User-Defined Reaction

[mikelgiro]

I am working on a simulation where I define the fuel as a mixture of PVC and ethylene. Since FDS does not have PVC predefined, I have used "Vinyl Radical" as the fuel name to represent it.

To define the reaction, I used the CO and soot yields obtained from the SFPE Handbook. Based on these, I calculated the stoichiometric coefficients and the volumetric fractions of each combustion product.

However, I have the following question: Is the oxygen used as a reactant taken directly from the ambient air, or does FDS consider an unlimited external source? The latter would imply that the reaction never extinguishes. I appreciate any clarification on this matter. I also attach the code I used in case you can suggest improvements.

Thank you, and I look forward to any further comments or suggestions!

&SPEC ID='ETHYLENE', FORMULA='C2H4' /

&SPEC ID='VINYL RADICAL', FORMULA='C2H3Cl', ENTHALPY_OF_FORMATION=297.492,
DENSITY_SOLID=1400, CONDUCTIVITY=0.17, SPECIFIC_HEAT=1.25 /

&SPEC ID='OXYGEN', LUMPED_COMPONENT_ONLY=T /
&SPEC ID='NITROGEN', LUMPED_COMPONENT_ONLY=T /
&SPEC ID='HYDROGEN CHLORIDE', LUMPED_COMPONENT_ONLY=T /
&SPEC ID='WATER VAPOR', LUMPED_COMPONENT_ONLY=T /
&SPEC ID='CARBON MONOXIDE', LUMPED_COMPONENT_ONLY=T /
&SPEC ID='CARBON DIOXIDE', LUMPED_COMPONENT_ONLY=T /
&SPEC ID='SOOT', LUMPED_COMPONENT_ONLY=T /

&SPEC ID='AIR',
SPEC_ID(1)='OXYGEN', VOLUME_FRACTION(1)=1.0,
SPEC_ID(2)='NITROGEN', VOLUME_FRACTION(2)=3.761904,
BACKGROUND=T /

&SPEC ID='PRODUCTS_1',
SPEC_ID(1)='HYDROGEN CHLORIDE', VOLUME_FRACTION(1)=1.0,
SPEC_ID(2)='WATER VAPOR', VOLUME_FRACTION(2)=1.0,
SPEC_ID(3)='CARBON MONOXIDE', VOLUME_FRACTION(3)=0.14,
SPEC_ID(4)='CARBON DIOXIDE', VOLUME_FRACTION(4)=0.96,
SPEC_ID(5)='SOOT', VOLUME_FRACTION(5)=0.9,
SPEC_ID(6)='NITROGEN', VOLUME_FRACTION(6)=5.755714 /

&SPEC ID='PRODUCTS_2',
SPEC_ID(1)='NITROGEN', VOLUME_FRACTION(1)=10.885071,
SPEC_ID(2)='WATER VAPOR', VOLUME_FRACTION(2)=2.0,
SPEC_ID(3)='CARBON MONOXIDE', VOLUME_FRACTION(3)=0.013,
SPEC_ID(4)='CARBON DIOXIDE', VOLUME_FRACTION(4)=1.887,
SPEC_ID(5)='SOOT', VOLUME_FRACTION(5)=0.1 /

&REAC ID='PVC Reaction', FUEL='VINYL RADICAL', HEAT_OF_COMBUSTION=16430.0,
SPEC_ID_NU='VINYL RADICAL','AIR','PRODUCTS_1', NU=-1,-1.53,1 /

&REAC ID='C2H4 Reaction', FUEL='ETHYLENE', HEAT_OF_COMBUSTION=43280.0,
SPEC_ID_NU='ETHYLENE','AIR','PRODUCTS_2', NU=-1,-2.8935,1 /

&SURF ID='Fire', RGB=255,0,0, HRRPUA=589.0,
SPEC_ID(1)='VINYL RADICAL', MASS_FLUX(1)=0.012,
SPEC_ID(2)='ETHYLENE', MASS_FLUX(2)=0.012 /

[mcgratta]

I don't know the answer to your question, but it might be moot. I suggest that if you want to have multiple reactions and more complex chemistry, declare only primitive species, like O2, CO2, CO, N2, etc. The purpose of a the "lumped species" approach is to save on computational time. You are not saving any time here, so just declare all the primitive species and the reactions of those species.

[rmcdermo]

FDS does not consider an unlimited supply of O2. If you use up the AIR in the compartment, the reaction will stop.