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Old 02-18-2009, 07:28 PM
Fiddle Peghead Fiddle Peghead is offline
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Mid 19th Century Locomotive MPC (Miles per Cord)

Having just seen Buster Keaton's "The General", I was struck with the following question: How far could a steam locomotive like the General or the Texas travel on a cord of wood? While I'm at it, how much water would be needed to produce the steam for this amount of wood, and how often would the locomotive have to stop for a refill?
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Old 02-18-2009, 08:19 PM
Xema Xema is offline
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It's not much help for a general answer, but the Mt. Washington (NH) cog railroad steam engines burn a ton of coal and consume 1000 gallons of water in a 3-mile trip to the summit and back.

A ton of coal has roughly the energy content of a cord of wood.
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Old 02-18-2009, 08:37 PM
UDS UDS is offline
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There’s a lot of variables. How big is the locomotive? How heavy is the train it is pulling? How far? And how fast?

Short journeys are particularly heavy on fuel, because the fire must be lit a long time before the start of the journey to build up heat to raise sufficient pressure of steam, without which the locomotive cannot be started. If the journey was short enough, most of the fuel might be consumed before the journey started at all.

Steam, and therefore water, is heavily used when the train accelerates. Thus a stopping-and-starting journey would use a lot more water than the same journey at a steady rate.

So I don’t know that it’s possible to generalise. I do know, though, that at least in terms of bulk locos would carry a lot more water than coal.
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Old 02-18-2009, 08:57 PM
BlakeTyner BlakeTyner is offline
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I love it when there's a question on the Dope that I can actually answer.

Background: For 7 years I was the fireman/engineer at a tourist railroad which ran a replica 4-4-0 steam locomotive. The loco itself was built by Crown Locomotives Products of Pennsylvania in 1962, but based on the mid 1800's design. The only real "modern" touches were lifting-type Penberthy water injectors (typically, engines of the time would have had crosshead driven pump injectors); a modern Manzell forced-lubrication system (rather than sticks of grease everywhere); and a welded boiler (period locos, obviously, were riveted.)

Our locomotive was built to burn wood. It was, however, converted to propane long ago--before I was even born. However, I think I can provide enough information to at least answer the question.

First, as I'm sure you realize, the amount of fuel consumed varied by locomotive. Even within the same design, each engine had her own personality and fired/drove differently. Mostly that had to do with operating conditions and maintenance. A locomotive which continually ran "hard" water through the boiler would quickly develop a layer of 'scale' inside the boiler. Scale acted as an insulator, making the engine less efficient.

The proper care, including lubrication, was also important, obviously.

There was also the fireman. The wonderful book "Basic Steam Locomotive Maintenance" has this to say on p. 7:

"On every railroad the problem of fuel economy is largely in the hands of the engineers who operate the locomotives. If the engineer is interested in this subject and insists on his fireman firing according to correct principles, fuel will be saved each trip."

So, right off the bat, the answer is variable.

In direct reference to your question:

We burned 1.6 gallons of liquid propane to go 1 mile.
We converted roughly 20 gallons of water into steam per mile.

Our locomotive was built very, very similarly to The General. There are 32 fire tubes, roughly 500 gallons of water in the boiler, with a firebox volume of 3ft x 3ft x 3ft.

"Basic Steam Locomotive Maintenance" says that the heat units (BTU) produced by burning one pound of dried wood is 8,000. So if you or anyone else would like to do the rough math, it's possible to see how much wood one would need to burn to keep that much water boiling inside a pressure vessel. My education is in English, so I'm woefully behind on figuring the math. Other than the BTU of wood, I can provide the following information from the book:

"less than 20 percent of the heat energy in the fuel is converted into effective work"

"A horsepower is equivalent to 33,000 foot-pounds of work per minute. To produce 1 horsepower continuously for 1 hour would mean an expenditure of 33,000 x 60, or 1,980,000 foot-pounds of work. As one BTU is equivalent to 778 foot-pounds of work, it would require 2,545 heat units to produce 1 horsepower continuously for 1 hour."

So, one pound of wood, properly burned, gives off 8,000 BTU (enough to produce a little over 3 horsepower continuously for one hour.)

The book goes on to say that, due to losses, "in practical service, a performance of 25 pounds of water (steam) per indicated horsepower per hour was considered a fair average, as was a boiler evaporation of 2.5 pounds of water per 1 pound of wood."

Without laboring on, I can give the following information about the locomotive:

Boiler capy: 500 gallons
Ideal operating pressure (PSI): 170
Maximum allowed operating pressure (PSI): 200
Boiler horsepower: 29.5

As I said, I'm not well-skilled in even basic math, so I don't want to make myself look like a fool by screwing up some simple arithmetic. Perhaps a math person can figure exactly how many pounds of wood are needed to move a locomotive with the above specs.

Lastly, I'll say that our average speed was only about 10MPH, due to curves. The General could do more than that.

Very very simplified:

We burned 1.6 gallons of LP each mile. Without accounting for losses, that translates to (I think) 11.4 pounds of wood.

We used 20 gallons of water per mile, at 10MPH.

~Blake
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