CO and soot yield #12953
Replies: 7 comments 37 replies
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Soot yield is not an intrinsic property of the molecular formula. It generally comes from doing an experiment and measuring the amount of particulate matter that is generated by the fire. |
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&SPEC ID='CARBON DIOXIDE',LUMPED_COMPONENT_ONLY = .TRUE./ What does the user's guide say the input LUMPED_COMPONENT_ONLY=.TRUE. means? |
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The logical parameter LUMPED_COMPONENT_ONLY indicates that the species is only present as part of a |
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Do you see why you have gotten the error message? |
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Yes thank you I completely understand the problem, however, I defined the input file for the first case by defining primitive species, and the second case using lumped species approach, the HRR for these two cases with identical conditions is different. Am I missing something related to this issue? Two inputs are as follows: 1: &SPEC ID = 'FUEL',SPEC_ID='METHANE','CARBON MONOXIDE','CARBON DIOXIDE','HYDROGEN', VOLUME_FRACTION=0.13,0.5,0.15,0.22 / &INIT XB = 0.0,0.1,0.0,0.1,0.0,0.1, &COMB FIXED_MIX_TIME=0.1 / &REAC FUEL='FUEL' |
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2: &INIT XB = 0.0,0.1,0.0,0.1,0.0,0.1, &COMB FIXED_MIX_TIME=0.1 / &REAC FUEL='METHANE' &REAC FUEL='CARBON MONOXIDE' &REAC FUEL='CARBON DIOXIDE' &REAC FUEL='HYDROGEN' |
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Double check your math. When I do a quick calc with integer values for molecular weight: |
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Thank you so much. All calculations were checked and the mass fractions are now correct. Although the difference is not significant like previous case, there is still a small deviation between two HRR plots versus time in both cases. Calculated heat of combustion by FDS in Lumped species approach is larger than the heat of combustion that I can calculate manually based on EPUMO2 for lumped fuel. Inputs are as follows: Lumped: &SPEC ID = 'FUEL',SPEC_ID='METHANE','CARBON MONOXIDE','CARBON DIOXIDE','HYDROGEN', VOLUME_FRACTION=0.13,0.5,0.15,0.22 / &INIT XB = 0.0,0.1,0.0,0.1,0.0,0.1, &COMB FIXED_MIX_TIME=0.1 / &REAC FUEL='FUEL' Primitive: &INIT XB = 0.0,0.1,0.0,0.1,0.0,0.1, &COMB FIXED_MIX_TIME=0.1 / &REAC FUEL='METHANE' &REAC FUEL='CARBON MONOXIDE' &REAC FUEL='CARBON DIOXIDE' &REAC FUEL='HYDROGEN' |
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See 13.1.2 in the User's Guide. |
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Hello, Thank you for your help. I am running this input file; however, I am encountering an error indicating numerical instability with the warning "Minimum density, 0.098 kg/m3, clipped in Mesh 2." Additionally, for this input file, although I have defined a combustion reaction, the HRR versus time remains zero until 2.13 seconds when the aforementioned error occurs. Could you please assist me with this issue? Thank you. &HEAD CHID='pine_needles_fire', TITLE='Flame Spread Over Bed of Pine Needles' / &MESH ID='mesh1', IJK=10,17,50, XB=0.0,0.1,0.0,0.17,0.0,0.30, COLOR='BLUE', CHECK_MESH_ALIGNMENT=T / &RADI RADIATION=.TRUE. / ! Radiation exists &SURF ID = 'AIR_INLET', &SURF ID='WALL', &VENT XB=0.0,0.0,0.0,0.17,0.0,0.3, &VENT XB=0.0,0.70,0.17,0.17,0.0,0.30, &VENT XB=0.0,0.70,0.0,0.17,0.30,0.30, &VENT XB=0.0,0.70,0.0,0.17,0.0,0.0, &SPEC ID = 'CARBON MONOXIDE'/ &SURF ID ='IGNITER', &RAMP ID = 'RAMP_IGN', T = 0, F = 1/ &OBST XB = 0.094,0.098,0.0,0.08,0.012,0.024, &MATL ID = 'MOISTURE' &MATL ID='PINE_NEEDLES', &MATL ID = 'CHAR', &MATL ID = 'ASH', &SURF ID = 'PINE_NEEDLE_BED', &PART ID = 'PINE_NEEDLE_BED_PART', &INIT ID = 'PINE_NEEDLE_BED', &SURF ID = 'ASBESTOS_SHEET', &PART ID = 'ASBES', &INIT ID = 'ASBESTOS_SHEET', &SURF ID = 'FIRE_CLAY', &PART ID = 'FC', &INIT ID = 'FIRE_CLAY_F', &OBST XB = 0.1,0.1,0.0,0.08,0.012,0.032, COLOR = 'GREEN', SURF_ID = 'PINE_NEEDLE_BED'/ &OBST XB = 0.0,0.0,0.0,0.08,0.0,0.012, COLOR = 'YELLOW', SURF_ID = 'ASBESTOS_SHEET'/ &OBST XB = 0.1,0.1,0.08,0.09,0.0,0.032, COLOR = 'ORANGE', SURF_ID = 'FIRE_CLAY'/ &REAC ID = 'CO_COMBUSTION', &DEVC XB = 0.0,0.70,0.0,0.17,0.0,0.30, QUANTITY='TEMPERATURE', STATISTICS='MEAN', ID='TEMP' / &TAIL / |
