Model train collectors strive to make their model train sets look as realistic as possible by painting them the colours of real-life trains, adding different cars to their trains and creating diorama around the tracks. So it only makes sense that model train collectors and owners would make their locomotives produce "smoke" as they chug around the track, despite the fact the trains run on electricity. Different mixtures can be combined to create model train smoke.
Fill a quarter of the measuring cup with glycerine. Fill the measuring cup the rest of the way with distilled water. Glycerine will settle at the bottom, so use a stirrer to mix it with the distilled water.
Pour the cup of mixed glycerine and distilled water into an eye dropper using a funnel. There will probably be more fluid then the eye dropper can hold so you should have some extra left over.
Use the eye dropper to put a few drops on top of the heating element in your model train locomotive. The mixture will create different amounts of smoke, based upon the solution's mixture. Adjust this accordingly if you want thicker or thinner smoke.
Clean the smoke stack often with a pipe cleaner so the smoke comes out of the locomotive more smoothly. Make sure you are using distilled water, as regular water can clog and damage the model train.
Make sure your brand of model locomotive can handle liquid smoke mixtures, as there are models that are made solely for pellets. If it can't and add liquid, your locomotive can short out and even cause a fire, permanently damaging it and your model train set.