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-   -   Methane combustion (http://www.cfd-online.com/Forums/fluent/37489-methane-combustion.html)

Steve August 5, 2005 05:51

Methane combustion
 
Has anyone tried the Jones and Lindstedt four equation mechanism for methane combustion in Fluent?

I have implemented the four steps in the "propdb.scm" file. It works fine for the EDM, but when EDC is activated Fluent gives the error message:

********** ISAT_ABORT ************** routine = phi2y location = 1 message = non-positive species sum

****** END ISAT_ABORT **************

Error: isat terminated. Error Object: #f

Does anyone know how to implement this mechanism in Fluent so the EDC works?

Steve

San Siro November 17, 2011 22:26

Hi
 
Quote:

Originally Posted by Steve
;123005
Has anyone tried the Jones and Lindstedt four equation mechanism for methane combustion in Fluent?

I have implemented the four steps in the "propdb.scm" file. It works fine for the EDM, but when EDC is activated Fluent gives the error message:

********** ISAT_ABORT ************** routine = phi2y location = 1 message = non-positive species sum

****** END ISAT_ABORT **************

Error: isat terminated. Error Object: #f

Does anyone know how to implement this mechanism in Fluent so the EDC works?

Steve

Hi Steve,I encountered the same question just like you did.I'm wondering if you have solved this problem.Looking forward to you reply.

sberg November 18, 2011 08:07

Hi San Siro
 
At that time I contacted Fluent support and they said I had to use a Chemkin file. They even provided me the file. It's named 4_reactions.che and I attached it below. As far as I remembered the Chemkin file ran smoothly with the EDC model in Fluent 5.3 and 6. I hope it will work for you as well.

Kind regards
Steve
----------------

ELEMENTS
H O C N
END
SPECIES
CH4 O2 CO2 CO H2O H2 N2
END
THERMO
END
REACTIONS KJOULES/MOLE
!Units are cm, mol, s, kJ/mol and K.
2CH4+O2=>2CO+4H2 7.824435194e13 0.0 0.12552
FORD/CH4 0.5/O2 1.25/
CH4+H2O=>CO+3H2 3.1E11 0.0 0.12552
CO+H2O=>CO2+H2 2.75E12 0.0 0.08368
2H2+O2<=>2H2O 4.44566E21 -1.0 0.16736
FORD/H2 0.5/O2 2.25/
RORD/H2O -1.0/
END

San Siro November 22, 2011 23:03

HI
 
When I used the laminal finite-rate model to simulate a reaction involves both volumetric reactions and wall surface reactions,I selected the Two-Step Solution Procedure.I begin by solving the flow, energy, and species equations with reactions disabled.When the basic flow pattern has been established,I enable the reactions and continue the calculation.
Then fluent gives the error message:

Error: Non-physical Specific Heat = 0.000000e+000.
Error Object: ()

I ignore the message and continue to calculate,fluent gives the following error message:

Error: isat terminated.
Error Object: ().
This problem has troubled me for a long time.Is there any suggestions how can I solve this problem and continue my calculation.
Thank
San Siro

Micael March 9, 2012 17:04

Quote:

Originally Posted by sberg (Post 332657)
At that time I contacted Fluent support and they said I had to use a Chemkin file. They even provided me the file. It's named 4_reactions.che and I attached it below. As far as I remembered the Chemkin file ran smoothly with the EDC model in Fluent 5.3 and 6. I hope it will work for you as well.

Kind regards
Steve
----------------

ELEMENTS
H O C N
END
SPECIES
CH4 O2 CO2 CO H2O H2 N2
END
THERMO
END
REACTIONS KJOULES/MOLE
!Units are cm, mol, s, kJ/mol and K.
2CH4+O2=>2CO+4H2 7.824435194e13 0.0 0.12552
FORD/CH4 0.5/O2 1.25/
CH4+H2O=>CO+3H2 3.1E11 0.0 0.12552
CO+H2O=>CO2+H2 2.75E12 0.0 0.08368
2H2+O2<=>2H2O 4.44566E21 -1.0 0.16736
FORD/H2 0.5/O2 2.25/
RORD/H2O -1.0/
END

How reverse order for H2O should be interpreted? It is written as -1 (minus one). What the minus sign means? I mean, it is unphysical to have a negative order, that would mean the less concentration, the fastest kinetic (and infinite kinetic at zero concentration!)

---
Edit: My guess so far is that adding a minus or plus sign mean a correction on the order. Anybody can confirm?

sberg March 9, 2012 20:05

The H2 + 0.5 O2 --> H2O reaction is a global one and it includes several elementary steps with many reactive intermediates like H, O, OH. Such global reactions have complicated rate laws. The reaction orders are usually not integers and they can be negative.

You can probably find some more details, if you are interested, in Warnatz, Maas and Dibble's textbook "Combustion."

sberg March 9, 2012 20:28

And of course, a negative reaction order means the rate decreases when the concentration of that component increases

r = k(T) [H2]^0.5 [O2]^2.25 [H2O]^(-1) = k(T) [H2]^0.5 [O2]^2.25 / [H2O]

Micael March 10, 2012 18:25

Thanks for your reply.

It is still not clear to me. I thought the chemkin format means:

r = kf(T) [H2]^0.5 [O2]^2.25 - kb(T) [H2O]^(-1)

kf: forward constant
kb: reverse constant

Of course, put this way, it does not make sense (as the product decrease, the reverse kinetic increase).

Looking at the file, it seems that the reaction is considered reversible. The way you put it, I don't see how it can be reversible.

sberg March 10, 2012 20:04

Yes, you are correct.

2H2+O2<=>2H2O is often simplified to be non-reversible and represented by r = k(T) [H2]^0.5 [O2]^2.25 [H2O]^(-1). But according to the Chemkin output, as you noticed, it isn't the case. The reaction seems to be reversible with a reaction order of -1.

leexit April 1, 2014 17:33

Different version of chemkin
 
Hi
I just wonder if the chemkin file that is available in Fluent can be older version of chemkin. I use CHEMKIN-II Version 3.1 and do not think it allows me to enter the reaction order. Has anyone ever tried to use the Jones and Lindstedt mechanism with my version of chemkin?
Thank you in advance


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