Impacts Of NO₂ On The Nanostructure,functional Groups And Oxidative Characteristics Of Diesel Exhaust Soot Particles

Nanostructure,surface functional groups and oxidative characteristics during soot oxidation of diesel engines are closely related to the oxidation atmosphere.Therefore,the research on the evolution law of nanostructure,surface functional groups and oxidative characteristics of diesel exhaust soot under different oxidation atmosphere can provide certain theoretical reference for optimizing diesel particulate matter emission.Based on Thermogravimetric,Transmission electron microscopy,Raman spectroscopy and Fourier transform infrared spectrometer,the impacts of oxidation atmosphere on the nanostructure,surface functional groups and oxidation characteristics of soot particles were studied in this paper.Major conclustions from this dissertation are as follows:During the oxidation of diesel soot particles,with the reaction proceeding,the fringe length and graphitization degree increase,and the fringe separation distance and tortuosity decrease.The values of the fringe length and graphitization degree present an order of 10%O₂+1000ppm NO₂>10%O₂ at the same burnout rate of soot,and the values of the fringe separation distance and tortuosity present an order of10%O₂+1000ppm NO₂<10%O₂.Adding 1000ppm NO₂ to 10%O₂ can promote the oxidation of diesel soot particles,futher increase the fringe length and graphitization degree,and futher decrease the fringe separation distance and tortuosity.The relative content of C-H and C-OH functional groups on the surface of soot particles decreases as a whole.The relative content of C-H functional groups decreases most significantly in the range of 20%-30%of the burnout rate,while the relative content of C-OH functional groups decreases significantly in the range of0-20%of the burnout rate.The enthalpy of dissolution of O-O and ON-O bonds is498 k J/mol and 306 k J/mol respectively,which means that NO₂ is easier to dissociate and react with surface functional groups than O₂.Therefore,adding 1000ppm NO₂ to10%O₂ can promote the oxidation of the two functional groups.Adding 1000ppm NO₂to 10%O₂ decreases the initial and bunt-out temperatures of soot oxidation,and the effect of 1000ppm NO₂ on the characteristic temperature of oxidation reaction above increases with the increase of heating rate（10,12,15℃/min）.The influence of 1000ppm NO₂ on the initial oxidation temperature shows that NO₂has good low temperature oxidation characteristics.Under the condition of 10%O₂,the intrinsic activation energy of soot oxidation is 164.43 k J/mol with the reaction order of 1.After adding 1000ppm NO₂,the intrinsic activation energy decreases to113.02 k J/mol and the reaction order changes to 2.