In situ diagnostic investigation on the structure distribution of inverse diffusion flames based on laser-induced breakdown spectroscopy

Abstract

Laser-induced breakdown spectroscopy (LIBS) was applied to the measurement of methane-oxygen inverse diffusion flames. The correlation between the LIBS emission spectra intensity of different atoms and the overall flame equivalence ratio was investigated by varying the oxygen-fuel equivalence ratio ([O/C]e). Moreover, the applicability of LIBS for local chemical composition measurement in flames was analyzed. The results indicate that the dependence of O(777.2 nm)/H(656.3 nm) spectral intensity ratio on laser energy is negligible. The spectral intensities of C, H and O atoms first increase and then decrease with the increase of axial height, and the radial variations are symmetrically distributed. In addition, the variation of C(247.8 nm)/H(656.3 nm) and O(777.2 nm)/H(656.3 nm) atomic spectral intensity reflects the characteristics of soot formation in flame. The local equivalence ratios at different radial positions at different heights of lean and rich flames were characterized by establishing the linear relationship between the oxygen-hydrogen intensity ratio and the flame equivalence ratio, and the information on the flame structure and dynamics was provided. Thus, it is of great significance for the analysis of flame to reasonably clarify the stability of the determination of atomic composition by LIBS.