Study On Long Life And Low Emission Mechansism Of Three-way Catalyst And Performance Optimiation

Automotive exhaust emission has become the major pollution source of Chinese cities.Three-way catalytic converter is a kind of external purification device, which is installed in automobile aftertreatment system. Wtih noble metal catalyst loaded by the catalyst supports channel surface, catalytic converter can transform CO, HC and NOx in the exhaust, to harmless CO₂, H₂O and N₂. This article has mainly worked on solving following problems related to catalytic converter:1. The exhaust of CO and HC during engine cold start is 60⁸0% of total emission in a fixed time quantum. Therefore, researching on the emission characteristics of three-way catalytic converter during engine cold start and increasing the conversion efficiency during engine cold start are very important.2. While the active components and physical properties of catalyst getting"old"with time, series problems appear, such as the decreasing of conversion efficiency and power performance or the increasing of exhaust back pressure and fuel consumption. So, researching on the deactivation mechanism of catalytic converter, improving the anti-deactivation ability of catalyst and prolonging catalyst life become a research emphasis.3. Most of the catalyst in three-way catalytic converter contains expensive noble metals and rare earth elements. While meeting the performance requirements, nowadays researches focus on using different distribution patterns of the catalyst monolith to low the catalyst loading and manufacturing cost. In other words, the focus is improving the performance price ratio of catalyst maximally.The main research work of this article is expressed as follows:1. The three-way catalytic converter model, which had contained mass transfer model, heat transfer model and detailed elementary reaction model was established. Based on the operating principle of three-way catalytic converter, this article treated the catalytic converter and reactions in it as a Perfectly Stirred Reactor Model. Then, resolved this model into chemical reaction process and transfer process. By calculating mass and energy conservation of the reactor and considering transfer process, kinetics, detailed reaction mechanism and promoter reaction mechanism, three-way catalytic converter reactor model was established. Numerical simulation of catalytic converter conversion efficiency under steady conditions was carried out. The result showed the the validity of the model.2. The transient condition performance and influence factors of three-way catalytic converter were studied. Based on the established three-way catalytic converter reactor model, a prediction was made by using gas phase chemical reaction kinetics software. Under cold start transient condition, three-way catalytic converter simulation research and bench test were carried out. The result showed that the model had worked well in transient condition, especially in cold start work condition. On this basis, the effect of exhaust flow pulsation, ambient temperature and exhaust temperature to conversion efficiency were studied. And, the effect rules of different factors to various exhaust components were discovered. It provided the optimal design, reliability consideration, diagnosing and emission control of catalytic converter with very important reference value.3. Chemical deactivation and high temperature deactivation of three-way catalytic converter were analyzed and studied. On both side of sintering rate and reaction rate, the chemical deactivation mechanism of three-way catalytic converter was researched. Before and after chemical deactivation, the numerical simulation of three-way catalytic converter under steady state condition was done, and the change law of the conversion efficiency and air-fuel ratio, which changed with exhaust poisonous substance concentration, was gotten. Considering of the decreasing of catalyst relative activity during deactivation procedure, the chang law of deactivation characteristics parameters and the three-way catalytic converter kinetics model, the steady emission and transient emission simulation of the catalytic converter after high temperature deactivation were done. Under transient condition, the adaptability change law of catalyst after high temperature deactivation also was gotton.4. In the end, Honeycomb Monolith reactor was established. Considering of reaction kinetics model and detailed surface reaction mechanism without deactivation factors, the simulation research of the catalyst, which was in axially non-uniform distribution, was done. The light-off characteristics law of catalyst, which was in step distribution or parabola distribution, was gotton. Considering of the request of light-off characteristics and anti-deactivation, the optimal distribution of catalyst also was gotton. Meanwhile, a type of three-way catalytic converter, which had various cell densities and radial non-uniform distribution structural, was invented. It could improve the conversion efficiency of the catalytic converter central part and the flow field distribution in monolith.