fire star conclusive symposium: marseille march 18th 2005 1 physical sub-models to be included in...

Fire Star conclusive symposium: Marseille March 18th 2005 1

Physical sub-models to be included in the main model

In Physical Modelling the conservation equations

(mass, momentum, energy) are solved

Observations, experiments, and modelling

show that there is gas flow ...

... ahead of the flame near the fuel bed ...

... and inside the porous fuel bed

Bellemare, 2000

Obviously, there is also flow inside shrubs and inside foliage



Several sub-models are used to deal with a number of phenomena

The temperatures of fuel bed, shrubs, foliage, and of the gas

that flows inside them are not necessarely the same

heat transfer between the gas and these fuel matrixes occurs

This energy exchange plays an important role in the

decrease of fuel moisture content and in the fuel pyrolysis

The flow inside the fuel matrices is subjected to aerodynamic drag

sub-models for heat transfer and aerodynamic drag are,

therefore, necessary



There is no data on porous beds similar to forest fire fuel matrices

Data on packed beds from chemical engineering have been used

But ...... chemical packed beds are very different from

the forest fuel matrices

Objective :

- to measure the heat transfer coefficient h and pressure drop through matrices of forest fuels



Existing wind tunel(used for aerodynamic studies very good performance)

Section 1 : electric resistances (5 kW) to heat the flow

Section 2 : working section packed with pine needles

1000 x 160 x 240 mm (l x h x w)

6 thermocouples and pressure taps

insulated walls

1 honeycombhoneycomb

heating elementsworking section

honeycomb pine needles

heating elements

or twigs and leavesor just twigs

o o o o o o

working section

honeycomb pine needles

thermocouple

heating elements

pressure tap



125m K type thermocouple

“inserted” at the fuel particle’s surface

125m K type thermocouple in the air at the

vicinity of the fuel particle

Thicker wire

(250m) to which

the thin wire is

attached

Thin thermocouples had to be “inserted” at the fuel surfaces



Examples of the curves obtained for h and for pressure drop

0

2

4

6

8

10

12

0 20 40 60 80 100 120 140 160

Re

Nu

This work (Pinus pinae) J Rodrigues (Pinus pinaster)

Zabrosky Bellemare (Pinus sp.)

This work (Quercus coccifera) Incropera (cylinders)

Mills (spheres & cylinders)

Quercus coccifera

0

5

10

15

20

25

30

35

40

0.0 1.0 2.0 3.0 4.0 5.0

Mean velocity inside the fuel bed (m/s)

Pre

ssu

re d

rop

pe

r u

nit

len

gth

(P

a/m

)

Upper level with leaves Upper level without leaves

Medium level with leaves Medium level without leaves

Poly. (Upper level with leaves) Poly. (Upper level without leaves)

Poly. (Medium level with leaves) Poly. (Medium level without leaves)

Pressure drop per unit lengthfor Quercus coccifera

Influence of the strata location

and existence (or not) of leaves

Nu as a function of Re forPinus pinaster and Quercus coccifera

h = Nu = Nu D 4 / SVR

k k


Experimental fires in the INIA wind tunnel

Experimental fires in the wind tunnel were devoted to:

• Validate the behaviour model of wildland fire

• Analyse effects of

• Wind speed

• Shrub moisture content

• Width of a discontinuity

on the fire behaviour

in a fuel complex of Pinus pinaster litter

and Chamaespartium tridentatum shrubs

General view of

INIA wind tunnel



Example of test :• Wind speed = 1 m/s• Shrub m.c.: 40 %• Width of discontinuity = 0 m

P. pinaster litter

C. tridentatum shrubs


Example of Test on discontinuous fuel:

Wind speed = 0 m/s Shrub m.c.: 40 % Width of discontinuity = 2 m



Variation of Rate of Spread with Wind Speed

Similar set of results are available for:

* Flame height

* Byram´s fireline intensity

Examples of results obtained at INIA wind tunnel


y = 0.2101e0.5977x

R2 = 0.9264

y = 0.3663e0.6013x

R2 = 0.9407

0

0.5

1

1.5

2

2.5

0 1 2 3 4

Wind speed

Ro

S

High Level FMC Low level FMC

a

b

a

a

b

a

y = 0,0008x3 - 0,19x2 + 6,85x + 645,53R2 = 0,975

y = 0,0008x3 - 0,19x2 + 7,71x + 739,68R2 = 0,9889

0

200

400

600

800

1000

0 50 100 150 200

TPK Height (cm)

Tem

p m

ax (

ºC)

Hih level FMC Low level FMC

a

b

ba

ba

a

b

Variation of Maximum

Temperatures with Height

Width of discontinuity = 0 m


LIR-UC3M Fire parameters obtained by IR Spectral Imaging 1. Equipment set up and Images Acquisition• Tunnel and lab meas.: 2 cameras one for each band (MIR &TIR). • Field measurements: 1 camera: up to 4 MIR sub-bands

