Recent Research on Flames of Gaseous Fuel Aboard the International Space Station
Dennis P Stocker
Experiments: ACME, CFI, SLICE, SPICE
Research for a set of six independent experiments with flames of gaseous fuels has been carried out on the International Space Station (ISS) since 2017 using the Combustion Integrated Rack (CIR) and a set of modular hardware. While ISS testing has been completed for most of the studies in the Advanced Combustion via Microgravity Experiments (ACME) project, it is expected to continue into 2022. The objectives and selected findings for each investigation are briefly discussed after a short review of the advantages of studying combustion in microgravity, previous research conducted in space, and the experimental hardware and its operation.
Test conditions.
Extracted from the paper by AI · “Verified” means a person checked it
| Fuel | O₂ | Pressure | Airflow | Sensors | Source | AI conf. | Status |
|---|---|---|---|---|---|---|---|
| Methane, Ethylene, Propane (C3H8), Butane (C4H10), Hydrogen/Methane mixtures Gas-jet, coflow, spherical, porous spherical burner |
Elevated oxygen concentrations (specific values not listed in snippet, but noted as variable) | Nominally 100-liter combustion chamber (pressure not explicitly stated as a variable parameter in text) | Coflow, gas-jet, still atmospheres (for BRE) | Thermopile detectors, PhotoMultiplier Tubes (PMTs) for CH* and OH*, Thermocouple rake, Silicon carbide (SiC) fibers for Thin Filament Pyrometry (TFP), Cameras (analog and digital), Ion current measurements | p. 5 | 95% | Pending |
| Methane, Ethylene Gas-jet and coflow flame configurations |
— | — | Coflow | Ion current measurements, Cameras | p. 7 | 90% | Pending |
| Ethylene, Methane Burning Rate Emulator (BRE) burner |
Below ~25% (by volume) and elevated concentrations | — | Still atmospheres | Cameras | p. 8 | 95% | Pending |
Findings.
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01
Microgravity eliminates buoyant convection, allowing for spherically symmetric flames and quasi-steady flames without flicker.
Other · p. 1 · AI confidence 95% · Reported · Pending
“Many flames are dramatically influenced by the near elimination of buoyant convection... it is possible to create spherically symmetric flames enabling one - dimensional analysis. More generally, the effective elimination of flicker yields quasi - steady flames.”
-
02
Space-based testing is necessary for combustion research because aircraft test durations are too short for quasi-steady soot conditions and are affected by g-jitter.
Other · p. 2 · AI confidence 95% · Reported · Pending
“NASA facilities, are too short for soot to achieve quasi - steady c onditions... low - momentum flames can be dramatically disturbed by the g - jitter present in aircraft testing... As a result, space - based testing is often necessary”
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03
In microgravity, electric fields can stabilize highly diluted flames, but high field strengths cause corona and arc discharges.
Prevention · p. 7 · AI confidence 90% · Reported · Pending
“It was found that h ighly diluted flam es can be stabilized with very weak electric fields. But at high field strengths, the flames exhibited corona and arc discharges.”
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04
Soot generation can be suppressed in microgravity flames under electric field influence, with correlations between luminosity, combustion intensity, and ion current.
Suppression · p. 7 · AI confidence 90% · Reported · Pending
“Soot generation could be suppressed and m ore broadly t here are clear correlations between the flame luminosity, combustion intensity, and ion current in the ISS data .”
-
05
BRE flames self-extinguish in oxygen concentrations below approximately 25% by volume.
Prevention · p. 8 · AI confidence 95% · Reported · Pending
“they were found to self - extinguish in concentrations below ~25% (by volume).”
-
06
Larger BRE flames generally self-extinguish within 1.5 minutes, while smaller flames can burn for minutes at elevated oxygen concentrations.
Prevention · p. 8 · AI confidence 95% · Reported · Pending
“While smaller flames ca n burn for minutes at elevated oxygen concentrations, larger flames were generally seen to self - extinguish within 1.5 minutes.”
-
07
Methane BRE flames self-extinguish within a minute, whereas ethylene flames can burn for minutes at elevated oxygen concentrations.
Prevention · p. 8 · AI confidence 95% · Reported · Pending
“While ethylene flames at elevated oxygen concentrations can burn for minutes, methane flames were seen to self - extinguish within a minute.”