Study On Numerical Simulation And Regeneration Control Strategies Of Car Diesel Particulate Filter

Diesel engine has some merits including good performance, economy and reliability, and it is one of the most energy-efficient mainstream power machinery equipment in the world. However, diesel particles emissions have been one of bottlenecks which restrict the further development of car engines and a miniature of energy security and environment pollution problems caused by the critical contradiction between supply and demand, so addressing the particle emission problem effectively has great significance in academic study, economy and nation defense.Diesel particle filter (DPF) has been acknowledged to be the most effective and mature technology to control particulate emission. During the DPF regeneration process, if too many particles deposit on SiC substrate in DPF, the substrate will be damaged because of superhigh temperature caused by the heat the combusting particle release; if too few particles deposit on the substrate, regeneration process will take place frequently so that the substrate also will failure to work and the regeneration cost will raise. Therefore, it is of great significance to develop a particle evaluation model which can evaluate state of the particles in DPF and adjust with real time to make DPF safe, where also this study starts.The working process of aftertreatment system (including DPF regeneration process) was investigated through numerical simulation and experiment. Firstly, analyze the working mechanism of diesel engine's aftertreatment system, propose a method to determine reaction rate of DOC and synthesized capture efficiency, make description the regeneration chemical reaction in DPF, develop a 3D numerical model of car engine's aftertreatment system based on DOC and DPF with catalytic coating and set simulation sample points.Secondly, test research on aftertreatment system characteristics of diesel engine was conducted on the platform which consists of test-bed and its matching data acquisition system. The results show that, in this test, if the other factors remain unchanged, the temperature and its rate both raise as the concentration of HC or exhaust gas flow increases; if temperature rising rate of DPF is bigger, inlet pressure drop of DPF decrease quickly, the particles in DPF combust also quickly as inlet temperature of DPF increase, and optimal inlet temperature range is between 450℃～500℃; Propose a method to determine the balance point temperature, in this test, it is 358.7℃; and verify the effectiveness of numerical simulation model through test research on aftertreatment system characteristics of diesel engine to supply test basis.Thirdly, numerical simulation study on working process of aftertreatment system especially regeneration process of DPF, the results indicate:1) the diffusor make the flow separation where the wall occurs and vortices form, while the DOC has distinct integration effect on the flow.2) If other factors remain unchanged, during regeneration process, particle density, exhaust gas flow, inlet temperature of DPF and temperature rising rate of DPF have a great influence on regeneration process of DPF. The peak temperature and average temperature increase as the aforesaid factor increases. When regeneration process stop suddenly, exhaust temperature drop down and exhaust flow increase, the heat will be taken away and the combustion of particle will be suppressed even go out. In this test, the optimal inlet temperature of DPF is 480℃.3) Propose a method determine particle density in DPF, in this test the optimal density of particle is 8g/L.Lastly, based on the test and numerical simulation research,1) Develop conditions-the pressure drop evaluation model. The particle capture mathematical model of DPF was developed and the judgment process was also determined based on the analysis refering to particulate emissions of diesel engine and particle capturing mechanism of DPF and those above are the basis of conditions-the pressure drop evaluation model.2) Set control strategy of aftertreatment system of diesel engine. This control strategy was based on conditions-the pressure drop evaluation model. According to this control strategy, self-test would ensure aftertreatment system good at first, then monitor the state of particle in DPF with real time and adjust the state of particle to make DPF safe.3) Develop regeneration control strategy of DPF. Propose three regeneration mode including imperative regeneration, active regeneration and passive regeneration and develop regeneration control strategy of DPF based on conditions-the pressure drop evaluation mode. Particle density evaluation method also was determined to make regeneration process of DPF safe.