I have noticed that in real steam locomotives, the smoke expelled from the stack is occasionally white, but it is also sometimes black. I am a bit confused because there doesn't always seem to be a strict correlation between the speed of the loco and the color of the smoke. I have also noticed that sometimes the smoke expelled on starting is black, yet it seems that other times this same starting smoke is white. There also doesn't seem to be a strict correlation between the weight (or speed) of the locomotive's consist and this effect. I understand the basic premise of steam locomotion demands that excess steam be expelled through the stack. I also understand that contaminating soot particles from the burning of coal sometimes makes that smoke black. My question is when and why does that happen? Can the engineer or stoker be at fault for this effect? Can the effect be produced deliberately? Can anyone please explain this phenomenon? Thanks.
That "white stuff" you see is NOT necessarily "smoke"! What you see that is white is actually the steam VAPOR, and is generally visible ONLY when the outside temperature & humidity is cool enough so that the condensed VAPOR is visible. Once the outside temperature is high enough, i.e. HOT & DRY, then the exhausted steam is no longer visible, and any actual smoke from the fire is then visible as various shades of gray/black, or a light haze.
The white steam is effectively the same effect as when you go outside on a cold day and see your breath. What you are seeing is condensed water vapor that turns to steam when it hits the atmosphere. You get the same effect when you open the cylinder cocks starting off. Water tends to find it's way there and it doesn't compress very well. Opening the cylinder cocks lets any accumulated water out of the cylinders. If it's cold/damp, you see steam. If it's hot/dry, you likely won't see any steam.
As far as the gray/black smoke, it has a lot to do with the firing of the engine and--if coal burning--the quality of the coal. With a good fireman and good coal, you may not see much smoke at all. I'm not sure what kind of coal the TVRM crews were using with Southern 630 this summer, but it was very difficult to get any smoke at all from that thing. Good coal and good firing won't make much smoke.
Sometimes though, you have to resort to overfiring the engine for whatever reason. Basically, that means adding more fuel than you would normally use under the circumstances. It may be poor coal that doesn't have good heating capacity and you have to overfire to keep pressure up. Sometimes the overfiring is done intentionally to "make a show" for the fans. Either way, what doesn't get burned goes straight up the stack as smoke. Basically, for oil burners, the same rules apply.
Depending on weather conditions and such, you will often get both steam and smoke at the same time.
steam (white) + smoke (black) --> varying shades of gray.
The other possibility on oil burners is sanding the flues. Coal is abrasive enough that you don't get soot on the flues (which in turn makes it harder to keep pressure). With an oil burner, sand is used for the abrasive action. Since you are clearing out soot, you get smoke....very, VERY black smoke, and lots of it. Obviously, this can be done for runbys and such also.
Thank you Kevin and Hot Water. That explains it really well. It made me wonder if there is any practical reason (apart from showboating for the crowd) why an engineer would ever want to blow black(or grey) smoke. If there isn't any practical reason, then there certainly would not be any ecological reason for ever eliminating steam engines from mainline service. That means that the only reasons for switching to diesel power were strictly economical. From a purely aesthetic standpoint, steam locomotives were certainly the most beautiful machines ever to grace the world's steel rails. Thanks again.
If there isn't any practical reason, then there certainly would not be any ecological reason for ever eliminating steam engines from mainline service. That means that the only reasons for switching to diesel power were strictly economical.
There certainly are good environmental reasons for not using steam locomotives. And I don't mean something recent like concerns over CO2. New York City banned steam locomotives over 100 years ago because of the soot and cinders they emit. Other jurisdictions had anti-smoke ordinances as well. And steam locomotives, especially when fired with coal, were a fire hazard in forests and range lands in the west.
Even with a relatively clear stack there can still be a shower of particles from a steam locomotive. Passengers in the steam era new not look at the sky when a steam locomotive went by to keep from getting a cinder in their eye. And men didn't stop wearing hats in the 1960's just because President Kennedy made it fashionable. Once steam locomotives were gone you didn't need to wear a hat to keep cinders out of your hair.
Thank you Kevin and Hot Water. That explains it really well. It made me wonder if there is any practical reason (apart from showboating for the crowd) why an engineer would ever want to blow black(or grey) smoke.
If there isn't any practical reason, then there certainly would not be any ecological reason for ever eliminating steam engines from mainline service. That means that the only reasons for switching to diesel power were strictly economical. From a purely aesthetic standpoint, steam locomotives were certainly the most beautiful machines ever to grace the world's steel rails. Thanks again.
Other than putting on a show, there really isn't any reason one would "want" to make smoke that I can think of. Railroads were operated as a business then just as now, and if you could save coal on the run, you saved money. Any unburned coal going up the stack was simply a waste of money from management's perspective. Taken to the extreme, Chinese steam crews even as late as 2005 were hand-firing the QJs even though they were stoker-equipped. The reason was that you saved coal hand-firing, and the crew got more money if they used less coal.
Either way though, regardless of how good the coal is, you still end up with cinders. I can think of several times this summer around the 765 and 630 where there was no visible smoke and I got absolutely pelted with cinders. The environment may not mind as long as you are not in a dry area with fire danger, but the lady with her clothes out on the line sure did. Black cinders and white sheets don't mix. Of course, you have to realize that just like everything else, there are different grades of coal, and the good stuff is pricey. Using lesser-grade coal to fire your steam fleet was one of many ways to try and cut cost. That, of course, makes more smoke. Cue more complaints from the lady with the laundry.
As far as dieselization, it was a multi-edged sword. Some reasons were economical, some weren't. The end of steam in China has more to do with the government's perception of being "backwards" with tourists for the Olympics coming to Beijing moreso than anything else. It's cheaper to operate steam in China even now.
N&W proved that on a pure operational basis, steam could compete very well with current diesel technology. The final straw that broke the steam engine's back was the fact that you could run a railroad with considerably fewer people employed with diesels. With steam, you had a bunch of employees both out on the road, and especially in the shops. With diesel, you could survive with fewer employees, and many shops needed for maintaining steam were closed. Economics in the end? Yes. Money tends to be at the bottom line on a lot of decisions.
Our oil burner at the New Hope Valley Ry. in central NC will smoke, but not as a matter of "show." It's possible to keep it to a minimum, or even non-existent when at rest, but when starting with a heavy train, she'll smoke as the fireman attempts to create as large a fire as possible. Our firebox is only a few square feet in area (exceedingly tiny) and this may account for the creation of smoke. It simply is impossible to get the fire to the strength we need without some smoke. So in our instance, it's very practical. When running at a comfortable lope, we keep a "gray haze" at the stack (smoke, but not very much).
And Kevin, I've never seen a clear issuance of steam from cylinder cocks, no matter the tempurature. There are always white clouds.
Salt Lake City required that the Rio Grande clean up the coal smoke crudying up their city in 1947. The 'Grande responded by putting overfire jets on the fireboxes of locomotives working into Salt Lake. But funny thing, the overfire jets, from the photos I have seen, didn't make an ounce of difference and believe the Rio Grande's powerful, huge fireboxed locomotives remained, by photographic images, the smokiest steam locomotives in the USA! The L131's and L105's looked like volcanoes!
From most of what I've read, overfire jets were rarely used by crews out on the road because they were very loud. If anything, they were turned on in urban areas. That could be another explanation for the smoky pictures.