Prescribing a simplified burning material Edit
Real objects are often difficult to describe via the SURF and MATL parameters. So simplified descriptions of burning solid fuels are possible. If ignition temperature and burning rate as a function of time from ignition are known, add lines similar to the following:
&MATL ID='stuff', CONDUCTIVITY=0.1, SPECIFIC_HEAT=1.0, DENSITY=900.0 / &SURF ID='my_surf', MATL_ID='stuff', HRRPUA=1000., IGNITION_TEMPERATURE=500., HEAT_OF_VAPORIZATION=1000., RAMP_Q='fire_ramp', THICKNESS=0.01 / &VENT XB=0.6,1.0,0.3,0.7,0.0,0.0, SURF_ID='my_surf' / &RAMP ID='fire_ramp', T=0.0, F=0.0 / &RAMP ID='fire_ramp', T=10.0, F=1.0 /
• IGNITION_TEMPERATURE delays the emission of fuel gas until the specified temperature is reached: when the surface temperature reaches 500 °C, the object starts emitting fuel gas.
• HEAT_OF_VAPORIZATION tells FDS to account for the energy used to vaporize the fuel; in the example, the net heat flux at the material surface is reduced by a factor 1000 kJ/kg times the instantaneous burning rate.
If a MATL line is invoked by a SURF line containing a specified HRRPUA, then that MATL ought to have only thermal properties and no reaction parameters, product yields...
By specifying HRRPUA, you are controlling the burning rate rather than letting the material pyrolyze based on the conditions of the surrounding environment.