Flame Spread over a liquid pool

[Vikrant Goyal]

Hello,

I am a graduate student at Purdue University. I am modeling a pool fire case. In this case, there is a rectangular pan of 180 x 20 x 2.5 cm dimensions filled with heptane.

This hydrocarbon is ignited at one end using an igniter and flame spread rate is recorded using various imaging diagnostics.

I used PyroSim for modeling this case and the corresponding FDS code is attached.

The issue I am facing is that heptane pool is getting ignited at once, with or without the igniter. Possibly this is due to heptane reaction mechanism.

Can you please help me with this?

What I really want is that there is gradual spread of fire on ignition instead of entire pool burning altogether.

Regards,

Vikrant   

[fde]

You can use SPREAD_RATE parameter for this example. 

User guide §8.4.2

[Vikrant Goyal]

Thanks for directing me to this section. As I went through this methodology, it states that we have to specify a spread rate.

What I am looking for is to compute spread rate from the FDS simulation. Ignition should start at one end of the pool and fire then should spread out along the pool based on reaction parameters and liquid properties.

Can you please help me with this? 

[dr_jfloyd]

FDS is not going to compute the spread rate over a liquid pool if you are using fast chemistry.

[Vikrant Goyal]

Thank you for your advice. I will try with finite rate model.

[fde]

I did not want to open a new thread to ask. 

As of now, the spread is working by activating the next cell if the [time]*[spread rate] covers the end distance of the next cell. This gives an increase as step-wise. In order to get a continuous increase ( in terms of HRR) is it possible to add a function? Such as each cell ignites with a ramp in itself, instead of activating to 100% at a moment?

Thank you.

[Eric MARCHAND]

Hello,

I supplement these exchanges with a new question on the calculation of the Spread Rate flame by SDS, when the reaction of combustion of a liquid with detail has been defined.

By using & VENT, XYZ = and SPREAD_RATE, the combustion happens as expected.

Now, if I want to pilot my reaction by MATL_ID. Surprise: the inflammation of my spill is almost instantaneous, hence a SPREAD_RATE of more than 5 m / s. For FOD (Diesel), the value of the literature is around 3 cm / s at 20°C initial temperature.
I forced SPREAD_RATE in my MATL_ID but it did not change anything. I did not have this problem with FDS 6.5.1. What to do?
Could the parameter ABSORPTION_COEFFICIENT solve my problem?

FDS is it able to calculate by itself, the flame spread on a liquid fuel spill?

Here is the detail of my file.

 

&HEAD CHID='FODR13', TITLE='Combustion d une nappe rectangulaire de FOD par SURF ID $0'  /

&MESH IJK=24,16,32, XB=-12.0,12.0,-4.0,4.0,0.0,16.0 /

 

&TIME T_END=20.0 /

&DUMP NFRAMES=100.0 /

&MISC TMPA=15.0 /

 

&REAC ID                                        = 'Diesel'

      FYI                      = 'C16H34, NFPA Handbook, Babrauskas, ramené à C13H27.625'

      HEAT_OF_COMBUSTION    = 43027.

      SOOT_YIELD               = 0.10

      C                         = 7

      H                         = 14.875 /

 

&MATL ID                    = 'Carburant'

      FYI                   = 'Diesel FDS6'

      SPECIFIC_HEAT         = 1.99

      CONDUCTIVITY          = 0.127

      DENSITY               = 855.

      N_REACTIONS           = 1

      NU_SPEC               = 1.

      SPEC_ID               = 'Diesel'

      BOILING_TEMPERATURE   = 265.

      SPECIFIC_HEAT             = 1.0      

      HEAT_OF_REACTION      = 200./

 

&MATL ID            = 'STEEL'

      EMISSIVITY    = 1.0

      DENSITY       = 7850.

