抄録
In order to investigate early soot formation process in a diesel spray flame, 2-D imaging and spectral measurements of laser-induced emission from soot precursors and soot particles in a transient spray flame achieved in a rapid compression machine (2.8MPa, 710K) were conducted. 3rd harmonic (355nm) and 4th harmonic (266nm) Nd:YAG laser pulses were used as the light source for laser-induced fluorescence (LIF) from soot precursors and laser-induced incandescence (LII) from soot particles in the spray flame. The 2-D imaging covered an area between 30mm and 55mm downstream from the nozzle orifice. The results of 2-D imaging showed that strong laser-induced emission excited at 266nm appears only on the laser incident side of the spray flame, in contrast to an entire cross-sectional distribution of the emission excited at 355nm, indicating that 266nm-excited emitters are more abundant than 355nm-excited emitters in the spray flame. The spectral measurements were conducted at three different positions, 35, 45 and 55mm downstream from the nozzle orifice, along the central axis of the spray, where LIF from soot precursors was observed in a previous 2-D imaging study. The spectra measured in upstream positions showed broad emissionpeaked around 400 to 500nm, which is attributable to LIF from polycyclic aromatic hydrocarbons (PAHs). The spectra measured in downstream positions appeared very much like grey-body emission from soot particles.
