In-situ temperature and major species measurements of sooting flames based on short-gated spontaneous Raman scattering

TL;DR

This paper presents a novel, calibration-free Raman spectroscopy method for in-situ temperature and species measurements in sooting flames, overcoming interference challenges with optimized strategies and demonstrating accurate results in ethylene flames.

Contribution

Introduces a low-cost, interference-resistant Raman thermometry technique for sooting flames that does not require calibration and effectively measures temperature and species.

Findings

Successful temperature measurement with high accuracy

Effective suppression of interference signals

Agreement with simulation results

Abstract

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.