【作者】 谭理刚；

【导师】 龚金科；

【作者基本信息】 湖南大学 ， 车辆工程， 2014， 博士

【摘要】 柴油机应用日益广泛,NOx排放污染物对人体以及环境的影响日趋严重。柴油机Urea-SCR系统是降低NOx,达到欧Ⅳ以上排放法规的主要后处理装置。随着排放法规要求的日益严格,Urea-SCR系统必须满足高效转化和低压力损失的要求,并且尽量避免喷氨过多带来的二次污染问题。为此,本论文以863项目“新一代轿车用环保高效柴油机燃烧系统与后处理系统的研发”(2008AA11A116),科技创新扶持项目“柴油机尿素SCR系统尿素喷雾及混合规律的研究”等项目为依托,采用数值仿真和试验相结合的方法对柴油机SCR系统的喷射雾化、压力损失、反应特性、喷氨MAP等进行了研究与分析,其主要研究工作和创新之处如下：1、基于压力漩涡喷射模型和离散相雾化混合模型,系统地研究了喷嘴喷射距离、喷射位置与方向、喷孔数目与孔径等参数对催化剂载体入口处的浓度分布情况的影响规律。通过台架试验,采用喷距5D、径向、四孔、小孔径喷嘴方案可使NOx转化率达到95%以上,验证了仿真结果的合理性。2、建立了催化反应器的多孔介质湍流模型,在催化反应器自由流动区域,采用标准κ-ε的湍流模型,研究了催化反应器扩张锥角、体积与长度、载体与涂层厚度等因素对压力损失的影响。3、为改善尿素水溶液的雾化混合,设计了三种不同结构混合器,并针对两种典型工况进行了数值仿真分析。提出了基于试验测量点的均匀性指标。综合均匀性指标和压力损失,比较了仿真与试验的一致性,确定了优选结果。4、研究了柴油机SCR系统的反应机理及反应动力学模型,建立了基于瞬态吸解附反应的模型,分析了温度、空速对NH3的存储量及存储释放速度、氨氮比对氨气利用率的影响；同时分析了排气组分中NO2的浓度、氧气浓度,水分浓度等对系统NOx转化效率的影响。5、研究了充气系数和喷油脉宽的初始MAP,结合发动机原机的排放MAP、排气温度MAP、排气背压MAP、NOx转化率MAP,制定了基于开环控制的控制策略,分析研究了NOx生成速率和尿素水溶液喷射速率,结合试验,针对尿素水溶液温度、排气温度、催化剂储氨能力、氨氮比等影响因素对尿素水溶液的喷射量进行了修正。本文在柴油机Urea-SCR系统喷射雾化、催化转化以及控制策略等方面进行了深入研究,可为柴油机Urea-SCR系统提供设计依据和理论指导。更多还原

【Abstract】 The impact of NOx emissions on human and environment becomes more and more serious with rapidly increasing use of diesel engines. The Urea-SCR system of diesel is a major post-processing device that can reduce the NOx emission and meet Europe IV or above emission regulations. To meet the more and more restrict requirements of energy saving and environmental protection, the Urea-SCR system must achieve the object of high efficient transformation and low pressure loss, and avoid the secondary pollution problem brought by spraying ammonia too much.This research is based on the863Project-The Research and Development with Environmental Protection and Efficient Diesel Combustion System of The New Generation Cars and Post Processing System, whose number is2008AA11A116,and the science and technology innovation supported program-The Research on Urea Spray and Mixing Rule Of the Diesel Engine Urea-SCR System. The spray atomization, pressure loss, the reaction characteristics and ammonia injection MAP of diesel SCR system is studied and analyzed by combining the numerical simulation and experiment verification. The major research work and innovations are as follows:1. Based on the pressure swirl jet model and the discrete phase atomizer mixing model, the influence of nozzle spray distance, spray position and orientation, number and diameter of spray orifice on the concentration distribution of fluid drop at the entrance of the catalyst carrier were studied by numerical simulation. Using four orifices,0.5mm aperture, nozzle in the pipe center and radial spray can bring out the best result of spray atomization. With bench test, the NOx conversion rate can be improved to95percent or more, which verifies the rationality of the simulation results.2. A porous medium model for SCR system is set up. The effects of expansion cone angles, volume and length, carrier and layer thickness of the catalytic reactor on the pressure loss at the free flow region of catalytic reactor are investigated by using standard κ-ε turbulence model.3. In order to improve the atomization mixing of urea aqueous solution, three different structures of the mixer are designed. Numerical simulation analysis is conducted for two kinds of typical working condition. A corresponding uniformity indicator is proposed from simulation and experiment results. Combining the uniformity indicator and the pressure loss, the optimization result is obtained by comparing the consistency of simulation with experiment.4. The research is studied the chemical reaction mechanism and reaction kinetics model of the diesels SCR system and set up the model that based on transient absorption desorption reaction. The main content include:the influence of temperature and air flow rate for the storage and storage release rate of NH3; the effects of NO2, O2and H2O in the exhaust for the conversion efficiency of NOx in the SCR system.5. The research Analyzed the inflatable coefficient and the initial MAP of the fuel injection pulse width. The control strategy is drawn up based on open-loop control strategy combined with the emissions MAP, exhaust temperature MAP, exhaust back pressure MAP and NOx conversion rate MAP. Studied the NOx generation rate and injection rate of urea solution Combined with experiment, It made a correction for the temperature of urea solution, exhaust temperature, the ability to store ammonia of catalyst, ammonia nitrogen ratio and some influential factors.The research is studied the spray atomization, catalytic conversion and control strategy of the diesel urea-SCR system in details and depth. The results can provide design basis and theoretical guidance for realistic diesel urea-SCR system.更多还原