Study On Transient Temperature Control For SCR System Of Diesel Engine

Recently, the impact of NO_x emission on human health have attracted the people's attention due to the increasing motor vehicle. Particularly, the middle and heavy duty diesel vehicle take up more than 80% of total NO_x emission generated by the motor vehicle. Under the background of more and more stringent vehicle emissions standards, it has become more and more challenging to meet the requirement by reducing the NO_x emission due to the fluctuant exhaust temperature, because of the highly effective temperature window of SCR system catalyst which can not cover the total exhaust temperature of vehicle. In addition, the high exhaust temperature above 600 centigrade degree caused by the regeneration of diesel particulate filters will lead to the aging of catalyst. So the exhaust temperature control must be studied to ensure that the SCR system can work effectively and reliably.This study put forward transient temperature control system for the diesel vehicle SCR system based on the latent thermal storage and controllable heat pipes. It can effective control engine exhaust temperature based on the concept of peak load shifting, so that the SCR system can work stably and effectively to realize high efficient elimination of NO_x emission. Firstly, the temperature control sche me are made by the analysis of SCR system catalyst, urea injection characteristic, engine exhaust energy and test cycle of emission standards. Secondly, the macroscopic heat transport model and lattice Boltzmann method are combined to numerical study the temperature control effect and dynamic response characteristic of transient temperature control system. The heat transfer process of phase change materials are studied by the lattice Boltzmann method based on the mesoscopic dimension. The results not only validate the caculation reuslts of macroscopic model, but also achieve more novel conclusion which can provide thought and effective approach to optimize the transient temperature control system. Finally, the NO_x catalytic reduction model is built by the experimental data and structure parameters of SCR system based on the platform of AMESime software, so that it can research the impact of temperature control effect and dynamic response characteristic of transient temperature control system on the elimination of NO_x emission in SCR system.By the macroscopic heat transport model and the numerical validation of lattice Boltzmann method, it can find the transient temperature control system can control exhaust temperature limited to 0.18DT in the European transient test cycle(ETC), here DT indicate the difference between objectice temperature and initial temperature. Furthermore, it can finish start process after 50 s if the engine have warmed before, the time is acceptable for engine. After the exhaust temperature controlled, the average NO_x emission reduction efficiency can achieve 90% during the total ETC test, which is higher than the original with 12%. During the ETC test, the preparation time of phase change mateirals is 400 s, which is shorter than the world harmonized test cycle due to the high load test working points of ETC focus on the initial phase of test cycle. The temporal scale is the main impact factor of heat transfer rate by heat transfer mechanism study based on the lattice Boltzmann method. So if we can reduce the time scale of heat transport, the temperature control effect and dynamic response characteristic of transient temperature control system can be improved.