| As an ideal alternative fuel for diesel engine,biodiesel can effectively reduce CO,HC and PM emissions without changing the structure of diesel engine.The use of a certain percentage of biodiesel blended with petro diesel combustion can mitigate the impact of the oil crisis.The diesel oxidation catalysts(DOC)are commonly used to oxidize CO and HC emissions as well as partial particles.The particulate oxidation catalyst(POC)is considered as an effective particles reduction after-treatment technology.The combination of DOC and POC is a commonly and widely used after-treatment device.With the popularization of biodiesel,it is important to do the research of DOC+POC's effect on the emission characteristics and the physicochemical properties of particulate matter,which is of great significance to the application of biodiesel and the improvement and optimization of the DOC+POC device.In order to analyze the effects of DOC+POC on conventional emissions and physicochemical properties of particles varied with different blending biodiesel(B0,B10 and B20),bench test was carried out on a high pressure common rail diesel engine and the physicochemical properties of particulate matter were analyzed.(1)Conversion efficiency of conventional emission after using DOC+POC were analyzed by the exhaust analyzer.With the increase of biodiesel percentage,the emission of CO,HC and soot were decreased while NOx emission increased.After the installation of DOC+POC,the emission of CO,HC and soot were decreased significantly,and the NOx emission decreased slightly.The conversion of CO,HC and soot decreased with the increase of speed,and increased with the increase of load.At 2200r/min,the average conversion of CO,HC and soot of B20 was the highest,and the conversion rate was 87.7%,83.7% and 52.7% respectively.(2)Using micro-orifice uniform deposition impactor(MOUDI)to analyze particle samples' size distribution.When the content of biodiesel percentage was increased,the mass concentration within each size grade was decreased.The mass concentration peak value of particulate matter emitted from three fuels all ranged from 0.18?m to 0.32?m.After the installation of DOC+POC,the mass concentration of particulate matter was decreased.The conversion rate increased with the increase of the mixing ratio of biodiesel,and decreased with the increase of the speed.The convert efficiency of accumulation state particles was higher than that of coarse particles.At 2200r/min,the convert efficiency of accumulation state particles with B20 reached 60.2%.(3)The oxidation characteristics and composition proportion of particles before and after DOC+POC action were studied by thermogravimetric analysis.The results showed that with the increase of mixing ratio of biodiesel,the soluble organic components(SOF)in the particulate matter increased,soot and inorganic salts decreased,and the particles were easier to be oxidized.After the installation of DOC+POC,the mass fraction of SOF decreased obviously,the other components increased in varying degrees.With the increase of blending ratio of biodiesel,TG curve rose,the peak of SOF weight loss ratio decreased significantly in the DTG curve.(4)The effects of biodiesel blending ratio and DOC+POC on SOF content were studied by gas chromatography-mass spectrometer(GC-MS)analysis.When the content of biodiesel percentage was increased,the mass fraction of lipids and acids components in SOF were increased and alkanes,aromatic hydrocarbons and phenols compounds were decreased.Moreover,the mass fraction of carbon atoms in SOF of B0 and B20 showed a normal distribution with a peak at C16.DOC+POC had a significant effect on the conversion of lipid and acid substances.The decrease of mass fraction was 55.45% and 43.27%,respectively.Moreover,DOC+POC had obvious effect on the oxidation of C12~C18 in SOF of B20.(5)Influence of chemical heterogeneity,graphitization degree and other parameters particles before and after DOC+POC action were investigated by means of Raman spectroscopy.The results showed that compared with B0,particles of B20 had more kinds of substances,enhanced chemical heterogeneity,reduced graphitization and increased amorphous carbon content.After the installation of DOC+POC,the graphitization degree of particles of B0 and B20 increased,the chemical heterogeneity decreased,the amorphous carbon content decreased,and the particulate structure became more regular. |
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