Research On The Dimensionless Model Of Critical Adblue Injection Rate That Induce The Deposit Formation Of Diesel Engine SCR System

Air pollution is serious increasing with economic development of our country.China environment ministry's<China Vehicle Environmental Management Annual Report(2016)>indicate,vehicle annual NO_x emission quantity have be up to5,849K ton,which about 30%of national total NO_x emission;especially in Beijing,Shanghai and east–central China densely populated area,PM contribution of vehicle can be up to 30%~50%.Even though diesel engine vehicle only represents 12.6%of total automobile population,but it's NO_x emission can up to 70%and PM can up to 90%of entire vehicle emission.So,develop and improve diesel engine emission reduction technology is significant important.SCR technology have been recognized as the most preferred approach to meet stricting emission standards,which also is the most fit for our country situation.Adblue have been selected as the reductant in SCR system to reduce NO_x emission.But due to the restrict of engine working condition,exhaust pipe structure,urea injection system structure and environment condition,adblue often cannot decomposing completely,which leading deposits formation on the surface of dosing nozzle,exhaust pipe wall,mixer,flange and catalyst,result diesel engine and aftertreatment failure.In the field,dosing nozzle and exhaust pipe wall deposit issue are the most commmen compared with other positions.In order to solve dosing nozzle and exhaust pipe deposit issue,this paper focus on the research of the critical adblue injection rate which induce the deposit formation,and the research is based on both experimental and simulation.Finally get the dimensionless model of critical adblue injection rate to induce the deposit formation,which can guide SCR system optimize design and matching with diesel engine.The main contents and conclusions are as follows:(1)Prove there is a critical state of the deposit formation on the surface of urea nozzle and exhaust pipe,define critical adblue injection rate.Based on experimental data,prove there are critical adblue injection rates on all engine-working conditions.Sum up the rules between critical adblue injection rate and key parameters(exhaust temperature,space velocity,conductivity coefficient of the exhaust pipe).(2)The critical adblue injection rate model is established by linking the exhaust pipe CFD model and the detailed deposit mechanism model based on AVL Fire and Boost software,which can be used to calculate the critical adblue injection rate.The model parameters have been identified based on the engine bench test results,which make the model calculation error within 10%.(3)Based on critical adblue injection rate model,to do the influential factor simulation study.First going to do single factor simulation research,expose each rules between critical adblue injection rate and single factor;then based on DOE(design of experiments)method,select appropriate orthogonal array to design simulation scheme,to study each single factor weight and prove critical factor.(4)Build up the dimensionless model of critical adblue injection rate,establish SCR system optimize design method based on dimensionless model,prove dimensionless model's universality and accuracy according to the field tests results of different diesel engines.