Numerical Simulation Of Automotive Catalytic Converter

With the rapid development of economy, automotive exhaust emissions have gradually been becoming a major source of air pollution. Nowadays, the catalytic converter is one of the important measures for controlling emissions of gasoline effectively and widely. However, because of the catalytic converter's inlet cone, flow distribution will be not uniform at the monolith inlet, and conversion efficiency is also affected by the flow distribution, since only a part of the converter is utilized. Therefore, optimization of catalytic converter is of great significance.The FLUENT software coupled with CHEMKIN code is employed to establish a 2D single channel model and a 2D monolith model. And a detailed surface reaction mechanism for CO-O2 reaction on Rh is used to model the catalytic reactions in both models. The simulation results agree well with the experimental results, which proves that the flow model and the detailed reaction mechanism used in this thesis are reasonable. Furthermore, the models established can be used for catalytic converter design and optimization.From microscopic point of view, the process of mass transfer, heat transfer and surface reaction is simulated in the single channel model. The results show that light-off occurs first in the rear section of a channel. The reason of this phenomenon is that the rear section of the channel is affected by the heat released by surface reaction of the front section. Meanwhile, channels of different cell density monolith are simulated for comparison. The results show that mass transfer happens more quickly in the monolith with higher cell density, and the reaction surface is closer to the inlet of the channel. That means that a monolith with higher cell density has better light-off performance.From a macro point of view, the parameters of catalytic converter are studied in the monolith model with CO-O2 detailed reaction mechanism which has been validated in the single channel model. It is founded that although a monolith with higher cell density is better on light-off performance under lower temperature, the pressure loss along the monolith will rise greatly, which will lead to engine performance and fuel economy penalties. To solve this trade-off problem, an optimal monolith, radially variable cell density monolith, is studies in the thesis. The results show that flow distribution of a monolith with the radially variable cell density is very good, and the light-off temperature is lower than a monolith with uniform cell density, and at the same time pressure drop increases very little. Furthermore, this work potentially contributes to practical application.