  Spontaneous Raman spectroscopy (SRS) is a conventional in-situ laser
diagnostic method that has been widely used for measurements of temperature and
major species. However, SRS in sooting flames suffers from strong interference
including laser-induced fluorescence, laser-induced incandescence, and flame
luminosity, which is a long-lasting challenge. This work introduces a low-cost,
easy-to-implement, and calibration-free SRS thermometry in sooting flames based
on a 355-nm nanosecond laser beam. Several strategies were utilized to increase
the signal-to-noise ratio and suppress the interference: (1) nanosecond ICCD
gate width; (2) optimized ICCD gate delay; (3) specially designed focusing
shape of the laser beam; (4) ultraviolet polarizer filter. The temperature was
obtained by fitting the contour of Stokes-Raman spectra of N2 molecules, which
does not require additional calibration. Based on the measured temperature, the
mole fraction of major species can be obtained with calibration. This method
was used in the temperature and major species measurements of an ethylene-based
counterflow diffusion flame. The experimental results show an excellent
agreement with the simulation results, demonstrating the feasibility of
performing non-intrusive laser diagnostics of sooting and other particle-laden
flames accurately.

Optics;Instrumentation and Detectors