Beginners Guide to TikTok for Search - Rachel Pearson - We are Tilt __ Bright...
Gollner PhD Dissertation Defense: "Studies on Upward Flame Spread"
1. Studies on Upward Flame Spread
PhD Defense of
Michael J. Gollner
University of California, San Diego
Professor Forman A. Williams, Chair
July 24, 2012 1
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 1
2. Motivation
Flame Spread Theory
1. Corrugated Cardboard Flame Spread
2. Inclined Flame Spread
3. Discrete Fuel Flame Spread
Conclusions
July 24, 2012
Acknowledgements 2
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 2
3. Why Study Fire?
NFPA, 2009
July 24, 2012 3
$362 billion, or 2.5 % of the US GDP
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 3
4. Motivation
Industrial Fires The Built Environment
July 24, 2012 4
Wildfires Cable Trays
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 4
5. Review:
UPWARD FLAME SPREAD
THEORY
July 24, 2012 5
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 5
6. Upward Flame Spread
Thermal Boundary Layer
g
Excess
SOLID FUEL
1. Thermal Boundary Layer Pyrolyzate
2. Heat Flux to the Fuel yf xf Flame Height
3. Buoyancy
q f ( x, t )
Vp
y xp Pyrolysis Height
July 24, 2012 qp
6
x
m f H c ~ HRR
Diffusion Flame
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 6
7. Flame Spread Models
q Constant
q Constant
July 24, 2012 One of few models with q(x) [1]
7
1. Sibulkin and Kim, Comb. Sci. Tech. vol. 17, 1977
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 7
8. Results of Upward Spread Theories
2
Annamalai & Sibulkin: x f ~ A1 ( B1 t ) (Laminar)
t
Saito, Quintiere, Williams: x f ~ A2e (Turbulent)
Sibulkin & Kim: x f ~ A3t 2 (Laminar)
x f ~ B3e t (Turbulent)
Where A, B, and α are constants
NOTE: All results for non-charring fuels.
July 24, 2012 8
1. Annamalai, K. and Sibulkin, M., Combust. Sci. Tech., 1979, vol. 19, pp. 167-183.
2. Saito, J.G. Quintiere, and F.A. Williams, Fire Safety Science, vol.1, 1985, pp. 75-86.
3. Sibulkin and Kim, Comb. Sci. Tech. vol. 17, 1977
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 8
9. Industrial Fires
Part I:
UPWARD FLAME SPREAD OVER
CORRUGATED CARDBOARD
July 24, 2012 9
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Spread
PhD Effects on Burning Upward and Flame Spread 9
10. Cardboard Spread Experiments
• Uniform ignition at
base by Heptane wick
• Insulated board above
sample
• Sample filled with
plastics, but this study only addresses the
behavior before these plastics ignite
July 24, 2012 10
Gollner, M.J., Overholt, K., et al., Fire Saf. J., 46(6), 2011, pp. 305-316.
Overholt, K., Gollner, M.J, et al., Fire Saf. J., 46(6), 2011, pp 317-329.
Gollner, M.J., Williams, F.A., and Rangwala, A.S. Combust. Flame, 158(7), 2011.
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Spread
PhD Effects on Burning Upward and Flame Spread 10
11. Flame Height Observations
x f ~ t 3/2 fits x f ,max
50
Observed Trend
40
Why does the pyrolysis front and flame height x f ,avg
Height (cm)
30
grow SLOWER than what current theories
would predict? x p ,avg
20
10
0
0
July 24, 2012 10 20 30 40 50
11
Time from Ignition (s)
Gollner, M.J., Williams, F.A., and Rangwala, A.S. Combust. Flame, 158(7), 2011.
