Research On SCR Operating Characteristics Of Diesel Engine Under Multi Operating Conditions

According to the Euro V,Euro VI emission regulations,NO_X emission limits are becoming increasingly strict.Relying on diesel engine internal purification technology has been unable to meet the emission standards,the use of emission aftertreatment technology to reduce NO_X emissions has become the consensus of the industry.SCR technology is one of the promising ways for reducing NO_X emission,which has high denitration efficiency,unchanging the diesel engine structure,good economy,wide temperature range,and has been widely used in Europe and other developed countries.SCR technology is playing an increasingly important role in improving the diesel vehicle exhaust pollution.However,it is difficult to conduct in-depth research on SCR technology in china due to the constraints of the core technical barriers and the cost of test equipment.Therefore,the operating characteristics of the diesel engine SCR system under multiple conditions are studied by the coupling of the exhaust flow field and the SCR chemical reaction.This paper presented a 1D chemical reaction model and a 3D computational fluid dynamics?CFD?coupling method for a turbocharged diesel engine with a displacement of11.596L.This method not only can solve the shortage of experimental conditions,and can solve the time-consuming defect when CFD coupling bench test and can solve the 1D chemical reaction models without considering the gas distribution uniformity,which has a certain application prospect.Firstly,the SCR system was modeled.The gas flow model,urea spray model and 1D catalytic converter model were described in detail.The dimension design of inlet porous pipe and SCR catalyst box was determined,the 3D model of SCR system was established,and the 3D model was processed in CFD software.Then,the operating parameters of the SCR system were obtained and the structural parameters were determined.A 1D simulation model of diesel engine was established,and the rationality of the model was verified by engine bench test.The emission operating parameters of multiple operating conditions were obtained,and the size of catalyst carrier was determined.The exhaust operating parameters of typical operating conditions were chosen as the boundary conditions of CFD simulation,and the full scale simulation of SCR system was carried out.This paper proposed NH3 uniformity coefficient to evaluate the NH3 uniformity of SCR catalytic box entrance section.Determining the urea injection parameters and checking the system pressure drop through the operation parameters of the maximum power point,verifing that the SCR system meets the pressure drop requirements.Finally,the coupling analysis between 1D chemical reaction and 3D flow field in SCR system was realized.By establishing the whole machine model,the influence of SCR system on the power and economy of diesel engine was analyzed,and the relationship between exhaust operating parameters at different operating conditions was analyzed.The effects of exhaust temperature,ammonia NO_X ratio?ANR?,NO₂/NO_X on the conversion efficiency of NO_X and the formation of by-product N₂O were studied by coupling the one-dimensional chemical reaction with the three-dimensional flow field.The results showed that the conversion efficiency of NO_X was the highest and the by-product N₂O was the least when the exhaust temperature was 200??400?,the ANR was 1.1 and NO2/NOx was 0?0.5.