      CONDUCTIVITY  = 45.8

      SPECIFIC_HEAT = 0.46 /

 

&SURF ID               = 'NAPPE'

      COLOR              = 'YELLOW'

      MATL_ID                        = 'Carburant'

      SPREAD_RATE           = 0.03

      THICKNESS                 = 0.5 /

 

&SURF ID                = 'STEEL SHEET'

      COLOR              = 'BLACK'

      MATL_ID            = 'STEEL'

      BACKING           = 'EXPOSED'

      THICKNESS      = 0.003 /

 

&SURF ID = 'BURNER', COLOR = 'RED', HRRPUA = 1000. /

 

&VENT XB=8.5,9.5,-0.5,0.5,0.5,0.5, SURF_ID='BURNER' / Ignition sur la nappe

 

&OBST XB=-10.0,10.0,-2.0,2.0,0.0,0.5, SURF_IDS='NAPPE', 'STEEL SHEET', 'STEEL SHEET' /

&OBST XB=-10.0,-10.0,-2.0,2.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=10.0,10.0,-2.0,2.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=-10.0,10.0,-2.0,-2.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=-10.0,10.0,2.0,2.0,0.0,2.0, SURF_ID='STEEL SHEET' /

 

&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' /

 

&BNDF QUANTITY='RADIATIVE HEAT FLUX' /

&BNDF QUANTITY='INCIDENT HEAT FLUX' /

&BNDF QUANTITY='GAUGE HEAT FLUX' /

 

&SLCF PBY=0.00, QUANTITY='TEMPERATURE' /

&SLCF PBY=0.00, QUANTITY='HRRPUV' / Heat Release Rate per Unit Volume

 

&TAIL /

[Kevin]

You must not use the liquid fuel pyrolysis model and SPREAD_RATE at the same time. These are mutually exclusive routines.

[dr_jfloyd]

The default combustion model in FDS is infinitely fast chemistry, and the default extinction model parameters include an auto ignition temperature of 0 K.  The liquid pool model evaporates fuel over the entire pool surface. That fuel mixes with air. Since any temperature is above the default AIT of 0 K, a reaction is allowed to take place. The default parameters will not predict flame spread.  

Since you have an 0.5 m deep pool, how important is it to predict the flame spread? A 0.5 m deep pool is going to burn for an hour plus. Flame spread from edge to edge is going to be ~30 s.

On Thursday, January 25, 2018 at 2:19:27 PM UTC-5, Eric MARCHAND wrote:

[Eric MARCHAND]

Thanks for your assistance.
I do not focus for the moment on the speed of flame, but on the combustion of the pool. Following your explanation, I therefore added in REAC an AIT that I set equal to the flash point of the product (>55°C). However, I have no more combustion.

What's wrong with my test case? Does AIT need to be lowered? If so, Equal to what physical characteristic of my liquid ?

Le dimanche 11 juin 2017 18:25:52 UTC+2, Vikrant Goyal a écrit :

[Eric MARCHAND]

I complete my post.
I resolved my iignition problem: my "Burner" was too "cold" to produce enough vapors on my thick pool. I decreased my puddle thickness and raised TMP_FRONT to 1000 ° C.

After a new reading of the User Manual, I think that the AIT is equal to 400 ° C for diesel (FOD) and in no case equal to Flash Point (55°C). Am I in the right direction of thinking ?

Le dimanche 11 juin 2017 18:25:52 UTC+2, Vikrant Goyal a écrit :

[Kevin]

I told you above that you CANNOT use SPREAD_RATE and BOILING_TEMPERATURE  in the same simulation. The SPREAD_RATE is designed to model a fire with a known or specified spreading rate. BOILING_TEMP is designed for the case where you are trying to predict the burning rate.

[dr_jfloyd]

The flashpoint is the lowest temperature at which vapors from a liquid pool will burn in the presence of an ignition source.  The AIT is the temperature at which a material will spontaneously ignite. 

If you set TMP_FRONT to 1000 C, then you are not predicting heat transfer into the pool. You are stating that for the entire duration of the simulation that the pool has a surface temperature of 1000 C.  Since diesel fuel has a boiling point near 100, this is not an appropriate input.

You have two choices for modeling liquid phase:

You can specify the mass loss rate based on experimental data

You can specify material properties and attempt to predict the rate (keeping in mind that FDS does not simulate internal convection in the pool).

The extinction model is another decision. The default parameters means fuel will always burn in the presence of air. If you change this, then you will need to provide an ignition source. 

If you are trying to predict flame spread, you cannot treat FDS as a block box. You need to take the time to understand the FDS combustion model and the heat transfer calculation being performed in the pool. The details are found in the Technical Reference Manual.