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I will run the case. |
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I appreciate. Thank you so much |
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Reactions only consume TRACKED species. Your REAC consumes the tracked species of OXYGEN but you have initialized your domain with the tracked species of AIR. |
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Also, you put a mesh boundary right at the surface of the hot object and instantly turned on the flow. Do you need to do this? |
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Look at the data in the hrr.csv file. Do you notice anything unusual? |
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The obvious unusual thing is that HRR increases about a second and until getting error it has plateau. |
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There is more data than just the heat release rate. What is happening in pressure zone 1? What would the effect of that be on density? |
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Pressure zone 1 is decreasing and its value is negative. MLR plots are not reasonable since they have weird trend such as MLR products which is fluctuating and has a sudden decrease. Decreasing the pressure will decrease the density. |
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Try and figure out why the pressure is dropping. You probably want to first figure out where pressure zone 1 is and then think about what outputs might you add to your input file to let you understand what is happening inside the zone. |
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I have resolved the problem at 2.1 s of simulation. Now the pressure in zone 1 is not negative and it is increasing which makes sense and i really appreciate your help. HRR versus time trend is not exactly what I am expecting but reasonable. On the other hand for the attached input file now I getting again error which is now maximum density: WARNING: Maximum density, 14.875 kg/m3, clipped in Mesh 1 ERROR: Numerical Instability - FDS stopped &HEAD CHID='pine_needles_fire', TITLE='Flame Spread Over Bed of Pine Needles' / &MESH ID='mesh1', IJK=10,17,50, XB=0.0,0.1,0.0,0.17,0.0,0.30, COLOR='BLUE', CHECK_MESH_ALIGNMENT=T / &RADI RADIATION=.TRUE. / ! Radiation exists &SURF ID = 'AIR_INLET', &SURF ID='WALL', &VENT XB=0.0,0.0,0.0,0.17,0.0,0.3, &VENT XB=0.0,0.70,0.17,0.17,0.0,0.30, &VENT XB=0.0,0.70,0.0,0.17,0.30,0.30, &VENT XB=0.0,0.70,0.0,0.17,0.0,0.0, &SPEC ID = 'CARBON MONOXIDE'/ &SURF ID ='IGNITER', &RAMP ID = 'RAMP_IGN', T = 0, F = 1/ &MATL ID = 'MOISTURE' &MATL ID='PINE_NEEDLES', &MATL ID = 'CHAR', &MATL ID = 'ASH', &SURF ID = 'PINE_NEEDLE_BED', &PART ID = 'PINE_NEEDLE_BED_PART', &INIT ID = 'PINE_NEEDLE_BED', &SURF ID = 'ASBESTOS_SHEET', &PART ID = 'ASBES', &INIT ID = 'ASBESTOS_SHEET', &SURF ID = 'FIRE_CLAY', &PART ID = 'FC', &INIT ID = 'FIRE_CLAY_F', &OBST XB = 0.1,0.1,0.0,0.08,0.012,0.032, COLOR = 'GREEN', SURF_ID = 'PINE_NEEDLE_BED'/ &OBST XB = 0.0,0.0,0.0,0.08,0.0,0.012, COLOR = 'YELLOW', SURF_ID = 'ASBESTOS_SHEET'/ &OBST XB = 0.1,0.1,0.08,0.09,0.0,0.032, COLOR = 'ORANGE', SURF_ID = 'FIRE_CLAY'/ &OBST XB = 0.094,0.094,0.0,0.08,0.012,0.024, COLOR = 'BLUE', SURF_ID = 'IGNITER'/ &REAC ID = 'CO_COMBUSTION', &DEVC XB = 0.0,0.70,0.0,0.17,0.0,0.30, QUANTITY='TEMPERATURE', STATISTICS='MEAN', ID='TEMP' / &DEVC XB = 0.0,0.70,0.0,0.17,0.0,0.30, QUANTITY='MASS FRACTION', SPATIAL_STATISTIC='MEAN', SPEC_ID='CARBON MONOXIDE', ID='CO',TIME_AVERAGED=.FALSE. / &TAIL / |
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If reducing pressure decreased the density, then what might cause an increase in density? Do you see high pressures developing anywhere in the domain? Did you look at the hrr file data and check zone pressures? |
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Hello, I have a lumped fuel that defined as C0.77 H0.96 O0.79. I am trying to use the Default Hydrocarbon Combustion Chemistry section 5.1.2 reference guide to calculate the stoichiometric coefficients, however, I can not define the yield of soot and CO. Any suggestion on how I should proceed would be highly appreciated.
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All reactions