Issue With Fire Extinguishing On Its Own #16124

Asher19000349 · 2026-04-07T05:36:43Z

Asher19000349
Apr 7, 2026

I am developing a hydrogen fire scenario using the PyroSim version 2022.3.1208 running on FDS 6.5.3. To develop the model, I am following the exact source information, and mesh configuration from this paper: https://doi.org/10.1016/j.ijhydene.2021.01.130

The model replicated at my end matches the HRR, and flame characteristics appropriately. However, apparently, the combustion extinguishes after around 15-17 secs of simulation time. I tried the following workarounds:
(1) Using HRRPUA instead of MLRPUA. This does not change the physics, but I hoped if it could lead to better numerical stability.
(2) Using all OPEN boundaries, as well as, INERT/closed for all boundaries, and in one case all closed with ZMAX open, to reduce the excessive air entrainment and prevent flame blow-off.
(3) I also ran the software using latest FDS and PyroSim, but the results became disturbed, and the version I used was given correct results jut that the fire extinguishes.

I am pasting below the FDS code. and the smokeview video showing the fire extinguishing.

FDS CODE

&HEAD CHID='validation6'/
&TIME T_END=70.0/
&DUMP DT_RESTART=300.0, DT_SL3D=0.25/
&MISC SIMULATION_MODE='LES'/

&MESH ID='Mesh01', IJK=50,50,70, XB=4.0,9.0,2.55,7.55,6.0,13.0/

&REAC ID='Reaction1',
FUEL='HYDROGEN',
HEAT_OF_COMBUSTION=1.42E+5/

&DEVC ID='T1', QUANTITY='TEMPERATURE', XYZ=7.0,4.45,6.85/
&DEVC ID='T2', QUANTITY='TEMPERATURE', XYZ=6.8,4.45,6.85/
&DEVC ID='T3', QUANTITY='TEMPERATURE', XYZ=6.6,4.45,6.85/
&DEVC ID='T4', QUANTITY='TEMPERATURE', XYZ=6.4,4.45,6.85/
&DEVC ID='T5', QUANTITY='TEMPERATURE', XYZ=6.2,4.45,6.85/
&DEVC ID='T6', QUANTITY='TEMPERATURE', XYZ=6.0,4.45,6.85/

&SURF ID='Surface01',
FYI='Jet fire',
COLOR='RED',
MLRPUA=0.5,
ADIABATIC=.TRUE./

&OBST ID='jet release', XB=7.2,9.0,4.4,4.5,6.2,6.9/

&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=9.0,9.0,2.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=4.0,4.0,2.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=4.0,9.0,7.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=4.0,9.0,2.55,2.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [ZMAX]', SURF_ID='OPEN', XB=4.0,9.0,2.55,7.55,13.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [ZMIN]', SURF_ID='OPEN', XB=4.0,9.0,2.55,7.55,6.0,6.0/
&VENT ID='Vent', SURF_ID='Surface01', XB=7.2,7.2,4.4,4.5,6.8,6.9/

&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='temp', PBY=4.4/
&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='temp 2', PBY=4.45/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='Vel', PBY=4.4/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='Vel2', PBY=4.45/

&TAIL /

VIDEO

fire.extinguishing.mp4

Er9y714 · 2026-04-07T06:38:05Z

Er9y714
Apr 7, 2026

Have you tried it with the latest FDS version?

13 replies

drjfloyd Apr 8, 2026
Collaborator

The default thermal boundary condition is the ambient. You only need to set TMP_FRONT if you want a different temperature.

8.1 Basics

By default, the outer boundary of the computational domain is assumed to be a solid boundary that is
maintained at ambient temperature. The same is true for any obstructions that are added to the scene.

Asher19000349 Apr 11, 2026
Author

Dear Dr. Floyd,

The simulation is now running as expected after removing the adiabatic boundary condition. Thank you for the suggestion. However, I specified an MLRPUA of 0.5 kg/m²·s following the paper (https://doi.org/10.1016/j.ijhydene.2021.01.130
). The jet velocity is reported to be 20 m/s in the paper, but in my case it only reaches about 9 m/s (maximum), as shown below. Additionally, the resulting flame profile in my simulation is relatively vertical, whereas in the paper it follows a more diagonal trajectory. Please let me know if I have missed any important command or parameter that could be causing the difference in my results.