On Friday, January 26, 2018 at 3:08:43 AM UTC-5, Eric MARCHAND wrote:

[Eric MARCHAND]

Hi, Kevin,

I forgot to remove the line SPREAD_RATE in the file ... Just an oversight.

[Eric MARCHAND]

Hi Dr FLYOD

I have taken note of your recommendations. I have rewritten the attached file and the combustion starts. The entire pool gets into fire instantly. I can’t propose this simulations at my coworkers (French Commissariat for Atomic Energy: CEA), very picky with the kinetics of combustion.

&HEAD CHID='FODR15', TITLE='FOD combustion with MATL $0'  /

 

&MESH IJK=24,24,32, XB=-12.0,12.0,-12.0,12.0,0.0,16.0 /

 

&TIME T_END=40.0 /

&DUMP NFRAMES=200.0 /

 

&MISC TMPA=20.0, SUPPRESSION=.FALSE. /

 

&REAC ID                                = 'Diesel'

      FYI                        = 'C16H34, NFPA Handbook, Babrauskas, to C7H14.875'

      HEAT_OF_COMBUSTION                = 43027.

      SOOT_YIELD                     = 0.10

      AUTO_IGNITION_TEMPERATURE    = 400.

      C                           = 7

      H                           = 14.875 /

 

&MATL ID                               = 'Carburant'

      FYI                        = 'Diesel FDS6'

      SPECIFIC_HEAT                = 1.99

      CONDUCTIVITY                 = 0.127

      DENSITY                           = 855.

      N_REACTIONS                  = 1

      NU_SPEC                          = 1.

      SPEC_ID                           = 'Diesel'

      BOILING_TEMPERATURE   = 265.

      HEAT_OF_REACTION         = 200./

 

&MATL ID            = 'STEEL'

      EMISSIVITY    = 1.0

      DENSITY       = 7850.

      CONDUCTIVITY  = 45.8

      SPECIFIC_HEAT = 0.46 /

 

&SURF ID                    = 'NAPPE'

      COLOR                  = 'YELLOW'

      MATL_ID                = 'Carburant'

      THICKNESS                        = 0.25 /

 

&SURF ID        = 'STEEL SHEET'

      COLOR     = 'BLACK'

      MATL_ID   = 'STEEL'

      BACKING   = 'EXPOSED'

      THICKNESS           = 0.003 /

 

&SURF ID = 'BURNER', COLOR = 'RED', HRRPUA = 500. /

 

&VENT XB=8.5,9.5,-0.5,0.5,0.5,0.5, SURF_ID='BURNER' / Ignition

 

&OBST XB=-10.0,10.0,-10.0,10.0,0.0,0.5, SURF_IDS='NAPPE', 'STEEL SHEET', 'STEEL SHEET' /

&OBST XB=-10.0,-10.0,-10.0,10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=10.0,10.0,-10.0,10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=-10.0,10.0,-10.0,-10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=-10.0,10.0,10.0,10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

 

&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' /

 

&SLCF PBY=0.00, QUANTITY='TEMPERATURE' /

&SLCF PBY=0.00, QUANTITY='HRRPUV' / Heat Release Rate per Unit Volume

 

&TAIL /

On the 12-06-2017, you wrote: "FDS is not going to calculate the spread rate on a liquid pool if you are using fast chemistry.", So, I repeated my example with the "Complex fuel Model ". Ultimately, I will need this type of reaction, because the liquids fuels that can burn on our chemistry plant, contain Cl, N, S ... and other molecules.

&HEAD CHID='FODR20', TITLE='Combustion d une nappe rectangulaire de FOD $0'  /

 

&MESH IJK=24,24,32, XB=-12.0,12.0,-12.0,12.0,0.0,16.0 /

 

&TIME T_END=40.0 /

&DUMP NFRAMES=160.0 /

 

&MISC TMPA=20.0 /

 

&SPEC ID = 'OXYGEN',                        LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'NITROGEN',                     LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'NITROGEN DIOXIDE',      LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'WATER VAPOR',   LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'CARBON MONOXIDE',      LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'CARBON DIOXIDE',          LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'HYDROGEN CYANIDE',     LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'SOOT',                 LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'SULFUR DIOXIDE',           LUMPED_COMPONENT_ONLY = .TRUE. /

