# Steam Engine Exhaust Color Question



## Rover (Mar 6, 2019)

While I was watching this video of Steam trains now running in Britain, I noticed steam engine exhaust that was all black, partially black, and all white or slightly grey.





What causes the steam engine exhaust color to vary?


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## caravanman (Mar 6, 2019)

The stuff that emits from the chimney/funnel is not just steam, it is smoke as well. Some steam may be emitted as it helps to draw the fire.

Strictly speaking, what one calls steam is water vapour, steam is invisible!

E.


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## Metra Electric Rider (Mar 10, 2019)

I would think that the grade of coal would also affect the color of the, well, lets just call it exhaust. I have this vague memory of watching logs being thrown into a firebox, probably in an old movie or tv show - was wood actually used (at least commonly)?


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## ehbowen (Apr 3, 2019)

Caravanman, steam IS invisible...provided it's not cold out! That's why the most dramatic steam photos are taken in the winter...the cold air condenses the steam into a great visible cloud! 
As far as the black smoke...speaking as a professional boiler operator, that's just poor combustion. "Modern" (late 1920s and after) locomotive boilers are usually equipped with overfire jets which introduce additional combustion air above the fuel bed and, when properly adjusted, should eliminate most of that. Black smoke is just wasted fuel. But sometimes, especially for a photo runby, you get a fireman deliberately "making a show" by burning excess fuel with insufficient air, or perhaps "sanding the flues" ...a technique to clean soot (the sand blasts it off) while at the same time making a big plume of black smoke.


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## MARC Rider (Apr 3, 2019)

ehbowen said:


> Caravanman, steam IS invisible...provided it's not cold out! That's why the most dramatic steam photos are taken in the winter...the cold air condenses the steam into a great visible cloud!
> As far as the black smoke...speaking as a professional boiler operator, that's just poor combustion. "Modern" (late 1920s and after) locomotive boilers are usually equipped with overfire jets which introduce additional combustion air above the fuel bed and, when properly adjusted, should eliminate most of that. Black smoke is just wasted fuel. But sometimes, especially for a photo runby, you get a fireman deliberately "making a show" by burning excess fuel with insufficient air, or perhaps "sanding the flues" ...a technique to clean soot (the sand blasts it off) while at the same time making a big plume of black smoke.



Obviously, such a locomotive would not meet EPA Tier 4 requirements.


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## Maglev (Apr 3, 2019)

Metra Electric Rider said:


> I have this vague memory of watching logs being thrown into a firebox, probably in an old movie or tv show - was wood actually used (at least commonly)?



Wood was indeed commonly used as a fuel for steam locomotives. One of the two locomotives at the Golden Spike in Utah was wood-fired.


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## dcwldct (Apr 9, 2019)

Metra Electric Rider said:


> I would think that the grade of coal would also affect the color of the, well, lets just call it exhaust. I have this vague memory of watching logs being thrown into a firebox, probably in an old movie or tv show - was wood actually used (at least commonly)?



Wood firing was what created the need for the distinctive funnel-shaped spark arrestor chimneys in many 19th century American locomotives. Coal fired locomotives of the era didn't produce as many embers and typically had a more conventional chimney arrangement.


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## cirdan (Apr 11, 2019)

Maglev said:


> Wood was indeed commonly used as a fuel for steam locomotives. One of the two locomotives at the Golden Spike in Utah was wood-fired.



There have even been steam locomotives that burnt sugar cane.


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