Hello there, I don't know what is it that you want to simulate, but in general, the added species by default can be disabled simple by not using them. Meaning that, in your boundary conditions, for example the mass or velocity inlet, you put "O" mass fraction value for the species that you don't use (under species tap).

But if that does not work for you, you have the option to delete any material (under "materials" setup). But first this material has to be totally not used in fluent otherwise you will have error message!

In materials you have three types: mixture; fluid;solid. If you have air for example (under fluid) and you want to delete it you have to disable first all the boundary conditions that uses air, such as inlet, outlet and interior fluid by turning them to something else like "wall" for example. And you have to add another fluid alternative to replace air then you can delete air from your "materials" setup and then put your boundary conditions back to normal.

Under Materials /mixture, you have another option to add your special mixture rather than import it from fluent data-base. You can either read a "pdf" file with your species (file/read/PDF) if you have previously created and saved one. Or you can create one. You have to change first from species transport to non-premixed or partially- premixed model and create and write your pdf file even with secondary stream if you need. Then switch back to the species transport, and the pdf with your species will be automatically in your materials (under mixture).

Hopefully you find this answer helpful.          

Khaled Al-attab Can you please provide a bit more detail about how to save the materials separately so that it can be used again in a different workbench file. The "(file/read/PDF)" is not recognizing any pdf's. Also please help in as to how to read the materials file.