Abstract
In order to examine the mechanism on which diesel soot emission is reduced by using Fischer-Tropsch Diesel (FTD) fuel compared to the case of conventional diesel fuel (JIS#2) under EGR conditions, the soot formation processes in a diesel spray flame of two different fuels (FTD and JIS#2) under different ambient oxygen concentrations (21 to 10%) were investigated via Excitation-Emission Matrix (EEM) analysis of polycyclic aromatic hydrocarbons (PAHs) and high-speed laser shadowgraphy of soot particles. The experiments were conducted using an optically accessible constant volume combustion vessel under a diesel-like condition (Ta= 940K and Pa= 2.5MPa). In the FTD-fuelled diesel spray flame, the timing and region for the first appearance of PAH LIF and soot particles in the flame were delayed and shifted downstream compared to the case of JIS#2. In the JIS#2 case, the LIF appeared first in the shorter wavelength region (350 to 400nm) and then shifted to longer wavelength region (above 400nm), while in the FTD-fuel case, the LIF was observed not in the shorter wavelength but only in the longer wavelength region. The production of soot in the flame was increased by lowering the ambient oxygen concentration from 21 to 15% in either fuel cases, while the timing and region for the first appearance of soot and PAHs in the flame were delayed and shifted downstream. By lowering the oxygen concentration further down to 10%, the timing and region for the first appearance of PAHs and soot were further delayed and shifted downstream and the production of soot was decreased.
