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Old   November 25, 2014, 10:54
Default Multistep combustion, EBU combustion model,LES,methane two-step combustion
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Wen Xu
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Hello,foamers,
Now i'm struggling with the methane two step combustion using EBU model.
Quote:
CH4 + 1.5O2 = CO + 2H2O (1)
CO + 0.5O2 = CO2 (2)
The problem are as follows:
  • Temperature is around 3000K,which is higher than the adimetic combustion temperature(2200K around)
  • The strangest thing is that some places the h2o mass fraction is more than 0.7!!! And the mass fraction of co at the same location is almost equal to zero (if the second equation's reaction rate is much larger than the first one,this may happen), But the most strangest things is that the mass fraction of co2 is almost zero at the same location of h2o!!! (The results of my simulation [jet coal combustion ]is at the attachment. )
Also the reaction rate of each specie is as follows:
Quote:
species: CH4 stoichCoeff: 1 RR_: -1.38565462e-21
species: O2 stoichCoeff: 1.5 RR_: -2.07848193e-21
species: CO stoichCoeff: 1 RR_: 1.38565462e-21
species: H2O stoichCoeff: 2 RR_: 2.771309239e-21
species: CO stoichCoeff: 1 RR_: -1.236744301e-06
species: O2 stoichCoeff: 0.5 RR_: -6.183721505e-07
species: CO2 stoichCoeff: 1 RR_: 1.236744301e-06
And the mass fraction of each specie at the cellI=1000(index) is as follows:
Quote:
FIRST EQUATION:
ch4 mass species(reactant ): 4.646332203e-25
o2 mass species(reactant ): 0.08021798538
co mass species(as product): 4.147010944e-10
h2o+co mass species(products): 5.616767408e-08
SECOND EQUATION:
co mass species(as reactants): 4.147010944e-10
O2 mass fraction (reactant): 1.407059823e-08
CO2 mass fraction (product): 1.11712873e-07
And the strain rate |S| is calculated as:
Quote:
const volVectorField& U = this->db().objectRegistry::lookupObject<volVectorField> ("U");
volScalarField S=sqrt(2*(symm(fvc::grad(U))&&symm(fvc::grad(U)))) ;

Any other information that can solve my question i can attach here.
Thank you in advance, any suggestions will be helpful~!!!

regards,
wen
Attached Images
File Type: jpg testco.jpg (15.0 KB, 16 views)
File Type: jpg testco2.jpg (18.9 KB, 15 views)
File Type: jpg testh2o.jpg (15.2 KB, 12 views)
File Type: jpg testt.jpg (16.9 KB, 13 views)
File Type: jpg testU.jpg (17.0 KB, 12 views)
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Old   November 26, 2014, 07:39
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To equation (1) and (2), we could get the reaction rates for them. We assume them to be Wful1 and Wful2 respectively. Then the reaction rate for the global reaction rate should be the smaller one Wful=min(Wful1,Wful2)?
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Old   November 27, 2014, 02:53
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Hello,everyone.
Now, I use the equation (1.22) in the book----Theoretical and Numerical Combustion, second Edition, and i get the result. It seems ok.

cheers,
wen
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File Type: jpg muti-step.jpg (45.8 KB, 14 views)
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Old   July 9, 2015, 05:53
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Quote:
Originally Posted by wenxu View Post
Hello,everyone.
Now, I use the equation (1.22) in the book----Theoretical and Numerical Combustion, second Edition, and i get the result. It seems ok.

cheers,
wen
Hello, Friends. I am now trying to do combustion simulation in OpenFOAM, since I need to use multistep mechanism, I would like to ask which solver I can use? You mentioned EBU model could you give me some guide how to use this? Thank you so much.
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Old   July 9, 2015, 07:43
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Suggestions for solver:
(1) diffusion flame: reactingFoam
(2) premixed or partially premixed flame: XiFoam
the choice of other solvers can be guided by the standard solver description.

EDC model can be download from here: http://www.edcpisofoam.decgroup.org/index.html#
which can be used for both premixed flame and non-premixed flame with multi-step mechanism.

Good luck!
Wen
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