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Spread
PhD Effects on Burning Upward and Flame Spread 11
21. Boundary-Layer Extension
Traditional Boundary Hypothesized Modified
Layer Boundary layer
y~x 1/4 y ~ x1/3
q ~ 1/ x1/4
q ~ 1/ x1/3
x
y
Curled
July 24, 2012 21
Cardboard
May 15, 2012 Buoyancy Effects on Burning Behavior and Flame Spread 21
22. How Would this Affect xp & xf?
Temperature of a thick fuel with time-dependent heat flux [1,2]:
t
1
q
T T0 dt
k c 0 t t
Assuming material pyrolyses at fixed Tp, substitute τ=t/t’, integral becomes a
constant dependent on material properties:
1
q t
I d
0 1
Assuming a new q(x) power-law variation based on boundary layer extension:
q C / x1/3
The time, t of arrival of pyrolysis front will obey:
xp At 3/2
Assuming
x f ~ m ~ x p , where m is the burning rate per unit width:
xf Bt 3/2
July 24, 2012 recover what was observed in experiments!
You 22
1. H.E. Mitler, Proc. Combust. Inst., 23 (1991), pp. 1715–1721
2. Conduction of heat in solids, Carslaw, H. S.; Jaeger, J. C. Oxford: Clarendon Press, 1959, 2nd ed.
May 15, 2012 Buoyancy Effects on Burning Behavior and Flame Spread 22
23. Corrugated Cardboard Applications
Early-stage ignition and spread
Rack storage test, UL Laboratories
HVLS Fan, NFPA FPRF Study
Photo Taken while at Schirmer Eng.
July 24, 2012 23
Tupperware Warehouse Fire (NFPA)
May 15, 2012 Buoyancy Effects on Burning Behavior and Flame Spread 23
24. The Built Environment Wildfires
Part II:
INCLINED FLAME SPREAD
July 24, 2012 24
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 24
25. Burning & Spread over a Solid Fuel
g
y
July 24, 2012 25
x
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 25
26. Burning & Spread over a Solid Fuel
• Modify Heat Flux Profiles
g
• Will Modify V p and m f
q ( x, t , )
q f ( x, t ) f ~ xn
yf
qp
Vp
mf
HcQ xf
y'
July 24, 2012 26
x' xp
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 26
27. Experimental setup
July 24, 2012 27
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 27
28. Effects of orientation
July 24, 2012 28
*Video is shown at 5 times actual speed
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 28
29. 0.0
Spread Velocity
Spread Rate (cm/s)
0.0
0.0
0.09
0.0
0.08
Underside measurements
(-60 to 0 ) have not been 0.0
0.07 reported before
0.0
Spread Rate, Vp (cm/s)
0.06
0.05
The peak velocity appears
0.04
between 0 and -30
0.03
Vp (This study, w=10cm)
0.02 Pizzo (model)
Pizzo (exp, w=20cm)
0.01 Drydale and Macmillian (w=6cm)
Xie and DesJardin (model)
0
-60 -45 -30 0 30 45 60
Angle of Inclination,
July 24, 2012 29
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.
May 21, 2012 PhD Defense: Studies on Upward Flame Spread 29
30. Mass-loss Rate per unit Area
Steady rates from larger gas
burner is qualitatively similar
Steady rates from smaller
PMMA samples are parabolic
Steady rates averaged 800-1000
seconds after uniform ignition
Spreading rates measured when
xp reaches top of sample
July 24, 2012 30
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.
