Hey, yeah get it now...
I read some of the tutorials and tried to incorporate that into my thingy. (And keep on reading across the manual! Though the manual I have right now says species transport is chapter 15.
Though there I havent found how in Fluent I can specify to plot (streamline, contour,...) just one component of the mixture? In the Graphics section of Fluent to me it seems like it always plots everything together, is that correct?

That is correct.

You can make contour plots of individual mass fractions. But there is no such thing as a streamline of an individual component. The fluid particle model does not discriminate between whether the fluid is component a or b or c, that's merely the composition of a particular fluid particle or fluid parcel at a particular location.

In other words, what you are trying to plot is not a streamline. If you can come up with a working (but precise) definition of what it is you are trying to plot, maybe the community can help. =)

You are not talking about particle tracks or?
Since there also u cant specify the component.
What I want to do is visualize (in whatever way) the diffusion of the component through the small inlet in the bulk fluid.
Say I have the bulk fluid in blue and the other fluid through the small inlet in red, then maybe by little dots visualize the distribution of the component through that small inlet by little red dots in the blue background?! Isnt that what the full multicomponent diffusion solved for?

Hello again,
Sorry if I ask again, but what does it really mean:
Boundary Mach number exceeds Maximum limit?
What is the Maximum limit? And cant I just increase it?
what specifically is the problem with this?
Depending on the Mesh it varies between 1 and 4 faces only. So its not much...
As mentioned I have this nozzleoutlet where probably the speed reaches the speed of sound, but is that really an issue or just a note?