| Due to the rapid development of world’s population and economy, the demand for energy is increasing. Hydrocarbon fuels are the main source of China’s energy consumption. Soot is one of the pollutants generated because of uncompleted combustion of hydrocarbon fuels. The existence of soot particles in flame will significantly decrease the energy efficiency and shorten the lifetime of the energy conversion facility and equipment. At the same time, soot is an important carbon source of combustion generated dioxins and other persistent organic pollutants from waste incinerator or open fired flames. In addition, soot has a complex internal relation with PAHs, NOx and other pollutants that is harmful to human health. And soot may also cause global warming and reduce the visibility of atmosphere. Detailed investigation of the formation of soot particles is extremely important for the improvement of combustion efficiency and the control of pollutants emission.This paper proposed a quantitative study of the effect of oxygen concentration on soot forming in oxygen-lean and-rich C2H4/O2/N2diffusion flame. The spatial distribution of soot volume fraction was measured by in-situ laser-extinction method. The diameter of individual soot particle and mean size of agglomerates were estimated by combining thermophoretic sampling and transmission electron microscopy. The developing of soot particles under different flame condition was observed through SiC fiber deposition and scanning electron microscopy. The three-dimensional distribution of flame temperature was retrived from flame images. Results show that, for the examined diffusion flame, when the oxygen concentration is enhanced, the fuel decomposition and the formation of soot are promoted leading to the increase of flame temperature. Soot particle diameter and mean size of agglomerates will increase at the same axial position of flame centerline. Soot volume fraction will increase and the location of its peak value will shift towards flame bottom. The radial distribution range of soot volume fraction becomes narrow and its peak value near the flame edge rises remarkably. In addition, It is found that there are two scenarios of soot formation:the generation from soot precursors and the migration of small soot particles. Under the experimental condition of this paper, soot formation will be enhanced with enriched oxygen concentration. It is useful to the study of the forming and control of small particle pollutants during different combustion processes. The innovation of this paper is that it’s the first detailed analysis of the effect of oxygen concentration on soot evolution, agglomeration and flame temperature. |
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