No gases are released, so no combustion occurs.

[MinJoo Lee]

Hello.
I am a self-taught student of FDS. I am studying hard, but there are still many things I don't know and I need your help.

I'm trying to do a very simple example with FDS5.
Propane gas is ejected from a surface at a certain rate, and I want to see what characteristics it reveals as it burns.
I've written the code using the FDS5 user guide, and it appears that the propane gas is not emitted from the surface at all.
In FDS6, when I specify only the following amount, it burns well, but can you tell me why?
I know that by default, FDS will combust when in contact with air (oxygen) without the need to specify a specific ignition temperature, unless you specify an auto ignition temperature, but I'm not sure why what I tried didn't combust.
Any advice would be greatly appreciated and will help me study further.

Thank you.

&HEAD CHID='FDS5_exmp'/
&TIME T_END=10.0/
&DUMP DT_RESTART=5.0, DT_SL3D=0.25/
&MISC HUMIDITY=50.0, TMPA=20.0/

&MESH ID='Mesh05', IJK=200,200,200, XB=0.5,1.5,0.5,1.5,0.0,1.0/

&REAC ID='PROPANE',
      FYI='Propane, C_3 H_8',
C=3,
H=8,
      CO_YIELD=0.02,
      SOOT_YIELD=0.1,
      HEAT_OF_COMBUSTION=5.003E+4/

&SPEC ID='PROPANE'/

&SURF ID='propane gas',
      RGB=26,204,26,
MASS_FLUX(1)=8.49E-3,
      TAU_MF=1.0,/

&OBST ID='floor', XB=0.0,2.0,0.0,2.0,-0.01,0.0/
&OBST ID='ceiling', XB=0.0,2.0,0.0,2.0,1.99,2.0/
&OBST ID='fire', XB=0.95,1.05,0.95,1.05,0.0,0.1, SURF_IDS='propane gas','INERT','INERT'/

&VENT ID='Mesh Vent: Mesh05 [XMAX]', SURF_ID='OPEN', XB=1.5,1.5,0.5,1.5,0.0,1.0/
&VENT ID='Mesh Vent: Mesh05 [XMIN]', SURF_ID='OPEN', XB=0.5,0.5,0.5,1.5,0.0,1.0/
&VENT ID='Mesh Vent: Mesh05 [YMAX]', SURF_ID='OPEN', XB=0.5,1.5,1.5,1.5,0.0,1.0/
&VENT ID='Mesh Vent: Mesh05 [YMIN]', SURF_ID='OPEN', XB=0.5,1.5,0.5,0.5,0.0,1.0/
&VENT ID='Mesh Vent: Mesh05 [ZMAX]', SURF_ID='OPEN', XB=0.5,1.5,0.5,1.5,1.0,1.0/
&VENT ID='Mesh Vent: Mesh05 [ZMIN]', SURF_ID='OPEN', XB=0.5,1.5,0.5,1.5,0.0,0.0/

&SLCF QUANTITY='TEMPERATURE', VECTOR=.TRUE., XB=0.0,2.0,0.0,2.0,0.0,2.0/
&SLCF QUANTITY='MIXTURE FRACTION', VECTOR=.TRUE., XB=0.0,2.0,0.0,2.0,0.0,2.0/
&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., XB=0.0,2.0,0.0,2.0,0.0,2.0/
&SLCF QUANTITY='HRRPUV', VECTOR=.TRUE., XB=0.0,2.0,0.0,2.0,0.0,2.0/
&SLCF QUANTITY='VOLUME FRACTION', SPEC_ID='PROPANE', PBY=1.00 /

&ISOF QUANTITY='MIXTURE FRACTION', VALUE=0.06 /

&TAIL /

[o...@aquacoustics.biz]

It's been a while since I've used FDS 5.3 and I don't have this version currently installed.  But you might want to look at the syntax of the &SURF line, and in particular the parameter MASS_FLUX.  Where you have MASS_FLUX(1) I suspect that you want MASS_FLUX (PROPANE) = 8.49E-3, .  See Table 13.23 of the version manual.  Note that the TAU you have specified is redundant due to FDS defaults.

Some hints and tips.

Build your models progressively adding just one or two features at a time.  A good place to start for any model are the verification and validation examples or some previous file that you have written and simulated successfully.

When stuff doesn't work then read the error log, re-read the users manual, and try and progressively isolate the fault.

In general you're better to stick with the current version of FDS.  You don't want to be learning syntax that is no longer valid and the clever people at NIST are enhancing and improving stuff all the time.

I'm not sure if you are a fire engineering student or just interested in fire modelling, but there are  formal courses that will enhance your commendable self-study.

[dr_jfloyd]

&SURF ID='propane gas',
      RGB=26,204,26,
MASS_FLUX(1)=8.49E-3,
      TAU_MF=1.0,/

You haven't defined a species for the mass flux.

Would highly recommend that you use the latest release of FDS for new work. FDS 5.5.3 was released over 10 yrs ago with 29 releases between 5.5.3 and the current release. 

[MinJoo Lee]

Thank you so much for your thoughtful response.
1. you are right, I wrote the code thinking mass fraction(1) = mass fraction(propane). I will take your advice and study it, thank you.


2. I tried referring to the user guide of FDS5, but I couldn't use SPEC_ID in &SURF. As you said, my first thought was to specify what the species of mass fraction is, so I wrote the code in FDS6. However, this is not available in FDS5, so I wanted to ask for advice on what alternative methods are available in FDS5. Is it possible to set the combustion model in FDS6 to a Mixture Fraction model like FDS5 instead of EDC by adding INITIAL_UNMIXED_FRACTION=0 to the code?

2023년 9월 24일 일요일 오후 6시 31분 15초 UTC+9에 dr_jfloyd님이 작성:

[dr_jfloyd]

You cannot convert FDS 6 to a mixture fraction model. FDS 6 does not track the quantity Z which is used in the mixture fraction model. You could mimic the model by setting INITIAL_UNMIXED_FRACTION=0 and SUPPRESSION=F. However, there are reasons we went to the mixing controlled model rather than assume cells are always fully mixed. 

FDS 5.5.3 is no longer a supported release. There is limited help that you will be able to get using a decade old version of the software. There have been over 1000 commits of bug fixes and improvements to FDS made since the release of 5.5.3 plus a significant increase in efforts towards Verification & Validation. Strongly encourage that you use the current version with its recommended settings (unless you have a good physical reason to change them) for new work.