| The incomplete combustion of fossil fuels will produce soot particles and other substances that endanger human health and the surrounding environment.The newly issued emission standards have stricter restrictions on particulate matter than before.Under this trend,it is urgent to understand the evolution mechanism of soot particles and reduce particulate matter emissions.In this thesis,starting from the improvement of the passive regeneration efficiency of the catalytic diesel particulate filter(CDPF),and on the theoretical basis that the five-membered ring fuel can increase the oxidation activity of soot particles,the effects of hydrocarbon fuel dicyclopentadiene(DCPD)with a five-membered ring structure on the evolution and formation characteristics of soot in a diesel characterization fuel n-heptane flame at different stages of soot formation were investigated.An inverse diffusion flame(IDF)combustion platform was built to generate IDF and normal diffusion flames(NDF),using capillary-nozzle-hybrid sampling and quartz plate sampling methods to collect soot particles in pure n-heptane,n-heptane/DCPD IDF or NDF.The physicochemical properties of soot particles were characterized by well-established transmission electron microscopy(TEM),Raman analysis(Raman)and thermogravimetric analysis(TGA)techniques.Using laser induced incandescence(LII)technology,the soot distribution characteristics of n-heptane IDF/NDF and the effect of DCPD on soot formation characteristics of n-heptane flame were studied.The capillary-nozzle-hybrid sampling method was used to obtain the soot at different heights of pure n-heptane in IDF and NDF,and the evolution characteristics of soot particles under different flame forms were studied.The results were summarized as follows: the soot particles were surrounded by a large amount of liquid-like material,and the soot stripes inside the particles were chaotic.With the increase of flame height,the soot particle size did not change significantly,and the average crystallite length and crystallite tortuosity increased and decreased slightly.During the oxidation process,the peak temperature of the weight loss rate of soot particles was concentrated around 510 ℃,and there was a slight increase with the increase of sampling height.The morphology of the soot particles in NDF was obviously different from that in IDF: the NDF did not contain liquid-like substances,and the average particle length of the soot particles increased and then decreased with the flame height,and a distinct core-shell structure appeared inside the particles.With the increase of flame height,a multi-core structure gradually appeared inside the soot particles,and the fringe length increased and the fringe tortuosity decreased,the interior of the particles became gradually ordered,and the degree of graphitization gradually increased.The oxidation rate of soot particles obtained at a lower sampling position has two peaks around 510 ℃ and 580 ℃.As the sampling height increased,the peak near 510 ℃ disappeared,and there was only one peak temperature at 580 ℃.The above conclusions showed that due to the difference of flame structure,the soot particles formed by the IDF have not undergone obvious oxidation and were in a young state as a whole,which provided an appropriate method for the study of primary soot particles.Using DCPD as fuel additive,the effects of DCPD on the microstructure,graphitization degree and reactivity of soot in n-heptane IDF/NDF were studied.The results showed that: In the IDF,with DCPD doping ratio increasing from 0 to 20%,the liquid-like material in the particles were significantly reduced;the average fringe length of particles increased;the average fringe tortuosity decreased;the degree of graphitization increased;and the oxidation activity decreased.It was illustrated that DCPD promoted the growth of nascent soot in the IDF.In the NDF,with DCPD addition,the particle size increased significantly;the fringe length decreased and fringe tortuosity increased;the degree of graphitization decreased;and the oxidation activity increased.It was illustrated that DCPD could increase its oxidation activity by changing the nanostructure of soot particles in the NDF.Based on the LII system,the characteristics of n-heptane IDF and NDF in terms of soot distribution,as well as the influence of DCPD on soot formation of two flame forms were analyzed.The analysis showed that the soot of the IDF was mainly distributed on both sides of the flame,the distribution of soot on the central axis was less,and there was no obvious change with the increase of the flame height,and after doping DCPD,the flame height corresponding to the overall maximum peak of the soot concentration decreased,and the radial peak spacing of the flame height was increased.In NDF,the soot distribution curve gradually changed from the axially symmetrical double peak to the single peak on the axis with the increase of the flame height.As the doping ratio of DCPD increased,the spatial span on the flame axis increased gradually. |
PDF Full Text Request