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Federal AviationAdministration
Heat Release Rate in Cargo Fires
Presented to: The Fifth Triennial International Fire and Cabin Safety Research Conference
Atlantic City, NJ
Richard E. Lyon and David Blake
FAA William J. Hughes Technical Center
November 1, 2007
Federal AviationAdministration 2Heat Release Rate: Cargo Fires
November 1, 2007
OBJECTIVEOBJECTIVE
Measure release rate of combustion products from object(s) burning in a ventilated cargo compartment.
Use data as source term in CFD modeling of smoke movement in cargo compartment.
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MIXED PLASTIC SMOKE GENERATION SOURCEMIXED PLASTIC SMOKE GENERATION SOURCE
100 mm
Flaming ModeIn Cargo
CompartmentSimulates Burning Luggage
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November 1, 2007
APPROACHAPPROACH
Use perfect mixing model to relate exhaust gas concentration to
combustion product release rate in (cargo) compartments.
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EXPERIMENTALEXPERIMENTALGenerate known combustion product histories with a premixed propane-air burner.
Apply a perfect mixing model to exhaust gases drawn from cargo compartment.
Compare mixing model to:- oxygen consumption (heat release rate)
history.- temperature history.
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PROCEDUREPROCEDURE
• Position premixed propane-air burner at center of B707cargo compartment.
• Attach thermocouple to ceiling directly above burner.
• Measure exhaust gas flow rate (F) and [O2].
• Calculate HRR from F, Δ[O2] using spread-sheet mixingmodel.
• Test effects of forced circulation on results.
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TEST CONFIGURATIONTEST CONFIGURATION
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B707 CARGOB707 CARGOCOMPARTMENTCOMPARTMENT
ExhaustExhaustDuctDuct
PropaneBurner
Location
ThermocoupleThermocouple
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Fin Fout
[O2]in [O2]out
ρFin = ρFout = ρF
[O2]in - [O2]out = Δ[O2] = θ
Propane Burner
CargoCompartment
PERFECT MIXING MODELPERFECT MIXING MODEL
MASS BALANCE:
SPECIESBALANCE:
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HRR(t) = ρFE
τ =Compartment Volume (m3)
Flow Rate (m3/s)
MIXING MODEL SOLUTION FOR HRRMIXING MODEL SOLUTION FOR HRR
θ + τ d θd t
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TEST PARAMETERSTEST PARAMETERSCargo compartment volume = 26 m3
Exhaust flow rate, F = 0.018 m3/s
Heat of combustion of oxygen, E = 12.78 MJ/kg-O2 (propane)
Ambient temperature, T = 27 °C (81 °F)
Air Density (27 °C), ρ = 1.2 kg/m3
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FORCED CIRCULATION
-2
0
2
4
6
8
0 5 10 15 20
Hea
t Rel
ease
Rat
e (k
W)
HRRHRR(propane(propaneburner)burner)
Time (minutes)
Fan
No Fan
• Small improvement in fidelity
• But could spread flames
Federal AviationAdministration 13Heat Release Rate: Cargo Fires
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HRR STEP CHANGEHRR STEP CHANGE
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70 80
.003
.004
.005Propane Flow Rate
Oxy
gen
Con
cent
ratio
n(v
/v)
Ceiling Temperature
[O2] (v/v)
.185
.190
.195
.200
.205
.210
Time (minutes)
Temperature (°C
)m
3 /min
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HRR MODEL CALIBRATIONHRR MODEL CALIBRATION
0.185
0.190
0.195
0.200
0.205
0.210
0.215
0 10 20 30 40 50 60 70 80
Experimental Data
Best Fit of Model
Time (minutes)
Oxy
gen
Con
cent
ratio
n (v
/v)
Δ[O2] for Step Change HRR
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CALIBRATION RESULTSCALIBRATION RESULTS(Propane Burner Step Change HRR)(Propane Burner Step Change HRR)
Parameter
ρFE (kW)
τ (min)
Measured(Best Fit)Calculated
276 270 ± 10
24 28
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0
2
4
6
8
10
0 10 20 30 40 50 60 70 80
Hea
t Rel
ease
Rat
e, k
W
Time (minutes)
Model HRR (τ = 0)
Model HRR (τ = 28 min)HRR (Propane burner)
HRR STEP CHANGE HRR STEP CHANGE
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HRR SQUARE WAVEHRR SQUARE WAVE
-1
0
1
2
3
4
5
6
7
0 5 10 15 20
Hea
t Rel
ease
Rat
e, k
W
Time (minutes)
Model HRR(τ = 0)
Model HRR(τ = 28 min)
HRR (Propane burner)
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6 kW
4 kW
3 kW
2 kW
Propane Burner Flame Heights
MULTIMULTI--STEP HRR STEP HRR HISTORIESHISTORIES
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-1
0
1
2
3
4
5
6
7
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35 40
hrrun8
Time (minutes)
HR
R (k
W)
Temperature (°C
)HRR
(propaneburner)
Temperature
HRR(model)
MULTIMULTI--STEP HRR 1STEP HRR 1
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MULTIMULTI--STEP HRR 2STEP HRR 2
-1
0
1
2
3
4
5
6
7
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35 40
hrrun3H
RR
(kW
)
Time (minutes)
Temperature (°C
)
HRR (PropaneBurner)
Temperature
HRR (model)
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Temperature versus HRR for MultiTemperature versus HRR for Multi--Step Step HistoriesHistoriesTe
mpe
ratu
re (°
C)
Heat Release Rate (kW)
20
30
40
50
60
70
80
-1 0 1 2 3 4 5 6 7
HRR IncreasingHRR Decreasing
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DISCUSSIONDISCUSSIONMixing Model and Temperature Provide Comparable (R = 0.8) Resolution of Combustion Histories for Objects Burning in Compartments.
Advantage of Combustion Model is:• Measures Heat Release Rate• Easily Calibrated• Independent of Size and Position of
Burning Object(s) with good mixing.
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CONCLUSIONSCONCLUSIONS
Mixing Model Provides Reasonable Combustion Product Release Rates and Histories for Objects in Compartments When-
Burning Time ≤ τ ≈Compartment Volume
Exhaust Flow Rate