Secondary combustion reaction

[AmirrezaHBSH]

I would greatly appreciate your assistance with a question regarding the combustion reaction defined in my simulation. My fuel composition consists of CO, H₂, and CH₄. On the product side, I have specified a soot yield, while the CO yield is set to zero by default.

If I introduce a CO yield in the simulation, I understand that CO will become a product and exist within the domain. Could you please clarify:

Does FDS consider CO as a fuel, allowing it to react with O₂ again and undergo a secondary combustion reaction?
If the answer is yes, how can I disable this secondary combustion?
If the answer is no, how should I properly define the CO reaction to ensure accurate representation of the combustion process?

Thank you in advance for your time and guidance.

[mcgratta]

It is not clear how you are setting up the case. Can you write down the reaction or reactions that you want to model?

[AmirrezaHBSH]

For the case 2, species are the product of pyrolysis reaction which are defined as

&MATL ID = 'LIPID'
EMISSIVITY = 1.0
DENSITY = 415.64
CONDUCTIVITY = 0.41
SPECIFIC_HEAT = 2.7
N_REACTIONS = 1
A(1) = 5.84E-4
E(1) = 145100
N_S(1) = 7.01
N_T(1) = 0
NU_SPEC(1,1) = 0.5
SPEC_ID(1,1) = 'CARBON MONOXIDE'
NU_SPEC(2,1) = 0.15
SPEC_ID(2,1) = 'CARBON DIOXIDE'
NU_SPEC(3,1) = 0.13
SPEC_ID(3,1) = 'METHANE'
NU_SPEC(4,1) = 0.22
SPEC_ID(4,1) = 'HYDROGEN'
ALLOW_SHRINKING = F
HEAT_OF_REACTION(1) = 450 /

Therefore, for each species NU_SPEC has been defined. In contrast in the case 1, the gas product of the pyrolysis defined as a vapor fuel, which has volume fraction of four species mentioned above

[drjfloyd]

Not what I asked. You have defined a gas phase reaction. That reaction consumes some TRACKED gas species and produces some other TRACKED gas species. What TRACKED gas species does the reaction consume and do those TRACKED species exist in your domain. Hint: I am asking this because they don't.

[AmirrezaHBSH]

Not what I asked. You have defined a gas phase reaction. That reaction consumes some TRACKED gas species and produces some other TRACKED gas species. What TRACKED gas species does the reaction consume and do those TRACKED species exist in your domain. Hint: I am asking this because they don't.

So I need to define the INIT line and explicitly define volume fraction of gaseous products inside the domain?

[drjfloyd]

No. Please carefully look at all the examples for defining REAC in the User's Guide and compare them against your inputs.

[AmirrezaHBSH]

No. Please carefully look at all the examples for defining REAC in the User's Guide and compare them against your inputs.

Thank you for your hint. I compared my reaction lines based on the user guide, I have defined the gas phase species production from pyrolysis as I mentioned above, and they have already specified using &SPEC ID, and then the reaction line

  &REAC FUEL='METHANE'
  SPEC_ID_NU='METHANE','OXYGEN','CARBON DIOXIDE','WATER VAPOR'
  NU=-1,-2,1,2/

Since the TRACKED species are the products of the pyrolysis reaction, they should already exist in the domain.

NU_SPEC(1,1) = 0.5
SPEC_ID(1,1) = 'CARBON MONOXIDE'
NU_SPEC(2,1) = 0.15
SPEC_ID(2,1) = 'CARBON DIOXIDE'
NU_SPEC(3,1) = 0.13
SPEC_ID(3,1) = 'METHANE'
NU_SPEC(4,1) = 0.22
SPEC_ID(4,1) = 'HYDROGEN'

What TRACKED gas species does the reaction consume?

&SPEC ID='NITROGEN'/
&SPEC ID='METHANE'/
&SPEC ID='CARBON MONOXIDE'/
&SPEC ID='CARBON DIOXIDE'/
&SPEC ID='HYDROGEN'/
&SPEC ID='WATER VAPOR'/
&SPEC ID='OXYGEN'/
&SPEC ID = 'AIR', SPEC_ID = 'OXYGEN','NITROGEN', VOLUME_FRACTION = 0.2100271003 ,0.789295393 , BACKGROUND=.TRUE./

I have followed the same logic as the single-step reaction in Case 1. Am I still missing any key points?

[drjfloyd]

This REAC consumes the tracked species of METHANE and OXYGEN:
&REAC FUEL='METHANE'
SPEC_ID_NU='METHANE','OXYGEN','CARBON DIOXIDE','WATER VAPOR'
NU=-1,-2,1,2/

METHANE you presumably have some kind of burner that injects methane into the domain.
What have you defined as the initial mass fraction for the tracked species of OXYGEN?

You haven't defined anything:

&SPEC ID='OXYGEN'/

Per the User's Guide the default mass fraction for any tracked species is 0. You have no tracked species of OXYGEN in your domain. Your AIR species may have OXYGEN as a component, but your REAC does not use the tracked species of AIR.

Closely look at the example in 13.2.3.