Studies On The Morphology And Nanostructure Of In-cylinder Particulates During Combustion Process Of Diesel Engine Fueled With N-heptanes

The pa rticulate em issions o f d iesel e ngine h ave s ignificant i nfluence o n t he atmosphere environment and human health. Detailed investigations on the formation and gr owth mechanism of d iesel pa rticulates are t hus necessary for r educing t he particulate pollution. Based on a total cylinder dumpling system, t he e volution process an d formation mechanisms o f morphology a nd nanostructure of diesel in-cylinder soot w ere investigated us ing t he measurement techniques and analysis method such as digital i mage processing, R aman spectroscopy, a nd X-ray photoelectron s pectroscopy, a nd simultaneous thermal analysis. The database obtained from this study is of instructive significance for better understanding of the formation and growth of diesel particulates. The achievements of this dissertation are listed as follows:1. The in-cylinder particulates obtained from a diesel engine fueled with n-heptane present two types o f morphology: r epresentative pa rticulate an d amorphous particulate. T he r epresentative pa rticulates formed through a gglomeration of small sphere-like pr imary carbon particles during c ombustion pr ocess and are mainly composed of carbon and oxygen. The amorphous particulates were composed of a large number of metal-rich elements such as Fe, S, Na, Mg, Mn, Al, Si, P, K, Zn, Pb through elemental analysis.2. The size distribution o f pr imary pa rticles was investigated by analyzing large numbers o f digital images o f in-cylinder particulates. The results indicated that the size distribution of primary particles showed unimodal distribution with the increasing of crank angle, and the maximum value w as b etween 15 ~20nm. The variation tendency of the average diameter of primary particles was unimodal with a range of 14~19nm during combustion process3. The fractal dimension of representative in-cylinder particulates was in a range of 1.8~2.3 during the combustion history of diesel engine fueled with n-heptane. The results s howed that the s tructure of r epresentative pa rticulates transformed from compact morphology to chain-like structure and then to compact again. Moreover, the fractal dimension of particles decreased with the increasing EGR rate. 4. Based on the electron energy loss spectroscopy data, the percentage content of sp2 carbon atoms in the in-cylinder soot was obtained using the“double window”method. T he r esults indicated that the pe rcentage co ntent of s p2 carbon at oms generally increased with a sudden drop located at the ear ly d iffusion co mbustion phase. T his va riation t rend was c onsistent w ith that of t he r elative r atio of I G/ID obtained from Raman spectroscopy versus crank angle. As the EGR rate increases, the graphitization degree of soot increased as combustion proceeds.