Research On NO₂High Efficiency Utilization And The Ceria-based Composite Regenerating Mechanism For A Catalytic Diesel Particulate Filter

As the quantity of the diesel vehicle in our country become more and more, diesel exhaust particulate emission control has become the main task to prevent the automotive pollution due to increasingly stringent emission regulations. Diesel particulate filter(DPF) is an accepted most effective aftertreatment device for diesel particulate emission control, especially in medium and small displacement diesel vehicles and light commercial diesel vehicles. An extra heat source and complicated control systems are needed for traditional DPF, thus the oil consumpation and the cost was increased. It also needs a high-performance battery when using vehicle power as an extra heat source. Catalytic DPF can work without extra heat sources and contral systems, but it is sensitive to impurities in fuels, such as sulfur. In the new fuel standard of our country, the sulfur content of diesel oil is lower than50mg/kg, catalytic DPF can work normally in this sulfur content level. Using catalytic DPF instead of traditional DPF is significance to energy-saving and emission reduction for diesel vehicles.Because of no extra heat sources were needed, the regeneration of catalytic DPF was mainly processed by NO2, which is a strong oxidizing medium. NO2is a pollutant, and its concentration is very low in diesel exhaust gas. Thus, increasing the concentration of NO2and enhancing NO2utilization efficiency of the regenerating process based on control the overall NOX emission is a problem to be solved. Enhancing the activity of the regenerating reactions is another problem to be solved. The research is supported by the project of National Natural Science Foundation of China "Research on Compostie Regeneration Mechanism of Diesel Particulate Trapped Porous Medium Based on Microwave and Ce-Mn Fuel Additive(50876027)" and"Research on Compostite Regeneration and Multi-Field Synergy Mechanism of Diesel Particulate Filter Medium(51176045)". This article has mainly researched on NO2high efficiency utilization and ceria-based additive assisted composite regeneration for catalytic diesel particulate filter. It is designed to obtain a wide regerneration temperature window, low pressure drop loss and reliable catalytic diesel particulate filter. The main research work of this article is summarized as follows:(1) Based on the law of conservation of mass, momentum and energy, using the control volume of inlet channel, outlet channel, filter medium and soot layer in diesel particulate filter, a fluid field model was derived. Based on the chemical kinetics theory, a chemical kinetic model was derived. The effects of exhaust flow rate, exhaust temperature, NO2and O2concentration, NO2and soot mass ratio on NO2oxidation regeneration were considered in these models. The weight of these facors on regeneration performance was analysed using the grey relational analysis method, the result indicates the key factor of regeneration process in catalytic diesel particulate filter, and ways on high efficiency NO2utilization and composite regeneration for improving regenerating performance was proposed.(2) Using diesel oxidation converter to increase NO2concentration for catalytic DPF. A fluid field model and a chemical kinetic model for diesel oxidation converter were derived. This model indicates NO2concentration improving mechanism for catalytic particulate filter with diesel oxidation converter, the optimum working temperature window is300～400℃for NO convertion in DOC. the maximum conversion efficiency is in mid-load condition for various engine speed, and the conversion efficiency is rapidly decreased in high engine speed and high-load condition.(3) While the NO2concentration is insufficient in the regeneration process, noble metal catalytic coating was developed to enhance NO2utilization efficiency. Soot trap mechanism and deposition process in catalytic diesel particulate filter was analyzed. The results showed that regeneration process in catalytic coat is divided into two stages. A regeneration model was developed in each stage with new regeneration mechanisms, NO2utilization efficiency enhancement mechanism in catalytic diesel particulate filter with catalytic coating was studied. By using catalytic coating, catalytic diesel particulate filter regenerates normally in heavy load conditions. A pressure drop model was improved by considering the effect of catalytic coat, inlet channel pressure drop and outlet channel pressure drop was computed respectively. In order to assess the regeneration model, a bench experiment was established, it indicated that the result of regeneration model and the pressure drop model is approximately consistent with experimental data.(4) The NO2circulatory coefficient of catalytic diesel particulate filter was difined. The effect of condition on NO2utilization efficiency was studied by comparison of particulate deposit mass. the result indicated the effect of regenerating time on NO2circulatory coefficient in various conditions. The NO2circulatory coefficient reaches maximum and remains the same in low-load conditions, it reaches maximum and reduces gradually in mid-load conditions, it remains a steady value in high-load conditions.(5) Based on macroscopic reactions, a Ceria-based additive assist catalytic composite regeneration model was developed. The effect of Ceria-based additive on regeneration performance in various conditions was studied by numerical and experimental. The effective factor and the changing law of the soot oxidation rate of catalytic diesel particulate filter in various conditions were analyzed. The component ratio and the adding dosages of the Ceria-based additive were studied by experimental. By using Ceria-based additive, catalytic diesel particulate filter regenerates normally in low-load condition.The research work in this article provides theoretical basis of NO2high efficiency utilization in catalytic diesel particulate filter. And it also indicates the Ceria-based additive assist catalytic composite regeneration mechanism of catalytic diesel particulate filter. With these technologies, catalytic diesel particulate filter regenerates normally in low-load conditions, it is important for practicability of the catalytic diesel particulate filter. Some of research methods and results of this article can also be used as a reference for other diesel particulate filters.