How to achieve/measure a temperature step in a material? (Material ignition?)

[Elephant01XLY]

Hello everyone,
I want to simulate the thermal ignition of a solid material, i.e. after reaching a certain temperature, the temperature of the material will suddenly increase until it burns out. Similar to an explosion.
I have set up the thermal decomposition with reference to the FDS manual, but I can't measure the sudden increase in temperature after ignition of the object.
I don't know if it's a problem with the material settings or the temperature measurement point settings.
The code is as below, please help me to see what is wrong.

&HEAD CHID='28'/

&TIME T_END=800.0/

&DUMP DT_RESTART=300.0, DT_SL3D=0.25/

&MESH ID='Mesh01', IJK=40,40,40, XB=-1.0,1.0,-1.0,1.0,0.0,2.0/

&SPEC ID='PROPANE'/

&REAC ID='FDS6 METHANE',

  FYI='FDS6 Predefined',

  FUEL='METHANE'/

&DEVC ID='SOLID101', QUANTITY='ADIABATIC SURFACE TEMPERATURE', XYZ=0.0,0.0,0.7, IOR=3/

&DEVC ID='SOLID10', DEPTH=0.4, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=0.0,0.0,0.3, IOR=-3/

&DEVC ID='SOLID11', QUANTITY='INSIDE WALL TEMPERATURE', XYZ=0.0,0.0,0.3, IOR=-3/

&DEVC ID='SOLID2', DEPTH=0.399, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=-0.199,-0.199,0.3, IOR=-3/

&DEVC ID='SOLID6', DEPTH=1.0E-3, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=-0.199,-0.199,0.3, IOR=-3/

&DEVC ID='SOLID3', DEPTH=0.399, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=0.199,-0.199,0.3, IOR=-3/

&DEVC ID='SOLID7', DEPTH=1.0E-3, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=0.199,-0.199,0.3, IOR=-3/

&DEVC ID='SOLID8', DEPTH=1.0E-3, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=0.199,0.199,0.3, IOR=-3/

&DEVC ID='SOLID4', DEPTH=0.399, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=0.199,0.199,0.3, IOR=-3/

&DEVC ID='SOLID9', DEPTH=1.0E-3, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=-0.199,0.199,0.3, IOR=-3/

&DEVC ID='SOLID5', DEPTH=0.399, QUANTITY='INSIDE WALL TEMPERATURE', XYZ=-0.199,0.199,0.3, IOR=-3/

&DEVC ID='SOLID111', QUANTITY='ADIABATIC SURFACE TEMPERATURE', XYZ=0.0,0.0,0.3, IOR=-3/

&MATL ID='1',

  SPECIFIC_HEAT=1.176,

  CONDUCTIVITY=0.4644,

  DENSITY=1845.0,

  HEAT_OF_COMBUSTION=4.78E+12,

  N_REACTIONS=1,

  SPEC_ID(1,1)='PROPANE',

  NU_SPEC(1,1)=1.0,

  A=4780.0,

  E=1.439E+5/

&SURF ID='1',

  RGB=146,130,148,

  TEXTURE_MAP='psm_carpet_grey.jpg',

  TEXTURE_WIDTH=0.6096,

  TEXTURE_HEIGHT=0.6096,

  BURN_AWAY=.TRUE.,

  MATL_ID(1,1)='1',

  MATL_MASS_FRACTION(1,1)=1.0,

  THICKNESS(1)=0.4/

&SURF ID='burner',

  COLOR='RED',

  HRRPUA=1000.0,

  TMP_FRONT=300.0/

&OBST ID='Obstruction', XB=-0.2,0.2,-0.2,0.2,0.3,0.7, SURF_ID='1'/

&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=1.0,1.0,-1.0,1.0,0.0,2.0/

&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=-1.0,-1.0,-1.0,1.0,0.0,2.0/

&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=-1.0,1.0,1.0,1.0,0.0,2.0/

&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=-1.0,1.0,-1.0,-1.0,0.0,2.0/

&VENT ID='Mesh Vent: Mesh01 [ZMAX]', SURF_ID='OPEN', XB=-1.0,1.0,-1.0,1.0,2.0,2.0/

&VENT ID='Vent01', SURF_ID='burner', XB=-0.5,0.5,-0.5,0.5,1.0E-3,1.0E-3/

&BNDF QUANTITY='ADIABATIC SURFACE TEMPERATURE'/

&BNDF QUANTITY='BACK WALL TEMPERATURE'/

&BNDF QUANTITY='GAS TEMPERATURE'/

&BNDF QUANTITY='NET HEAT FLUX'/

&BNDF QUANTITY='WALL TEMPERATURE'/

&SLCF QUANTITY='TEMPERATURE', ID='1', PBX=0.0/

&SLCF QUANTITY='TEMPERATURE', ID='2', PBY=0.0/

&TAIL /

[drjfloyd]

Your combustion REAC uses METHANE, but you have defined your MATL to release PROPANE.

[Elephant01XLY]

Oh, thanks a lot. I will fix this problem !

[Elephant01XLY]

Hi! I have changed the FUEL from METHANE to PROPANE. However, the calculation stop with "ERROR: Numerical Instability - FDS stopped". Can u help me with that? Thanks a lot.

[drjfloyd]

Double check the values for all your MATL inputs.

[Elephant01XLY]

Hi, my friend! As u say, the values of my materials are wrong. And I have corrected them as below. However, I still can't get a temperature jump. In my mind, when explosives are thermally decomposed, they are violently exothermic, which leads to a sharp increase in temperature.
Can u give me some advice?

&MATL ID='1',
SPECIFIC_HEAT=1.02,
CONDUCTIVITY=0.302,
DENSITY=1845.0,
HEAT_OF_COMBUSTION=4780.0,
N_REACTIONS=1,
SPEC_ID(1,1)='PROPANE',
NU_SPEC(1,1)=1.0,
A=4.78E+12,
E=1.439E+5/

[drjfloyd]

Modern day high explosives decompose explosively when there is a shock wave moving through the material. They require a blasting cap or other initiator to get an explosion. If you just set them on fire, they just burn. Your cube is already immersed in a fire. It is already seeing the heat flux from a flame. The fuel you are adding from the cube isn't going to drastically change the heat flux to the cube as it isn't going to burn until it mixes with oxygen.

[Elephant01XLY]

Thank you very much! So is there a possibility that in a mesh the material is heated and suddenly gives off a lot of heat, which then leads to an extreme rise in temperature?

[drjfloyd]

Your MATL reaction does not describe the physics of a high explosive undergoing detonation where chemical bonds are being disrupted by shock in addition to heat.

[Elephant01XLY]

Is there a way to achieve this in FDS? For example, measuring the temperature profile shown below

[Elephant01XLY]

sorry for the preview picture, I have attached a new one. Do you think it is possible to measure the temperature profile in FDS as shown? It should be the curve of an explosive igniting and decomposing, with a violent exotherm.

[drjfloyd]

I have no idea what exaclty is being plotted or what the source of that data is.

Explosive materials do not generate heat solely by decomposing into a gas that burns outside the explosive material. Energy is released in the decomposition process itself. In a detonation the temperature rise is not primarily due to conduction but rather pressure shock. FDS is a low Mach number code that is not going to model the pressure compoment of the decomposition.

[Elephant01XLY]

Thanks very much. Your answer solved a problem that had been bothering me for a long time。