It's not that trivial, you have to create particle effects and possibly extend some bones/nodes to attach them to.
I take it you are using Mago's model editor?
For starters you should look at other comparable particle emitters, for example the exhaust fire from Steam Tanks. Using the node manager, the easiest way is to copy all details into a new particle node and take care to move it into the correct place in the hierarchy (no idea how your model is made up, though).
Rotation is set in the node details as well if I remember correctly, my WC3 modeling is a bit rusty.