Investigation Of Physical And Chemical Characteristic Of Diesel Particulate Matter During Exhaust

The physical and chemical characteristics of diesel particle change due to the nucleates,condense,collides and oxidation-reduction reactions in the diesel exhaust.This thesis collects the particle using a meet China-IV emission standard diesel with and without diesel oxidation catalyst at different engine operating mode.Analyses the composition of diesel particle,particle size distribution,particle number,micro topology,regular characteristic of particle micro structure,crystal characteristic,specific area,proe volume and thermal decomposition product via exhaust gas analyzer,Raman spectrometer,high-resolution transmission electron microscopy,X-ray photoelectron spectroscopy,nitrogen adsorption instrument,thermogravimetric analyzer and thermogravimetric-fourier transform infrared spectrometry-mass spectrometry(TG-FTIR-MS).In addition,it deduces the decomposition mechanism of the particle.(1)The soluble organic fraction concentration in particle increases as the distance from the exhaust transport increases.The polycyclic aromatic hydrocarbons condense on the surface of particle in order to overall PAHs concentration increases while its toxicity equivalence factor decreases.(2)The total PN decreases while the accumulation mode concentration and the average particle size increases as the distance from the exhaust transport increases.The application of DOC can reduce the concentration of total particle number under medium and low load conditions,but at high load condition,the total particle number concentration is slightly increased.(3)The organic fraction outside of the basic particle and the layer distance and the curvature increase while the fringe length decrease as the distance from the exhaust transport increases.The layer distance and the curvature decrease while the fringe length increase after the DOC.The inner part of particle is oxidized and the outer part becomes more regular.As the engine load increases,the core structure of the basic particle becomes blurred,and the hollow capsule structure will be formed at high load after DOC.(4)While the distance from the exhaust transport increases,the strength,the area and the half width between peaks(D₁,D₃ and D₄)increase,the C/O fraction becomes lower,graphite carbon content decreases and the Co/Cn fraction becomes higher,indicating a more irregular characteristic of particle micro structure,a higher fraction of organic compound,functional group,amorphous carbon,and a lower graphitization degree.The graphitization degree increases after DOC is adopted.(5)As the distance from the exhaust transport increases,the specific area,porous volume and size become larger.Mesoporous is the main kind.The specific area,porous volume and size increase after the installation of DOC.(6)As the distance from the exhaust transport increases,the ignition temperature,the maximum oxidation rate,the burn-up temperature and the activation energy decrease.The activation energy has no obvious change after DOC(7)Thermos gravimetric analysis shows that the thermal decomposition of the particles consists of three stages:thermal decomposition of low boiling volatile organic compounds,high boiling point volatile organic compounds and non-volatile organic compounds,and slow heat decomposition of dry soot.As the distance from the exhaust transport increases,the conversion rate at the first stage and the second stage increase,while that at the third stage decreases.(8)The pyrolysis products of particulate matter were analyzed by thermos gravimetric analysis-infrared spectrometry-mass spectrum.The results show that as the exhaust transport distance becomes larger,the combustible and small molecular compounds increase.Thermal decomposition product includes-OH,NH₃,H₂O,C_xH_y fraction,CO₂,benzene,toluene,phenol,etc in the first thermal decomposition stage.In addition,polycyclic aromatic hydrocarbons were also detected in the second thermal decomposition stage.It can be deduced from the pyrolysis products of particle,the formation mechanism of the particle include the dehydrogenation and broken chain of olefin and alkane,and poly cyclic aromatics.(9)The least square analysis of the 18 factors such as the soluble organic fraction concentration,physical structure and chemical characteristics,etc.that influence the particle oxidation activity reveals that the oxidation activity is significantly influenced by curvature,SOF fraction and oxidation temperature.