A good half Century ago when I was modeling in Horribly Oversized Scale, I had a few European Prototype steamer that "smoked". If I recall correctly, they were by Fleischmann and used Seuthe smoke units. Very messy to fill the tiny "smoke generator" in the stack with the appropriate fluid (even in Horribly Oversized); you had a few wispy curls of "smoke" for about 2 minutes which looked tacky as hell, and then you had to refill the blasted thing again. Definitely NOT worth the aggravation...