Burning of Inclined FuelStudies on Upward Flame Spread
May 21, 2012
July 24, 2012 PhD Defense: Surfaces WSS/CI Spring Meeting ASU 30
31. Radiant-Flux Estimates
July 24, 2012 31
Slide name - conference -
July 24, 2012 31
May 24, 2012
July 21, 2012 PhD Defense: Studies on Upward Flame Spread
location
Burning of Inclined Fuel Surfaces WSS/CI Spring Meeting ASU 31
31
32. Radiant-Flux Estimates
Total Heat Flux (estimated from
mass-loss rates)
Maximum heat flux in
combusting plume
Estimated radiant contribution
(from heat flux gauges)
qJuly 24,2012 m H p
p q rr 32
q rr Tp 4 6.1 kW/m2
Burning of Inclined FuelStudies on Upward Flame Spread
May 21, 2012
July 24, 2012 PhD Defense: Surfaces WSS/CI Spring Meeting ASU 32
33. Flame Standoff Distance
July 24, 2012 33
May 21, 2012
May 15, 2012 Buoyancy Effects Studies on Upward Flame Flame Spread
PhD Defense: on Burning Behavior and Spread 33
33
34. Flame-Standoff Distance
July 24, 2012 34
Burning of Inclined FuelStudies on Upward Flame Spread
May 21, 2012
July 24, 2012 PhD Defense: Surfaces WSS/CI Spring Meeting ASU 34
35. Flame Shape
July 24, 2012 35
Burning of Inclined FuelStudies on Upward Flame Spread
May 21, 2012
July 24, 2012 PhD Defense: Surfaces WSS/CI Spring Meeting ASU 35
36. Width Effects
July 24, 2012 36
Burning of Inclined FuelStudies on Upward Flame Spread
May 21, 2012
July 24, 2012 PhD Defense: Surfaces WSS/CI Spring Meeting ASU 36
37. Heat-Flux Profiles
15
10
5
-60o
2
-45o
q 1 -30o
0o
0.5
30o
0.25 45o
60o
1.2 1.4 1.6 1.8 2 2.2
x / xp
July 24, 2012 37
n
Power-law fit:
q f ( x) A( x / x p )
Burning of Inclined FuelStudies on Upward Flame Spread
May 21, 2012
July 24, 2012 PhD Defense: Surfaces WSS/CI Spring Meeting ASU 37
38. Inclined Flame Spread & Burning
Flame Spread Steady Burning
0.09 10
0.08 9
Gas Burner, 65 cm [5]
2
0.07
8
Spread Rate, Vp Vp (cm/s)
0.06
Mass-loss Rate (g/m s)
Spread Rate, (cm/s)
7
0.05
0.09
6
0.04
0.08 PMMA, Steady Burning
5
0.03
0.07
Vp (This study, w=10cm)
4
0.02 Pizzo (model)
0.06
PMMA, Spreading
Spread Rate (cm/s)
Pizzo (exp, w=20cm)
0.01 Drydale and Macmillian (w=6cm) 3
0.05
Xie and DesJardin (model)
0
0.04
2
-60 -45 -30 0 30 45 60 -60 -45 -30 0 30 45 60
Angle of Inclination, θ
Angle of Inclination, of
Angle Inclination, θ
0.03
Vp (This Study, w=10cm)
0.02
Pizzo (Model)
Pizzo (Exp, w=20cm)
0.01
Drydale and Macmillian (w=6cm)
Xie and DesJardin (Model)
July -80 2012-40
0 24, -60 -20 0 20 40 60 80 38
Angle of Inclination,
1. Y. Pizzo, J.L. Consalvi, B. Porterie, Comb. Flame. 156 (2009) 1856-1859. 4. H. Ohtani, K. Ohta, Y. Uehara, Fire Mat. 18 (1991) 323-193.
2. D. Drysdale, A. Macmillan. Fire Safety J. 18, no. 3 (1992): 245-254. 5. de Ris, J, L. Orloff. Proc. Comb. Inst. 15 (1975) 175-182.