Infrared images are simultaneous, co-registered and calibrated (brightness temperatures)

Multi-spectral

TIR MIR

Visible

Bi-spectral images (MIR & TIR bands)

Multispectral images (4 MIR bands)

TIR (8-12 m)MIR (3-5 m)


IR image: Physical parameters measured

T (K)

T (K)

Classmap

MIR

TIR

Bi-spectral image

(For multispectral images is

analogous)

• Brigthness temperatures• Scene classification• Rate of spread• IR flame height• Instantaneous Radiated power• Estimation of:

Total released power (roughly, 17% of the power released is radiated)Fire front intensityHeat released per unit area

LIR-UC3M Fire parameters obtained by IR Spectral Imaging2. Pixel Classification and image processing

In collaboration with INIA and CIF-Lourizan


spectral absorbance

Objective: to gain knowledge on the pyrolysis chemistry FTIR spectrometry: a) identification of gases by the spectral location of absorbance bandsb) determination of gas concentration from the band depthc) acquires simultaneously information on the whole spectral range (2-16 m) Gases under study: CO2 , CO , CH4 , NH3

2500 2400 2300 2200 2100 2000

0.0

4.0x10-3

8.0x10-3

1.2x10-2

1.6x10-2

2.0x10-2

2.4x10-2

2.8x10-2

ulex europaeusCO

2

CO

Sp

ec

tra

l a

bs

orb

an

ce

Wavenumber (cm-1

)

CO2 CO

3100 3050 3000 2950 2900 2850 2800 2750

0.000

0.002

0.004

0.006

0.008

0.010

0.012

erica umbellata

sp

ec

tra

l a

bs

orb

an

ce

wavenumber (cm-1

)

CH4

LIR-UC3M Fuel Pyrolysis Studies based on FTIRS- Fourier Transform IR Spectrometry: 1. Schematics and aims

255 cm 1 cm-1

32 scans1 s/scan

300 W / 330° C

90 W / 140° C

8.5 cm

4 g

FTIRIR emitter

Fuel sampleHeater

gases

In collaboration with INIA


0 10 20 30 40 50 60 70 80 900

10

20

30

40

50

Y = A + B * X

Value Error

--------------------------------------

A 0.40769 1.35236

B 0.63572 0.03323

--------------------------------------

[CO

] (

pp

m m

)

[CO2] + [CO] (ppm m)

combustion efficiency

36.0

COCOCO

CE2

2

0 10 20 30 40 500

1

2

3

4

5

Y = A + B1*X

Value Error-----------------------------------------A 0.06708 0.14521B1 0.06345 0.00546-----------------------------------------

[NH

3] (

ppm

m)

[CO] (ppm m)

- clear correlation of NH3 with CO emissions

23 105.03.6CONH

0 10 20 30 40 50 60 70 80 900

2

4

6

8

10

12

14

16

[CH

4] (p

pm m

)

[CO2]+[CO] (ppm m)

-data dispersion - low rate of CH4

emission

aver

4

COCH

02.008.0

LIR-UC3M Fuel Pyrolysis Studies based on FTIRS2. Some remarkable results

In collaboration with INIA


Sketch of the experiment

5.0 5.5 4.5 3.5 4.0 6.0 3.0 2.5

X

Y

X

5 thermocouples onto a vertical

DESIRE plate

median axis of DESIRE

infrared camera

UP VIEW

SIDE VIEW

camera field of view

INRADESIRE bench


Comparison of infrared signal and thermocouple temperature near fire front

thermocouple at 5 cm high gas temperature

thermocouple à 5 cm de haut température du gaz

1 pixel of the infrared image

solid fuel temperature

comparison of time signals

position of the cotton thread

position du fil de coton

INRADESIRE bench


0

100

200

300

400

500

600

700

800

250 260 270 280 290 300 310 320

Time (s)

Te

mp

era

ture

(°C

)

Brightnesstemperature

Thermocoupletemperature

Moving average on thermocouple data

Time evolutions of solid fuel and gas temperature – Slope 0°

Breaking of the cotton thread

Coupure du fil de coton

the thermocouple ‘enters’ the flame

le thermocouple ‘entre’ dans la flamme

Pre-heating of the litter

Préchauffage de la litière

solid fuel temperature gas temperature

INRADESIRE bench

Slope 0° Pente 0° Moyenne mobiledes données de température


0

200

400

600

800

1000

1200

90 95 100 105 110 115 120

time (s)

tem

pe

ratu

re (

°C)

Brightness temperature

Thermocouple temperature

Breaking of the cotton thread

Coupure du fil de coton

the thermocouple ‘enters’ the flame

le thermocouple ‘entre’ dans la flamme

Pre-heating of the litter

Préchauffage de la litière

solid fuel temperature gas temperature

INRADESIRE bench

Time evolutions of solid fuel and gas temperature – Slope 30°

Slope 30° Pente 30°

fire star conclusive symposium: marseille march 18th 2005 1 physical sub-models to be included in...

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