柴油机Urea-SCR系统两相流及结晶的准一维数值模拟（英文）
发布时间：2018-07-13 07:34
【摘要】：目的:对柴油机Urea-SCR系统还原剂添加过程进行建模,探讨SCR系统中尿素结晶的主要影响因素,研究排气温度、流量和尿素水溶液喷射速率等对结晶成分、位置和总结晶量的作用规律。创新点:1.考虑喷雾和壁膜内尿素热解过程的差异,分别采用尿素的直接分解和化学反应动力学方法对喷雾和壁膜内的尿素热解过程进行描述;2.提出一维壁膜的概念,将尿素热解的化学反应动力学模型嵌入一维壁膜中,实现对结晶成分、位置和总结晶量的计算。方法:1.采用欧拉方法求解气相流动以及拉格朗日方法跟踪喷雾运动,通过附加源项方式实现气液两相之间的耦合;2.对尿素水溶液喷雾的蒸发、热解、碰壁和结晶等过程进行建模,并对仿真结果进行验证;3.对SCR系统中尿素结晶进行仿真分析,对排气温度、流量和尿素水溶液喷射速率等影响因素进行变参数研究。结论:1.排气温度的降低可以减小壁膜范围以及结晶量;结晶成分与温度密切相关:当温度较低时,结晶以尿素为主,随着温度升高,缩二脲和三聚氰酸开始逐渐形成;2.尿素水溶液喷射速率会影响壁膜范围以及结晶量,但其对结晶成分影响不大;3.排气流量的增大能够促进排气与液滴以及排气管壁之间的传热,从而减小壁膜范围以及结晶量。
[Abstract]:Objective: to model the process of reducing agent addition in the Urea-SCR system of diesel engine, to explore the main factors affecting the urea crystallization in SCR system, and to study the effect of exhaust temperature, flow rate and urea aqueous injection rate on the crystallization composition. Position and the action law of summing up the quantity of crystal. The innovation point is 1: 1. Considering the difference of urea pyrolysis process between spray and wall membrane, the direct decomposition and chemical reaction kinetics methods of urea were used to describe the process of urea pyrolysis in the spray and in the wall membrane, respectively. The concept of one-dimensional wall film is proposed. The chemical reaction kinetic model of urea pyrolysis is embedded in the one-dimensional wall film to calculate the crystal composition, position and sum up crystal quantity. Method 1: 1. The Euler method is used to solve the gas phase flow and the Lagrange method is used to track the spray motion. The coupling between the gas and liquid phases is realized by adding the source term. The evaporation, pyrolysis, wall impingement and crystallization of urea aqueous solution were modeled, and the simulation results were verified. The urea crystallization in SCR system was simulated and analyzed. The influence factors such as exhaust temperature, flow rate and urea solution injection rate were studied. Conclusion 1. The decrease of exhaust temperature can reduce the range of wall film and the amount of crystallization, and the composition of crystallization is closely related to temperature: when the temperature is low, the main crystallization is urea, and with the increase of temperature, biuret and cyanuric acid begin to form gradually. The spray rate of urea aqueous solution will affect the range of the wall film and the amount of crystallization, but it has little effect on the crystalline composition. The increase of exhaust flow rate can promote the heat transfer between exhaust and droplet and exhaust pipe wall, thus reducing the range of wall film and the amount of crystallization.
【作者单位】： Institute
【基金】：Project supported by the National High-Tech R&D Program (863 Program) of China(No.2013AA065301) the Fundamental Research Funds for the Central Universities (No.2016QNA4014) the Fund of State Key Laboratory of Clean Energy Utilization at Zhejiang University (No.ZJUCEU2016006),China
【分类号】：TK421
本文编号：2118640
[Abstract]:Objective: to model the process of reducing agent addition in the Urea-SCR system of diesel engine, to explore the main factors affecting the urea crystallization in SCR system, and to study the effect of exhaust temperature, flow rate and urea aqueous injection rate on the crystallization composition. Position and the action law of summing up the quantity of crystal. The innovation point is 1: 1. Considering the difference of urea pyrolysis process between spray and wall membrane, the direct decomposition and chemical reaction kinetics methods of urea were used to describe the process of urea pyrolysis in the spray and in the wall membrane, respectively. The concept of one-dimensional wall film is proposed. The chemical reaction kinetic model of urea pyrolysis is embedded in the one-dimensional wall film to calculate the crystal composition, position and sum up crystal quantity. Method 1: 1. The Euler method is used to solve the gas phase flow and the Lagrange method is used to track the spray motion. The coupling between the gas and liquid phases is realized by adding the source term. The evaporation, pyrolysis, wall impingement and crystallization of urea aqueous solution were modeled, and the simulation results were verified. The urea crystallization in SCR system was simulated and analyzed. The influence factors such as exhaust temperature, flow rate and urea solution injection rate were studied. Conclusion 1. The decrease of exhaust temperature can reduce the range of wall film and the amount of crystallization, and the composition of crystallization is closely related to temperature: when the temperature is low, the main crystallization is urea, and with the increase of temperature, biuret and cyanuric acid begin to form gradually. The spray rate of urea aqueous solution will affect the range of the wall film and the amount of crystallization, but it has little effect on the crystalline composition. The increase of exhaust flow rate can promote the heat transfer between exhaust and droplet and exhaust pipe wall, thus reducing the range of wall film and the amount of crystallization.
【作者单位】： Institute
【基金】：Project supported by the National High-Tech R&D Program (863 Program) of China(No.2013AA065301) the Fundamental Research Funds for the Central Universities (No.2016QNA4014) the Fund of State Key Laboratory of Clean Energy Utilization at Zhejiang University (No.ZJUCEU2016006),China
【分类号】：TK421
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