Upward Flame Spread of an Inclined Fuel Surface

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Experimental Study of Upward Flame

Spread of an Inclined Fuel Surface

Michael J. GollnerUniversity of Maryland, College Park

Xinyan Huang, Jeanette Cobian and Forman A. WilliamsUniversity of California, San Diego

Ali S. RangwalaWorcester Polytechnic Institute

August 3, 2012 134th International Symposium on Combustion Warsaw, Poland


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Motivation

Maxima of both the flame-spread rate and mass-loss rate are

used to determine the fire hazards of materials

These quantities are both dependent on orientation

Flame spread is still not well understood for:

Forest fires (e.g. inclined slopes)

Warehouse fires

Undersides of burning roofs

August 3, 2012 2Experimental Study of Upward Flame Spread of an Inclined Fuel Surface


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3

fy

~ nt x

x

y

g

px

fx

pV

pq

( , )f tq x

1. Flame-Spread Rate =f()

2. Mass-Loss Rate =f()

f cm H Q

Excess

Pyrolyzate

Fire spread occurs because of

transfer of thermal energy

from flames to virgin fuel

Fire spread



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Experimental setup



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Effects of orientation

5

*Video is shown at 5 times actual speed



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Spread Velocity

-60 -45 -30 0 30 45 600

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Angle of Inclination,

SpreadRate,

Vp(cm/s)

Vp

(This study, w=10cm)

Pizzo (model)

Pizzo (exp, w=20cm)

Drydale and Macmillian (w=6cm)

Xie and DesJardin (model)

1. Y. Pizzo, J.L. Consalvi, B. Porterie, Comb. Flame. 156 (2009) 1856-1859.

2. D. Drysdale, A. Macmillan. Fire Safety J. 18, no. 3 (1992): 245-254.

3. W. Xie, P. Desjardin, Comb. Flame. 156 (2009) 522-530.

Underside measurements

(-60 to 0) have not been

reported before

The peak velocity appearsbetween 0 and -30



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Mass-loss Rate per unit Area

1. H. Ohtani, K. Ohta, Y. Uehara, Fire Mat. 18 (1991) 323-193.

2. de Ris, J, L. Orloff. Proc. Comb. Inst. 15 (1975) 175-182.

Steady rates averaged 800-1000

seconds after uniform ignition

Spreading rates measured when

xp reaches top of sample

Steady rates from smaller

PMMA samples are parabolic

Steady rates from larger gas

burner is qualitatively similar



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Inclined Flame Spread & Burning

-60 -45 -30 0 30 45 600

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Vp

(This study, w=10cm)

Pizzo (model)

Pizzo (exp, w=20cm)


Xie and DesJardin (model)

1. Y. Pizzo, J.L. Consalvi, B. Porterie, Comb. Flame. 156 (2009) 1856-1859.

2. D. Drysdale, A. Macmillan. Fire Safety J. 18, no. 3 (1992): 245-254.

3. W. Xie, P. Desjardin, Comb. Flame. 156 (2009) 522-530.

4. H. Ohtani, K. Ohta, Y. Uehara, Fire Mat. 18 (1991) 323-193.

5. de Ris, J, L. Orloff. Proc. Comb. Inst. 15 (1975) 175-182.

l li i

Vp(This Study, w=10cm)

Pizzo (Model)

Pizzo (Exp, w=20cm)


Xie and DesJardin (Model)

Flame Spread Steady Burning

-60 -45 -30 0 30 45 602

3

4

5

6

7

8

9

10

Gas Burner, 65 cm [5]

PMMA, Steady Burning

PMMA, Spreading

Angle of Inclination, Angle of Inclination,

SpreadR

ate,

Vp

(cm/s)

Mass-lo

ssRate(g/m2s)



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Radiant-Flux Estimates

Total Heat Flux (estimated from

mass-loss rates)

Maximum heat flux in

combusting plume

Estimated radiant contribution

(from heat flux gauges)


p rr pq q m H

4 26.1 kW/mrr p

q T


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September 1, 2014 Slide name - conference - location 10

Radiant-Flux Estimates



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Flame-Standoff Distance



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Flame-Standoff Distance



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Flame Shape



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Width Effects



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Heat-Flux Profiles

1.2 1.4 1.6 1.8 2 2.2

0.25

0.5

1

2

5

10

15

-60o

-45o

-30o

0o

30o

45o

60o

/ px x

q

( ) )( / nf pq x A x x

Power-law fit:



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Conclusions

Flame-spread rates were found to be greatest in

near-vertical orientations while burning rates are

maximized in near-horizontal orientations.

Qualitative trends, including the spread-rate

maximum at angles slightly less than vertical, are

general and should also apply in strictly 2D

configurations in the size range studied or larger.

Further study of the spread-rate maximum at anglesslightly less than vertical is continuing.



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Acknowledgements

Alexander Marcacci, Ulrich Neimann and Mario

Zuniga for their contributions to laboratory

experiments

John de Ris, Jose Torero, Adam Cowlard and Yuji

Nakamura for valuable discussions

Support from the Society of Fire Protection Engineers


Supported by:

Society of Fire Protection Engineers

Educational and Scientific Foundation


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18

Side-view during flame spread.


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Constant Heat Flux in Models

Tsai, K. (2009). Width effect on upward flame spread. Fire Safety Journal, 44(7), 962-967.



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Measurement of Heat Flux

Combined heat flux from calorimeter

(accounting for losses)

rq

Thin-Skin Calorimeter

iq

cq,i c r sto c st q q q q q

stoq

,c stq

American Society of Testing and Materials, Standard ASTM E 459-97



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Heat Flux in Flame-Spread Models

1. Sibulkin and Kim, Comb. Sci. Tech. vol. 17, 1977

One of few models with q(x) [1]q = constant

constantq



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Heat Flux in Combusting Plume

X-location (cm)

Heat FluxW/m2

-90o

5 10 15

30

40

50

-60o

5 10 15

30

40

50

-45o

5 10 15

30

40

50

-30o

5 10 15

30

40

50

0o

5 10 15

30

40

50

30o

5 10 15

30

40

50

45o

5 10 15

30

40

50

60o

5 10 15

30

40

50 90o

5 10 15

30

40

50

500

1000

1500

2000

Y-location(c

m)



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Sensor Locations

September 1, 2014 Slide name - conference - location 24


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TC Readings 0



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TC Readings 60



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TC Readings -60



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Upward Flame Spread of an Inclined Fuel Surface