"heat release rate per area" and "specify heat of combustion"

[xy1534...@gmail.com]

in FDS 6, when i set  the "heat release rate per area" ,and at the same time, i set the value of "specify heat of combustion" in reaction ,but the fds can run correct, but there is no smoke and reaction in the simulation, why this happen ?

[fde]

Heat of Combustion might be so low that physically cannot take place. Or HRRPUA is low that within the cell next to the boundary, the temperature is below critical flame temperature and it extinguishes. 

You can add SUPPRESSION=.FALSE. to MISC line and see what happens. Also see User guide § 13.1.4 Special Topic: Flame Extinction 

[dr_jfloyd]

You may have an error or conflicting input somewhere in your input file.  Simplify your file down as much as possible (e.g. a HEAD, MESH, TIME, SURF, and the VENT/OBST for your fire).  If you see a fire with that simple file, then start adding back in the rest of your inputs until you stop seeing a fire. If you still don't see a fire post that simple input file.

[xy1534...@gmail.com]

sorry for the delay, i went out for business yesterday. yes,when i add SUPPRESSION=.FALSE. to MISC,there is smoke and reaction. and i will read the  User guide . thank you for your help.

在 2017年8月9日星期三 UTC+8下午6:31:33，fde写道：

[xy1534...@gmail.com]

yes ,there is some paraments that i don'n know in the setting . but i know about the "heat release rate per area" and "specify heat of combustion",so when i use the two paraments. the fire can't show.i set the SUPPRESSION=.FALSE. to MISC line。 the fire show. so i think that is the   Flame Extinction  reason.

在 2017年8月9日星期三 UTC+8下午7:42:41，dr_jfloyd写道：

[dr_jfloyd]

I know what the issue is.  Sorry I didn't think of this yesterday.

The extinction model determines how much air (plus any combustion products present in the air) is needed to burn the fuel in a grid cell.  It then looks to see if the total energy released by combustion is high enough to raise the temperature of that mixture above a limiting flame temperature.  If it isn't, then combustion is not allowed.  If the fuel is propane and we have pure air (no combustion products to dilute the oxygen), the flame temperature will be ~1800 C and higher than the limiting flame temperature of ~1300 C.  Keep the fuel chemistry the same, but now tell FDS the heat of combustion is ~15000 kJ/kg rather than ~45000 kJ/kg. The same amount of air will be needed for combustion, but we are releasing 1/3 the heat.  So our computed flame temperature will be about ~600 C and we will never burn the mixture.  This is probably what is happening in your case, that the fuel chemistry you have defined doesn't comport with the heat of combustion you are using. If your overall fire scenario will be well ventilated that you don't expect extinction to ever occur, then setting SUPPRESSION=.FALSE. probably won't have a large impact.  If you do expect extinction to occur in your scenario, you may want to revisit your REAC inputs and make sure they are correct.