Effect of NH3 addition on soot morphology and nanostructure evolution in laminar ethylene diffusion flame

Ammonia, as a carbon neutral alternative fuel, has attracted wide attention. However, due to the defects in the combustion performance of pure ammonia, it is still necessary to further solve this problem in practical utilization. The purpose of this paper is to study the influence of ammonia on the morphology of soot and the evolution of nanoparticle structure in laminar flame of ethylene. In this work, the soot collected by thermophoresis probe was observed by the high resolution transmission electron microscope (HRTEM), and the image information in HRTEM images was statistically processed, and the graphitization degree of soot was measured by X-ray diffraction (XRD) spectrum of soot samples. The experimental results show that the addition of ammonia can inhibit the growth of soot nuclei and delay the formation of incipient soot, and has different effects on the evolution of soot morphology and structure in ethylene flame. It is noteworthy that the soot samples collected in the upstream part of the ammonia-doped flame show more mature core-shell structure in HRTEM images and more graphitized XRD diffraction data than those collected in pure ethylene flame. The main reason may be the chemical effect of ammonia and the thermal effect caused by the reduction of flame radiation loss, which have different effects on the nanostructure and morphology of soot at different stages of soot formation. Fringe structure model is used to describe and explain the influence of soot in flame with height before and after ammonia doped.