Combustion of a gas mixture

[Hosein Sadeghi]

Hi,

I have a gas mixture consists of six species. Every species has a single step combustion reaction. Is it correct that I define the mixture as a single gas like:

&SPEC ID='CO2', FORMULA='CO2', LUMPED_COMPONENT_ONLY=.TRUE. /

&SPEC ID='H2', FORMULA='H2', LUMPED_COMPONENT_ONLY=.TRUE. /

&SPEC ID='CO', FORMULA='CO', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='CH4', FORMULA='CH4', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='C2H6', FORMULA='C2H6', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='C2H4', FORMULA='C2H4', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='VENTED GASES',
  SPEC_ID(1)='C2H4',
  SPEC_ID(2)='C2H6',
  SPEC_ID(3)='CH4',
  SPEC_ID(4)='CO',
  SPEC_ID(5)='CO2',
  SPEC_ID(6)='H2',
  VOLUME_FRACTION(1)=7.7,
  VOLUME_FRACTION(2)=1.2,
  VOLUME_FRACTION(3)=8.6,
  VOLUME_FRACTION(4)=27.6,
  VOLUME_FRACTION(5)=24.9,
  VOLUME_FRACTION(6)=30.0/

&REAC ID='Reaction1',
      FUEL='VENTED GASES'/

Or I should define the reaction of every species separately (section 15.2.4 Multiple Fuels, of user guide)?

BR,

Hosein

[Kevin McGrattan]

Separately

[Hosein Sadeghi]

Thanks

On Sunday, August 28, 2022 at 7:10:58 PM UTC+1 Kevin wrote:

Separately

[Hosein Sadeghi]

Dear Kevin,

For this case I have 5 reactions as

H2+ 0.5O2->H2O
CH4+ 1.5O2-> CO+ 2H2O
C2H4+ 2O2-> 2CO+ 2H2O
C2H6+ 2:5O2-> 2CO+ 3H2O
CO+ 0.5O2-> CO2

and I have soot yield of 0.5 from the experimental data, out of all the reactions. When defining the reactions in FDS, to which reaction I should assign the soot yield? can I divide it to five and assign SOOT_YIELD=0.1 to each of the reactions?

BR,

Hosein

[dr_jfloyd]

If you have a single fuel stream where a burner is emitting a mixture of CH4, C2H4, and C2H6, then you probably want to follow the example in 15.2.2 in the User's Guide. If you want to have H2 and CO oxidation as well then look at the existing two-step scheme discussed in 15.1.3.

[Hosein Sadeghi]

Thank you

[Hosein Sadeghi]

Do I need to specify PRIORITY=2 for CO oxidation?

[dr_jfloyd]

If you are following the examples in the Guide that I noted, then no. If you are specifying reactions for each fuel on your own, then yes.

[Hosein Sadeghi]

Thank you for your reply.

Each of the species in my initial fuel mixture has a volume fraction. For instance, 30% of the mixture is H2. How can I consider this in the separate reaction that I am defining for H2 ?

Is it correct to multiply the equation coefs by 0.3?

[dr_jfloyd]

REAC inputs can only use tracked species. In your case the only fuel species that is tracked is the lumped fuel species VENTED GASES.  Your input has it currently is shown does not have H2 as a tracked species and you cannot define a reaction for it.  

With a lumped species, all the species are transported and mixed the same. With fast chemistry each fuel component will burn in proportion to its need for oxygen. You don't need to specify an H2 equation. Since you have only C,H, and O in your lumped species you can follow 15.2.2 and 15.1.2 in the guide. You will only need one REAC line for the lumped species and one COMB line to enable the CO and H2 reactions.  You will just need to decide what fraction of the H and C and the fuel goes to H2, CO, and C in the first reaction step.

If you want to have individual reactions for each fuel, then you cannot track the fuel as a lumped species. You will need to specify each fuel as a tracked species along with reactions for each fuel. 

[Hosein Sadeghi]

Thank you for your help.

[Hosein Sadeghi]

Dear Jason,

I ended up with the following setting. Does it make the gas mixture combustion based on the FDS definitions? (I could run it without error)

&SPEC ID='CARBON DIOXIDE',  LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='METHANE',         LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='ETHYLENE',        LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='ETHANE',          LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='CARBON MONOXIDE', LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='WATER VAPOR',     LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='NITROGEN',        LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='SOOT',            LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='OXYGEN',          LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='HYDROGEN',        LUMPED_COMPONENT_ONLY=.FALSE./
&SPEC ID='AIR',
      BACKGROUND=.TRUE.,
      SPEC_ID(1)='OXYGEN',
      SPEC_ID(2)='NITROGEN',
      VOLUME_FRACTION(1)=1.0,      
      VOLUME_FRACTION(2)=3.76/

