Steam at High Altitude

The belief that diesels could not perform at high altitudes kept the last std. gauge class 1 railroad steam locomotive - C&S 2-8-0 #641 - active on the Climax Spur in Leadville, CO until Oct. 1962. Then it was replaced by an SD9, when, after testing a turbocharged SD24 on the line, it was determined diesels could operate w/o difficulty. So steam, diesel, and even humans can adapt to high altitude! Climax, CO has an altitude of 11,360 feet.

       

The Alpine Tunnel in Colorado was 11,500 ft elevation. Biggest issue there were snow slides, blizzards etc.

http://en.wikipedia.org/wiki/Alpine_Tunnel

The pressure INSIDE the boiler is what determines the boiling point of the water IN the boiler. The pressure OUTSIDE the boiler is irrelevant.

Of course, I should have realized that!  However, when firing up a loco at altitude, you might reach the first few psi little faster.  

At 10,000 feet the water would begin boiling at about 90 degrees C.  Seems like the big problem would be getting enough combustion air since the air pressure (and available oxygen) is down to 70% of sea level.

As stated earlier, the air at altitude would be thinner and the combustion from natural air pressure would be a bit weaker, etc., but certainly by even the late 19th century designers would have understood and been able to take that into consideration.  

 

I've dealt with this issue with regard to stationary steam power - both recip and turbine, located at high altitudes.

 

Rich is correct about the pressure inside the boiler being what matters most, and that is not affected by atmospheric pressure.  However, the boiler pressure is a steam engine is dumping its exhaust steam through the cylinders into the atmosphere, which being slightly lower pressure at, say, 15,000 feet, would make the locomotive slightly more efficient - at least on paper.  Theoretically at altitude the ratio of boiler to atmosphereic pressure would be slightly better, and depending on the design of the pressure control valves for the boiler (some types use a spring to maintain, say, 200 pounds above atmospheric pressure, some are absolute, maintaining 200 pounds, period, etc., and don't vary a tiny bit as atmospheric pressure does).  In either case there would be a tiny, tiny advantage, theoretically, at altitude (probalby not enough to make up for what is lost in the combustion, I suspect), and in the latter valve case, there might actually be something approaching a half percent higher net power gain.  The effect would be tiny - what I would classify as a tertiary, not even, secondary,effect as altitude changed.  I suspect overall if run well it just would not matter up to a reasonable altitude, probably 11 to 12 thousand feet anyway.

 

Interesting, though

I make paintings of trains. At least I did. This one was oil on board of a narrow gauge loco in the Durango shops.

In one episode, "Three Miles High," of the BBC series "Great Railway Journeys of the World" the host describes how in Peru they replaced steam locomotive rated at 1600 HP with 1600 HP diesels, and found that the diesels couldn't handle the same train as the steam locomotives could.  So they has to buy diesels rated at 2400 HP instead.  "Progress."

 

Stuart

 

 

 

But your argument would seem to indicate the engine would work just as well if the density is a near vacuum, doesn't it?

This is why we have turbochargers and blowers(superchargers) for internal combustion piston engines.

Kelly,

To the extent I still remember my Aerospace Engineering classes from the last decade, the reason for commercial aircraft flying at high altitudes was that the air density was lower, thereby reducing drag, both around the body of the aircraft & in the engine. The other reason is that it takes less fuel to maintain the optimum fuel / air ratio for complete combustion. Also reduced variation in temperature in the lower levels of the stratosphere where these aircraft cruise, results in less turbulent air.

Other factors according to random people on the internet include

Dedicated flight corridors under an Air Traffic control who monitor the specified separation between aircraft

Sufficient glide distance to an alternate airport, if the aircraft loses 1 (or more) engines

Fly above the clouds to get around bad weather at lower altitudes

Minimize bug splatter on windshield & bird hits at higher altitudes

 

But realize that these benefits only apply to aircraft already cruising at that altitude. It takes considerable energy to rise to that altitude fighting against gravity through thicker air at lower altitudes.

The limits you mentioned if the aircraft approaches the limits of space (near vacuum), comes with efficiency losses due to

Much lower (approaching none) oxygen to maintain combustion hence thrust to maintain airflow over wings for lift & to propel the aircraft forward

More energy needed to overcome earth’s gravity to rise to that altitude, with reducing thrust from the reason above

More pressurization in the cabin to sustain human life & comfort without a space suit, adding more weight in cabin structure while getting less thrust

The issue of ozone depletion at the top of the Stratosphere (according to one of my professors)

Thanks,

Naveen Rajan