Application of 266-nm and 355-nm Nd:YAG laser radiation for the investigation of fuel-rich sooting hydrocarbon flames by Raman scattering

Abstract

We describe the use of linear Raman scattering for the investigation of fuel-rich sooting flames. In comparison, the frequency-tripled and -quadrupled fundamental wavelengths of a Nd:YAG laser have been used as an excitation source for study of the applicability of these laser wavelengths for analysis of sooting flames. The results obtained show that, for the investigation of strongly sooting flames, 266-nm excitation is better than 355-nm excitation. Although the entire fluorescence intensity of polycyclic aromatic hydrocarbons (PAHs) decreases with rising excitation wavelength, there is increased interference with the Raman signals by displacement of the spectral region of the Raman signals toward the fluorescence maximum of the laser-induced fluorescence emissions. Besides the broadband signals of PAHs, narrowband emissions of laser-produced C2 occur in the spectra of sooting flames and affect the Raman signals. These C2 emission bands are completely depolarized and can be separated by polarization-resolved detection. A comparison of the laser-induced fluorescence emissions of an ethylene flame with those of a methane flame shows the same spectral features, but the intensity of the emissions is larger by a factor of 5 for the ethylene fuel. Using 266-nm radiation for Raman signal excitation makes possible measurements in the ethylene flame also.

Application of linear Raman spectroscopy for the determination of acetone decomposition

“…The decomposition process was analyzed directly inside the calibration cell by Raman spectroscopy. Compared to other optical techniques, it enables simultaneous in situ measurements of different species with a comparatively simple setup [19]. Hence, the simultaneous investigation of tracer stability is possible during LIF calibration measurements.…”

Recent Advances in the Characterization of Gaseous and Liquid Fuels by Vibrational Spectroscopy

“… Interference from laser-induced fluorescence may be a problem in some applications. In order to avoid such effects a number of approaches have been developed including near-infrared Raman [26], deep-UV Raman [27], polarization-resolved detection Raman [28], and shifted-excitation Raman difference spectroscopy (SERDS) [29][30][31][32]. An overview can be found in reference [23].…”

Development of a Raman spectroscopy technique to detect alternate transportation fuel hydrocarbon intermediates in complex combustion environments.

“…Accordingly, few reported studies exist of line imaged Raman spectroscopy applied to flames fueled by complex hydrocarbons. For those that do [16,17,29,30], compromises in signal-to-noise were made from non-optimal line selection or overly lean mixtures near the global extinction limits were used to minimize fluorescence and incandescence interferences. Recently acquired C-H bond stretch Raman spectra from premixed DME flames appear to be sufficiently distinct such that unique signal decomposition can be achieved [38].…”

“…More recently, these Raman/Rayleigh scattering diagnostics, when combined with cross-plane OH laser induced fluorescence (LIF) imaging, have been extended to measure 3D reaction progress variable gradients required for much needed scalar dissipation measurements [33,36] [37] environments. To reduce photofluorescence and incandescence interferences the impact of ultraviolet (UV) excitation has been explored [19,24,29,30]. However, luminosity interference reductions are often outweighed by reduced laser fluences and photo-detector quantum efficiencies at the lower wavelengths.…”