Research On Control Technology For SCR To Reduce Diesel NO_x Emission

In this paper, I will find a solution to boost the ability of SCR system reducing NO_xemission,which is based the diesel engine. And use the diesel engine bench connect withUrea-SCR system to test the diesel engine stable condition ESC exhaust emissionparaments.The dSPACE instruments are uesd to control the Urea-SCR system to getrealtime tenperature and exhaust pressure paraments index,and control the dosing pumpinjecting content.On the basis of dSPACE ControlDesk experament tool to study theUrea-SCR system electric control strategy,and use the NO_x sensors to test NO_x contentand NO_x conversion ratio,make further steps to study the Urea system dosing and injectingstrategy questions.The main research works are focused on the following aspects:(1) Research on NO_x emissions performance of the original diesel engine and thetheoretical demand model of urea solution. The NO_x emission performance of the originaldiesel engine was researched. the original engine emission experiment in accordance withGB17691-2005, obtained the original NO_x emission values of diesel engine and the supplyof urea solution at different ESC conditions, learnd t urea injection strategy of SCR system.(2) The theoretical demand model of urea solution was built. According to thequantitative relationship between urea, NH3and NO_x in SCR reactions, derived thetheoretical demand formula of urea solution, built theoretical demand model based onoriginal diesel NO_x emission values. Compared theoretical demand model with actualsupply of urea solution, analyzed the reasons of the differences between theoreticaldemand and actual supply.(3) Base on the ESC exhaust emission experiments research of original diesel SCRsystem, making the exhaust emission testify experiments in whole working condition ofthe diesel SCR system.Then we study on to design the exhaust emissions contentmap,exhaust air pressure map,exhaust air flow map of the original diesel.So it the urea injecting content map on the diesel different working condition.The NO_x reducing contentmap by injecting same content urea,the NO_x conversion map of the diesel exhaustemission,the output NO_x map of SCR system by injecting urea,the NO_x reducing contentmap of the diesel exhaust emission.(4) Using the dSPACE tools to control the SCR system urea injecting,design therealtime voltage signals to control the input digital information of the module in thedSPACE software Control Desk.Design the DAC conversion pins in the dSPACE/Mirco-Autobox hardware to connect the analogy signal voltage input pins of the dosingpump,the input voltage content could be accepted by the NEW DOSE pump,using theConstant/Value module to control the realtime voltage content of the DAC inputpins.When we input a series of voltage content so that the dosing pump could accept therealtime voltage.Then we design to control the realtime voltage content that have sent bythe dosing pump to adjust the urea realtime injecting content,the software design dependon the dSPACE/Control Desk and dSPACE/Simulink.So the plan could be uesed in thediesel SCR system realtime control interface.（5） In the next experiment we use flowmeter to record the urea realtime injectingcontent,the experiment mainly study on the exhaust NO_x emission reducing result whichis controlled by the urea injecting content.The four NO_x exhaust emission experimentsdivide into the original diesel exhaust emission experiment, on the conditon of SCRcatalyst is not installed,we could get the NO_x exhaust emissions content by using originalDCU system control the urea injecting, on the conditon of SCR catalyst is installed,wealso get the optimize NO_x exhaust emissions content by using original DCU systemcontrol the urea injecting, on the conditon of SCR catalyst is installed,we use the dosingpump that developed by ourself to control urea injecting.After analysising the last tworesults,so it can achieve the euro Ⅳ standard.But the exhaust NO_x emission reducingresult and NO_x emission conversion result by use the dosing pump that developed byourself to control urea injecting is better than the result by use original DCU systemcontrol urea injecting,enhance the ability of original SCR system reducing NO_x emissions.