Investigation On Microcosmic Morphology And Structure Characterof Soot From Diesel And Oxygenated Fuel Combustion

Engine combustion generated soot is the main air pollution source.Soot generation mechanism and structure characteristic have been concerned by investigators for a long time.With the development of advanced internal combustion engine technology,the combustion process in engine has been tremendous proved.The size,structure and morphology of combustion produced soot has also changed.The size gets finer,the component gets more complicated,and gain extra optical,catalytical and adsorptive properties.Hence the vehicle emission standards became more and more strict.Blending oxygenated fuel into diesel is a practice method to reduce soot emission,while the detail mechanism remains to be explored.To investigate the soot formation mechanism,size distribution and microcosmic morphology is meaningful for engine soot emission control and management.The main objective of this thesis is to explore the soot microcosmic morphology,structure and formation mechanism from diesel and oxygenated fuel combustion in high temperature high pressure environment.The influence of engine operate condition,combustion environment,fuel property on soot morphology and formation is investigated.Soot morphology analysis method and theory is concluded.In the first part,Soot sampling theory and method are introduced.The connection between soot formation process and soot morphology is discussed.And the main parameters to describe soot pattern and morphology are concluded.To perform in-flame soot sampling in a constant combustion chamber,a specially sampling probe are designed to realize multiple point-direct sampling in spray flame.Single-nozzle spay flame in high and low-pressure condition are conducted for soot sampling.TEM observation and subsequent analysis are conducted to obtain detail information of soot morphology.The soot in spray flame mainly exist as form as primary particle and small aggregated particle.The average diameter of soot particle in flame is less than 80nm.The aggregation reaction is mainly affected by soot concentration and environment temperature,which is restricted in flame.The aggregation extent of soot in spray flame increase as the combustion process.The concentration of solid soot is large at the center of the spray flame,and less at the fringe.Soot formation process and distribution feature vary as combustion environment changed.Blending butanol into diesel normally delays the ignition of spray flame,decrease combustion duration,and significantly reduce soot number and mass concentration.With more proximate properties as diesel,the effect on combustion and soot concentration of blending biodiesel is relatively implicit.The operation condition and in-cylinder combustion environment will affect the soot concentration and morphology in emission gas.A single cylinder diesel engine without EGR and after treatment device,and a high pressure common rail diesel engine are adopted to investigate soot emission in engine exhaust gas.Exhaust soot sampling bench are design and build to conduct engine exhaust transient soot sampling.Size,structure and morphology of exhaust soot are analyzed and compared with engine operation status.The influence of engine operation condition and consuming fuel on soot formation and morphology are discussed.Blending butanol could transparently decrease exhaust soot mass and number concentration,and increase primary particle size,aggregation size,and fractal dimension.The influence of fuel injection strategy and engine load on soot high-resolution nanostructure are also concluded.The soot diameter of engine exhaust gas decrease as fuel inject pressure increased,soot aggregation fractal dimension first decreases and then increase,crystal layer length first increases then decrease,crystal layer thickness and curvity first increase,and then decrease.As the engine load increased,the primary particle diameter increase,soot aggregation fractal dimension decrease,crystal layer length increase,crystal layer thickness and curvity decrease.Fuel injection strategy and engine load change soot concentration and smoke intensity of the exhaust gas,as well as the primary particle diameter,fractal dimension and internal nanostructure of emission soot,which affect the absorption,transmission and chemical activity characteristic of engine combustion formed soot.