2019 Volume 98 Issue 8 Pages 176-185
An inverse diffusion flame is formed during the partial combustion of the reformed gas for tar reduction in the producer gas generated by the gasification of woody biomass. The polymerization and decomposition of tar occur simultaneously in the vicinity of this inverse diffusion flame. The combustion reaction of producer gas proceeds in the diluted phase. In order to decompose tar without it polymerizing into soot, it is necessary to understand the flame structure. Therefore, this study is aimed at understanding the flame structure of an inverse diffusion flame. In particular, in order to analyze the influence of the diluent, the effect of the concentration of carbon dioxide as an oxidizer on the flame structure and tar decomposition was investigated by observing the CH* chemiluminescence, the planar laser-induced fluorescence (LIF) of polycyclic aromatic hydrocarbons (PAHs), and the laser-induced incandescence (LII) of soot. The results showed that the peak intensities of CH* chemiluminescence, LIF signals from PAHs, and LII signals from soot are distributed in the stated order in a radial direction from the central axis. While PAHs are formed in the upstream of the flame and decrease gradually along the mainstream direction, the relative volume fraction of primary soot particles continued to increase along the mainstream direction. Further, a high carbon dioxide concentration resulted in a longer flame. At the same time, it led to a large volume fraction of soot downstream of the flame. As the concentration of carbon dioxide in the oxidizer increased, carbon yield decreased, suggesting an increase in soot formation.