Fluent Modeling

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  • Last Post 27 February 2019
anmol07 posted this 09 February 2019

Hi All,

 

I am trying to simulate Methane combustion in high pressure system. The case is laminar. Now, the moment I trun on volumetric reactions after simulating cold flow, I get this error:

 routine = phi2y

location = 1

message = non-positive species sum

 

 

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

 

I am using GRI 3.0 mechanism. 

 

Thank you

 

Regards,

Anmol

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rwoolhou posted this 11 February 2019

Will the model run without the chemistry? Check the mesh quality & resolution, then move onto boundary conditions etc.  When models fail it's best to remove anything complex (chemistry in this case) and then build back up. 

anmol07 posted this 25 February 2019

Hi,

Thank you for your message. So, I am simulating a case for Methane combustion in a high-pressure system. The simulations were fine with the Fluent's 3 steps mechanism for  Methane combustion but the moment I switch to another mechanism (from some paper, hardcoded into fluent) I get the above-mentioned error. 

 

Thank you

 

Best,

Anmol

rwoolhou posted this 26 February 2019

Check the mechanism and that it balances. Can you post the set up of the reactions?

anmol07 posted this 26 February 2019

Hi,

Thank you for your message. The Mechanism I am using is as follows:

1. CH3 + HCO = CH4 + CO             8.41E+13 0.0 0.0

2. CH2O + CH3 = CH4 + HCO    2.12E+04 2.8 5860.0

3. HCO + M = CO + H + M           5.75E+16 -1.0 17000.0

4. HCO + OH = CO + H2O           2.90E+12 0.0 0.0

5. CO + O2 = CO2 + O                 3.12E+10 0.0 47700.0

6. CO + OH = CO2 + H                 1.93E+14 -0.6 331.8

Duplicate

7. CO + OH = CO2 + H                 7.37E+04 2.0 -355.7

Duplicate

8. CO + O (+M) = CO2 (+M)          2.35E+10 0.0 2384.0

Low /1.27881E+25 -2.79 4191.0/

H2O/12.0/ CO2/3.6/ CO/1.75/

9. HCO + O = CO2 + H                   3.82E+10 0.0 0.0

10. HCO + O = CO + OH                2.14E+16 0.0 0.0

11. CO + HO2 = CO2 + OH            1.26E+06 2.1 17942.6

12. CH3 + HO2 = CH4 + O2           6.33E+12 0.0 0.0

13. CH3 + O2 = CH2O + OH          2.16E+11 0.0 8940.0

14. CH3 + H2O2 = CH4 + HO2      6.33E+02 2.5 5180.0

15. H + O2 = O + OH                     2.32E+16 -0.7 17041.0

16. HO2 + OH = H2O + O2            2.23E+134 -40. 34800.0

Duplicate

17. H + H2O2 = H2O + OH             5.82E+14 0.0 3970.0

18. H2O2 + O = HO2 + OH             5.94E+08 2.0 3970.0

19. HO2 + OH = H2O + O2             2.82E+16 -1.8 60.0

Duplicate

20. HO2 + OH = H2O + O2            1.79E+85 -22. 26900.0

Duplicate

21. HO2 + OH = H2O + O2             3.74E+69 -17. 32900.0

Duplicate

22. HO2 + OH = H2O + O2             5.59E+12 2.0 40000.0

Duplicate

23. H2O2 + OH = H2O + HO2         4.78E+11 0.0 427.0

Duplicate

24. H2O2 + OH = H2O + HO2        2.85E+41 -7.0 37600.0

Duplicate

25. CH3 + H (+M) = CH4 (+M)        1.05E+17 -0.6 383.0

Low /2.17162E+34 -4.76 2440.0/

TROE /0.783 74.0 2941.0 6964.0/

CH4/2.0/ H2O/6.0/ CO2/2.0/ CO/1.5/

26. CH3 + O = CH2O + H                1.41E+13 0.0 0.0

27. CH2O + O = HCO + OH             1.20E+16 0.0 3540.0

28. CH2O + HO2 = H2O2 + HCO     2.64E+12 0.0 8000.0

29. CH2O + OH = H2O + HCO         2.49E+09 1.1 -447.0

30. CH2O + O2 = HCO + HO2          3.65E+18 0.0 40000.0

31. 2 O + M = O2 + M                       6.25E+16 -1.0 0.0

32. H + O + M = OH + M                   1.98E+18 -1.0 0.0

33. H + O2 (+M) = HO2 (+M)             5.43E+11 0.4 0.0

Low /3.75013E+21 -1.4 0.0/

TROE /0.5 1e-30 1e+30 0.0/

H2O/11.89/ CO2/2.18/ CO/1.09/ O2/0.85/

34. H + HO2 = H2O + O                    5.99E+10 0.0 671.0

35. 2 OH (+M) = H2O2 (+M)             1.21E+15 -0.4 0.0

Low /9.04468E+14 -0.584 -2293.0/

TROE /0.7346 94.0 1756.0 5182.0/

H2O/6.0/ CO2/3.6/ CO/1.75/

36. HO2 + O = O2 + OH                    9.55E+15 0.0 0.0

37. H + HO2 = 2 OH                         1.20E+15 0.0 295.0

38. 2 HO2 = H2O2 + O2                   3.54E+13 0.0 12000.0

Duplicate

39. 2 HO2 = H2O2 + O2                  5.46E+10 0.0 -1630.0

Duplicate

40. CH4 + O = CH3 + OH                 1.82E+10 1.5 8600.0

41. CH4 + OH = CH3 + H2O            4.60E+08 1.6 3120.0

42. H + OH + M = H2O + M             9.32E+23  -2.0     0.0

43. 2 OH = H2O + O                        1.90E+02   2.4   -2110.0

44. H + HCO (+M) = CH2O (+M)     7.71E+11   0.5    -260.0

Low /8.89016E+23 -2.57 1425.0/

TROE /0.7824 271.0 2755.0 6570.0/

CH4/2.0/ H2O/6.0/ CO2/2.0/ CO/1.5/

45. H2O + HCO = CO + H + H2O   1.17E+18   -1.0   17000.0

46. HCO + O2 = CO + HO2             4.67E+07   0.8   -727.0

Also, other than the non-positive species sum error, I am also getting a dasac failure at certain temperatures. 

 

Thank you 

 

Best,
Anmol

 

rwoolhou posted this 27 February 2019

Try removing the duplicates: if you have two reactions with different rates the solver can't work out which one to use. 

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