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152-52662339Paper141-49759319Ceanothus88-53474311Oak
164-52861346Manzanita
Range (+/- 3*σ)
Standard Deviation
(σ)Average Ignition Temperature (ºC)
Ignition Temperature Statistics
The Experimental Design
• Apparatus designed to closely resemble forest fire flame front
• Modes of heat transfer
•Radiation: 6000W, 10”-square quartz heating panel (center)
•Convection: Flat-falme burner (FFB) (lower left)
• Fuel sample attached to a cantilever-type mass balance (top right)
Infrared Images
• Optimal sample placement determined with IR camera (FLIR)
• Sharp interface between the post-flame gases and surrounding air
• Sample height of 2” is well within the hot zone of the post-flame gases
Vertically Oriented Manzanita Sample
• Shape and orientation effects studied with video monitoring
• Samples cut in square and rounded shapes
• Horizontally oriented square-shaped samples ignite first at corners
• Horizontally oriented round-shaped samples ignite along the entire edge
• Vertically oriented samples ignite at edge closest to the flame
• Thermocouple placed at ignition location1000
800
600
400
200
0
Surf
ace T
em
pera
ture
(o C
)
403020100
Time (s)
0.57 mm 0.59 mm 0.62 mm 0.70 mm 0.72 mm 0.74 mm 0.78 mm
Temperature Profiles of Manzanita with Varying Thickness
• Thicker manzanita samples have slower heat-up times
• We want to develop a correlation to describe these and other effects
J. D. Engstrom, J. K. Butler, T. H. Fletcher, L. L. Baxter
Department of Chemical Engineering, Brigham Young University
and
D. R. Weise
USDA Forest Service, Pacific Southwest Research Station, Forest Fire LaboratoryThis project is sponsored by the USDA/USDI National Fire Plan administered through a Research Joint Venture Agreement No. 01-CR-11272166-168 with the Forest Fire Laboratory, Pacific Southwest Research Station, Riverside, CA.
Ignition Temperature Histograms
• Ignition temperature determined for live samples
• Ignition temperature defined when a flame is first visible
• Distributions of ignition temperatures measured (see figure above)
C. Ceanothus
0 01
4
0
3
10 0
0
2
4
6
Temperature (ºC)
Freq
uenc
y
A. Manzanita
0 0 0
54 4
3
10
0
2
4
6
Temperature (ºC)
Freq
uenc
y
B. Oak
01
3 3
54
01
00
2
4
6
Temperature (ºC)
Freq
uenc
y
D. Paper
0 01
2
6
4
01
00
2
4
6
Temperature (ºC)
Freq
uenc
y
Time to Ignition Histograms
• Ignition times determined for each samples
• Ignition time defined as time for sample to ignite
• Paper demonstrates experimental repeatability
A. Manzanita
02 1
6
13
1
4
0
5
10
Time (s)
Freq
uenc
y
B. Oak
36
1 2 1 0 02
0
5
10
Time (s)
Freq
uenc
y
D. Paper
3
10
20 0 0 0 0
0
5
10
Time (s)
Freq
uenc
y
C. Ceanothus
0 1 2 1 0 0 0
4
0
5
10
Time (s)
Freq
uenc
y
Gas Temperature Profiles
• CH4, H2, N2, and air fed into FFB
• Post-flame conditions ~ 10 mol% O2
• 127 m diameter type K thermocouple 2” above the FFB
• Demonstrates great repeatability
1200
1000
800
600
400
200
0
Ga
s T
em
pe
ratu
re (
oC
)
14121086420
Time (s)
Average Temperature 987 ºC
Standard Deviation 11.9 ºC
Purpose• To better understand the combustion behavior of live fuels
• To add physics into forest fire modeling
Conclusion• Sample types are important in determining ignition temperature
• Heat and mass transfer effects play an important role in sample heat-up time
• Time to ignition significantly affected by size, shape and orientation
Future Work• Improve technique to determine accurate ignition temperature and time to ignition
• Incorporate knowledge of leaf burning into models of bush burning
• Develop heat transfer correlations to avoid excessive computational costs
Representative California Chaparral Samples
Manzanita (Arctostaphylos
densiflora)
•Scrub Oak (Quercus
berberidifolia)
•Hoaryleaf Ceanothus ( Ceanothus crassifolius)
Chamise