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-   -   high temperature in methane combustion (http://www.cfd-online.com/Forums/fluent/47955-high-temperature-methane-combustion.html)

David April 17, 2008 00:23

high temperature in methane combustion
 
Hi there, Does anybody meet such problem? The temperature will be 3000K! or higher. According my knowledge, It is impossible.

Anyone have a similar case in FLUENT website? Thank you.

David

Ant April 17, 2008 00:57

Re: high temperature in methane combustion
 
Hi David,

The temperature predicted would depend upon the combustion model, reaction kinetics and specific heat polynomials.

Check the following:

1. Combustion model: The temperature predictions can be set right quickly by using the simplified PDF model. The flame shape would also be predicted well. The main constraint is that this model over predicts the flame stability.

2. Oxidant used: Are you using Air, pure oxygen or oxygen enriched air? If you are using pure oxygen or high concentration of oxygen as oxidant you should either use PDF model or add dissociation reactions to the reaction mechanism.

3. Reaction mechanism: Are you using single step or two step global reaction? Are you adding and dissociation reaction? The temperature would be over predicted if you use a single step chemistry.

4. Cp: Do not use constant values. Use polynomials. It has been seen that the polynomials for CH4 and N2 used in the fluent database are incorrect above 1100 K. You need to use CET89 polynomials of CH4 & N2.

I would not be able to tell you more details on reaction mechanism since we are working on similar lines. My suggestion is to use PDF model to give quick and reasonable predictions.

Regards, Ant

David April 17, 2008 01:25

Re: high temperature in methane combustion
 
Great Thanks Ant!

davedong August 2, 2010 02:37

Quote:

Originally Posted by Ant
;150081
Hi David,

The temperature predicted would depend upon the combustion model, reaction kinetics and specific heat polynomials.

Check the following:

1. Combustion model: The temperature predictions can be set right quickly by using the simplified PDF model. The flame shape would also be predicted well. The main constraint is that this model over predicts the flame stability.

2. Oxidant used: Are you using Air, pure oxygen or oxygen enriched air? If you are using pure oxygen or high concentration of oxygen as oxidant you should either use PDF model or add dissociation reactions to the reaction mechanism.

3. Reaction mechanism: Are you using single step or two step global reaction? Are you adding and dissociation reaction? The temperature would be over predicted if you use a single step chemistry.

4. Cp: Do not use constant values. Use polynomials. It has been seen that the polynomials for CH4 and N2 used in the fluent database are incorrect above 1100 K. You need to use CET89 polynomials of CH4 & N2.

I would not be able to tell you more details on reaction mechanism since we are working on similar lines. My suggestion is to use PDF model to give quick and reasonable predictions.

Regards, Ant

I'm facing the same problem. well, it does well in the pdf-LES or pdf-RANS simulation. but the eddy-dissipation simulation is still odd with 2400 K or even more higher. i guess the reaction is too simple to describe the flame. right?
PS: i use single step methane-air to model sandia flame d.


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