Smoke gradualy appears

[Fabrice]

Hello,

You can animate smoke density from the source that emits it, or if you want to increase the smoke density in the shole grid, you can use Effector that is
in the smoke channel and that will multiply the smoke in the whole grid. You could also animate the density in the shader parameters which gives you the freedom to change appearance without the need to resim.
You can also use FumeFX 6 NodeWorks where you can read smoke voxel by voxel and use math node to multiply its value, or do whatever you want actually.

Ok thanks for the explanation!