Pyrolysis modeling parameters are incorrectly configured

[hahaha666123-arch]

Hi,

I'm currently conducting a combustion simulation of corrugated cardboard with the following configuration:

（1）Structure: Six 0.007mm planar layers with designed interstitial spaces

（2）Pyrolysis parameters: Pre-exponential factor (A) and activation energy (E) set according to literature values

Prior to the full simulation, I performed TGA analysis in FDS which validated the parameter settings. However, during the actual simulation run, I'm observing pyrolysis and combustion initiation at room temperature（20℃） - behavior that contradicts expected thermal decomposition thresholds.
Thank you so much for your guidance and sorry if the question is too dumb.
the DOI：https://doi.org/10.1016/j.firesaf.2017.04.008
The FDS code is as follows:
&HEAD CHID='NEW-LUNWEN1'/
&TIME T_END=600/
&MISC SIMULATION_MODE='LES'/
&MESH ID='mesh1'IJK=100,100,30, XB=-0.35,0.35,-0.35,0.35,0.0,0.21/
&MESH ID='mesh2'IJK=50,50,100, XB=-0.35,0.35,-0.35,0.35,0.21,1.61/
&SLCF QUANTITY='TEMPERATURE',CELL_CENTERED=T,PBY=0/
&SLCF QUANTITY='VELOCITY',CELL_CENTERED=T,PBY=0/
&SLCF QUANTITY='VOLUME FRACTION' SPEC_ID= 'CARBON DIOXIDE',PBY=0/
&SLCF QUANTITY='VOLUME FRACTION' SPEC_ID= 'CARBON DIOXIDE',PBX=0/
&SLCF QUANTITY='VOLUME FRACTION' SPEC_ID= 'CARBON DIOXIDE',PBZ=0.5/
&SLCF QUANTITY='VOLUME FRACTION' SPEC_ID= 'CARBON MONOXIDE',PBY=0/
&SLCF QUANTITY='VOLUME FRACTION' SPEC_ID= 'CARBON MONOXIDE',PBX=0/
&SLCF QUANTITY='VOLUME FRACTION' SPEC_ID= 'CARBON MONOXIDE',PBZ=0.5/
&SPEC ID='MYFUEL2'
FORMULA= C3.4H6.2O2.5
/
&REAC ID='PAPER_REAC',
FUEL='MYFUEL2',
SOOT_YIELD=0.01,
CO_YIELD=0.0065,
/
&MATL ID='CONCRETE',
SPECIFIC_HEAT=1.04,
CONDUCTIVITY=1.8,
DENSITY=2280.0/
&MATL ID='STEEL',
SPECIFIC_HEAT=0.46,
CONDUCTIVITY=45.8,
DENSITY=7850.0,
EMISSIVITY=0.95/
&MATL ID='CARTON',
DENSITY=183.7,
CONDUCTIVITY=0.42,
SPECIFIC_HEAT=2.697,
EMISSIVITY=0.9,
HEAT_OF_REACTION=2.92E2
N_REACTIONS=1,
MATL_ID(1,1)='CHAR',
NU_MATL(1,1)=0.15,
SPEC_ID(1,1)='MYFUEL2',
NU_SPEC(1,1)=0.85,
A=3.3E10,
E=1.31E5
N_S(1)= 1.26/
&MATL ID='CHAR',
DENSITY=23.6,
CONDUCTIVITY=0.33,
SPECIFIC_HEAT=1.45,
EMISSIVITY=0.9,
HEAT_OF_COMBUSTION=2.92E2/
&SURF ID= 'CARTON'
MATL_ID= 'CARTON'
THICKNESS=0.007
BURN_AWAY =.TRUE/
&SURF ID='Beton',
RGB=212,172,174,
MATL_ID(1,1)='CONCRETE',
MATL_MASS_FRACTION(1,1)=1.0,
THICKNESS(1)=0.001/
&SURF ID='STEEL',
MATL_ID(1,1)='STEEL',
MATL_MASS_FRACTION(1,1)=1.0,
THICKNESS(1)=0.01,
/
&OBST ID= '底Carton'
XB= -0.3 0.3 -0.2 0.2 0 0.007
SURF_ID='CARTON'
THICKEN = .TRUE/
&OBST ID= '上1Carton'
XB= -0.3 0.3 -0.2 -0.193 0.193 0.2
SURF_ID='CARTON'
THICKEN = .TRUE/
&OBST ID= '上2Carton'
XB= -0.3 0.3 0.193 0.2 0.193 0.2
SURF_ID='CARTON'
THICKEN = .TRUE/
&OBST ID= '左1Carton'
XB= -0.3 -0.293 -0.2 0.2 0 0.2
SURF_ID='CARTON'
THICKEN = .TRUE/
&OBST ID= '右Carton'
XB= 0.293 0.3 -0.2 0.2 0 0.2
SURF_ID='CARTON'
THICKEN = .TRUE/
&OBST ID= '前Carton'
XB= -0.3 0.3 -0.2 -0.193 0 0.2
SURF_ID='CARTON'
THICKEN = .TRUE/
&OBST ID= '后Carton'
XB= -0.3 0.3 0.193 0.2 0 0.2
SURF_ID='CARTON'
THICKEN = .TRUE/
&VENT MB='XMIN', SURF_ID='OPEN' /
&VENT MB='XMAX', SURF_ID='OPEN' /
&VENT MB='YMIN', SURF_ID='OPEN' /
&VENT MB='YMAX', SURF_ID='OPEN' /
&VENT MB='ZMAX', SURF_ID='OPEN' /
&VENT ID='Vent', SURF_ID='Beton',
XB=-0.35,0.35,-0.35,0.35,0.0,0/
&DEVC ID= 'T-11'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 0.1/
&DEVC ID= 'T-22'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 0.3/
&DEVC ID= 'T-33'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 0.5/
&DEVC ID= 'T-44'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 0.7/
&DEVC ID= 'T-55'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 0.9/
&DEVC ID= 'T-66'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 1.3/
&DEVC ID= 'T-77'
QUANTITY = 'TEMPERATURE'
XYZ= 0 0 1.5/
&DEVC ID= 'T-1'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 0.1/
&DEVC ID= 'T-2'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 0.3/
&DEVC ID= 'T-3'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 0.5/
&DEVC ID= 'T-4'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 0.7/
&DEVC ID= 'T-5'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 0.9/
&DEVC ID= 'T-6'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 1.3/
&DEVC ID= 'T-7'
QUANTITY = 'THERMOCOUPLE'
XYZ= 0 0 1.5/
&DUMP DT_DEVC=3/
&TAIL /
The TGA data (with temperature as the x-axis) are presented below:

