Flame and soot boundaries of laminar jet diffusion flames

    Authors

    F. Xu; Z. Dai;G. M. Faeth

    Comments

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    Abbreviated Journal Title

    Aiaa J.

    Keywords

    HYDRODYNAMIC SUPPRESSION; BEHAVIOR; SHAPES; Engineering, Aerospace

    Abstract

    The shapes (flame-sheet and luminous-flame boundaries) of steady weakly buoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and collowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue CO2 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet-exit Reynolds numbers of 3-54, initial air/fuel velocity ratios of 0-9, and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at microgravity conditions; essentially nonbuoyant flames in collowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smoke-point conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smoke-point conditions. Flame-shape predictions were based on simplified analyses using the boundary-layer approximations along with empirical parameters to distinguish flame-sheet and luminous-flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in collowing air approaching (2)/(3) of the lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions because of the presence of luminous soot particles in the fuel-lean region of the flames.

    Journal Title

    Aiaa Journal

    Volume

    40

    Issue/Number

    12

    Publication Date

    1-1-2002

    Document Type

    Article

    Language

    English

    First Page

    2439

    Last Page

    2446

    WOS Identifier

    WOS:000179662000008

    ISSN

    0001-1452

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