The Quantification of Laser-Induced Incandescence (LII) for Planar Time Resolved Measurements of the Soot Volume Fraction in a Combusting Diesel Jet

Quantitative Laser-Induced Incandescence (LII) has been applied to investigate the soot formation in a combusting Diesel jet for various conditions.

For the quantification of the LII signal the local soot volume fraction of a diffusion flame burner was measured using laser beam extinction. These data were used for the calibration of the LII signal.

The investigation of the soot formation in a combusting Diesel jet was performed in a high pressure, high temperature combustion chamber with optical access. A wide range of pressure (up to 10 MPa) and temperature (up to 1,500 K) conditions could be covered using a hydrogen precombustion, which is initiated inside the chamber before fuel injection. The influence of different gas atmospheres have been investigated by varying the gas composition (H₂, O₂ and N₂) inside the chamber.

Local soot volume fractions (up to 12 × 10^-6) of different combusting Diesel sprays were measured time (<100 ns) and 2D-spatially resolved (578 x 384 Pixel, <100 μm per pixel). The measurements indicate, that at the initial stage of combustion a decrease of the oxygen concentration of 25% (compared to air) reduces the maximum local soot volume fraction by a factor of 5 to 6. Additionally at this condition the ignition delay is longer.