Thickness and Fuel Preheating Effects on Material Flammability in Microgravity from the BASS Experiment
Ferkul, Paul V., Olson, Sandra L., Takahashi, Fumiaki, Endo, Makoto, Johnson, Michael C., T'ien, James S.
The Burning and Suppression of Solids (BASS) experiment was performed on the International Space Station. Microgravity combustion tests burning thin and thick flat samples, acrylic spheres, and candles were conducted. The samples were mounted inside a small wind tunnel which could impose air flow speeds up to 40 cms. The wind tunnel was installed in the Microgravity Science Glovebox which supplied power, imaging, and a level of containment. The effects of air flow speed, fuel thickness, fuel preheating, and nitrogen dilution on flame appearance, flame growth, and spread rates were determined in both the opposed and concurrent flow configuration. In some cases, a jet of nitrogen was introduced to attempt to extinguish the flame. Microgravity flames were found to be especially sensitive to air flow speed in the range 0 to 5 cms. The gas phase response is much faster compared to the solid and so as the flow speed is changed, the flame responds with almost no delay. At the lowest speeds examined (less than 1 cms) all the flames tended to become dim blue and very stable. However, heat loss at these very low convective rates is small so the flames can burn for a long time. At moderate flow speeds (between about 1 and 5 cms) the flame continually heats the solid fuel resulting in an increasing fuel temperature, higher rate of fuel vaporization, and a stronger, more luminous flame as time progresses. Only the smallest flames burning acrylic slabs appeared to be adversely influenced by solid conductive heat loss, but even these burned for over 5 minutes before self-extinguishing. This has implications for spacecraft fire safety since a tiny flame might be undetected for a long time. While the small flame is not particularly hazardous if it remains small, the danger is that it might flare up if the air convection is suddenly increased or if the flame spreads into another fuel source.
Test conditions.
Extracted from the paper by AI · “Verified” means a person checked it
| Fuel | O₂ | Pressure | Airflow | Sensors | Source | AI conf. | Status |
|---|---|---|---|---|---|---|---|
| Cotton-fiberglass fabric 2-cm wide flat |
— | — | 10 cm/s to 1 cm/s (decreasing steps) | Digital Still Camera, Video | p. 8 | 95% | Pending |
| Ultem 1000 10 mil thick film |
21% to 22% O2 | — | ~15 cm/s | Digital Still Camera, Video | p. 24 | 98% | Pending |
| Nomex HT90-40 12 mil thick fabric |
21% to 22% O2 | — | ~15 cm/s | Digital Still Camera, Video | p. 24 | 98% | Pending |
| Nomex-III 2 cm wide sample |
22% O2 | 1 atm | 14 cm/s (0g) / 15 cm/s (ISS) | Digital Still Camera, Video | p. 24 | 95% | Pending |
| PMMA (Acrylic) 2-cm diameter sphere |
17% O2 | 1 atm | 12 cm/s | Digital Still Camera, Video | p. 29 | 90% | Pending |
| PMMA (Acrylic) 1-cm diameter sphere |
17% O2 | 1 atm | < 1 cm/s | Digital Still Camera, Video | p. 29 | 90% | Pending |
| PMMA (Acrylic) 15-mm initial diameter sphere |
17% O2/N2 | 1 atm | Flow reductions to zero; Nitrogen jet 500 cc/min | Digital Still Camera, Video | — | 95% | Pending |
| Acrylic 1-cm wide flat |
Air (approx 21% O2) | — | ~9 cm/s | Digital Still Camera, Video | p. 46 | 95% | Pending |
Findings.
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01
Microgravity flames are especially sensitive to air flow speed in the range of 0 to 5 cm/s.
Other · AI confidence 95% · Reported · Pending
“Microgravity flames were found to be especially sensitive to air flow speed in the range 0 to 5 cm/s.”
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02
Gas phase response to flow changes is much faster than the solid phase, resulting in almost no delay in flame response.
Other · AI confidence 95% · Reported · Pending
“The gas phase response is much faster compared to the solid and so as the flow speed is changed, the flame responds with almost no delay.”
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03
At flow speeds less than 1 cm/s, flames become dim blue and very stable, burning for a long time due to small heat loss.
Other · AI confidence 95% · Reported · Pending
“At the lowest speeds examined (less than 1 cm/s) all the flames tended to become dim blue and very stable. However, heat loss at these very low convective rates is small so the flames can burn for a long time.”
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04
At moderate flow speeds (1-5 cm/s), the flame continually heats the solid fuel, increasing fuel temperature and vaporization rate over time.
Other · AI confidence 95% · Reported · Pending
“At moderate flow speeds (between about 1 and 5 cm/s) the flame continually heats the solid fuel resulting in an increasing fuel temperature, higher rate of fuel vaporization, and a stronger, more luminous flame as time progresses.”
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05
Thicker solids can store significant heat, making extinction with a nitrogen jet difficult at given flow rates.
Suppression · AI confidence 95% · Reported · Pending
“Thicker solids can store a great deal of heat even with only a small flame. One result is that extinction with the nitrogen jet was not possible for the given flow rate.”
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06
Concurrent flow flame spread rate increases linearly with increasing flow speed.
Other · p. 19 · AI confidence 95% · Reported · Pending
“Concurrent flow: • Flame spread rate increased linearly with increasing flow.”
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07
Opposed flow flame spread rate is fastest at an intermediate value of flow speed.
Other · p. 19 · AI confidence 95% · Reported · Pending
“Opposed flow: • flame quickly reached steady spread • spread rate was fastest at an intermediate value of flow speed”
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08
Quenching extinction was observed in concurrent flow around 1 cm/s.
Suppression · p. 19 · AI confidence 95% · Reported · Pending
“Quenching extinction was observed (around 1 cm/s )”
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09
Nomex fibers swell and seal spaces between fibers when exposed to heat, inhibiting heat transfer through the fabric.
Prevention · p. 24 · AI confidence 95% · Reported · Pending
“When exposed to a heat source, the Nomex fibers swell and seal the spaces between the fibers, stopping air movement through the fabric and thus inhibiting heat transfer through the fabric.”