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CLC number: TK421.5

On-line Access: 2016-08-05

Received: 2015-11-10

Revision Accepted: 2016-06-17

Crosschecked: 2016-07-28

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Citations:  Bibtex RefMan EndNote GB/T7714


Dong-wei Yao


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Journal of Zhejiang University SCIENCE A 2016 Vol.17 No.8 P.597-613


Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems

Author(s):  Xu-bo Gan, Dong-wei Yao, Feng Wu, Jia-wei Dai, Lai Wei, Xing-wen Li

Affiliation(s):  Institute of Power Machinery and Vehicular Engineering, Zhejiang University, Hangzhou 310027, China

Corresponding email(s):   dwyao@zju.edu.cn

Key Words:  Selective catalytic reduction (SCR), Two-phase flow, Wall film, Deposit components, 1D model

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Xu-bo Gan, Dong-wei Yao, Feng Wu, Jia-wei Dai, Lai Wei, Xing-wen Li. Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems[J]. Journal of Zhejiang University Science A, 2016, 17(1): 597-613.

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publisher="Zhejiang University Press & Springer",

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%A Xu-bo Gan
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%A Feng Wu
%A Jia-wei Dai
%A Lai Wei
%A Xing-wen Li
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T1 - Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems
A1 - Xu-bo Gan
A1 - Dong-wei Yao
A1 - Feng Wu
A1 - Jia-wei Dai
A1 - Lai Wei
A1 - Xing-wen Li
J0 - Journal of Zhejiang University Science A
VL - 17
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SP - 597
EP - 613
%@ 1673-565X
Y1 - 2016
PB - Zhejiang University Press & Springer
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A quasi 1D model of two-phase flow for a urea-selective catalytic reduction (SCR) system is developed which can calculate not only the generation of reducing agent but also the formation of deposits in the exhaust pipe. The gas phase flow is solved through Euler method, variables are stored on staggered grids, and the semi-implicit method for pressure-linked equation (SIMPLE) algorithm is applied to decouple the pressure and velocity. The liquid phase is treated in a Lagrangian way, which solves the equations of droplet motion, evaporation, thermolysis, and spray wall interaction. A combination of a direct decomposition model and a kinetic model is implemented to describe the different decomposition behaviors of urea in the droplet phase and wall film, respectively. A new 1D wall film model is proposed, and the equations of wall film motion, evaporation, thermolysis, and species transport are solved. The position, weight, and components of deposits can be simulated following implementation of the semi-detailed kinetic model. The simulation results show that a decrease in the exhaust temperature will increase the wall film region and the weight of deposits. deposit components are highly dependent on temperature. The urea-water-solution (UWS) injection rate can affect the total mass of wall film and expand the film region, but it has little influence on deposit components. An increase in exhaust mass flow can decrease the total weight of deposits on the pipe wall because of the promotion of the mass and heat transfer process both in the droplets and wall film.

The paper deals with an interesting analysis of UWS evolution (spray and chemical reactions resulting in NH3 availability) in exhaust systems of Diesel Engines. A new, quasi-1D code simulating the UWS drops evolution and the main chemical reactions was developed and validated with simplified experiments. Overall, a good paper, well written and with a clear presentation of the hypotheses used for the simulation code.


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。


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