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Jong Que Kim January 8, 2001 22:03

gas/liquid reburning combustion

Currently I solving gas/oil reburning problem using finite rate/eddy dissipation model in Fluent 5.4. (oil is main fuel and methane is reburning fuel.)

In that case, what kind of methane reaction mechanism is modeled include CH, CH2, CH3 radicals?

Waiting for your help.

Kind regards.

Jin-Wook LEE January 9, 2001 00:14

Re: gas/liquid reburning combustion
Dear Jong-Que Kim

If you include many species and/or radicals, maximum flame temperature might be slightly(or fairly) lower compared to the case of neglecting them. Consequently, some result, for example NOx prediction, might be more accurate. However, the computational cost(CPU and convergency) would be more expensive if you use finite rate / eddy dissipation model. And one more difficult aspect is, how to judge which reaction, among couple of tens(or hundreds) reactions, can be neglected without affecting much accuracy to the result.

So, if you really want to include more species and/or radicals, rather than only considering major species(CH4, O2, N2, CO2, H2O, CO and evaporating species), I recommend PDF combustion model. This model can treat many species without much increase of computational effort. Its non-benificial effects are, as you might know, to over-predict CO, and it should be applied to the high temperature combustion system because of its limitation of fast chemistry.

My 'personal' opinion is, the reaction of minor species(whose residence time is very short) can be neglected if your main purpose is not related to the NOx prediction and if your purpose is engineering design(not advanced research). Many engineers, including CFD specialists, are doing so.

Sincerely, Jinwook

Jong Que Kim January 9, 2001 00:39

Re: gas/liquid reburning combustion
Dear Jin-Wook LEE

Thanks for your response.

The main purpose of this calculation is NOx, so I have to include the CH radicals to postprocess of NOx module.

And in my experinece, the calculation of 3D problem with two mixture fraction pdf model(liquid/gas) takes more time than using the finite rate/dissipation model of 10 steps of reactions.

Therefore I think that it's better to use finite rate/dissipation model include simplified methane reactions in high temperature and fuel rich conditions.

Sincerely, Jong Que Kim

Jin-Wook LEE January 9, 2001 21:53

Re: gas/liquid reburning combustion
Dear Jong-Que Kim

O.K., Now, I understand your meaning and your purpose. I agree that you should include CH, CH2, and CH3 to model the NOx reburning.

However, I do not agree that finite rate / eddy dissipation model with many species(eg, 10 species : CH4, evap. species, O2, N2, CO2, H2O, CO, CH, CH2, CH3) takes less time than two mixture fraction pdf model. As you know, two mixture fraction pdf model requires 4 transport equations, whereas 10 species finite rate / eddy dissipation model requires 9 transport equations. Of course, two mixture fraction pdf model requires some auxiliary calculation such as interpolation of look-up table and some numerical integration. But I do not think that these auxiliary equations take more time than five transport equations. One possible way is, I think, the difference of total iteration number for convergence.

O.K., let me consider the above mentioned opinion as my personal one. And I think that it's very important to select which combustion model you are going to use, by yourself, based on your experience. I fully appreciate your experience.

Hoping good luck with you for your future research.

Sincerely, Jinwook

aouissi mokhtar February 3, 2001 15:48

Re: gas/liquid reburning combustion
Iam looking for basic software simulate nitrogeneous emissions in internal combustion engine -diesel engines so that to reduce NOx emissions by reburning exhauts gases.

aouissi mokhtar February 3, 2001 15:57

Re: gas/liquid reburning combustion

Currently I try to solve gas/oil reburning problem (in internal combustion diesel engine) using psr software ,( methane is reburning fuel.) Waiting for your help.

or yor probleme I think that you must use chemkin software package

Kind regards.

Jong Que Kim February 28, 2001 04:34

Re: gas/liquid reburning combustion

I'm sorry for very late replay.

Until now, I trying to solve the reburning problem.

You said, I have to chemkin software. How to use the chemkin software with FLUENT or chemkin only for boiler problem.

And what is the psr?

Waiting for your response.

Best regards.

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