Study on the mechanism of nitrogen conversion in NH3-doped methane premixed flame based on multi-spectral analysis methods

Abstract

It is essential to obtain the in-situ key radicals and components in the combustion process of NH3 oxidation to reveal the volatile nitrogen conversion mechanism. In this work, multi-spectral analysis methods, including image spectroscopy, Tunable diode laser absorption spectroscopy (TDLAS), and plane laser-induced fluorescence (PLIF) were used to obtain the spatial distribution characteristics of the main excited radicals (C2*/CH*/CN*/OH*), H2O, and NO in NH3-doped methane flames, respectively. Furthermore, the kinetic simulation was combined to obtain the key reactions and main pathways of nitrogen conversion. The experimental results showed that when the concentration of NH3 was low, the NO generated in lean flame was less than that in rich flame, which was more than that in rich flame when the concentration of NH3 was high. NH3 also promoted the formation of H2O in flames. The image spectral intensity of CN* had a significant linear relationship with the CN concentration obtained by simulation, indicating that CN* was mainly generated by CN thermal excitation. The results of sensitivity and path analysis indicated that rich flame contributed to the reaction of N-species with H and that high NH3 concentration promoted the conversion of NH2 to HNO. With increasing NH3 concentration and equivalence ratio, the proportion of CH3 conversion to C2H6 was enhanced, while the proportion of CH3 oxidized decreased. This work reveals the mechanism of volatile nitrogen (NH3) conversion and the influence of equivalence ratio and NH3 concentration on it, which provides theoretical guidance for NOx emission reduction.