Study on Oxidation Catalytic Converter for Vehicle Diesel Engine

　　Study on Oxidation Catalytic Converter for Vehicle Diesel Engine
　　In order to meet the more strictly emission control regulationsafter-treatment device has been widely applied in automotive engines. Thediesel engine has gained more and more fractions in vehicle power trainsbecause of its inherent advantages such as high efficiency and economy andlow HC, CO, NOx emissions comparison with gasoline engines. But dieselengine is of high PM emissions. PM is much harmful to human being’s healthand has to be controlled. There are many measures to decrease the PMemissions, but adapting after-treatment system is most effectively and littlemodifications in prototype structure of diesel engine. Nowadays, severalkinds of after-treatment systems have been used include DOC、DPF etc. TheDOC can be used independently and coupled with other after-treatmentdevices to meet the stricter emissions regulations. Because the DOC is ofsimple Cylinder neodymium magnet structure and regenerating free and it’s is simple, it has become one ofthe most widely used after-treatment system.The mechanism of DOC decreasing NOx emissions was discussedthoroughly in this dissertation. Test results showed that the main fraction ofNOx decreasing by DOC is resulted by SOF oxidizing and the other smallfraction is contributed by DS oxidizing.
　　The main contains of this paper can bedescribed as following.1、The mechanism of catalytic converter is introduced. The process andchemical kinetics of the interaction between reactants and catalysts has beendescribed. The basic structure characteristics and specifications of catalyticconverter have been pointed out. The actions of catalysts in catalysis reactionhave been analyzed. The characteristics of catalysts such as platinum,rhodium lanthanide and substitute precious metal elements have beenintroduced. The main factors which affect the decontamination efficiency ofcatalytic converter have been investigated. The effects of sulfur fraction in fuelon the catalytic converter and the measures to prevent sulfur poison havebeen concluded.2、The meaning of the catalytic converter performance indexes such asdecontamination efficiency, air-fuel ratio, light-off characteristic and air speedhas been explained in detail. The normative test cycle which was composedof small catalytic converter specimen test, single catalytic converterperformance test etc. has been pointed out.3、The catalyst performance evaluating test bench was built up and thediffluence technology was adopted to prevent the back pressure of outletmanifold becoming too high in small cubage catalytic converters performancetesting, The flux through the catalytic converter was kept in proper range bycontrolling the back pressure of outlet manifold.4、Experimental catalyst samples validating and improving.1)5 kinds of 1.1L catalytic converters (labeled as DCC2-DCC6) and 6kinds of 1.6L catalytic converters (labeled as DCC-11—DCC-14、DCC-KGS、DCC-WF) were tested to found out the best one. Test results showed thatDCC-5、DCC-3 and DCC-6 were capable to meet the expected requirement(the decontamination efficiency is 53.9%、48.6% and 43.3% respectively) andhad the potential to be adopted to widely using.
　　The decontaminationefficiency of 1.6L catalysts except DCC-12 was much lower compared withDCC-WF (baseline, the decontamination efficiency is 19%).2) The performance of DCC-5、DCC-3 and DCC-6 was improved byadding Lanthanide into the catalyst, redesigning the converter volume andoptimizing the ingredient of catalyst. Test results showed that only the changeof DCC-6 catalytic converter meet the target. The catalytic converter labeledas DCC-10 (improved from DCC-6) was of higher decontamination efficiencyat high temperature and kept the same under other operations. Moreover, itcould restrain the emission deterioration resulted by sulfur under hightemperature operations.5、The key factors that contribute much effects on the http://www.chinamagnets.biz decontaminationefficiency were investigated at last. Conclusions can be drawn as following:1) The ceramic cordierite honeycomb carrier could adsorb the emissionsPM by 16%;2) The effects of temperature especially the light-off temperature ofcatalytic converter on the decontamination efficiency was studied. Testresults showed that the DCC-5 catalytic converter has lower light-offtemperature (T50 is 180℃) compared to other two catalytic converters.3) The relation between air speed and decontamination efficiency wasfounded out by testing and calculating. Results showed that thedecontamination efficiency is higher at low air speed from 20000 h-1 to 40000h-1, and the decontamination efficiency would decrease dramatically when theair speed beyond 40000 h-1.4) The effect of sulfur fraction of fuel on the PM emissions was studied bychemical measuring the SO 42? quantity. It is found that sulfur fraction hadlittle effects on the decontamination efficiency of DCC-5 catalyst, whichmeans the DCC-5 has higher ability of sulfur restraining.5) The reliability of DCC-5 catalytic converter was validated by long timetesting. Test results showed that it still has high decontamination efficiency(50%, mean value) after 30-hour uninterrupted testing. The decontaminationefficiency decreased briefly at middle load, while increased again at highload.