Study On Performance Of Composite Catalytic Convert To Reduce NO_x And PM

As the environment problem increasingly prominent,the increasingly stringent emission regulations put forward higher requirements for automotive diesel engine emissions.China?emission regulations,not only limits the quality of particulate emissions,but also limits the particulate number.Faced with stringent emission regulations,we can't simply rely on someone technology to meet the regulations.This paper mainly studied on the performance of DOC + CDPF + SCR,DOC +SCR + CDPF and SCRF system to reduce NO_x and PM.The first part mainly studied on the various catalysts performance,the reaction principle of the catalysts and matched the catalytic converter with the engine displacement.We also make converter packaging design and catalyst selection.The specific research results are as follows:(1)As for the DOC,we generally coated with platinum,rhodium and palladium and other precious metal catalyst.The Volume of the DOC is about 1times of the engine displacement,in this experiment the parameter of the DOC is ? 190.5 * 101.6 mm,400 cells/in2,and 6 mil wall thickness.(2)The SCR carrier is a flow-through structure,can be coated vanadium base,copper base,iron base and composite catalyst.SCR volume is commonly 2-3 times of engine displacement.In this test vanadium catalyst,we use the vanadium catalyst.(3)The DPF generally choose wall-flow structure,volume is about 1.5-2 times of engine displacement.In this test the parameter of the DPF is ?.190.5 * 203.2 mm,200 cells/in2,12 mil thickness.(4)As for SCRF carrier,the volume is 5.8 L,the specific parameter is ? 190.5 * 203.2 mm,200 cells/in2,12 mil thickness.(5)We also design the sampling tube to guarantee the particulate sample running smoothly.The second part mainly introduces the electronic control unit of the after-treatment system,as well as the signal acquisition system.(1)Understand the function of the after-treatment system control unit,and select the freescale microcontroller as the control unit.(2)Select the urea nozzle,match a dc-motor drive board to make the urea nozzle solenoid valve work,and control the nozzle opening by adjusting the PWM module.(3)Set up signal acquisition system and take advantage of LabVIEW software to communicate with acquisition system.The third part mainly carried on the engine bench test,through test and data analysis,research the influence of different catalysts combination arrangements on exhaust emissions.(1)According to this experiment,performance of single SCR is superior to the DOC/CDPF+SCR and DOC+SCR+CDPF in reducing NO_x,the causes of this phenomenon is mainly: first,oxidizing converter can't match with SCR catalysts;Second,this SCR catalysts itself has certain ability of oxidation;Third,the existence of copper element,to a certain extent,affect the NH3 oxidation.(2)In this test,test found that,due to the intervention of oxidation catalysts,integrated post-processing system perform better in THC reduction,DOC + CDPF + SCR system has a high THC conversion efficiency.(3)According to this experiment,due to low particle emissions and high THC emissions of the engine,the quality of particle capture efficiency is low,mainly because the particulate trap system has higher efficiency of the soot,and THC can flow through the trap as gaseous,causing low quality of particle capture efficiency.(4)Due to the limitations of the existing technical conditions,the SCRF used in this experiment can't completely finish test plan,but still leave some experience to subsequent research.