(3-22) Two-Dimensional Imaging of Reaction Zone Structure in Diesel Spray Flame by LIF technique((D-3)Diagnostics 3-Applications and Advamced Technolog)

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To investigate the structure of the reaction zone and the early process of young soot formation in a diesel spray flame, CH radical and polycyclic aromatic hydrocarbons (PAH) formed in the diffusion burner flames and the diesel spray flames were visualized two-dimensionally. CH radical was used as the indicator of the reaction zone in the flame because CH is produced and destroyed in the fuel decomposition zone and exists in the thin layer near the stoichiometric contour in the flame. For the visualization of early soot formation zone in the flame, PAH were used as tracers in LIF technique. PAH are well known as the precursors of young soot. An Nd : YAG pumped dye laser was used as a light source. The wavelength of the incident light was tuned to 390.58 nm to excite CH with the Q1(8.5) transition of B^2Σ-Χ^2 Π (v'=0, v''=0) band. The sheet of light passed through the mid-plane of the flame and the LIF from the species in the flame were imaged by an ICCD camera. A narrow band optical filter with a central wavelength of 430 nm and a FWHM of 10 nm was used to detect the fluorescence from CH with the transition of A^2Σ-Χ^2 Π (v'=0, v''=0) band. PAH formed in the flame were excited by the incident lights with the wavelengths of 266, 355, and 391 nm and the LIF spectra from PAH were detected by a spectrometer. For the experiments with diffusion burner flames, methane and propane were used as the fuel. The LIF images excited at the excitation wavelength of 390.58 nm showed that very thin layers of LIF from CH with the width of less than 1 mm is located in the jet periphery. In the central region surrounded by the CH thin layer, strong LIF from PAH were observed. However, the LIF signals of both species did not coexist with each other. The spectra of LIF observed in the central region of the jet had broad band structure which had a peak around 440 nm and spread over 600 nm. This spectra structure is similar to the that of some 3-6 rings PAH such as anthracene, fluoranthene, benzo(ghi)fluoranthene, anthanthrene, and benzoperylene, which were reported in the past studies. The LIF images of free diesel spray flames in a rapid compression machine showed that the fluorescence appears in the whole cross section of leading portion of spray immediately after the ignition. The thin layer of LIF from CH was not observed. The structure of the LIF observed in diesel spray flame was broader than that of diffusion burner flames of methane or propane. This LIF intensity increased monotonously with the increase in wavelength in a range between 350 nm and 650 nm. The shape of LIF spectra from diesel flame was relatively insensitive to the excitation wavelength.
一般社団法人日本機械学会の論文
2001-07-01

(3-22) Two-Dimensional Imaging of Reaction Zone Structure in Diesel Spray Flame by LIF technique((D-3)Diagnostics 3-Applications and Advamced Technolog)

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