CODE

&HEAD CHID='validation6'/
&TIME T_END=70.0/
&DUMP DT_RESTART=300.0, DT_SL3D=0.25/
&MISC SIMULATION_MODE='LES'/

&MESH ID='Mesh01', IJK=50,50,70, XB=4.0,9.0,2.55,7.55,6.0,13.0/

&REAC ID='Reaction1',
FUEL='HYDROGEN'/

&DEVC ID='T1', QUANTITY='TEMPERATURE', XYZ=7.0,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T2', QUANTITY='TEMPERATURE', XYZ=6.8,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T3', QUANTITY='TEMPERATURE', XYZ=6.6,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T4', QUANTITY='TEMPERATURE', XYZ=6.4,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T5', QUANTITY='TEMPERATURE', XYZ=6.2,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T6', QUANTITY='TEMPERATURE', XYZ=6.0,4.45,6.85, ORIENTATION=1.0,0.0,0.0/

&SURF ID='Surface01',
FYI='Jet fire',
COLOR='RED',
MLRPUA= 0.5/

&OBST ID='jet release', XB=7.2,9.0,4.4,4.5,6.2,6.9/

&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=9.0,9.0,2.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=4.0,4.0,2.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=4.0,9.0,7.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=4.0,9.0,2.55,2.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [ZMAX]', SURF_ID='OPEN', XB=4.0,9.0,2.55,7.55,13.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [ZMIN]', SURF_ID='OPEN', XB=4.0,9.0,2.55,7.55,6.0,6.0/
&VENT ID='Vent', SURF_ID='Surface01', XB=7.2,7.2,4.4,4.5,6.8,6.9/

&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='temp', PBY=4.4/
&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='temp 2', PBY=4.45/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='Vel', PBY=4.4/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='Vel2', PBY=4.45/

&TAIL /

drjfloyd Apr 11, 2026
Collaborator

Have you done a hand calculation for your surface temperature, vent size, and mass flux to see what velocity you expect to see?

Asher19000349 Apr 12, 2026
Author

Yes, I did the hand calculation. For the given conditions of MLRPUA, vent area, ambient pressure (1 atm) and temperature (20 C) conditions, the resulting velocity is around 6 m/s.

To get the desired jet velocity of 20 m/s for the same MLRPUA, vent area, and atmospheric pressure, the localized temperature should be high. So, I did the back calculation and specified the TMP_FRONT= 710. in Surface01 code block. The jet velocity increased to around 20 m/s in the jet release area as shown below. However, the flame inconsistencies emerged as was happening earlier, even though no ADIABATIC condition or HEAT_OF_COMBUSTION is specified.

FDS CODE

&HEAD CHID='validation6'/
&TIME T_END=70.0/
&DUMP DT_RESTART=300.0, DT_SL3D=0.25/
&MISC SIMULATION_MODE='LES'/

&MESH ID='Mesh01', IJK=50,50,70, XB=4.0,9.0,2.55,7.55,6.0,13.0/

&REAC ID='Reaction1',
FUEL='HYDROGEN'/

&DEVC ID='T1', QUANTITY='TEMPERATURE', XYZ=7.0,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T2', QUANTITY='TEMPERATURE', XYZ=6.8,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T3', QUANTITY='TEMPERATURE', XYZ=6.6,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T4', QUANTITY='TEMPERATURE', XYZ=6.4,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T5', QUANTITY='TEMPERATURE', XYZ=6.2,4.45,6.85, ORIENTATION=1.0,0.0,0.0/
&DEVC ID='T6', QUANTITY='TEMPERATURE', XYZ=6.0,4.45,6.85, ORIENTATION=1.0,0.0,0.0/

&SURF ID='Surface01',
FYI='Jet fire',
COLOR='RED',
MLRPUA= 0.5,
TMP_FRONT=710./

&OBST ID='jet release', XB=7.2,9.0,4.4,4.5,6.2,6.9/

&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=9.0,9.0,2.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=4.0,4.0,2.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=4.0,9.0,7.55,7.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=4.0,9.0,2.55,2.55,6.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [ZMAX]', SURF_ID='OPEN', XB=4.0,9.0,2.55,7.55,13.0,13.0/
&VENT ID='Mesh Vent: Mesh01 [ZMIN]', SURF_ID='OPEN', XB=4.0,9.0,2.55,7.55,6.0,6.0/
&VENT ID='Vent', SURF_ID='Surface01', XB=7.2,7.2,4.4,4.5,6.8,6.9/

&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='temp', PBY=4.4/
&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='temp 2', PBY=4.45/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='Vel', PBY=4.4/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., CELL_CENTERED=.TRUE., ID='Vel2', PBY=4.45/

&TAIL /

drjfloyd Apr 12, 2026
Collaborator

I'm converting this to an issue.

Provide feedback

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Issue With Fire Extinguishing On Its Own #16124

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Issue With Fire Extinguishing On Its Own #16124

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Asher19000349 Apr 7, 2026

Replies: 1 comment · 13 replies

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Er9y714 Apr 7, 2026

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drjfloyd Apr 8, 2026 Collaborator

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Asher19000349 Apr 11, 2026 Author

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drjfloyd Apr 11, 2026 Collaborator

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Asher19000349 Apr 12, 2026 Author

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drjfloyd Apr 12, 2026 Collaborator

Asher19000349
Apr 7, 2026

Replies: 1 comment 13 replies

Er9y714
Apr 7, 2026

drjfloyd Apr 8, 2026
Collaborator

Asher19000349 Apr 11, 2026
Author

drjfloyd Apr 11, 2026
Collaborator

Asher19000349 Apr 12, 2026
Author

drjfloyd Apr 12, 2026
Collaborator