Is Fire Point represented in FDS / a decent metric to maintain burning after ignition is reached in thermally thick liquid fuels?

[clarkhinz23]

Hello all,

I am pursuing a model recreation of a restaurant fryer fire for suppression system modeling. In the development of the fryer model (before suppression is defined), I need to reach ignition and maintain a steady burn, which has been completed through assigining the surface temperature = boiling temperature for a period of 60 seconds, then assigning the surface temperature = a proposed fire point (listed as T_reignite in chart below). Does FDS recognize fire point in simple chemistry liquid fuels? Is there a better way to maintain burning without prescribing an arbitrary surface heat flux/burner?

The parameters for this examination require that the fuel used is a Canola Oil/Triglyceride with specified chemical formula, molecular weight, conductivity, density, boiling temperature, etc. There is no prescribed HRRPUA or MLRPUA for the fuel. I have attached the range of T_reignite values tested against their steady state mass flux during the reignition window, T_boil = 588 degrees Celsius. I can also send a base input fds file for these tests

[drjfloyd]

FDS does not recongnize fire point as an input. If you are trying to get bulk liquid to ignite and burn with a predicted heat release rate you can initialize the entire liquid pool to an elevated temperature using TMP_INNER.

Keep in mind FDS is not modeling internal conveciton in the pool, not modeling how pool boiling will result in frothing or forming fuel aerosol droplets above the surface, and is not going to account for interactions between water sprays and the bulk pool (flashing of water droplets to steam if they penetrate into the hot liquid).

[clarkhinz23]

Hey Dr. Floyd,

Thanks for the insight. I am currently utilizing TMP_FRONT to prompt ignition and reignition (code found below). My prior efforts were directed towards experimentally determining a pseudo-fire-point for this fuel (minimum surface temperature to maintain burning through vapor production) but there does not appear to be clear indication of a value to utilize. If FDS does not recognize Fire Point as an input value, is it still recognized within the simulation? Could fire point be assumed to occur between 560 and 570 in this case? Or does FDS not recognize an internal fire point, and the liquid fuel will continue to burn at reduced rates for any surface temperature tested above?
I am trying to gain understanding if this testing process produces arbitrary results, or if there is an indication of fire point occurring within an FDS simulation

FDS Surface ID setup: (T_surf = T boil from 1 to 60 seconds, then T_surf = 560 for this example at 61 seconds and onward)
&SURF ID = 'CANOLA POOL'
COLOR = 'YELLOW'
MATL_ID = 'CANOLA LIQUID'
THICKNESS = 0.1
TMP_FRONT=588.0,
RAMP_T = 'TEMP_RAMP' /
&RAMP ID = 'TEMP_RAMP', T = 0.0, F = 0.0 /
&RAMP ID = 'TEMP_RAMP', T = 1.0, F = 1.0 /
&RAMP ID = 'TEMP_RAMP', T = 60.0, F = 1.0 /
&RAMP ID = 'TEMP_RAMP', T = 61.0, F = 0.95238 /

[drjfloyd]

I suggest you review the Techinical Reference Guide chapter on combustion which details how FDS deals with ignition and extinction.