&SPEC ID = 'PRODUCTS_HYDROGEN',
      SPEC_ID(1) = 'WATER VAPOR',    VOLUME_FRACTION(1) = 1.0,
      SPEC_ID(2) = 'NITROGEN',       VOLUME_FRACTION(2) = 1.88/


&SPEC ID = 'PRODUCTS_METHANE',
      SPEC_ID(1) = 'CARBON MONOXIDE',VOLUME_FRACTION(1) = 1.0,
      SPEC_ID(2) = 'WATER VAPOR',    VOLUME_FRACTION(2) = 2.0,
      SPEC_ID(3) = 'NITROGEN',       VOLUME_FRACTION(3) = 5.64/


&SPEC ID = 'PRODUCTS_ETHYLENE',
      SPEC_ID(1) = 'CARBON MONOXIDE',VOLUME_FRACTION(1) = 2.0,
      SPEC_ID(2) = 'WATER VAPOR',    VOLUME_FRACTION(2) = 2.0,
      SPEC_ID(3) = 'NITROGEN',       VOLUME_FRACTION(3) = 7.52/  


&SPEC ID = 'PRODUCTS_ETHANE',
      SPEC_ID(1) = 'CARBON MONOXIDE',VOLUME_FRACTION(1) = 2.0,
      SPEC_ID(2) = 'WATER VAPOR',    VOLUME_FRACTION(2) = 3.0,
      SPEC_ID(3) = 'NITROGEN',       VOLUME_FRACTION(3) = 9.4/


&SPEC ID = 'PRODUCTS_CO',
      SPEC_ID(1) = 'CARBON DIOXIDE',VOLUME_FRACTION(1) = 1.0,
      SPEC_ID(2) = 'NITROGEN',      VOLUME_FRACTION(2) = 1.88/

     
&SPEC ID='VENTED GASES',

      SPEC_ID(1)='ETHYLENE',
      SPEC_ID(2)='ETHANE',
      SPEC_ID(3)='METHANE',
      SPEC_ID(4)='CARBON MONOXIDE',
      SPEC_ID(5)='CARBON DIOXIDE',
      SPEC_ID(6)='HYDROGEN',

      VOLUME_FRACTION(1)=7.7,
      VOLUME_FRACTION(2)=1.2,
      VOLUME_FRACTION(3)=8.6,
      VOLUME_FRACTION(4)=27.6,
      VOLUME_FRACTION(5)=24.9,
      VOLUME_FRACTION(6)=30.0/

&REAC ID = 'Reac_HYDROGEN',
      FUEL = 'HYDROGEN',
      SPEC_ID_NU = 'HYDROGEN','AIR','PRODUCTS_HYDROGEN',
      NU = -1,-0.5,1 /

&REAC ID = 'Reac_METHANE',
      FUEL = 'METHANE',
      SPEC_ID_NU = 'METHANE','AIR','PRODUCTS_METHANE',
      NU = -1,-1.5,1 /

&REAC ID = 'Reac_ETHYLENE'
      FUEL = 'ETHYLENE'
      SPEC_ID_NU = 'ETHYLENE','AIR','PRODUCTS_ETHYLENE'
      NU = -1,-2.0,1/
     
&REAC ID = 'Reac_ETHANE'
      FUEL = 'ETHANE'
      SPEC_ID_NU = 'ETHANE','AIR','PRODUCTS_ETHANE'
      NU = -1,-2.5,1/
     
&REAC ID = 'Reac_CO'
      FUEL = 'CARBON MONOXIDE'
      SPEC_ID_NU = 'CARBON MONOXIDE','AIR','PRODUCTS_CO'
      NU = -1,-0.5,1,
      PRIORITY = 2/

[dr_jfloyd]

If you want to track each fuel species as a separate species then don't make a lumped species for the fuel mixture. REAC operates on the tracked species that are present. If you define that ETHYLENE is a tracked species by setting LUMPED_PARAMETER_ONLY but at the burner inject the lumped species VENTED GASSES, you will have no combustion because you will have not injected the tracked species of ETHYLENE only the tracked species of VENTED GASSES.

I suggest you start with a much simpler case and play with a simple input file where you have a lot of diagnostic output and spend some time learning how FDS works.

[Hosein Sadeghi]

Thank you.

[Hosein Sadeghi]

Dear Jason,

Is it possible to define PRIORITY higher than 2?   e.g., PRIORITY=3, 4 ... for a chain of reactions.

BR,

Hosein

[dr_jfloyd]

yes

[Hosein Sadeghi]

Hi, 

In case of fuel species like section 15.2.2 (natural gas), can I still define a Radiative Fraction for the lumped fuel?

In section 16.5, it is explained that the radiative fraction of each species defined in the lumped fuel is applied based on their volume fractions, but I think it happens when we don't define any radiative fraction.

BR,

Hosein