Study On Emissions Of Biodiesel Blend Fuel And Catalytic Oxidation Characteristics Of Soot

Energy shortage and environmental pollution are becoming more and more serious.Biodiesel from a wide range of raw materials can be directly used without changing the structure of diesel engines and can effectively reduce particulate emissions.However,the combustion of biodiesel with different chemical composition and molecular structure will change the physicochemical properties and oxidation characteristics of emission particles.Therefore,different proportions of palm oil biodiesel/0^#diesel blended fuel were prepared in this paper.The bench tests of different fuels were carried out on a high-pressure common rail diesel engine and the effects of biodiesel blending ratio on pollutant emissions,surface functional groups of soot,catalytic oxidation characteristics of soot and DPF regeneration were analyzed.The specific research contents of this paper are as follows:（1）The fuel components of biodiesel were measured by gas chromatography-mass spectrometry（GC-MS）.The biodiesel blended fuels with different proportions were prepared,recorded as B0,B20,B50,B70 and B100.The viscosity,oxygen content and cetane number were calculated.The emission performance of biodiesel blended fuel was explored on the bench test system.The results showed that the addition of biodiesel in diesel had a good reduction effect on soot,HC and CO emissions and the emission reduction effect was more obvious with the increase of the proportion of biodiesel.The reduction of smoke emission was the largest at engine 100%load,which decreased by 6.67%,18.09%,28.02%and 36.86%,respectively.The reduction ranges of HC and CO emissions of blended fuels with different concentrations were 6.02%～21.2%and12.7%～31.6%,respectively.The overall unconventional emissions were at a low level,some of them are extremely harmful.The addition of biodiesel inhibits the emission of soot precursors such as polycyclic aromatic hydrocarbons（PAHs）,ethylene and acetylene,but the combustion of biodiesel at medium and small loads will produce more toxic substances such as aldehydes and1,3-butadiene.（2）The surface functional groups,O/C atomic ratio,C atom hybrid form and oxidation characteristic parameters of several soot particle samples were studied by Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy and thermogravimetric analyzer.The surface of soot mainly included various oxygen-containing functional groups,hydrocarbon functional groups and aromatic ring functional groups.The addition of biodiesel make the reaction components different of soot formation process.The content of aliphatic C-H functional group increased by about 27.5%～132%,and the content of-OH and-C=O oxygen-containing functional groups increased by 8.78%～12.8%and 9.98%～27.8%.Due to the different mixing ratios,the O/C atomic ratio of each sample was about 0.158～0.185 and the degree of carbon atomic disorder increased by 4.14%～12.4%.The addition of biodiesel reduced the oxidation characteristic temperature such as initial temperature and peak temperature of soot oxidation.The results of chemical reaction kinetics analysis showed that the activation energy of soot oxidation was significantly reduced by 7.9k J/mol～28.9k J/mol.（3）KNO₃ was loaded on Ce_0.5Mn_0.5O₂ catalysts to prepare K_z-Ce_0.5Mn_0.5O₂ catalysts with different loadings.The catalytic activity of the catalysts for soot oxidation was evaluated by thermogravimetric analyzer,NO-TPO,O₂-TPD and NO-TPD.The results showed that K salt loading increased the number of O^-atom adsorbed in the middle temperature range,increased the peak area of weak NO_x and NO₂^-peaks in the low temperature range,increased the number of oxygen species on the surface of the catalyst and improved the low temperature desorption performance of NO.When z was 0.2,the characteristic temperature of soot catalyzed oxidation by the catalyst was reduced to the minimum and the NO conversion rate was up to 71.2%at 350℃.NO₂ concentration had a good synergistic effect on the catalytic oxidation process of soot.With the increase of NO₂ concentration,the activation energy of B0 soot sample oxidation decreased from 74.65k J/mol to 60.44 k J/mol,and that of B20 soot sample oxidation decreased from69.43k J/mol to 58.71k J/mol.（4）The K_0.2-Ce_0.5Mn_0.5O₂ catalyst was coated on the cordierite carrier,and the catalytic removal effect of DPF before and after coating the catalyst on the pollutants from two kinds of fuel was evaluated in the actual exhaust atmosphere.The results showed that the capture of particles by DPF went through the deep bed capture stage,the transition stage and the filter cake layer capture stage in turn and the pressure drop increase rate of CDPF was significantly lower than that of the blank DPF.The addition of biodiesel made the regeneration equilibrium temperature point of DPF shift to the low temperature zone.Under the effect of catalyst coating,the smoke and NO_x emissions of B0 and B20 fuel decreased most at full load,with smoke emissions decreased by 19.4%and 29.5%and NO_x emissions decreased by 17.1%and 22.8%,respectively.The emissions of highly toxic aldehydes and polycyclic aromatic hydrocarbons were reduced to varying degrees under different loads.HCHO decreased by 37.2%and 43.6%,CH₃CHO decreased by 28.4%and 28.0%.The average decrease of PAHs was about 60%.