Flame-temperature, light-attenuation, and CO measurements by spontaneous Raman scattering in non-sooting diesel-like jets

Abstract

Quantitative spatially resolved measurements of temperature and species are lacking particularly in the core of combusting diesel jets. Major problems are light attenuation and interfering light emissions. However, these factors are reduced in non-sooting diesel-like jets, as demonstrated in the present work, because light is not attenuated by soot and interfering LIF (laser-induced fluorescence) from PAHs (polycyclic aromatic hydrocarbons) is substantially lower. The current results show that thermometry by SRS (spontaneous Raman scattering) excited by a UV (ultraviolet) laser is therefore feasible even in the core of a non-sooting diesel-like jet in a combustion vessel. Two diagnostic approaches are assessed. The first one is based on the spectral band shape of the Stokes (red-shifted) ro-vibrational SRS from N2, whereas the ratio of integrated ro-vibrational Stokes to anti-Stokes (blue-shifted) N2-SRS bands is exploited in the second one. It turns out that the first method is advantageous in terms of light attenuation by molecular species, the influence of interfering emissions, and resulting single-shot capability. However, these investigations also show that the anti-Stokes N2-SRS signal can be used for quantification of light attenuation. This is particularly attractive because this SRS band at ∼235 nm nearly coincides with a LIF emission from NO at ∼237 nm, leading to improved attenuation correction of NO-LIF. Furthermore, the recorded spectra indicate that additional quantitative species measurements by SRS are feasible in the non-sooting jet. For instance, the mole fraction of CO is quantified in this work for the first time in the jet core.