Numerical Simulation Of Three-way Catalytic Converter

In this paper, it is introduced that the production of automobile exhaust and the serious harm which creates to the environment, the laws and regulations of automobile discharges in developed countries and our country at present, the structure and the work principle of catalytic converter, as well as the development course of mathematical model and research present situation of three-way catalyst (TWC). The paper also made simple classification and compared automobile exhaust modeling with the overseas at present, summarized research starting point and innovation spot of the paper.The temperature characteristic and concentration characteristic of three-way catalyst (TWC) are researched in this thesis. Through setting up mathematics model for exhaust pipe of exhaust system and catalyst converters, solving the model, we systematically investigates the temperature variation tendency and concentration change space velocity inlet flow temperature and density , hydrogen converter property in the converter ,and the influence of catalyst loading quantity and loading pattern on catalysis combustion initiation temperature characteristic and exhaust conversion rate. Moreover, according to three kind of main pollutant reaction mechanisms in the automobile exhaust, the certain discussion of the automobile exhaust catalytic reaction dynamics has been carried on in this paper.When the automobile exhaust system is modeled, the exhaust system is divided into two parts-the exhaust pipe and the catalytic converter. The energy balance equation is established to the exhaust pipe. It is considered that there is water vapor in exhaust in the preliminary stage, produces water membrane on the cool wall face, and therefore with the Nusselt number proposed by Gnielinski solves the heat transfer coefficient. Then carries on the material balance and the energy graduated arm to the catalytic converter calculated that, uses dynamics speed expression proposed by Voltz , revised by Oh and Cavendish, the heal transfer coefficient is solved with the heat transfer coefficient correlation, which proposed by Baba and so on.The finite difference method and the iteration process is used when the model is being solved. Temperature field and the density field distribution in the catalytic converter are obtained, the space velocity, the inlet flow temperature and density, the hydrogen, converter property in the converter, and the influence of catalyst loading quantity and loading pattern on catalysis combustion initiation temperature characteristic and exhaust conversion rate areinvestigated. The findings indicated: in order to speed up the catalyst combustion initiation and enhances the conversion rate, space velocity is not suitable oversized, as far as possible enhances the inlet flow temperature, the integral-type carrier cannot excessively be long, the increase carrier surface opens the porosity, reduces wall thickness, when carrier load catalyst, should front end the carrier the load high quantity precious metal, in the tail load few precious metals, namely be possible to reduce the combustion initiation time like this, also may increase the conversion rate.According to three kind of main pollutant reaction mechanisms in the exhaust, the catalytic reaction dynamics model has been inferred, the preliminary discussion to in the catalytic converter oxygen storage sub module has been made, and the corresponding solution means is provided.