White and Black Smoke

[NW Mailing List]

Steam locomotives exhaust the 'waste' steam expanded in the cylinders up
through the smoke box and smoke stack.  The reason that they do this is to
create a low pressure area on the other side of the boiler so that the
burning and hot gases will be drawn through the boiler flues.  The exhaust
steam flows through a nozzle, called the exhaust stand, inside the smoke
box.  The nozzle acts as a diverging nozzle which will drop the pressure of
the exhausting steam as it exits the nozzle.  This flow of steam will then -
if designed properly- expand slightly and flow upwards through the entire
smoke stack, 'sealing' it off and forming the low pressure area in the smoke
box necessary for draft. Thus, the exhaust consists of exhausted steam and
burned gas from the fire.  When starting up the fires or when operating at a
low speed and low boiler pressure, a draft forcing device would be started
by the fireman to force the draft.  ( Design of the smoke stack, exhaust
stand and the space/volume around them to create good, free draft with the
minimum of back pressure at the cylinder exhaust was a 'black art' in those
days.  Much measurement and trial-and-error experimentation was necessary to
optimize the front end; the N&W made many improvements to the M's, Y's, E's,
Z's, and K's concerning the stack, nozzle and smoke box in the early part of
the century.) 

 

Thus, the white smoke is generally steam.  This is very obvious in cool or
cold weather.

 

Black smoke is indicative of the locomotive fire being 'too much' for the
locomotive working energy requirements and the fire is burning "rich".  This
would be common when the locomotive is accelerating its train and the
fireman is "pouring on the coals" to keep the fire and the boiler pressure
ahead of the demand required by the accelerating locomotive.  The
accelerating locomotive requires more horsepower as the mass of the train is
accelerated to a higher velocity, thus it needs a larger fire and more steam
at a high pressure.  

 

It would be up to the fireman to use proper firing techniques to minimize
the 'black' smoke.  He could be reprimanded for poor firing performance on a
given run.

 

Gary Rolih

Cincinnati

 

 

  _____  

From: nw-mailing-list-bounces at nwhs.org
[mailto:nw-mailing-list-bounces at nwhs.org] On Behalf Of NW Mailing List
Sent: Saturday, March 29, 2008 8:27 AM
To: NW Mailing List
Subject: White and Black Smoke

 

Good morning.

 

I am not worried about my Arrow not arriving yet and will not be posting
when it arrives.

 

The purpose of my post this morning is to inquire as to why on many of the
programs that I watch on RFD TV (Trains and Locomotives) some of the smoke
is black and some is white.  What is the cause of this? Have a great weekend
and thank you in advance for any responses.

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