Study On Light-off Characteristics Of Two Stage Three Way Catalytic Converter During Cold Start Period

The number of vehicles in China increases at the speed of 320,000 peryear, and now it ranks NO.3 in the whole world. The car industry promotesthe development of the nation's economy, but meanwhile the pollution of thecar emissions is not a negligible problem that people have to be faced with,air quality improvement in urban areas of the states has been an urgentproblem for people to solve. As a result the nation's EnvironmentalProtection Agency has been legislating a series of emission control criterionsand legislations, including the aim that we'll carry out Euroâ… in the year2001 and Euroâ…¡in 2004 and Euroâ…¢ in 2008 and Euroâ…£ in 2012 and will becomparative with the international nations at that time. The fact has provedthat the vehicles can satisfy Euroâ… and Euroâ…¡ through using nonleadgasoline, electronic control, closed loop control and three way catalyticconverter techniques. And nowadays Euroâ… and Euroâ…¡legislations havebeen carried out successfully all around China, moreover, Euro â…¢legislation has been carried out on Dec 30 of 2005 in Beijing in advance dueto the Olympics which will be held in Beijing in 2008.Compared to Euro II legislation, the emission limit of Euro III legislationshut down about 40%, more important ,it takes the first 40s idle emissionsinto measurement. While up to 60-80% emissions are produced during thecold start, hence, the reduction of the emissions during the cold start periodbecomes more demanding. Three way catalytic converter has been anindispensable device for the control of CO,HC and NOx emissions ofgasoline engines, and the most vital problem during the cold start is that thecatalyst hasn't reach its light-off temperature due to the cold exhaust gasduring cold start so that the exhaust gas runs through the catalyst withoutbeing converted. Therefore, how to make the catalyst light off as soon aspossible becomes a focus of increasing R&D activities.In this paper, studies have been done on the match between catalystand engine aiming to make the catalyst light off as soon as possibleaccording to the project Study and Demonstration of the Key Technologyof the Industrialization for Low-emission Vehicles "Development andResolution of the Key Technology for the Low-emission ElectronicControlled Gasoline Vehicles Whose Weight Are below 3.5 tons". Thelight-off characteristics of TWC during cold start have been mainly studied.Considering that doing experiment on the bench is a waste of manpower,material resources and money, simulation using computational fluiddynamics software was adopted to make up this shortcoming. Then theinfluence of the control strategies on the light-off characteristics had beenforecasted for the catalyst which matched the engine better. As for the lessone, suggestions had been given from the point of structure design toimprove the light-off characteristics of TWC. The main content of this paperis as follows:1) According to the legislation, the emissions have to be tested on thewhole vehicle bench, but this kind of bench is expensive and notflexible for use and adjustment so that it is not suitable for researchand study. Therefore another method called three-section methodwas chosen to simulate the exhaust temperature, which usingengine bench instead of whole vehicle bench. Experiments about thelight off characteristics of TWC were done using this method in thispaper, which gave the experiment and simulation results practicalmeanings.2) Data acquisition system had been designed in this paper in order tosatisfy the need of high speed of data acquisition. Data acquisitionand conservation can be done synchronously and as a result thenumber of data to be acquired were not be restricted by thecapability of EMS memory any longer. And the data acquired canalso be displayed in the form of graph, which made theexperimenter grasp the status of the engine and TWC and know thecourse of the experiment in time.3) A series of experiments had been designed in order to supply withall kinds of parameters which were needed by the simulation work.The simulation results turned to be satisfactory on account of theexperiments.4) The evolvement of the inner TWC temperature had been knownthrough the simulation on the TWC. And according to thesimulation results, difference between the two catalysts can be seenclearly, and the influence of the TWC structure on the light offcharacteristics can also be analyzed, furthermore, suggestions canbe put forward to direct the catalyst design and choice.5) The influence of the engine ignition advance on the TWC light offcharacteristics had been forecasted using the method of minorsimulation plus secondary bench experiments. The forecastconclusion is a direction for the match between catalyst and engine.The main meaning of this paper is that it changed the actuality thatpeople only use experiments to match the catalyst with engine, andmeanwhile it took advantage of simulation which can supply with the datathat can't be acquired through experimental method, and explained theinfluence of engine strategy and catalyst structure on the light offcharacteristics of the catalyst from the point of theory. The result turned outthat using the simulation method can reach the same conclusion as theexperimental method and using the simulation method had manyadvantages compared to experimental method, such as reducing theexperiment amount, reducing manpower, material resources and money.Most of all, it supplied with a new way for the match between engine andcatalyst.