| Diesel engine is widely used in automobile,construction machinery,agricultural machinery and other fields of industrial and agricultural production due to its advantages of high thermal efficiency and good economy.The particulate matter discharged from diesel engine is a major source of environmental pollution.At present,diesel particulate filter is recognized as the most effective way of post-treatment of particulate emissions from diesel engines.The use of diesel particulate filter in diesel engines can effectively reduce particulate emissions,but with the increase of vehicle mileage,the accumulation of particulate in the diesel particulate filter causes the gradual increase of exhaust back pressure.Studies have shown that when the exhaust back pressure exceeds 25 k Pa,the engine performance will deteriorate.Therefore,the diesel particulate filter must be regenerated regularly.The fuel additive diesel particulate filter catalytic regeneration greatly reduces the ignition temperature of particulate matter by adding fuel additives.Diesel particulate filter regeneration can be achieved at normal exhaust temperature of diesel engine,which has high research and application value.In this paper,Fe-FBC fuel was prepared with organic iron-based additives,and its effects on diesel engine economy,emission performance and particulate characteristics were studied,which provided parameters for subsequent diesel particulate filter fuel additive regeneration simulation,thus providing experimental and theoretical basis for the research of fuel additive particle filter regeneration.Based on the particulate matter oxidation classic Bissett-Konstandopoulos model,considering the change of particle specific surface area and the influence of inhibitory factors,the soot oxidation kinetic model was improved,and a numerical model of diesel particulate filter using fuel additive catalytic regeneration on the basis of FLUENT platform was established.The regeneration characteristics and regeneration reaction mechanism of diesel particulate filter catalytic regeneration with fuel additives were explored,so as to realize the purpose of rationally organizing the regeneration process and improving the regeneration performance of diesel particulate filter.The research work and main conclusions are as follows:（1）Four kinds of iron-based fuel additive fuel samples,Fe100,Fe200,Fe300 and Fe400,were prepared by selecting organic iron-based metal additives.The effects of different proportions of fuel born catalyst/ diesel mixed fuel on the economy and emission performance of diesel engine were studied on the test bench.The test results showed that the specific fuel consumption and thermal efficiency of iron-based fuel additive fuel were lower than that of standard diesel,and they were more obvious at low load.The oxynitride and the exhaust smoke of diesel engine decreased with the increase of iron-based fuel additive concentration,and the decrease trend was more obvious at high load.The carbon monoxide and hydrocarbon emissions of the Fe-FBC fuel were lower than those of standard diesel fuel.According to the effect of different proportions of Fe-FBC fuel on effective specific fuel consumption and effective thermal efficiency,oxynitride,exhaust smoke,carbon monoxide and hydrocarbon emissions,it was found that the optimal adding proportion of Fe-FBC was Fe300.The mass concentration distribution and the quantity concentration distribution with particle size of Fe-FBC and standard diesel were measured by using Micro-Orifice Uniform Deposition Impactor（MOUDI）and particle size spectrometer for exhaust emission（EEPS）.The results showed that the particle mass concentration distribution of standard diesel and Fe300 were unimodal lognormal distribution.Compared with the standard diesel particles,the total mass concentration of Fe300 particles decreased by 20.58%,and more than 90% of Fe300 particles were concentrated in the accumulation mode.The mass median diameters of diesel and Fe300 particles at rated power were 0.426μm and 0.374μm respectively.The particle number concentration of standard diesel and Fe300 presented logarithmic bimodal distribution,and the soot particle size of Fe300 fuel is shifted towards small particle size compared with that of the standard diesel.The quantitative median diameters of the standard diesel and Fe300 were 50.8 nm and 39.2 nm,respectively.（2）Scanning electron microscope（SEM）and transmission electron microscope（TEM）were used to qualitatively and quantitatively analyze the micromorphology of soot particles burning standard diesel and Fe300 in diesel engine under rated working conditions.The disorder degree of particles was analyzed and calculated by fractal theory.The microcrystalline size,layer spacing and microcrystalline curvature of basic carbon particles were measured and analyzed by digital micrograph.The results showed that the morphology of particles in SEM images mainly presented irregular cluster structure.Compared with the standard diesel,the microstructure of Fe300 soot particles was smaller than that of the standard diesel,and most of them were dendritic chain structure.The specific surface area increased,and the number of particles increased.In the TEM images,Fe300 fuel particles had obvious solitary nucleus particles compared with the reference diesel fuel.In HRTEM images,Fe300 fuel particles had obvious Fe lattice.Compared with the reference diesel,the box counting dimension of fe300 fuel soot particles decreased,the interlayer spacing increased,the microcrystalline size decreased,the microcrystalline curvature increased,the graphitization degree of the carbon layer of the basic carbon particle structure decreased,and the oxidation activity increased.（3）Thermogravimetric analysis（TGA）was used to analyze the initial oxidation temperature,spontaneous combustion temperature,maximum combustion rate temperature and burnout temperature of soot particulates from diesel engine fueled with standard diesel and Fe300 under rated working conditions.The pyrolysis kinetic parameters of particles were analyzed by Coats-Redfern integral method.The combustion characteristics of particles were analyzed by single particle combustion simulation.The analysis results showed that the soluble organic fraction content in Fe300 particles increased,and the temperature peak of weight loss rate moved to the low temperature region.In the soot oxidation process,the initial oxidation temperature,spontaneous combustion temperature,maximum combustion rate temperature,burnout temperature of Fe300 particles decreased all compared with those of the standard diesel particles,indicating that the addition of Fe-FBC improved the oxidation activity of soot particles.The activation energy of diesel soot particles was higher than that of Fe300 fuel soot particles（4）When Bissett and Konstandopoulos analyzed the soot oxidation kinetics model of diesel particulate filter regeneration,the specific surface area of soot particles were assumed unchangable with the change of soot oxidation conversion rate,while the specific surface area of soot particles was constantly changing during diesel particulate filter regeneration.At the same time,the soot oxidation process was also affected by a semiempirical inhibition modification term.Based on the B-K（Bissett-Konstandopolos）model,the kinetic model of soot oxidation reaction was improved by considering the change of specific surface area and inhibition factor during the reaction process of soot particles.The regeneration process of diesel particulate filter was simulated by FLUENT software combined with UDF,and the effectiveness of FLUENT combined with UDF to simulate the regeneration process of diesel particulate filter was verified through numerical simulation and experiments,which laid a solid foundation for subsequent diesel particulate filter regeneration simulation on different condition.（5）Based on the new soot oxidation kinetic model,the regeneration of diesel particulate filter was simulated by using FLUENT software combined with UDF numerical simulation method,and the diesel particulate filter regeneration simulation results using different soot particles（diesel and Fe300 fuel）were compared and analyzed,The effects of structural parameters（filter wall thickness,length and channel width）and operating parameters（incoming oxygen volume fraction,mass flow rate and sediment thickness）on the catalytic regeneration process of particle filter with iron-based fuel additive were revealed.The study showed that the soot particles in the middle section of diesel particulate filter first reacted completely,and then reacted from the middle to both ends.The curve of the maximum wall temperature changing with time could be divided into the warm up,the rapid combustion and the slow combustion.Because the activation energy of diesel particles was higher than that of Fe300 fuel particles,the temperature of soot oxidation reaction increased,the reaction rate decreased and the regeneration time becomed longer.With the increasing of the filter body wall’s thickness and length,the decreasing of the filter body channel width,the maximum wall temperature became lower and the time of the maximum wall temperature was delayed.The mass residual ratio of total soot decreased slowly and the regeneration efficiency decreased. |
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