3. W. Xie, P. Desjardin, Comb. Flame. 156 (2009) 522-530.
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Spread
PhD Effects on Burning Upward and Flame Spread 38
39. Inclined Flame Spread Applications
Large, inclined atria ceiling
ASTM E108 (Roof Fire Test, Top)
Future KEPKO Headquarters
(Korea)
July 24, 2012 39
Flame spread on slopes ASTM E108 (Roof Fire Test, Bottom)
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Spread
PhD Effects on Burning Upward and Flame Spread 39
40. Cable Trays Industrial Fires Wildfires
Part III:
DISCRETE FUEL FLAME SPREAD
July 24, 2012 40
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 40
40
41. Discrete Fuel Spread & Burning
July 24, 2012 41
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 41
41
42. Matchstick Spread & Burning
Pyrolysis Spread Burnout Time
xp ~ t1.6 to t1.7
x p ~ t 3/2
S
xp ~ t
xp tb
(cm)
S 0
t (s) x (cm)
u ~ gx ~ Re ~ Nu
July 24, 2012 42
Gollner, M.J., Xie, Y., Lee, M., Nakamura, Y., and Rangwala,
A.S., 2012, In Press, Comb. Sci. Tech.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 42
42
43. Calculating Ignition Time for Spread
• Flame spread is a sequence of ignitions
• Matchsticks assumed to be thermally thin1, so
the pyrolysis or ignition time can be reduced
to tp s c p , s d (Tp
T )/q
• Simple heat transfer correlations can be used
to determine q for two limiting cases:
S 0 S 0
July 24, 2012 43
1Matchstick thickness
less than thermal thickness, lth ~ ks (Tig T ) / q
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 43
43
44. Heat Transfer, S = 0
S 0
• Primarily convection-driven heat transfer from
burning matchsticks below to wall above2
• Correlation for flow over a wall can be used1
Nu x 059(Grx Pr)1/4
• Where Gr ( g (T T ) x ) / is the Grashof number,
x s
3 3
Pr / t is the Prandtl number and Nu d hd / k is
g
the Nusselt number
July 24, 2012 44
1.F. P. Incropera and D. P. DeWitt. Introduction to Heat Transfer, Fifth Edition. John Wiley & Sons, New York, 2002.
2. G. F. Carrier, F. E. Fendell, and M. F. Wolf., Combust. Sci. Technol., 75(1-3):3151, 1991.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 44
44
45. Heat Transfer, S > 0
S 0
• Primarily convection-driven heat transfer from
burning matchstick below to stick above
• Correlation for flow over a cylinder can be used [1]
Nu d 0.344Re0.56
d
• Assuming the buoyant velocity follows ug gx , the
Reynolds number, Re u d/ can be calculated d g g g
• The average rate of heat transfer, q can be calculated
from the Nusselt number for each matchstick
July 24, 2012 45
q h (Ts T )
1. F. A. Albini and E. D. Reinhardt. Int. J. Wildland Fire, 5(2):8191, 1995.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 45
45
46. Matchstick Spread & Burning
Pyrolysis Spread Burnout Time
xp ~ t1.6 to t1.7
x p ~ t 3/2
S 0
xp ~ t
xp tb
(cm)
S
t (s) x (cm)
u ~ gx ~ Re ~ Nu
• Predictions suggest the spread
process 24, 2012
July is dominated by convection 46
Gollner, M.J., Xie, Y., Lee, M., Nakamura, Y., and Rangwala,
A.S., 2012, In Press, Comb. Sci. Tech.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 46
46
47. Burnout Time Prediction
• We again analyze two limiting cases, S 0 and S
• For S 0 , heating from the flame to the solid occurs
as conduction from the flame to the fuel surface:
q kg (Tf Ts ) / y f
• If the fuel is thermally thin and yf is uniform along
the side of the fuel, a balanced equation of energy is
tb Tf Ts c (Ts T )d
s p ,s H pd s
kg dt
0 yf 2
• Integrating and solving for the burnout time
yf s d [c p ,s (Ts T ) Hp]
tb
2k g (T f Ts )
S 0
July 24, 2012 47 47
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 47
47
48. Burnout Time Prediction
• For S , we assume a match is nearly burning
free in the air
• Burning rate theory for a spherical fuel droplet
can be extended to a cylindrical geometry [1]
• Assuming a matchstick is nearly cylindrical with
initial radius ri d / 2 and unit length, the burning
rate becomes
d 2 drs
m ( s r )
s 2 rs s
m(rs ),
dt dt
Where rs is the radius of the cylinder at time t
July 24, 2012 48
1. C. K. Lee. Burning rate of fuel cylinders. Combust. Flame, 32:271276, 1978.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 48
48
49. Burnout Time Prediction
• The time necessary to deplete all fuel in the cylinder,
the burnout time is then
tb 2 rs s
tb dr .
