The porous medium approach applied to CFD modelling of SCR in an automotive exhaust with injection of urea droplets
The porous medium approach applied to CFD modelling of SCR in an automotive exhaust with injection of urea droplets
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多孔介质方法应用于喷射尿素液滴的汽车尾气中 SCR 的 CFD 建模
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发表时间：
2014
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通讯作者：
Benjamin
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文献类型：
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作者：
Benjamin
预计从2010年起，汽车行业将采用SCR后处理技术来控制柴油乘用汽车的NOx排放。氨促进NOx还原，并作为尿素水溶液液滴的喷雾引入排气中。这是排气后处理CFD建模的一个新方面。当模拟喷雾时，网格必须是3D的，因此多孔介质方法是适当的，避免了对代表性单通道建模的需要。多孔介质技术是建立在模型的三效催化和SCR的应用证明在本文中，使用的动力学方案在文献中。液滴直径的实验室测量已被用于指定输入到CFD模型的尿素水溶液。代表性的液滴包裹建模使用拉格朗日模型内的计算流体动力学代码。以这种方式，可以在汽车催化剂系统的3D模型中对SCR进行完全建模。符号AV每单位反应器体积的几何表面积（m /m）APM催化剂每单位反应器体积的贵金属表面积（m /m）C质量分数Ci g气相中物质i的质量分数Ci溶胶固相或载体涂层孔中物质i的质量分数D物质扩散率（m /s）Dd液滴直径（微米）Kmi传质系数（m/s）L通道长度，整料长度（m）Mi物质i的摩尔质量（kg /mol）PARP压降（Pa）PO 2氧浓度摩尔分数q Rosin-Rammler液滴尺寸分布的拟合变量Q直径< Dd的液滴中总体积的分数Ri反应产生物质i的速率（mol /s /m反应器）t时间（s）
The automotive industry is expected to adopt SCR after-treatment to control NOx emissions from Diesel passenger cars from 2010. Ammonia promotes NOx reduction and is introduced into the exhaust as a spray of aqueous urea droplets. This is a new aspect of CFD modelling of exhaust after-treatment. When modelling sprays the mesh must be 3D and so the porous medium approach is appropriate, circumventing the need for representative single channel modelling. The porous medium technique is well established for modelling three-way catalysis and its application to SCR is demonstrated in this paper, using a kinetic scheme available in the literature. Laboratory measurements of droplet diameters have been used to specify the input of aqueous urea to the CFD model. Representative droplet parcels are modelled using a Lagrangian model within the CFD code. In this way it is possible to fully model SCR in a 3D model of an automotive catalyst system. NOTATION AV geometric surface area per unit reactor volume (m /m) APM catalyst precious metal surface area per unit reactor volume (m /m) C mass fraction Ci g mass fraction of species i in the gas phase Ci sol mass fraction of species i in the solid phase or washcoat pores D species diffusivity (m /s) Dd droplet diameter (microns) Kmi mass transfer coefficient (m/s) L channel length, monolith length (m) Mi molar mass for species i (kg /mol) ∆P pressure drop (Pa) PO2 oxygen concentration mole fraction q fit variable for Rosin-Rammler droplet size distribution Q fraction of total volume in drops with diameter < Dd Ri rate of production of species i by reaction (mol /s /m reactor) t time (s)