 

&SPEC ID = 'AIR',

            SPEC_ID(1) = 'OXYGEN', VOLUME_FRACTION(1)=1,

            SPEC_ID(2) = 'NITROGEN', VOLUME_FRACTION(2)=3.76,

            BACKGROUND=.TRUE. /

 

&SPEC ID = 'FOD', FORMULA = 'C7H14.875' /

&SPEC ID = 'PRODUCTS_FOD1',

            SPEC_ID(1) = 'CARBON DIOXIDE', VOLUME_FRACTION(1) = 6.614380,

            SPEC_ID(2) = 'CARBON MONOXIDE', VOLUME_FRACTION(2) = 0.042436,

            SPEC_ID(3) = 'WATER VAPOR', VOLUME_FRACTION(3) = 7.418434,

            SPEC_ID(4) = 'SOOT', VOLUME_FRACTION(4) = 0.381315,

            SPEC_ID(5) = 'NITROGEN', VOLUME_FRACTION(5) = 38.896508 /

 

&REAC ID = 'Diesel Fuel'

            FUEL = 'FOD',

            HEAT_OF_COMBUSTION = 43027,

            SPEC_ID_NU = 'FOD','AIR','PRODUCTS_FOD1'

            NU=-1,-10.34482,1 /

 

&MATL ID                               = 'FOD'

      FYI                        = 'Diesel FDS6'

      SPECIFIC_HEAT                = 1.997

      CONDUCTIVITY                 = 0.127

      DENSITY                           = 855.

      BOILING_TEMPERATURE   = 265.

      HEAT_OF_REACTION         = 200./

 

&MATL ID            = 'STEEL'

      EMISSIVITY    = 1.0

      DENSITY       = 7850.

      CONDUCTIVITY  = 45.8

      SPECIFIC_HEAT = 0.46 /

 

&SURF ID                                = 'NAPPE'

      COLOR                              = 'YELLOW'

      MATL_ID                           = 'FOD'

      THICKNESS                                   = 0.25 /

 

&SURF ID        = 'STEEL SHEET'

      COLOR     = 'BLACK'

      MATL_ID   = 'STEEL'

      BACKING   = 'EXPOSED'

      THICKNESS           = 0.003 /

 

&SURF ID = 'BURNER', COLOR = 'RED', HRRPUA = 500. /

 

&VENT XB=8.5,9.5,-0.5,0.5,0.5,0.5, SURF_ID='BURNER' / Ignition sur la nappe

 

&OBST XB=-10.0,10.0,-10.0,10.0,0.0,0.5, SURF_IDS='NAPPE', 'STEEL SHEET', 'STEEL SHEET' /

&OBST XB=-10.0,-10.0,-10.0,10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=10.0,10.0,-10.0,10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=-10.0,10.0,-10.0,-10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

&OBST XB=-10.0,10.0,10.0,10.0,0.0,2.0, SURF_ID='STEEL SHEET' /

 

&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' /

 

&SLCF PBY=0.00, QUANTITY='TEMPERATURE' /

&SLCF PBY=0.00, QUANTITY='HRRPUV' / Heat Release Rate per Unit Volume

 

&TAIL /

I have never been able to start the burning of the pool. Even with HRRPUA very high for my BURNER. For this choice of pyrolysis modeling, I understood that it was not possible to indicate to FDS: INGNITION_TEMPERATURE. Because FLASHPOINT is not a possible variable for FDS too, I don’t know what to add, or to remove, to have ignition and flame spreading on the pool. I necessarily have evaporation around my burner. Because AIT is not specified, all vapors produced should ignite. What’s wrong?

Would you have an example of a liquid pool combustion, with an complex fuel model, so that I can analyze it and without wasting your time?

Thanks in advance.

[Eric MARCHAND]

I have taken note of your recommendations. I have rewritten the attached file and the combustion starts. The entire pool gets into fire instantly. I can’t propose this simulations at my coworkers, very picky with the kinetics of combustion.
(File 1.fds)

On the 12-06-2017, you wrote: "FDS is not going to calculate the spread rate on a liquid pool if you are using fast chemistry.", So, I repeated my example with the "Complex

fuel Model ". Ultimately, I will need this type of reaction, because the liquids fuels that can burn on our chemistry plant, contain Cl, N, S ... and other molecules.

