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-   -   how to ignite the mixture (https://www.cfd-online.com/Forums/fluent/213338-how-ignite-mixture.html)

Weiqiang Liu December 22, 2018 10:14

how to ignite the mixture
 
hello all,

I am doing a simulation of methane catalytic combustion in a micro-channel. The inlet temperature is 300K and the solid wall has convection thermal boundary condition with the ambient. Therefore I have to 'ignite' the mixture with some specific methods.

what I am doing is patch a high enough temperature to the whole computation domain, like 2000k. However, the results show the whole process is just like a hot region cooled by the cold inlet flow.

I am wondering how you guys usually 'ignite' the mixture in fluent combustion simulation.

by the way, my model uses chemkin imported mechanism of both gas and surface mechanism. The computation domain is two-dimensional and steady-state. The chemical reaction rate is model by laminar finite rate.

thanks very much!

weiqiang

LuckyTran December 22, 2018 10:56

Depending on the combustion model, patching only the temperature might not be enough. You also need to patch the progress variable and so on also.

Weiqiang Liu December 25, 2018 00:24

Quote:

Originally Posted by LuckyTran (Post 719899)
Depending on the combustion model, patching only the temperature might not be enough. You also need to patch the progress variable and so on also.

hello,

Can I ask what is progress variable in my case?
To be specific, carbon monoxide and water are burned species, methane and oxygen are unburned species.

So to patch a progress variable means to give the burned species an initial mass fraction instead of zero mass fraction?

Thanks very much!

LuckyTran December 25, 2018 01:59

I don't know... you didn't state what combustion model you are using. Hint! Hint!

Mass fraction is mass fraction. It sounds like you have no clue what a combustion model is. Progress variable is progress variable which delineates burnt/unburnt. Progress variable isn't the only way to model combustion. There's several ways.

Weiqiang Liu December 25, 2018 10:02

Quote:

Originally Posted by LuckyTran (Post 720062)
I don't know... you didn't state what combustion model you are using. Hint! Hint!

Mass fraction is mass fraction. It sounds like you have no clue what a combustion model is. Progress variable is progress variable which delineates burnt/unburnt. Progress variable isn't the only way to model combustion. There's several ways.

I am using species transport model. the chemistry solver is stiff chemistry solver and the reaction rate is finite rate without turbulence-chemistry interaction


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