An experimental study of a low-Reynolds-number diffusion flame has been conducted to provide further insight on the structure of diffusion flames representative of fire in microgravity. A gas fuel (ethane) injected through a porous burner into a stream of oxidizer flowing parallel to the surface of the burner has been chosen to simulate a condensed fuel. The flow conditions (oxygen concentration between 18% and 50%, fuel flow velocity VF approximately 5 mm/s, and oxidizer flow velocity Uinfinity < 150 m/s) have been set to correspond to a potential fire onboard of a spacecraft. Visualization and particle image velocimetry are conducted with nonreacting flow to determine the characteristics of the mixing zone. Reacting flow experiments are conducted in microgravity using a 2.2.-s drop tower and parabolic flights. The burner is a 200 x 95 mm stainless-steel plate with an aerodynamic leading edge to prevent flow separation. A 60 x 60 mm bronze plate is placed 40 mm behind the leading edge and centered in the burner plate. Flow visualizations have shown that a three-dimensional flow pattern is introduced by the injected flow resulting in separation of the oxidizer flow and a mixing zone detached from the porous plate. Three characteristic flow regimes have been identified. For CQ = VF/Uinfinity < 0.15 the flow field at the leading edge of the burner has a significant effect on the mixing zone. For CQ > 0.15 and VF y 4 mm/s, the flow near the plane of symmetry is two-dimensional and not affected by the side boundaries of the burner. For CQ > 0.15 and VF > 4 mm/s, lateral entrainment results in a lift of the oxidizer boundary, and therefore the physical boundaries of the burner have an effect on the structure of the mixing zone. In the combustion experiments, a minimum fuel injection velocity is shown to be necessary for a stable flame. Three characteristic types of flames have been observed depending on VF and Uinfinity. In region 1 (Uinfinity < 40 mm/s, VF < 2.6 mm/s), the flame covers the burner with an elliptical shape; region 3 (Uinfinity > 60 mm/s, VF > 3.5 mm/s) concerns flames with linear shapes, and region 2 (the intermediate region) concerns flames with parabolic shape. In region 1, the flame standoff distance is much larger than that of the mixing zones revealed from the nonreacting flow visualizations. This indicates that the thermal expansion plays a dominant role on flame geometry and flow field. As both fuel and oxidizer velocities increase, the influence of thermal expansion is reduced to the leading edge.


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    Title :

    Microgravity laminar diffusion flame in a perpendicular fuel and oxidizer stream configuration


    Additional title:

    Untersuchung einer quer angestömten laminaren Diffusionsflamme bei Schwerelosigkeit


    Contributors:
    Brahmi, L. (author) / Vietoris, T. (author) / Rouvreau, S. (author) / Joulain, P. (author) / David, L. (author) / Torero, J.L. (author)

    Published in:

    AIAA Journal ; 43 , 8 ; 1725-1733


    Publication date :

    2005


    Size :

    9 Seiten, 11 Bilder, 36 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English