(File 2.fds)

I have never been able to start the burning of the pool.

Even with HRRPUA very high for my BURNER. For this choice of pyrolysis modeling, I understood that it was not possible to indicate to FDS: INGNITION_TEMPERATURE. Because FLASHPOINT is not a possible variable for FDS too, I don’t know what to add, or to remove, to have ignition and flame spreading on the pool. I necessarily have evaporation around my burner. Because AIT is not specified, all vapors produced should ignite. What’s wrong?

Would you have an example of a liquid pool combustion, with an complex fuel model, so that I can analyze it and without wasting your time?

Thanks in advance.

[dr_jfloyd]

Attempting to use fds to predict flame spread borders on a research application. It is something you would need to figure out how to do, we cannot tell you what inputs to use. We have not run this simulation.

What is  the goal of your simulation?  Any model that you use is only an approximation of reality. Unless your application depends upon what happens in the first minute after the pool is ignited (when flame spread matters), I would suggest not trying to model the spread. 

[Eric MARCHAND]

Our request is certainly unusual. When there is accidental spreading of hydrocarbon wastes, creating large pool (spill) on the ground, our plant also has fireman on the place where the waster transfer occurs. They are ready to fight. That's why the spread of the first minute of combusion is so important to us and the fire department our plant.

Now, my big question, Why fire with complex chemistry does not start, no matter what modification we do into the file. What is our mistake?
We do not think we have set contradictory evaporation / pyrolysis parameters ...?

Waiting for your help

[dr_jfloyd]

You have not specified a specific heat for your fuel species; therefore, per the User's Guide FDS is assuming gamma=1.4.  This assumption is not valid for a large molecule, and the derived specific heat will not be correct. Specific heat is used in the extinction routine and a bad value for the fuel can lead to extinction under conditions where you expect burning. Add a reasonable specific heat for your fuel or turn off the extinction model.

[Eric MARCHAND]

Hi,

I come back to my liquid pool combustion problems and the most realistic  modeling of the flame spread of fuel burning.
I tried most solutions, but with a complex combustion, and I can't have any other phenomena than an immediate ignition of the integral pool. What to change in my fds. file to watch a realistic spread rate of the flame in SmokeView ?

Eric

[Kevin McGrattan]

You are trying to model flame spread over a liquid pool using 1 m grid cells. This is too crude. However, I hacked your case to do it, maybe. But I would not trust these results. I just did it to test a few things.

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[fde]

Where can we see the calculated specific heat of the FUEL in the CHID.out file?

[dr_jfloyd]

In the case of pool burning:

For the FUEL gas phase there is a section in CHID.out for each tracked species that summarizes thermophysical properties.

For the FUEL in liquid phase (the pool), this is something you have given as an input on &MATL, and FDS is just using the input.

[fde]

Thank you, I guess this is the part. 

   REAC_FUEL

   Molecular Weight (g/mol)           139.17174

   Ambient Density (kg/m^3)            5.786

   Initial Mass Fraction               0.000

   Enthalpy of Formation (J/kg)     -2.81E+06

   Sub Species                    Mass Fraction     Mole Fraction

   REAC_FUEL                      1.000000E+00      1.000000E+00

 

     Viscosity (kg/m/s) Ambient,  293 K:  3.88E-05

                                  500 K:  5.60E-05

                                 1000 K:  8.80E-05

                                 1500 K:  1.14E-04

   Therm. Cond. (W/m/K) Ambient,  293 K:  1.14E-02

                                  500 K:  1.65E-02

                                 1000 K:  2.59E-02

                                 1500 K:  3.37E-02

        Enthalpy (J/kg) Ambient,  293 K: -2.81E+06

                                  500 K: -2.77E+06

                                 1000 K: -2.66E+06

                                 1500 K: -2.56E+06

    Spec. Heat (J/kg/K) Ambient,  293 K:  2.09E+02

                                  500 K:  2.09E+02

                                 1000 K:  2.09E+02

                                 1500 K:  2.09E+02

   Diff. Coeff. (m^2/s) Ambient,  293 K:  1.54E-05

                                  500 K:  3.82E-05

                                 1000 K:  1.22E-04

                                 1500 K:  2.38E-04