| Summary: | Ethylene/Air diffusion flames were studied at sub and super-atmospheric pressures to simulate a microgravity environment at fuel flow rates of 0.482 mg/s and 1.16 mg/s. Flame properties including flame dimensions, soot formation, temperature, and attachment mechanisms were investigated. Overall, luminous flame height decreased with decreasing pressure to the point of visible luminosity disappearance, resulting in blue flames. Flame width increased with decreasing pressure until the flame was almost spherical. Soot formation decreased with decreasing pressure to negligible concentrations in a near vacuum. At 0.482 mg/s, the percentage of carbon converted into soot was between 0.01% and 0.12%, whereas at 1.16 mg/s, this percentage was between 0.5% and 11% at sub-atmospheric pressures. Maximum flame temperatures increased with decreasing pressure. Regardless of fuel flow rate, the diffusion flames remained attached to the exterior of the burner. This attachment point moved further down the burner exterior as pressure decreased until a near vacuum.
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