【摘要】：目的:對柴油機Urea-SCR系統(tǒng)還原劑添加過程進行建模,探討SCR系統(tǒng)中尿素結晶的主要影響因素,研究排氣溫度、流量和尿素水溶液噴射速率等對結晶成分、位置和總結晶量的作用規(guī)律。創(chuàng)新點:1.考慮噴霧和壁膜內尿素熱解過程的差異,分別采用尿素的直接分解和化學反應動力學方法對噴霧和壁膜內的尿素熱解過程進行描述;2.提出一維壁膜的概念,將尿素熱解的化學反應動力學模型嵌入一維壁膜中,實現(xiàn)對結晶成分、位置和總結晶量的計算。方法:1.采用歐拉方法求解氣相流動以及拉格朗日方法跟蹤噴霧運動,通過附加源項方式實現(xiàn)氣液兩相之間的耦合;2.對尿素水溶液噴霧的蒸發(fā)、熱解、碰壁和結晶等過程進行建模,并對仿真結果進行驗證;3.對SCR系統(tǒng)中尿素結晶進行仿真分析,對排氣溫度、流量和尿素水溶液噴射速率等影響因素進行變參數研究。結論:1.排氣溫度的降低可以減小壁膜范圍以及結晶量;結晶成分與溫度密切相關:當溫度較低時,結晶以尿素為主,隨著溫度升高,縮二脲和三聚氰酸開始逐漸形成;2.尿素水溶液噴射速率會影響壁膜范圍以及結晶量,但其對結晶成分影響不大;3.排氣流量的增大能夠促進排氣與液滴以及排氣管壁之間的傳熱,從而減小壁膜范圍以及結晶量。
[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.
【作者單位】： 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
【分類號】：TK421

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