PREDICTION OF FLAMMABILITY LIMIT OF A THIN SOLID
MATERIAL IN MICROGRAVITY ENVIRONMENTS
Shuhei Takahashi, kandai Tsuboi and Keisuke Maruta
Department of Mechanical Engineering, Gifu University, Japan
1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japane-mail: shuhei@gifu-u.ac.jp
Objectives of the FLARE Projectct

Flammability limit in reduced gravity environments
tsOxygen concentration

 To investigate the flame spread behavior over solidmaterials in microgravity.
 To establish an evaluation method to give an index
to the material used in reduced gravity environments
for developing ISO Standard.
The FLARE project is the International Space Station orbital experimentconducted by international team; JAXA, NASA, ESA etc.

Problems of the current flammability testst

Buoyant flow velocity~ 35cm/s

Flammable

Blow-off
extinction/2&J

Radiative
extinction

˂2
0/2&

Critical Vg
AsteroidMoon Mars

Opposed flow velocity(forced flow)

Earth

G level (buoyant flow)

Critical G level

NASA STD-6001 B Test1

 Most materials have lower limiting oxygen concentration
than LOC1g in a mild flow, which can be realized only inthe reduced gravity environments.
 The gap between LOC1g and the minimum limiting
oxygen concentration (MLOC), ΔO2, is an importantvalue to discuss the flammability of the material in
reduced gravity environment.

ISO 4589-2 (Oxygen Index)

 Pass/fail test is not a convenient method for choosing
materials for space use. An index method is preferable.
 Both downward and upward spreads are influenced bybuoyant flow significantly.
Scale analysis of flame spread in an opposed floww
Vr =Vf +Vg ~Vg2322 N2 balanceLg

Oxygen level (%)

Vg,effτxd

Heat balance with including radiation loss and finite kinetic effect(T f  Tv )1 ·§V f U s cs LsyW (Tv  Tf )  H (1  D abs )V Tv 4  Tf 4 LgW ~ ¨1 LgxW¸O g
Da ¹Lgy©

K  Rrad Rrad ~Da {1Da

1

where20
19181615Lg / Vr D g~
U gYO A exp( E / RT f )U g / Z Vr2

MLOC=14.7%
BL modelEPL model
1/3 model
Original model

13121Combustion heat inthe preheat zone

Lg 2Z 'hrLg Og (T f  Tv ) / Lg

Vg ,eff ~Pr Re x1/ 4Vg
Pr Re x1/ 3

EPL model (Lg is determined by Vg,eff; Lg~α/Vg,eff)
1/3 model (Empirical model by Bhattacharjee et al.)PMMADimensions

8cm x 2cm x 0.125mm

Density, ρs (kg/m3)

1190

Specific heat, cs (kJ/Kg K)

1.465

Vaporization temperature, Tv (K)670

Enthalpy of reaction, ΔHr (kJ/kg)

25900

Surface emissivity, ε1.0Pre-exponential factor, A (m3/kg s)

1.36  109

Activation energy, E (J/mol)

1.50  105

1.

Measure the LOC of the downward spread. (OI may be used.)2.

Measure the LOC at a certain high opposed velocity, Vg=80cm/s.

3.

Draw blow-off limiting line. (Empirical A and E are obtained.)

4.

Draw radiative extinction line with Tv and other gas properties.

5.

Draw the limiting line on which Rrad+1/Da=1.
Rrad=1Da=1䠎䠐Flammable
Blow-off䠍

RadiativeLOC in normal GΔO2

extinction

䠏Gas phase at T=670K
Cpλg

αg

[W/m K][mm2/s]

Critical Vg
Opposed flow velocity

aabsAsteroidN230.47

0.0444

80.1

Steady spread below LOC1g

Extinction due to recovery of G

MoonMars

0.0
Critical G levelEarth Accurate and proper A and E for blow-off extinction are required
to predict the limiting line.
 Adding blow-off test with high upward flow to the existing ISO4589-2 is one of possible solutions.
 The flammability of other materials can be checked easily.
The example of blow-off test
For NOMEX HT90-40
Eemp=3.5x105 (J/mol)
Aemp=5x1015 (m3/kgs)
Tv=750 (K)The flammability ofNOMEX can be predicted!

䠑A.C. Fernandez-Pello, S.R. Ray, I. Glassman, Flame spread in an opposed forced flow: the MLOC
effect of ambient oxygen concentration, Proc. Combust. Inst., 18 (1981), p. 579-589.

[J/mol K]

IgnitionIssues and potential of the proposed methododRequired heat to keep gasphase temperature gradient

BL model (Lg is determined by bulk Vg; Lg~α/Vg)

Solid phase

100(Finite kinetic effect)

Oxygen level

Vg ,eff ~Vg
Pr Re x1/ 2Vg

10Opposed flow velocity, Vg (cm/sec)

Effect of boundary layer for blow-off modelVg ,eff ~ The BL model leads to reasonable agreementwith the flight experimental results. The
predicted ΔO2 was quantitative.
 The limiting line can be drawn by the values
which can be obtained by ground-based
experiments only.

14K { V f / V f ,th(Radiative effect)

LOC1g=17%

1711

H (1  aabs )V Tv 4  Tf 4
U g cgVr T f  Tv

Flammable
Extinct
Blow-off

21Lg(forced flow)
G level (buoyant flow)

The similar configuration ofISO 4589-2
High upward flow: 50 ~ 140 cm/s(beyond the buoyant flow)

Oxygen level (%)

VgδComparison with flight experimental results ((PMMAA sheet)t)

3634
3230
2826
2422
20
18
16
14
12
10

NOMEXConditions which
can be conductedby ground-basedtests

PMMA
1

Flamm
Flammablem ableExtinct

10100

Opposed flow velocity, Vg (cm/sec)