Analysis of some formulations to measure the fireline intensity Università di Corsica

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1 Analysis of some formulations to measure the fireline intensity Paul-Antoine Santoni Université de Corse UMR SPE UMR CNRS SPE ème journées du GDR feux, LNE-Paris 20-21/01/2011

2 Contents The frontal fire intensity concept FI by Oxygen Consumption calorimetry Results and test of some formulations What can we do at field scale? Conclusion

3 The frontal fire intensity concept Definition of Fireline Intensity (FI) Charing zone Discontinuous flaming zone Active flaming zone Wind FI represents the heat release per unit time per unit length of the active flaming zone of the fire front (kw/m) 1

4 The frontal fire intensity concept Comments on FI FI is used To evaluate the effects of fuel treatment on fire behaviour To establish limits for prescribed burning To assess fire impacts on ecosystems To support fire suppression activities (indicator) To calculate fire Risk Index (pre-suppression activities). Limitation of FI Result obtained for a specific fuel type cannot be generalised For fire impact other quantities must be used Remarks FI is poorly used to test fire spread models FI is difficult to measure accurately Few attempts to measure FI : billy calorimeter and wind tunnel 2

5 The frontal fire intensity concept Methods to measure the FI Byram s formulation for a quasi-steady linear fire front I B = Hwr H L = H c, net M p M H (kj/kg) heat yield w (kg/m 2 ) weight of fuel consumed r (m/s) ROS Comment : the fuel loadings used are based on total consumption rather than flaming combustion only Burning rate approach I S Remark : ( m& H ) W = F F I S = I B for steady state fires m& W (m) (kg/s) rate of mass loss width of the fire front 3

6 Contents The frontal fire intensity concept FI by Oxygen Consumption calorimetry Results and test of some formulations What can we do at field scale? Conclusion

7 FI by oxygen consumption calorimetry Large scale heat release calorimeter Experimental device Exhaust gases Measuring section Filtering and condensing system Hood Plenum Baffles O2 Analizer Sample pump CO/CO2 Analizers q & = E ( s n& ) O n& 2 O W 2 O2 Control volume 3 m Combustion bench 2 m Load cell 4

8 FI by oxygen consumption calorimetry Full scale calorimeter vs bench scale calorimeter Why do we use a full scale calorimeter? Studies on combustion dynamics of wildland fuels with bench scale calorimeter are recent No mathematical model that uses bench scale data as input to predict the heat release in large scale test Advantages Bench scale allows only studying compact fuels: 3 cm high up to now Shrub type fuel can be studied Effect of holders on the combustion dynamics is avoided Drawbacks Higher uncertainty at full scale Lower repeatability at full scale 5

9 FI by oxygen consumption calorimetry Basic equations q & = E ( s n& ) O n& 2 O W 2 O2 Heat release rate q& ( a a E,, V, X, X,... ) α = q& & α, s O2 O2 V& s = A k k t p P T S Flow rate in the duct 6

10 FI by oxygen consumption calorimetry Uncertainty and calibration q & = E ( s n& ) O n& 2 O W 2 O2 Heat release rate q& ( a a E,, V, X, X,... ) α = q& & α, s O2 O2 V& s = A k k t p P T S Flow rate in the duct U q& = k N i = 1 ( u q& x ) x i i 2 7

11 FI by oxygen consumption calorimetry Uncertainty and calibration Combustion (Fuel dependent) E = 13.1 MJ/kg of O 2 α = n α s n air Energy constant Expansion factor Probe factor Oxygen analyzer Specific value Specific value n moles of air required for complete combustion and for all oxygen consumed is replaced by moles of products n air Flow rate & Oxygen (Device dependent) k p a O X 2 Specific calibration Specific calibration kt Duct Burner calibration 8

12 FI by oxygen consumption calorimetry Uncertainty and calibration 120 HRR (kw) Ratio 1, ,8 60 0,6 40 0,4 20 0,2 0 Time (s) HRR from LSHR HRR of propane burner Ratio of smoothed HRR 9

13 Contents The frontal fire intensity concept FI by Oxygen Consumption calorimetry Results and test of some formulations What can we do at field scale? Conclusion

Results & test of some formulations FI for quasi-steady fires and

O 2 xco x y z 2 2 2 + y 2 H O E fuel st = H n fuel c, net O 2 W W O 2

66 5.74 2.77 1.159 14.39 Genista salzmannii GS 4.26 6.72 2.32 1.124 13.

