D&S 25 years apart, what's the difference?

I've been looking at a lot of my photos of the Durango and Silverton. I had noticed something odd, but it didn't sink in until I saw two pictures of a K36 in almost the same location, the first from September 1990, and the second from August 2015:




Trains magizine, in the October 2015 issue, totally destroyed my railfan confidence when they printed why sometimes steam engines emit black smoke, and sometimes it is white. I always thought it was because sometimes they used black coal and sometimes the burned white coal.:-)

Anyway in these two photos, why is the smoke plume so distinct in the 1990 photo and so "difused" in the 2015 photo? Is it operational, or it mechanical? Maybe a different type of spark arrester? All my D&S photos from the last couple years show the same effect, but I can't recall anyone else mentioning this.

Bill Kepner



Edited 1 time(s). Last edit at 09/04/2015 05:29PM by drgw0579.