Research On The Effect Of Diesel Particulate Filter Regeneration On Selective Catalytic Reduction Performance

To overcome global energy shortage,wide application of diesel engine has become the trend of automotive industry due to its higher fuel economy,lower carbon dioxide emission and greater torque compared to its gasoline counterpart.However,diesel exhaust contains large amounts of particulate matter from incomplete in-cylinder combustion at low temperatures and nitrogen oxides from in-cylinder combustion under high temperature and rich oxygen.The in-cylinder purification of nitrogen oxides and particulate emissions in diesel engines is a mutual constraint,which cannot reduce the emissions of both simultaneously.With the increasingly strict emission regulations(Euro VI,TIER 2 or China VI),the in-cylinder purification technology can no longer meet the requirements.Diesel particulate filter(DPF)and selective catalytic reduction(SCR)have become one of the most effective technologies to reduce particulate and NO_X emissions of diesel engines.As a result,a variety of aftertreatment technologies have emerged worldwide and current diesel vehicles have to be equipped with integrated aftertreatment systems.Both passive regeneration(low temperature)and active regeneration(high temperature)of diesel particulate filter in the aftertreatment system affect the performance of downstream equipments such as selective catalytic reduction catalyst.The concentration of pollutant NO₂ in diesel engine exhaust is very low,but it affects the passive regeneration of diesel particulate filter and selective catalytic reduction.Moreover,both diesel particulatefilter regeneration and selective catalytic reduction involve chemical reaction process.Therefore,the NO₂ concentration and temperature are the key factors influencing the system performance.Optimizing the NO₂ concentration and temperature at the inlet of each converter in the aftertreatment system can improve the synergistic effect and thereby improve the system performance.To this end,based on NO₂ concentration and temperature,this dissertation studies the effect of diesel particulate filter regeneration on SCR performance through mathematical modeling and experiments,combined with relevant theories and algorithms.The results not only provide a theoretical basis for the design and application of selective catalytic reduction and diesel particulate filter for diesel engines,but also have theoretical and practical significance for diesel engine emission control.The main research work of this dissertation is as follows:(1)Considering the influence of mass transfer on SCR performance,the SCR reaction-mass transfer model of Cu-ZSM-5 catalyst is modeled,including sinuousoidal capillary bundle model;the influence of external mass transfer and internal mass transfer on the reaction is analyzed;the transition mechanism of the standard SCR reaction between kinetics and mass transfer control regime is studied;research on SCR performance factors is conducted to offer reasons for NO₂concentration improvement and particulate filter regeneration and provide a theoretical basis for aftertreatment system research.(2)Two mechanisms of NO₂ concentration increase are proposed;the models of increasing NO₂ concentration reactors are established;an analysis of the factors influencing the NO conversion of the diesel oxidation catalyst is conducted;the NO conversion performance of the through-flow diesel oxidation catalyst(DOC)and the wall-flow catalytic particulate filter(CDPF)is compared and analyzed.(3)The passive and active regeneration models of particulate filters are established;low temperature(<300?),medium temperature(300–550?)and high temperature(>550?)performance of the continuous regenerative diesel particulate filter(CR-DPF)assisted by electric regeneration and the influence of key factors on its performance are investigated;the passive and active regeneration performance of various types particulate filters are compared and analyzed,which provides a theoretical basis for the selection of catalyzed continuously regenerating diesel particulate filter(CCDPF)in the aftertreatment system.(4)The CCDPF+SCR(DOC+CDPF+SCR)system model is established;the transformation evolution of aftertreatment system in WHTC cycle is studied;The influence of temperature,oxygen concentration,NO₂/NO_X ratio and other factors on the performance of downstream SCR during DPF passive regeneration and active regeneration is studied,and the effect of CDPF regeneration mechanism on SCR performance is obtained.