14 Results & test of some formulations FI for quasi-steady fires and unsteady fires Energy constant and expansion factor C H O + x + y 4 z O 2 xco x y z y 2 H O E fuel st = H n fuel c, net O 2 W W O 2 fuel Species x (mol) y (mol) z (mol) α E st (MJ/kg) Avena fatua AF Genista salzmannii GS Pinus pinaster PP Hugget s value

15 Results & test of some formulations FI for quasi-steady fires and unsteady fires 40 FI for Genista salzmannii 0.9 kg/m² Fireline intensiy (kw/m) E = Calculated for GS E = 13.1 Huggett's constant Difference of HRR Time (s)

16 Results & test of some formulations FI for quasi-steady fires and unsteady fires FI for Avena Fatua 0.6 kg/m² Fireline intensity (kw/m) E = Calculated for AF E = 13.1 Huggett's constant Difference of HRR Time (s)

17 Results & test of some formulations Test of Byram s formulation FI for Pinus pinaster 0.6 kg/m² 60 Fireline intensity 50 (kw/m) HRR by OC calorimetry Mass loss Byram's intensity Mass (g) Quasi-steady state Time (s)

18 Results & test of some formulations Test of Byram s formulation Byram s formulation versus OC calorimetry Fireline Intensity by OCC (kw/m) AF 0.6 kg/m 2 GS 0.6 kg/m 2 PP 0.6 kg/m PP 1.2 kg/m 2 I I y = 0,843x R² OC = 0,949 B 0.84 WHY? 25 0 Fireline Intensity by Byram (kw/m)

19 Results & test of some formulations Burning rate and combustion efficiency Burning rate approach during the quasi-steady stage 60 Fireline m& F H intensity I S = (kw/m) W 50 I S 40 I S = T T 1 m& F H m H dt = F W 0 W m& F H W & AF (0.6 kg/m 2 ) HRR by OC calorimetry Mass loss Byram's intensity m X = H F = Hwr = I B XW T GS (0.6 kg/m 2 ) PP (0.6 kg/m 2 ) Mass (g) 1000 = Burning rate approach for quasi-steady stage is an alternative method to measure Byram s intensity PP (1.2kg/m 2 ) I OC I B 10 I0 OC I S Quasi-steady state Time (s)

20 Results & test of some formulations Burning rate and combustion efficiency Combustion efficiency χ = H eff H AF (0.6 kg/m 2 ) GS (0.6 kg/m 2 ) PP (0.6 kg/m 2 ) PP (1.2kg/m 2 ) χ I OC I S

21 Results & test of some formulations Burning rate and combustion efficiency Modification of Byram s formulation & burning rate approach FI for Pinus pinaster 1.2 kg/m² I B = χ Hwr Fireline intensity (kw/m) HRR by OC calorimetry HRR by by burning rate χ & Byram's intensity χhwr ( H ) W m F I S = ( χ m& H ) W F Time (s)

22 Results & test of some formulations Burning rate and combustion efficiency Modification of Byram s formulation & burning rate approach FI for Avena Fatua 0.6 kg/m² I B = χ Hwr Fireline intensity (kw/m) HRR by OC calorimetry HRR by burning rate ( χ m& F H ) W I S = ( χ m& H ) W F Byram's intensity χhwr Time (s)

23 Contents The frontal fire intensity concept FI by Oxygen Consumption calorimetry Results and test of some formulations What can we do at field scale? Conclusion

24 What can we do at field scale? Modified Byram s approach Fireline intensity can be measured for prescribed burning 19

25 What can we do at field scale? Modified Byram s approach Fireline intensity can be measured for prescribed burning I B = k = χ h w R k k I B 4330 kw/m 20

26 What can we do at field scale? Modified Byram s approach Fireline intensity can be measured for prescribed burning Can fireline intensity be estimated for actual fires? Do we know the vegetation? Do we know the ROS? Idea : to use a flame descriptor (flame length) to assess the fireline intensity 21

27 What can we do at field scale? Flame length formulation at laboratory scale FI 180 L

28 What can we do at field scale? Flame length formulation at field scale L y 5 à 6 m FI = H GS.w GS.R.χ GS = 4328 kw/m I OUR1 = kw/m I OUR2 = kw/m I N1 I N2 = kw/m = kw/m 23

29 What can we do at field scale? Flame length formulation at field scale L y 3 à 3,5 m FI = H GS.w GS.R.χ GS = 2080 kw/m I OUR1 = kw/m I OUR2 = kw/m I N1 I N2 = kw/m = kw/m 24

30 Conclusion Steady and unsteady FI were measured by OC calorimetry Byram s formulation overestimates FI (15-20%) Burning rate formulation overestimates FI (10%) Combustion efficiency χ 0.9 for the three fuels Byram s formulation with χ is relevant for FI of steady fires Burning rate formulation with χ is relevant for FI of unsteady fires Flame length correlation to be further validated at field scale 25

31 Contributeurs Calorimétrie Barboni Toussaint Morandini Frédéric Mesures de terrain Cancellieri Dominique Cancellieri Valérie Leoni Eric Marcelli Thierry Manenti Ange Perez Yolanda Rossi Jean-Louis Rossi Lucile

32 Thank you for your attention Acknowledgement: This work was carried out in the scope of project PROTERINA-C supported by the EU under the Thematic 3 of the Operational Program Italia/France Maritime , contract: G25I UMR CNRS SPE 6134

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