[drjfloyd]

It is a violation of the rules for this forum and copyright law to post copyrighted material to which you do not own the copyright. Your post was deleted. Please repost without the copyrighted material and instead simply provide a DOI number.

EDIT: removed the attachment as could not delete the post.

[hahaha666123-arch]

Sorry, I have added the DOI.

[drjfloyd]

After running with the current release for ~30 s I see this for the hrr. An hrr of 6E-9 kW is effectively zero. If you are seeing something different make sure you are using the current release.

The A, E, and N_S values from the FM paper do not seem to be from a pyrolyiss model that is fully consistent with the FDS pyrolysis model. Your FDS TGA_ANALYSIS results show the peak mass loss rate for the cardboard is at ~250 C. If you look at raw data (https://materials.fsri.org/materialdetail/corrugated-cardboard [or simple wood shavings which cardboard would be made from https://materials.fsri.org/materialdetail/excelsior] under mass loss rate and then simultaneous thermal analyzer) you will see that the peak rate in measured data is ~350 C.

[hahaha666123-arch]

Thank you for your help. The pyrolysis model used in the paper is indeed different from FDS. I was just curious why the cardboard would combust (although the HRR was very small) without an external heat source—Perhaps it's due to differences in the pyrolysis models.

[drjfloyd]

Plug in your MATL inputs plus ambient temperature into Eq 7.35 in the Tech Ref. What result do you get? Is the mass loss rate zero?