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Relationship Between Blow-Off Behavior and Limiting Oxygen Concentration in Microgravity Environments of Flame Retardant Materials

  • Shuhei TakahashiEmail author
  • Kaoru Terashima
  • Muhammad Arif Fahmi bin Borhan
  • Yoshinari Kobayashi
Article

Abstract

The flammability characteristics of materials in microgravity are some of the most important factors for fire safety in space. It has been reported that the limiting oxygen concentration (LOC) in microgravity is different from that in normal gravity (LOC1g), which is measured by downward spread tests and is often used as an index of flammability. However, it is expensive and time consuming to conduct screening flammability tests in microgravity environments. Hence, it is necessary to develop a novel procedure for predicting the flammability of a material with data measured in normal gravity. In our previous study, we developed a simplified model for flame spread tests in opposed flow by scale analysis. Here, we present the flammability maps of several flame retardant materials in opposed flow obtained by ground-based blow-off tests and parabolic flight experiments, and the trends of the flammability maps are discussed with the developed model. Materials whose LOC increased monotonically with the opposed flow velocity and whose pyrolysis temperature was less than 823 K had a lower LOC in microgravity environments than in normal gravity; the other investigated materials showed larger LOC in microgravity than that in normal gravity. These trends were well explained by the simplified model, and the predicted limiting curve agreed quantitatively with the experimental result for thermally thin materials, which indicates the usefulness of the developed model.

Keywords

Flammability limit Flame retardant materials Blow-off Microgravity 

List of Symbols

A*

Empirical pre-exponential factor by blow-off test

B2

Empirical constant for Rrad, B2 = 2.67

aabs

Absorption coefficient of gas

cg

Specific heat of gas

cs

Specific heat of solid

Da

Damkohler number

E*

Empirical activation energy by blow-off test

Pr

Prandtl number

R

Gas constant

Rrad

Radiation loss number

Tf

Characteristic flame temperature

Tv

Pyrolysis temperature

T

Ambient temperature

t

Sample thickness

Vg

Opposed flow velocity

Vcr

Critical opposed flow velocity

Vf

Flame spread rate

Vf,th

Flame spread rate in thermal regime

xd

Location for blow-off, xd = 0.04 [m]

Y0

Oxygen mass fraction

αg

Thermal diffusivity of gas, evaluated at Tv

ε

Surface emissivity

η

Non-dimensional spread rate, η = Vf/Vf,th

ρg

Gas density evaluated at Tv

ρs

Solid density

σ

Stefan–Boltzmann constant

Notes

Acknowledgements

This study was conducted as a part of the FLARE project supported by JAXA. We are also thankful to the staff of Diamond Air Service for their excellent technical support in the parabolic flight experiments.

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringGifu UniversityGifuJapan

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