| As an ideal alternative fuel,biodiesel can improve combustion and reduce emission of pollutant without changing the structure of diesel engine.The oxidation catalytic converter(DOC)is an important diesel engine aftertreatment device,which can significantly reduce the emission of CO and HC,and also has a certain effect on particulate emission.With the popularization and application of biodiesel,the research of DOC's effect on particle emission and physicochemical properties is of the great theoretical and practical significance to improve the function of aftertreatment device.In this paper,the influence of biodiesel blending ratio and DOC on particle emission and physicochemical properties was studied.Firstly,biodiesel with different blending ratio was firstly prepared(marked as B0,B10,B20).Secondly,bench tests was conducted based on a 186 F diesel engine.Thirdly,by using transmission electron microscopy(TEM)and fractal theory,thermogravimetric analysis(TGA)and gas chromatograph-mass spectrometer(GC-MS),the particle physicochemical properties was analyzed.(1)The effects of DOC on conventional emission were studied by bench tests.The results indicate that the addition of biodiesel can effectively reduce the emission of CO,HC and soot,however NO emission shows a increase trend.Under the maximum torque speed,average emission of CO,HC and soot of B20 under different loads decreases by 17.4%,14.7%,and 30.1% respectively compared with B0,while NO emission increases by 15.6%.After the installation of DOC,the conversion efficiency of CO,HC,NO and soot increases with increasing load.Adding biodiesel improves the conversion efficiency of CO,HC,NO and soot.Under the maximum torque speed,the average conversion efficiency of CO,HC,NO and soot of B20 was 73.3%,62.8%,20.1%,20.0% respectively.(2)Particle samples with different size grades were achieved from MOUDI and mass concentration distribution was obtained by weighting the particle samples.The results show that the mass concentration of B0,B10,B20 peaked between 0.18 and 0.32 ?m and mass concentration show a decline with the increase of particle size.The addition of biodiesel leads to the decrease of particle mass concentration with different size grades,among which it reduced by 70.7% totally by using B20.After the installation of DOC,particle mass concentration decreased obviously when particle size is less than 0.56 ?m while it shows no obvious change when particle size is more than 1 ?m.Conversion efficiency of mass concentration decreases with the increasing particle size and accumulated particles have better conversion efficiency than coarse particles.(3)Through the TEM test,the microstructure characteristics of the particles before and after DOC were analyzed.The morphology and the structure of the particles were also measured with image processing and the box counting dimension algorithms.The addition of biodiesel can reduce the particle size of the basic carbon particles and the fractal dimension particles.After adding the DOC,the particle size of the basic carbon particles is decreased,and the surface of the particles becomes more clear.Under the maximum torque and speed load,the fractal dimension of exhaust particles with B0,B10 and B20 was reduced by 10.1%,12.3% and 15.5%,respectively.(4)The oxidation process and component content change was studied by thermogravimetric analysis.With the increase of the additive proportion of biodiesel,oxidation weight loss of PM tended to be easier during the heating process,the mass fraction of SOF and H2 O also showed an increasing trend while the mass fraction of Soot and inorganic salt decreased.After the installation of DOC,TG curve rose,DTG curve changed from a bimodal curve into a single-peak curve,the peak of SOF weight loss ratio disappeared when the mass fraction of H2 O,SOF and inorganic salt had an ascending tendency.(5)The effects of biodiesel blending ratio and DOC on SOF content was studied by GC-MS analysis.Carbon atom of B0,B10 and B20 was distributed in C3 to C35 and concentrates between C14 and C21.With the increase of bending ratio,mass fraction of acids and alkanes increases while mass fraction of PAHs and phenols indicate a opposite trend and mass fraction of C23~C35 shows a decline.After the installation of DOC,PAHs,phenols accounts for a larger proportion while alkanes,esters,acids accounts for a smaller proportion.Alcohols,Ethers and Olefins show a climb. |
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