Mixed Convection Blowoff Limits as a Function of Oxygen Concentration and Upward Forced Stretch Rate for Burning Pmma Rods of Various Sizes
Marcum, Jeremy W., Ferkul, Paul V., Olson, Sandra L.
Experiments: BASS, BASS-II, SAME
Normal gravity flame blowoff limits in an axisymmetric pmma rod geometry in upward axial stagnation flow are compared with microgravity Burning and Suppression of Solids II (BASS-II) results recently obtained aboard the International Space Station. This testing utilized the same BASS-II concurrent rod geometry, but with the addition of normal gravity buoyant flow. Cast polymethylmethacrylate (pmma) rods of diameters ranging from 0.635 cm to 3.81 cm were burned at oxygen concentrations ranging from 14 to 18 by volume. The forced flow velocity where blowoff occurred was determined for each rod size and oxygen concentration. These blowoff limits compare favorably with the BASS-II results when the buoyant stretch is included and the flow is corrected by considering the blockage factor of the fuel. From these results, the normal gravity blowoff boundary for this axisymmetric rod geometry is determined to be linear, with oxygen concentration directly proportional to flow speed. We describe a new normal gravity upward flame spread test method which extrapolates the linear blowoff boundary to the zero stretch limit to resolve microgravity flammability limits, something current methods cannot do. This new test method can improve spacecraft fire safety for future exploration missions by providing a tractable way to obtain good estimates of material flammability in low gravity.
Test conditions.
Extracted from the paper by AI · “Verified” means a person checked it
| Fuel | O₂ | Pressure | Airflow | Sensors | Source | AI conf. | Status |
|---|---|---|---|---|---|---|---|
| cast polymethylmethacrylate (PMMA) rods with radii 0.318 cm, 0.476 cm, 0.635 cm, 1.270 cm, and 1.905 cm |
14% to 18% by volume | — | upward axial stagnation flow; forced flow velocity varied to determine blowoff limits | color video camera, hot wire anemometer | p. 2 | 95% | Pending |
| cast polymethylmethacrylate (PMMA) rod radius 0.635 cm |
14% | — | 2 cm/s forced flow in ZGRF wind tunnel | video camera | p. 5 | 95% | Pending |
| cast polymethylmethacrylate (PMMA) rod radius 0.635 cm |
15% | — | forced flow in ZGRF wind tunnel | video camera | p. 5 | 95% | Pending |
Findings.
-
01
The normal gravity blowoff boundary for the axisymmetric rod geometry is linear, with oxygen concentration directly proportional to flow speed.
Other · p. 1 · AI confidence 95% · Reported · Pending
“the normal gravity blowoff boundary for this axisymme tric rod geometry is determined to be linear, with oxygen concentration directly proportional to flow speed.”
-
02
Normal gravity blowoff limits compare favorably with BASS-II microgravity results when buoyant stretch is included and flow is corrected by considering the blockage factor of the fuel.
Other · p. 1 · AI confidence 95% · Reported · Pending
“These blowoff limits compare favorably with the BASS - II results when the buoyant stretch is included and the flow is corrected by considering the blockage factor of the fuel.”
-
03
A new normal gravity 'upward flame spread test' method extrapolates the linear blowoff boundary to the zero stretch limit to resolve microgravity flammability limits.
Detection · p. 1 · AI confidence 90% · Reported · Pending
“We describe a new normal gravity ‘upward flame spread test’ method which extrapolates the linear blowoff boundary to the zero stretch limit to res olve microgravity flammability limits”
-
04
The forced stretch rate at blowoff varies linearly with oxygen concentration and as the square root of the rod radius.
Other · p. 6 · AI confidence 95% · Reported · Pending
“reveali ng that the forced stretch rate at blowoff varies linearly with oxygen in addition to varying as the square root of the rod radius.”
-
05
At 14% oxygen in the quartz tube, the flame did not blow off due to ambient flow entrainment back into the tube, unlike in the larger wind tunnel.
Other · p. 6 · AI confidence 90% · Reported · Pending
“Non - symmetric flame in quartz tube at 14% oxygen, left, does not blowoff due to ambient flow entrainment back into the tube.”
-
06
Blowoff at 14% oxygen in the quartz tube was discarded from further analysis due to entrainment effects.
Other · p. 5 · AI confidence 95% · Reported · Pending
“Given these results, the 14% O 2 data are discarded from further analysis.”