Research And Analysis On Internal Flow Field Characteristics Of Catalytic Ceramic Turbine For Gasoline Engine

The treatment of exhaust pollution is the research hotspot and difficulty of automobile technology development.With the continuous improvement of environmental standards,it is necessary to develop efficient exhaust gas recovery and treatment system.Three-Way Catalyst（TWC）has high conversion efficiency for the main pollutants CO,NO_X,HC and other tail gas components,and is considered as one of the important devices to control emissions and solve tail gas pollution.The results show that the service life and conversion efficiency of the three-way catalytic converter are largely limited by the flow field inside the catalytic converter,including the flow uniformity and flow resistance characteristics.And only when the ignition temperature of catalyst is reached inside the catalytic converter can the conversion efficiency be higher.Therefore,during the cold start of the engine（within1-2 minutes）,the harmful gas components are almost not treated.Therefore,it is particularly important to find a more suitable and economical means to optimize the conversion efficiency of the three-way catalytic converter and effectively control the emission pollution of motor vehicles.Catalytic ceramic turbine technology（CCT）can increase the converter efficiency by rapidly increasing the exhaust temperature throughout the cold start of the engine.Therefore,the discussion of the internal flow characteristics of catalytic ceramic turbines during the occurrence of catalytic reactions is of great significance for the optimization of turbine body and the design of catalytic coating,and will also play a positive role in the comprehensive control of harmful gas emissions in the cold starting stage of the engine.Based on this,the flow field characteristics of catalytic ceramic turbines are studied in this paper.Firstly,the grid processing of turbine rotor model was carried out using NUMECA software,and the grid adjustment was carried out in ICEM.Finally,the numerical calculation was carried out by FLUENT to obtain the pressure field,temperature field and mass distribution of the full channel and single channel under different conditions of the catalytic turbine and the ordinary turbine,as well as the evolution of the two types of turbine boundary layer.By comparing the conversion efficiency of harmful gases and the temperature difference between inlet and outlet of turbine single channel and full channel at different inlet temperatures（600K and 700K）,it can be found that when turbine inlet temperature increases from 600K to 700K,the catalytic efficiency of CCT for C₃H₆,CO and NO increases by about 21.95%,19.73%and 11.67%.The turbine outlet temperature increases by 28K compared with the outlet temperature.This indicates that the increase of intake temperature can rapidly improve the conversion efficiency of CCT during engine cold start,and also promote the use effect of downstream TWC.Both the minimum concentration of harmful gas and its catalytic reaction distance change significantly with the increase of intake temperature.This indicates that the temperature difference generated by the gas and carrier in the turbine varies with the difference of inlet temperature.The catalytic reaction rate is directly proportional to the temperature,and is mainly concentrated in the leading edge and trailing edge of the blade.The concentrated intense reaction area corresponds to 20%chord length of the high suction front edge of the middle and low blades.In this thesis,the interaction mechanism between turbulence and catalytic reaction was studied,and the influence of turbulence on catalytic reaction was explored.It was found that turbulence had a significant influence on catalytic reaction within the range of 1%-3%turbulence,and the conversion efficiency decreased when the turbulence exceeded the range.In addition,it is found that the turbulent flow process and the chemical reaction process have a bidirectional influence in the catalytic turbine.The turbulent fluid enhances the catalytic reaction rate on the turbine blade surface,and the heat release process of the catalytic reaction affects the laminar flow to the turbulent flow at the same time.There is a mutually beneficial symbiotic relationship between the them.