柴油机后处理系统ASC化学反应动力学模型分析

庞斌^1,2，闫彩彩^1,2，梁恒山^1,2，吕志华^1,2，代子阳^1,2

1.潍柴动力股份有限公司，山东 潍坊  261061；2.内燃机与动力系统全国重点实验室，山东 潍坊  261061

摘要：为满足不断提高的NO_x排放及NH₃泄漏标准要求，基于氨逃逸催化剂（ammonia slip catalyst，ASC）反应机理，结合反应器试验，分析NH₃在ASC上的转化过程及生成产物。通过在NH₃氧化生成N₂、N₂O的反应中引入与NO浓度相关的抑制因子以分配NH₃氧化路径，建立ASC动力学模型进行仿真分析，并结合台架试验对模型进行验证。仿真结果表明：反应温度低于350 ℃时，NH₃氧化产物主要为N₂和N₂O；反应温度为250 ℃时，生成的N₂O体积分数最大；反应温度高于350 ℃时，NH₃的氧化对产物NO_x的选择性增加。反应器试验及台架试验结果表明：ASC动力学模型能够预测ASC下游NO_x、N₂O的体积分数，NH₃转化率的预测误差不超过±10%，表明模型能够准确反映ASC试验规律。

关键词：柴油机后处理；ASC；NH3氧化；NO_x体积分数；N₂O体积分数

Analysis on chemical reaction kinetic model of ASC for a diesel engine aftertreatment system

PANG Bin^1,2, YAN Caicai^1,2, LIANG Hengshan^1,2, LÜZhihua^1,2, DAI Ziyang^1,2

1.Weichai Power Co., Ltd., Weifang 261061, China;

2. State Key Laboratory of Engine and Powertrain System, Weifang 261061, China

Abstract:  To meet the increasingly stringent requirements for NO_x emissions and NH₃ slip, based on the reaction mechanism of ammonia slip catalyst (ASC) combined with reactor tests, the conversion process andproducts of NH₃ over ASC are analyzed. By introducing inhibition factors related to NO concentration in the reactions of NH₃ oxidation to N₂ and N₂O to distribute the NH₃ oxidation pathways, an ASC kinetic model is established and simulated, and verified by bench tests. The simulation results show that when the reaction temperature is lower than 350 ℃, the main products of NH₃ oxidation are N₂ and N₂O; the volume fraction of generated N₂O reaches the maximum at 250 ℃. When the reaction temperature exceeds 350 ℃, the selectivity of NH₃ oxidation products increasing NO_x emission. Reactor tests and bench tests indicate that the ASC kinetic model can predict the volume fraction of NO_x and N₂O downstream of ASC, and the prediction error is no less than ±10% for NH₃ oxidation conversion rate. The model can accurately reflect the experimental characteristics of ASC.

Keywords: diesel engine aftertreatment; ASC; NH₃oxidation; volume fraction of NO_x; volume fraction of N₂O