0 (rs ) s
m
• Replacing m(r ) with the solution for the burning rate
s
k
over a cylinder fuel surface, c ln(1 B) ln(r / r ) , where
2
g
p, g
f s
1
B c p (T f Ts ) / H p and integrating the burnout time is
c
s p, g ln(rf / rs )ri 2
tb .
4k g ln(1 B)
• The standoff distance ratio is estimated from a
correlation:
0.75
ln(rf / rs ) 02(d / 2)
July 24, 2012 49
1. C. K. Lee. Burning rate of fuel cylinders. Combust. Flame, 32:271276, 1978.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 49
49
50. Matchstick Spread & Burning
Pyrolysis Spread Burnout Time
xp ~ t1.6 to t1.7
x p ~ t 3/2
S 0
xp ~ t
xp tb
(cm)
S
t (s) x (cm)
u ~ gx ~ Re ~ Nu Analytical Predictions
c ln(rf / rs )ri 2
• Predictions suggest the spread
s p, g
tb .
S 4k g ln(1 B)
process 24, 2012
July is dominated by convection 50 s d[c p,s (Ts
yf T ) Hp]
Gollner, M.J., Xie, Y., Lee, M., Nakamura, Y., and Rangwala,
S 0 tb
2k g (T f Ts )
A.S., 2012, In Press, Comb. Sci. Tech.
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 50
50
51. Discrete Fuel Spread Applications
Upward spread through cable trays/ wire arrays
July 24, 2012 51
Tranisition to crown fire behavior (especially important for controlled burns)
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 51
51
52. Conclusions
• Even non-charring fuels can modify the boundary layer
- Corrugated cardboard delaminates (not in current models)
• The heat flux within the B.L. is crucial to understanding
both the flame-spread rate and steady burning
• Discontinuous fuels can achieve spread rates faster than
continuous fuel beds
- Important for transition in wildfires & spread in cable trays
• Flame-spread rates were found to be greatest in near-
vertical orientations while burning rates are maximized in
near-horizontal orientations.
July 24, 2012 52
- Worst-case scenario important for small-scale flammability tests
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 52
52
53. Acknowledgements
• Jonathan Perricone, Garner Palenske and all my colleagues at
Schirmer Engineering for introducing me to this field
• UCSD Graduate Students: Xinyan Huang, Ulrich Niemann and
Ryan Ghemlich for their contributions to laboratory
experiments
• UCSD Undergraduate Students: Jeanette Cobian, Mario Zuniga
and Alexander Marcacci for their contributions to laboratory
experiments
• Worcester Polytechnic Institute Students and staff: Simon Xie,
Minkyu Lee, Randy Harris, Kris Overholt and Todd Hetrick
July 24, 2012 by:
Supported
53
Society of Fire Protection Engineers
Educational and Scientific Foundation
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 53
53
54. Acknowledgements
• John de Ris, Jose Torero, Adam Cowlard and Yuji
Nakamura for valuable discussions
• The faculty and staff of the UCSD MAE dept.
• Outstanding advisors: Professors Forman A. Williams
and Ali S. Rangwala
• The support of all my family and friends
July 24, 2012 by:
Supported
54
Society of Fire Protection Engineers
Educational and Scientific Foundation
May 15, 2012
May 15, 2012
21, 2012 BuoyancyDefense: Studies onBehavior Flame Flame Spread
Buoyancy Effects on BurningUpward and Flame Spread
PhD Effects on Burning Behavior and Spread 54
54
Fire is still dangerous. In 2010: 1,331,500 fire department calls 3,120 civilian deaths 17,720 civilian injuries 72 firefighter deathsLawyers can make any building legal, only engineers can make it safe. -Vincent Brannigan
My personal motivation began at Schirmer Engineering with industrial fires – Jonathan Perricone who is here today. Met in job fair, was curious, got me hooked on fire research
Coordinates and fuel. 2. theta – angle of orientation to gravity3. Ignition – flame and thermal boundary layer (Tp reached)4. Pyrolysis/flame length. Standoff distance, spread velocity, BL thickness5. Heat flux – to the pyrolsyis region. From flame to virgin fuel. Highlight thermal BL – studiedHighlight heat flux from flame to surface – being studiedInfluence of angle from horizontal – being studied.
