IGNITION TEMPERATURE

[Antonio Silvestro]

hello, i'm simulating fires in gallery.

i have made two cars, the first  starts to burn immediately .The problem is that does not catch fire never second car. I setting the ignition temperature of  the surface  of 25 degrees, i know  that is low but is for test.

I copy the code , i hope  that you manage to give a hand, are days that i read the guidance but i can not understand what mistake

&MISC GVEC= 0 , 0 , -9.81 , TMPA= 18

&SURF ID='Burning_CAR' HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]' IGNITION_TEMPERATURE=25., COLOR='RED'/

&SURF ID='BurningC' HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]' /

&SURF ID='CAR' COLOR= 'GRAY' MATL_ID(1:3,1)= 'ALUMINIUM', 'FABRIC', 'FOAM' BACKING = 'EXPOSED', THICKNESS(1:3)=0.007,0.003,0.1/

&MATL ID = 'ALUMINIUM'

DENSITY =2710

SPECIFIC_HEAT = 0.89

 CONDUCTIVITY    = 180/

&MATL ID                   = 'FABRIC'

      FYI                   = 'Properties completely fabricated'

      SPECIFIC_HEAT         = 1.0

      CONDUCTIVITY          = 0.1

      DENSITY               = 100.0

/

&MATL ID                    = 'FOAM'

      FYI                   = 'Properties completely fabricated'

      SPECIFIC_HEAT         = 1.0

      CONDUCTIVITY          = 0.05

      DENSITY               = 40.0

  /

&OBST XB= 100.00 , 103.50 , 5.00 , 7.00 , 0.00 , 2.00 SAWTOOTH=.FALSE. OUTLINE=.TRUE. SURF_ID= 'CAR' /

&OBST XB= 103.50 , 107.00 , 5.00 , 7.00 , 0.00 , 2.00 SAWTOOTH=.FALSE. OUTLINE=.TRUE. SURF_ID= 'CAR' / OBS

&VENT XB= 100.00 , 101.00 , 5.20 , 6.20 , 2.00 , 2.00 SURF_ID='BurningC' , RGB=255,127,0 , /

&VENT XB= 103.50 , 104.50 , 5.20 , 6.20 , 2.00 , 2.00  SURF_ID='Burning_CAR' , RGB=255,127,0 , /

[dr_jfloyd]

I recommend you use the latest release (FDS 6.2) rather than FDS 5.  

&SURF ID='Burning_CAR'  HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]'  IGNITION_TEMPERATURE=25., COLOR='RED'/

How is this surface going to heat up? The default temperature boundary condition is a fixed temperature boundary at the ambient temperature (in your case 18 C). You have not changed this. It will always be 18 C.

[Antonio Silvestro]

hi dr_jfloyd

 i use a ramp-car but is very long for post here.

i don't setting tmpa?

[dr_jfloyd]

IGNITION_TEMPERATURE=25 means the ramp will not start until the surface reaches 25 C.  You have not specified any inputs that will allow the surface to heat up. You have no MATL_ID on the SURF line;  therefore, the SURF has the default temperature boundary condition of INERT. INERT is a fixed temperature surface. It will never heat up to 25 C.

[Antonio Silvestro]

SORRY I HAVEN'T COPIED

I DEFINED:

[dr_jfloyd]

This surface has a pyrolysis model defined that will impose a predefined heat release rate based on whatever RAMP_CAR is when the surface reaches 25 C.  No heat release will never happen, since the surface will never heat up as I have already explained:

&SURF ID='Burning_CAR'  HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]'  IGNITION_TEMPERATURE=25., COLOR='RED'/

This surface has a pyrolysis model defined that will impose a predefined heat release rate based on whatever RAMP_CAR is:

&SURF ID='BurningC'  HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]'  /

This surface has no pyrolysis model defined (there will be no heat release rate), but it will heat up based on the MATL inputs for ALUMINUM, FABRIC, and FOAM.

&SURF ID='CAR' COLOR= 'GRAY' MATL_ID(1:3,1)= 'ALUMINIUM', 'FABRIC', 'FOAM' BACKING = 'EXPOSED', THICKNESS(1:3)=0.007,0.003,0.1/

There is no surface defined where you have both a pyrolysis model and and the ablity for the surface to heat up. 

[Antonio Silvestro]

thank you for help me.

Can you tell me how i setting a pyrolysis model for the SURF?

[dr_jfloyd]

FDS 6.2 User's Guide:

8 Fire and Thermal Boundary Conditions

8.1 Basics

8.2 Surface Temperature and Heat Flux

8.3 Heat Conduction in Solids

8.4 Simple Pyrolysis Models

8.5 Complex Pyrolysis Models

8.6 Testing Your Pyrolysis Model

[Antonio Silvestro]

hi, sorry but if i insert a temperature reference resolve? ps, i find it to literature.

the temperature reference is the same to ignition? 

Il giorno giovedì 16 luglio 2015 15:27:12 UTC+2, Antonio Silvestro ha scritto:

[dr_jfloyd]

Did you read the User's Guide? Did you look at the example in 8.4.3 Solid Fuels that Burn at a Specified Rate?

Compare the example there to your input.  Here is your input:

&SURF ID='Burning_CAR'  HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]'  IGNITION_TEMPERATURE=25., COLOR='RED'/

Here is the FDS User's Guide Input (I've replaced values in the example with those from your input to make it easier for you to compare):

&SURF ID='Burning_CAR'  HRRPUA= 8000.00 , RAMP_Q='RAMP_CAR' , PART_ID='SMOKE[100009]'  IGNITION_TEMPERATURE=25., COLOR='RED', MATL_ID='XXXXXX', THICKNESS=YYYYYY/

[Antonio Silvestro]

THANK YOU!

Il giorno giovedì 16 luglio 2015 15:27:12 UTC+2, Antonio Silvestro ha scritto:

[a.pod...@email.it]

I don't know if this i the right place to post, but dr_jfloyd looks expert in what I am interested: in particular, simply heating up a surface (via a temperature ramp for example) does not give place to any HRR, does it? And second thing, when you impose an HRRPUA, do you always have something burning?  I have set two lines like these, with all other surfaces as inert:

&SURF ID = 'FIRE', HRRPUA = 2500. /
&REAC FUEL='METHANE', AUTO_IGNITION_TEMPERATURE=15000. /

and I cannot see any HRR or burning rate, nor realistic 3d fire (so it looks like nothing is burning).
What's wrong with it?

[dr_jfloyd]

Read the User's Guide section on flame extinction.

[a.pod...@email.it]

Now it works. I just canceled the AIT parameter in the REAC line. In this way methane ignites istantaneously, whatever temperature is, and combustion is controlled by ventilation. Thanks a lot for your suggestion