I know what they look like but when were different smoke stacks, (onion, straight, balloon etc) used on geared locos? Or did it make any difference?
A lot of the time it was based on the fuel used. Oil burners, coal burners, wood burners, etc. The big Hunter stacks and such a lot of the time were used on wood burners. Oil burners usually have short little stove pipes. I also know that even the different coals used had different stacks. So I think a more prudent question than “when” is “what” was the fuel.
here is a good post on the subject https://www.mendotraintony.com/smokestacks-of-steam-locomotives-article-in-live-steam-magazine-of-december-1984/
Those different stacks were used to stop sparks and embers from flying out and setting fires along the right of way. The shapes were determined by what fuel was being used, and the type of screening invention was applied. Different types of wood, and different hardness of coal, could each have different types of screening, and in different stacks. There were also different inventors, and patents… Some fuels required longer, or shorter smoke boxes, and fire boxes were different also. Oil fired locomotives are another story too.
Fred Mills
Also as Dave has shown us with #315, there are baffles in modern smokeboxes to trap the cinders and embers.
After that the stacks could be designed for best drafting of air through the firebox, producing more efficient fires.
Great thanks!