Flow Type

Fire: Emit only fire. Note that the domain will automatically create some smoke unless you set to zero the parameter ‘Smoke’ in Smoke Flames Tab (see Smoke)

Smoke: Emit only smoke.

Fire + Smoke: Emit both fire and smoke.

Outflow: Remove smoke and fire. (the shape of the outflow will use the object’s bounding box).

– Note the difference between an Outflow and an Obstacle (Collider) :

Blender Smoke Flow Type