Twodimensional imaging of formaldehyde in a transient fuel spray

To investigate the ignition processes in a diesel spray, the two-dimensional techniques of silicone oil particle scattering imaging (SSI) and laser induced fluorescence (LIF) were used. The sequential and two-dimensional images of SSI reveal that the first ignition occurs in the periphery of spray head vortices, not in spray tip. The fluorescent images of intermediate products which are formed during the ignition reaction were taken by the LIF method with the laser sheet of the 3rd harmonic of Nd: YAG laser. We conducted these visualization techniques and measured the chamber pressure under the same conditions. The the ignition delays obtained by each technique were compared. This comparison showed that both the time when the first local heat release is detected by SSI method and the time when the first fluorescence is detected by LIF method are nearly equal to the time when the total heat release due to ignition reaction exceeds the heat absorption of fuel evaporated.