Spectroscopic Study on Luminous Counterflow Propane-Air Diffusion Flames: Measurement of Local Emissive Properties from Soot Cloud—1st Report: Non-Gray Body Feature of Luminous Flame & Its Applicability to Soot Diagnostics
Yuji NAKAMURA, Shinichi TAKAHASHI, Yuichi KAMATA, Taro HIRASAWA
Spectroscopic study on local radiative properties of luminous flame, i.e. emission from soot could, is performed by utilizing counterflow burner. By means of propane-air counterflow diffusion flames, measurements of one-dimensional (perpendicular to the flame surface) distributions of temperature and radiative quantities in the stationary flame are accomplished. Examined spectral range is in the visible and near-infrared regime (0.6 μm-1.0 μm). It turns out that bulk emissivity from the luminous flame, εLF, shows apparent wavelength dependency in the observed spectral range (εLF=εLF(λ-α)), and its power-law constant, α, varies along the perpendicular to the flame surface. By taking the longer observed wavelength in the visible regime (eg., 0.9 μm), α closes to the constant irrespective of the observed location. By taking the shorter observed wavelength (eg., 0.7 μm), on the other hand, α tends to be monotonically decreased to the high temperature regime (α has inverse correlation to the flame temperature). This trend is somewhat similar to the particle diameter or volume fraction of the soot cloud according to the previous literatures. It is suggested that non-gray body feature of the luminous flame (i.e. wavelength dependency on bulk emissivity) is pronounced when the large soot fragments are coarsely distributed. Adopting the shorter wavelength may work for better diagnostics on local soot status.
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