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-   -   Combustion Chamber Species Transport (http://www.cfd-online.com/Forums/fluent/77958-combustion-chamber-species-transport.html)

 Catthan July 8, 2010 09:50

Combustion Chamber Species Transport

Dear Fluent users,

I am modeling the combustion of methane in a Stirling Engine burner in fluent 12 and I need to ask some questions.

I am using the species transport model and I was advised to do the following steps by a fellow student who did a similar simulation.

the steps he suggested are the following.

1. Set my BCs and run a few calculations to allow the air and methane to mix in the burner.
then,
2. Once I get convergence, patch a high temperature somewhere (e.g. gas jet) to initiate combustion.
All the above using the laminar finite rate model, the k - ε realizable viscous model and variable specific heat

I do not understand the necessity of step 1 since it is not mentioned in the tutorial but at this stage I trust my co-worker's experience.

My problem is that after a few iterations in step 1, I get production of CO2 and water.

It makes sence from one point of view since I have specified the methane oxidation reaction.
However, I have not patched any high temperature yet to ignite the mixture so I am surprised that combustion occured..

Does this mean that once I set the combustion reaction I don't need to patch any high temperature?

Do I still have to do it after I get convergence from step 1?

Thanks for your time.
All the best

 Modest Cat November 2, 2011 21:14

"The eddy-dissipation model requires products to initiate reaction (see Equation 7–25). When you initialize the solution for steady flows, ANSYS FLUENT sets all species mass fractions to a maximum in the user specified initial value and 0.01. This is usually sufficient to start the reaction. However, if you converge a mixing solution first, where all product mass fractions are zero, you may then have to patch products into the reaction zone to ignite the flame. For details, see Ignition in Combustion Simulations in the User’s Guide."

Oops~I think I found the reason in theory guide.:o

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