Did Altitude Have Any Effect On a Big Boy..?

For normal air pressure I found this chart:

Coal burns at what, somewhere around 850 degrees F depending on type and quality?  27.4 degrees F difference (0-14,000 altitude ) isn't anything to worry about in a locomotive firebox.

Rusty

Not correct or applicable...the interior of the boiler is not at atmospheric pressure. It's at some higher pressure and is not affected by the external pressure (or lack thereof) of the atmosphere.

A coal-fired steam locomotive fire box is a LOT hotter than 850 degrees! When the locomotive is working hard, the fire is almost white-hot and the temperature is near 2,500 degrees F. When I purchase coal for the 765, one of the most critical coal specs I look at is the "Fusion Temperature." This is the temperature at which the ash starts to melt and form clinkers. If the fusion temperature is HIGHER than 2,500 degrees, we don't have any problems with clinkers. Lower than 2,500 F and the fireman is going to have a bad day. 

Meant to say "coal begins to burn at somewhere around 850 degrees..."

Rusty

I would think the amount of oxygen available for normal combustion is  less with altitude/atmospheric pressure decrease, at the very least the fire is going to burn slower, with less oxygen available.  Maintaining a fire box temperature as altitude increases might be more difficult. You can always add more fuel, tough to add more oxygen.   Also keep in mind that there is a pretty good chance the air temperature at higher altitude is also going to be less, which cuts another small portion of energy from the fire box.    There is a reason those mountain climbers use bottled oxygen.  Assuming Up-hill-load, working hard, boiling water absorbs energy quickly from the hot coals in the fire box, can combustion with less oxygen keep up with the demand??

Don't think the Big boys were climbing Mt. Everest, nor did it run in any elevation that required extra oxygen.  Besides, a locomotive firebox draws air from both sides and under the firebed.  Not the tiny little openings that are the human mouth or nose.

I don't think any steam locomotive ever had a flameout in the mountains for lack of oxygen.

Rusty

Altitude has no measurable effect on a steam locomotive.

A steam locomotive is an EXTERNAL COMBUSTION engine, as opposed to a INTERNAL COMBUSTION engine.

HUGE difference.

Altitude did not affect any steam loco at all.  My uncle (1954 photo below-not sure what loco he is in there) worked for ATSF and told me that.  He took me on a ride up and over Raton Pass in the early '50s in a 2900 Northern (major reason it is my favorite loco).  The trip took about half a day (and an hour by car with my Dad bringing me back to Trinidad from Raton.  I recall my uncle explained that the high altitude in some parts of the Rockies could affect diesels and how they ran, but would do nothing to a steam loco (he was proud of that ), but that the quality of coal he would pick up on long trips, say in Chicago vs Topeka vs La Junta vs Calif, was a factor he had to keep in mind and adjust for.  

Interesting photo BTW - note the little belts he has around the ankles of his pants legs to avoid them catching in things.

If Altitude had no effect, that appears to be a pretty good indication of just how inefficient these machines were.

Does a steam locomotive have any way of regulating the air being drawn into the firebox? I understand used steam from the cylinders travels through an exhaust nozzle and up the smokestack which helps draw more air into the firebox through the grates?

And then there is humidity. The more humidity there is in a volume of air, the less oxygen molecules there will be. Moisture displaces the oxygen molecules. At 0% humidity, a volume of air will have more oxygen in it than the same volume of air at 100% humidity. That is why people feel so bad when the humidity is high, they breath in less oxygen with each lung full. For a steam engine, it probably makes no more difference than altitude does.

Humidity doesn't stand a chance in a locomotive firebox.

Rusty

I'm no expert. Solid fuel, coal.  The exhaust draft principle that you mentioned works extremely well, a fireman looks for holes in the fuel layer, in the fire box, usually the back two corners that solid fuel, coming off the stoker, tends to miss. The Fireman would hand shovel these corners.  The rest of the fire box is evenly fueled by the use of steam jets that the fireman can adjust. The steam jets push the solid fuel where it is needed in the firebox.  Holes in the fuel layer allow for un-even drafting which is a problem.  Properly fueled, a fireman gets the most out of the energy available with the least amount of lost fuel and smoke out the smoke stack.  IMO

Seems like folks are searching for problems that didn't exist. 

Quality of coal (or oil), water, the skills of the engineer, fireman and their cooperation with each other had much more of an effect on steam locomotive (Big Boy or otherwise) operation than altitude or humidity...

Rusty

Typical steam engines have always had an efficiency rating of only about 15%, simply due to the nature of the beast and the laws of physics. A slight change in environmental factors would do next to nothing to change this one way or the other.

Add to that the fact that the steam produced is superheated under tremendous pressure well above the normal boiling point, so that its boiler function is not at all like a pot of water boiling on a stove under atmospheric pressure.

Jim

Not relevant at all. A steam locomotive is an EXTERNAL combustion engine, and THAT is what is responsible for the lack of altitude effect on the machine.

Your understanding is basically correct. The harder the locomotive works, the more air is drawn through the fire...exactly what you want. Beyond that there is no need to regulate the air coming through the fire. In a sense, it is self-regulating.

AMEN! Some of you are over-analyzing this to death!