inside the boiler?
timz wrote: marknewton wrote:I have to ask, what practical experience do you have on steam locos? None.
marknewton wrote:the gauge will read zero at whatever pressure it was calibrated to off the master gauge.
Cool the boiler all the way down to outside air temperature and open a cylinder **** (see below) or a safety valve, or whatever will bring the pressure inside the boiler exactly equal with the air pressure outside (say 14.7 psi outside). If the gauge has been calibrated correctly, what will it read then?
marknewton wrote:the Bourdon tube that drives it only connects with the steam space inside the boiler, nowhere else. The outside air pressure has no bearing on how it reads.
Is the Bourdon tube surrounded by a vacuum? Or by air, at 14.7 psi at sea level?
I looked thru my books and only found a couple of passing references to this matter-- apparently they figured the fact that the pressure gauge reading is the difference between the inside pressure and the outside pressure is too well-known to need stressing. If you have Bruce's book it's on page 151, or if you happen to have one of Baldwin's "Locomotive Data" editions the table of "Properties of Saturated Steam" suggests the same. I'll look around and see what steam tables I can find online.
(Well I'll be darned-- in the first line, it bleeps out that word that rhymes with "lock" but begins with a "c".)
I think Timz has it right, that the pressure gauge on a steam locomotive is psig, not psia. Pressure gauges that read other than gage pressure are rare. A simple bordoun tube pressure gage read normally reads psig.
http://www.dynisco.com/literature/Application%20Notes/Sanitary/GageAbsPress.pdf
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
timz wrote:...bring the pressure inside the boiler exactly equal with the air pressure outside (say 14.7 psi outside). If the gauge has been calibrated correctly, what will it read then?
...bring the pressure inside the boiler exactly equal with the air pressure outside (say 14.7 psi outside). If the gauge has been calibrated correctly, what will it read then?
I looked thru my books and only found a couple of passing references to this matter-- apparently they figured the fact that the pressure gauge reading is the difference between the inside pressure and the outside pressure is too well-known to need stressing.
marknewton wrote:Now I see why we are at cross purposes. You're talking gauge pressure, whereas our boiler code stipulated the use of gauges that showed absolute pressure.
My first thought is why?
The mechanical stress put on a pressure vessel is due to the difference between the internal and external pressure. Unless the boiler is being operated at very low pressure above atmospheric, the steam temperature and enthalpy isn't going to vary much between a given gauge pressure at sea level and the same gauge pressure at say 14,000'.
One advantage of running a steam locomotive at altitude is that the absolute back pressure will be less, which could off an improvement in efficiency.
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