Burning and Suppression of Solids–II (BASS-II) Summary Report
Sandra L. Olson, Paul V. Ferkul, Subrata Bhattacharjee, Fletcher J. Miller, Carlos Fernandez-Pello, Shmuel Link, James S. T'ien, Indrek Wichman
Experiments: BASS, BASS-II, SAME
The Burning and Suppression of Solids (BASS) experiment hardware is a small flow duct that provides containment for small scale burning of solid samples within the Microgravity Science Glovebox (MSG) aboard the International Space Station (ISS). A video camera with a data overlay and a 35-mm still camera record the combustion events. The controls (ignition, fan speed, etc.) are operated by an astronaut while the principal investigator team monitors the experiment from the ground and communicates directly with the astronaut. For the first time on ISS, BASS–II utilized MSG working volume dilution with gaseous N2. We developed a perfectly stirred reactor model to determine the N2 flow time and flow rate to obtain the desired reduced O2 concentration in the working volume for each test. We calibrated the model with the Compound Specific Analyzer-Combustion Products (CSA-CP) O2 readings offset using the Major Constituents Analyzer reading of the ISS ambient atmosphere data for that day. This worked out extremely well for operations, and added a new vital variable, ambient O2 level, to our test matrices. The main variables tested in BASS–II were ambient O2 concentration, ventilation flow velocity, and fuel type, thickness, and geometry. BASS–II also utilized the onboard CSA-CP for O2 and CO readings, and the Carbon Dioxide Monitor for CO2 readings before and after each test. Readings from these sensors allow us to evaluate the completeness of the combustion. The O2 and CO2 readings before and after each test were analyzed and compared very well to stoichiometric ratios for a one-step gas-phase reaction. The CO versus CO2 followed a linear trend for some datasets, but not for all the different geometries of fuel and flow tested. We calculated the heat release rates during each test from the O2 consumption and burn times, using the constant 13.1 kJ of heat released per gram of O2 consumed. The results showed that most of the tests had heat release rates well below 100 W. Lastly, the global equivalence ratio for the tests is estimated to be fuel rich, 1.3 on average using mass loss and O2 consumption data.
Test conditions.
Extracted from the paper by AI · “Verified” means a person checked it
| Fuel | O₂ | Pressure | Airflow | Sensors | Source | AI conf. | Status |
|---|---|---|---|---|---|---|---|
| PMMA (polymethylmethacrylate) 10 cm long by either 1 or 2 cm wide with thicknesses ranging from 1 to 5 mm |
Varied to determine flammability limits | — | Forced-flow velocity varied | — | p. 61 | 85% | Pending |
| PMMA (polymethylmethacrylate) 1- and 2-cm-wide thin films |
21 percent (ambient) | — | Opposed-flow velocity varied; extinction velocity ~1 cm/s for 100-300 µm, ~1.5 cm/s for 400 µm | — | p. 20 | 95% | Pending |
| PMMA (polymethylmethacrylate) 1- and 2-cm-wide thin films |
16 percent | — | Opposed-flow velocity varied | — | p. 31 | 90% | Pending |
Findings.
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01
The extinction velocity for PMMA thin films does not depend on fuel thickness in the thermally thin regime.
Other · p. 31 · AI confidence 95% · Reported · Pending
“It can be safely concluded that the extinction velocity does not depend on the fuel thickness.”
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02
The minimum oxygen concentration for flammability in BASS-II tests was 13.5 percent at a stretch rate of 8 to 12 s^-1.
Prevention · p. 83 · AI confidence 90% · Reported · Pending
“The minimum O2 concentration of 13.5 percent O2 at a of 8 to 12 s –1 is significantly lower th”
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03
Forward conduction through the solid is relatively unimportant for flame spread in homogeneous fuels like PMMA.
Other · p. 41 · AI confidence 90% · Reported · Pending
“Of these, forward conduction through the solid has been shown to be relatively unimportant theoretically (Ref. 9) and experimentally (Ref. 13).”
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04
The de Ris coefficient F for PMMA in an oxidizing mixture of 21 percent O2 and 79 percent N2 is 4.76.
Other · p. 51 · AI confidence 95% · Reported · Pending
“A curve fit of maximum spread rate against fuel thickness using de Ris formula for the thermal regime was used to determine the de Ris coefficient F as 4.76 for an oxidizin g mixture of 21 perc ent O2 and 79 percent N2.”
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05
Materials in microgravity with adequate ventilation may burn as well or better than in normal gravity, challenging the conservatism of terrestrial upward burning tests.
Prevention · p. 11 · AI confidence 90% · Reported · Pending
“thesis that materials in microgravity, with adequate ventilation, burn as well if not better than the same material in normal gravity with other conditions being identical”