Visible and U.V. Spectral Emission and Extinction Measurements in Oil Spray Flame

Abstract

Emission and extinction measurements in the visible and U.V. were performed along the axis of vertical unconfined fuel oil flames produced on a variable swirl burner. The flow rate of the fuel was around 6 Kg/hr and the theoretical equivalence ratios was varied from 0.9 to 1.15. The emissions due to the radicals OH, CH and C₂ were compared with the continuum emission due to the soot particles. The profiles of the brightness and colour temperature were obtained from the measurements of the absolute intensity of the continuum in the spectral range 4000÷8000A. The colour temperature was much higher than the brightness temperature near the burner nozzle while the difference decreased in the final part of the flames. In the first part of the flame the monochromatic extinction coefficient at λ = 6500Å decreases, due to fuel droplets, which are evaporating, but increases downstream where the soot formation process prevails. The study of its spectral variation in the range 4000Å-8000Å allows the determination of the dispersion exponent n (defined by the expression K = K₀λ-n) in the different regions of the flames. It was almost equal to zero near the burner nozzle, where the droplets prevail, equal to 1.5 in the final part of the flames and had a more complex behaviour in the intermediate regions. The monochromatic emissivity and true temperature profiles were also obtained from the above data and are discussed, in comparison with the measured extinction, and with reference to the flame structure, droplets evaporation and soot formation processes.