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.

Federal AviationAdministration 3Heat Release Rate: Cargo Fires

November 1, 2007

MIXED PLASTIC SMOKE GENERATION SOURCEMIXED PLASTIC SMOKE GENERATION SOURCE

100 mm

Flaming ModeIn Cargo

CompartmentSimulates Burning Luggage

Federal AviationAdministration 4Heat Release Rate: Cargo Fires

November 1, 2007

APPROACHAPPROACH

Use perfect mixing model to relate exhaust gas concentration to

combustion product release rate in (cargo) compartments.

Federal AviationAdministration 5Heat Release Rate: Cargo Fires

November 1, 2007

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.

Federal AviationAdministration 6Heat Release Rate: Cargo Fires

November 1, 2007

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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November 1, 2007

TEST CONFIGURATIONTEST CONFIGURATION

Federal AviationAdministration 8Heat Release Rate: Cargo Fires

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B707 CARGOB707 CARGOCOMPARTMENTCOMPARTMENT

ExhaustExhaustDuctDuct

PropaneBurner

Location

ThermocoupleThermocouple

Federal AviationAdministration 9Heat Release Rate: Cargo Fires

November 1, 2007

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:

Federal AviationAdministration 10Heat Release Rate: Cargo Fires

November 1, 2007

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

November 1, 2007

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

Federal AviationAdministration 16Heat Release Rate: Cargo Fires

November 1, 2007

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)

Federal AviationAdministration 21Heat Release Rate: Cargo Fires

November 1, 2007

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