| Nowadays,it is very difficult to resort to in-cylinder control strategies only to meet the increasingly rigorous laws and regulations for diesel emissions control.In addition,even though the in-cylinder control technology could reduce the total mass of particulate emissions,the number of particles remains almost the same and smaller diesel particles are generated.More and more studies have shown that those smaller diesel particulates are more harmful to human health.And it is quite probable that future laws and regulations will set a limit to the quantity of diesel particulates emissions.Therefore,more and more countries have focused their attention on the control of the number of small particulates emissions.The particulate filter is one of the most effective methods to solve such problems.In this paper,a series of research has been carried out concerning the diesel particulate filter system.1.Research on influences of diesel particulate components of diesel particulate filters.A particulate sampling device has been designed to sample the diesel engine particulates in three cases:base line engine without any filters,engine with bag filter,engine with ceramic filter.The influence of diesel engine operating conditions on the characteristics of particulate components is analyzed,as well as the emission characteristics of alkane and aromatic hydrocarbons in SOF(Soluable Organic Fraction).The research results show that at the same engine speed particulate emissions increase with the increasing engine load.The results also show that with the increase of engine load,the percentage of SOF in particulate decreases gradually,while the percentage of IOF(IOF- Insoluble Organic Fraction) increases gradually.The percentage of SOF increases from 15%to 45%,its influence on particulate characteristic can not be ignored.The total content of n-paraffin hydrocarbon in SOF of particulate ranges from 70%to 80%,and that of branched paraffin is between 2%and 22%;multiring hydrocarbon takes up from 1%to 13%.Under different operating conditions,the number of carbon atom in SOF is distributed slightly different.In addition,the percentage of SOF in particulate is a little smaller with the bag filter than with the ceramic filter.With the bag filter,the percentage of each component in SOF after filtration is all below 20%,relatively evenly filtered.The relatively content of individual component in certain operating mode is nearly 40%after filtered by the ceramic filter.The filtration efficiency of bag filter to multiring hydrocarbon is higher than that of the ceramic filter.In summary,bag filter is a better post-treatment device.2.Research on combustion characteristics of diesel particulates. By the use of the thermal gravimetric analysis technique,this paper studies the combustion performances of those collected diesel exhaust particulates under the following conditions:the oxygen content is 10%,20%,30%;heating rate is 10℃/min,20℃/min, 30℃/min,40℃/min;and the particulate mass is more than 5mg, from 3.5mg to 3mg,less than 1.5mg.The experimental results show that the particulate combustion is clearly divided into two stages, volatile matter burning(low-temperature stage) and fixed carbon burning(high-temperature stage ).The weight loss at low-temperature stage takes up about 20%of the total weight loss, and the high-temperature stage about 70%.It shows that the combustion of carbon is the main part of the combustion process. When the oxygen content was lower,the combustion of the particulates needs higher temperature.When reaction temperature is lower,it requires higher oxygen content.In summary,the combustion performance tends upwards with the increase of the oxygen content at low oxygen content.Meanwhile,the results also show that the combustion performance is almost the same when the oxygen content is 20%and 30%.While compared with the performance at 10%oxygen content,the difference is obvious.This indicates that increasing the oxygen content has little effect on the combustion performance of particulates when oxygen content changes from 20%to 30%.The research also finds that average reaction activation energy is about 60kJ/mol when the oxygen content is 20%and 30%,which is equivalent to the value caused by the addition of fuel additives used in ceramic filter.At present,the use of fuel additives can reduce the activation energy of particles to this figure,that is to say,when setting a combustion reaction atmosphere with air or higher-oxygen-content gas,the requirements of passive filter regeneration to the activation energy of particles can be met.3.Based on the sound propagation control equation of ideal fluid particle,the equation used in particulate filter is deduced taking flow velocity,thermal conductivity and viscosity into account. On this basis,by using Darcy's law to solve the pressure drop problem of hole wall at neighboring filter unit,the filter propagation constant and the computation model of transfer matrix are set up. Based on this,the insertion loss of engine under specific operating mode is calculated and compared with the measured value,verifying the correctness of the theoretical analysis.4.The three-dimensional numerical model of gas flow of particulate filter is set up.On the basis ofκ-εturbulent flow theory,the filtration unit is assumed to be the porous medium and the exhaust flow characteristics in bag filter is simulated and solved with the FLUENT software.The comparison of numerical values and experimental values verifies the correctness of the established model. The calculating results show that the pressure decreases progressively in the bag filter,while decreases abruptly in filtration unit.This indicates that the filtration unit is the main cause of pressure loss.In addition,the neighborhood of the entrance wall surface is another concentrated position of pressure loss.The structural parameters will also affect the whole pressure loss of bag filter.5.The stationary particulate-discharging system is designed.It can be applied to stationary diesel engines as well as buses and other equipment with little request to location and which use bag filter to control particulate emissions.The difficult problem of regeneration is solved.
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