UV-Absorption Measurements by Spontaneous Raman Scattering in Low-Sooting Diesel-Like Jets

UV-absorption measurements are sparse in diesel(-like) combustion, particularly close to the premixed burn. Thus, such measurements are conducted in diesel-like jets in a high-pressure vessel in this work, using 1D spontaneous Raman scattering (SRS) from N₂. Stokes (~263 nm) and anti-Stokes (~235 nm) SRS induced by a krypton fluoride excimer (KrF*) laser (~248 nm) is exploited. Anti-Stokes SRS can be directly used for attenuation correction of laser-induced fluorescence (LIF) from NO at ~236 nm. Results show the importance of attenuation correction, although the jets are largely non-sooting. To identify absorbers, effects of SRS wavelength, measurement time in the injection event, location in the flame, jet width (JW), temperature, CO concentration, and injection pressure are considered. Particularly strong attenuation observed around the time of second-stage ignition appears to be primarily caused by combustion intermediates such as partially oxidized fuel. In the quasi-steady period (QSP) of the injection event, non-negligible contributions of these absorbers are also found by comparing measured attenuation data to simulated absorption by hot CO₂ and O₂. This is particularly indicated by the wavelength dependence of attenuation. However, the simulations also show that CO₂ appears to be the dominating absorber in the QSP relatively far away from the premixed burn.