Question on f.boundary_emissivities in FreeFlame Simulation with Radiation Enabled

[Surakshya Neupane]

Dear Cantera Users,

I am currently working on a freely propagating premixed methane-air flame simulation using Cantera. I came across the f.boundary_emissivities attribute and would like to understand its physical interpretation and practical usage.

In my code, I have used:

f.boundary_emissivities = 0.0, 0.0

f.radiation_enabled = True

I’d like to ask:

1. What do the two values in f.boundary_emissivities = (x, y) correspond to? Are they the emissivities of the left and right boundaries?

2. Do we always have to set them to 0.0? What happens if we use values like 0.1, 0.5, or 0.9?

3. How does changing these values affect the temperature profile or NOx prediction in radiation-enabled flame simulations?

For reference, I’ve attached a part of my simulation script to this post. Any insights or references would be greatly appreciated!

Best regards,
Surakshya Neupane

[Daniel Thomas]

Hi Surakshya,

You're right, the boundary emissivities are for the left and right boundaries of the 1D domain.  I don't think this has been included yet in the Cantera reference docs, but you can see what is happening starting on line 475 of Flow1D.cpp.  These emissivity values are used for calculating radiation from the boundaries to the flame.  For flame simulations, radiation is largely out from the flame to the boundaries, and radiation from the (often room-temperature) boundaries is negligible.  As a result, changing the boundary emissivity values usually has no significant effect on the simulation.

Daniel