Configure the oxygen concentration in the ambient atmosphere.

[boyu-dotcom]

I read a paper stating: "In order to study the influence of different oxygen concentrations on the heat release rate (HRR), numerical simulations were conducted under 21% (v/v), 22% (v/v), and 23% (v/v) oxygen concentrations."
I would like to ask: How can I set the oxygen concentration in the simulation?

[mcgratta]

Y_O2_INFTY=... on the MISC line. Note that this is a mass fraction, not a volume fraction.

[boyu-dotcom]

Does this refer to the default value indicated in this section?

[Vojta-Salek]

Yes. In the User's Guide, there is also an example explicitly showing the default background species. Section 12.2 Specifying Lumped Species (Mixtures of Primitive Species).

[boyu-dotcom]

So if I don't specifically set any parameters, does that mean the file will use the default values?

[Vojta-Salek]

Yes, that's the whole point of default parameters.

This is what makes FDS (and other CFD software) tricky — even by not explicitly setting something, you're already making a lot of decisions that can significantly affect the simulation. Understanding and being aware of defaults is our responsibility, not the developers'.

[boyu-dotcom]

Thank you