Xp is where material reaches temperature, Tp
what happens when the fuel is inclined (and thus the buoyancy is modified)
What if we incline the fuel? Can modify the heat fluxes with gravity.
Coordinates and fuel. 2. theta – angle of orientation to gravity3. Ignition – flame and thermal boundary layer (Tp reached)4. Pyrolysis/flame length. Standoff distance, spread velocity, BL thickness5. Heat flux – to the pyrolsyis region. From flame to virgin fuel. Highlight thermal BL – studiedHighlight heat flux from flame to surface – being studiedInfluence of angle from horizontal – being studied.
Mass-loss rates per unit area. Steady rates here are averages, measured 800-1000s after uniform ignition of the entire sample. For spreading tests, measured mass-loss rates and pyrolyzing surface area increases with time, so result is given once the entire face is ignited, when xp reaches top. Steady rates are significantly higher than spreading rates because of deeper penetration of thermal wave into material at later times. Principal observation – both sets of data exhibit same dependence of MLR on angle, with rates continuously increasing from ceiling to vertical to pool configurations. This results is in contrast to data from Ohtani et al., obtained with the same fuel. They used appreciably smaller samples and agree qualitatively with liquid wick experiments of Blackshear and Kanury, which are what one would expect for convection-controlled burning, because the component of gravity parallel to the fuel surface is maximum in the vertical configuration. Also, since convection-controlled rates would increase with decreasing boundary-layer thicknesses, the observed higher average mass-loss rates per unit area for the smaller samples are expected for this mechanism; in fact, data in that paper point toward a decrease in the rate per unit area with increasing size. It thus appears in the present experiments, at least between vertical and pool configurations, the controlling mechanism is different from that of the smaller samples. Similar to de Ris and Orloff, they suggested that randiant transfer is important in the present experiments (their scale, 0.65m with sidewalls, ours, 10 cm)Could suggest greater propensity for radiant emissions from PMMA than from typical gaseous fuels.
Radiative heat flux varies from 10 to 70 percentQp = qrr + m delta HpQrr = sigma Tp^4 = 6.1 kw/m2Reasons for radiant flux increase with angle: - flux mainly from soot emissions, intensity increase with increased soot volumes and concentrations, and soot made by finite-rate processes in fuelrich zones, so longer fuel-rich residence times lead to more soot and greater emissions. Residence times are minimum with flames, largely blue, on underside and maximum rising above, in pool-burning configuration. In addition, view angle is greatest with pool-burning configuration. Thinner flames at negative angles, this is expected.
Power-law fits appear as straight lines (log-log)-60d to 0d, n=-230d, n=-545d, n=-660d, n=-7Large angles, radiation controlled and view factor between flame and fuel is decreased with increasing angle. Also contribution of convective cooling ahead of fuel surface, instead of convective heating, (go back to diagram)These decrease Vp with increasing theta, explaining our first flame-spread figure for positive angles. The same qualitative differences are expected for very wide samples, since necking and enahnced edge regression cause quantitative not qualititative differences. Fig. 1 is not likely to be different for infinite width. This difference may arise from the mean flow becoming more two-dimensional with increasing distance along the non-pyrolyzing surface; the outflow to the side affects the burning rate but has not yet influenced the heat flux ahead significantly at these angles. The reason for the slight increase of convective heat flux with decreasing angle near vertical is unclear but may be associated with the normal component of gravity pressing the flame closer to the fuel surface, a possibility that deserves further study.
The peak flame-spread rate occurs near -30°The peak mass-loss rate per unit area occurs near +90°In the present experiments, at least between vertical and pool configurations, the controlling mechanism is different from that of the smaller samples1de Ris and Orloff2 suggest radiant transfer is important in their experiments (though larger scales)Could suggest a greater propensity for radiant emissions from PMMA than from typical gaseous fuels.
UL 94 – upward and horizontal spread.
Extending work on boundary layers – what happens when the fuel is discontinuous?
Experimental design approached conditions encountered in practice.