An Investigation on the Structure of Spray Flames Using the Spectral Analysis and the Image Processing of Light Emissions and Mie-scattering from Droplets

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(1) The chemiluminescence characteristics of OH, CH, and C_2 radicals in flames were investigated and the visualization technique for radical luminescences was examined in terms of computer simulation based on the spectroscopic observation of a Wolfhard-Parker burner flame which had a geometry suitable for optical observation. Then, we developed an optical system which enabled us to separate the radical luminescences from the background flame luminosity (principally solid emission from soot) and to visualize them after processing simultaneously a few flame images obtained through different optical interference filters.(2) We constructed two identical imaging systems consisting of one or a few interference filters, an image intensifier, a set of coupling lenses and a CCD camera, and installed in each a focalーplane shutter controlled by a personal computer. Then, we manufactured a control device which enabled us to obtain the most suitable combination of flame images ; e. g., an OH radic … More al luminescence image coupled with a flame image at C_2 radical emission band (principally solid emission from soot) or a Mie-scattering image of droplets, simultaneously, as well as to obtain two successive frames of a flame image.(3) We also manufactured an optical system for monitoring through appropriate filters the light emissions in OH- and CH-bands as well as the light scattered by droplets at a point in the flame.(4) The flame structure of premixed sprays was observed by visualizing the light emissions in various radical bands and the droplet Mie-scattering using the above mentioned optical devices. The image informations were combined with those of local continuous monitoring of radical emissions and Mie-scattering. The experimental results were summarized as follows : (a) Flame propagated preferentially through the regions where gaseous fuel and droplets coexisted ; (b) In case of a small liquid-fuel fraction in the total fuel (consisting of liquid kerosene, and the vapors of kerosene and/or propane), the liquid fuel (droplets) completed evaporation and combustion in a thin reaction zone, and the gas-phase reaction in premixed-combustion mode prevailed throughout a whole droplet cluster ; (c) In case of a large liquid-fuel fraction in the total fuel, the gas-phase reaction occurred outside a large-scaled droplet cluster, whereas small dense clusters involved in it burned with diffusion flame-lets emitting intense solid emissions from soot, which implied that sprays burned not in a simple group combustion mode but in a hierarchic one. Less