双SCR系统中紧耦合SCR尿素结晶预测及应用
周海磊1,2,吕志华1,2,耿磊1,2*,王明达3
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;
3.中国环境科学研究院,北京 100012
摘要:为匹配双级选择性催化还原(selective catalytic reduction,SCR)装置中前级SCR混合器的设计要求,基于Fluent平台,根据化学动力学模型搭建SCR尿素结晶预测模型,预测尿素结晶的质量、位置和成分,通过发动机台架结晶试验验证模型的准确性,重新设计前级SCR混合器并评估其性能。结果表明:低、中、高温工况尿素结晶质量的仿真准确度分别为76%、79%、78%;仿真的结晶位置与试验结晶位置吻合度较好,且结晶位置受排气温度和排气流量的影响;不同温度下的结晶成分与已有相关研究基本吻合;新设计混合器的各项性能指标均优于现有产品,其中抗结晶能力提高约68%;氨均匀性、速度均匀性与背压正相关,氨均匀性与抗结晶能力负相关。
关键词:柴油机后处理系统;紧耦合混合器;SCR结晶预测模型;Fluent
Prediction and application of urea deposition in close-coupled dual SCR system
ZHOU Hailei1,2, LÜZhihua1,2, GENG Lei1,2*, WANG Mingda3
1. Weichai Power Co., Ltd., Weifang 261061, China;
2. State Key Laboratory of Engine and Powertrain System, Weifang 261061, China;
3. Chinese Research Academy of Enviromental Science, Beijing 100012, China
Abstract: To meet the design requirements of the front-end selective catalytic reduction(SCR) mixer in a two-stage SCR device, a SCR urea crystallization prediction model is built in Fluent based on a chemical kinetics model to predict the quality, location, and composition distribution of urea crystals. The accuracy of the model is verified through engine bench crystallization tests. A new front-end SCR mixer is designed based on the crystallization prediction model to evaluate its performance. The results show that the simulation accuracy of crystal quality under low, medium, and high temperature conditions is 76%, 79%, and 78%, respectively. The simulated crystallization position matches well with the experimental crystallization position, and the crystallization position is affected by exhaust temperature and exhaust flow rate. The crystal composition at different temperatures is basically consistent with existing related studies. The performance indicators of the new mixer are superior to existing products, with an increase of about 68% in anticrystallization ability. Ammonia uniformity and velocity uniformity are positively correlated with back pressure, while ammonia uniformity is negatively correlated with anticrystallization ability.
Keywords: diesel engine after treatment system; close coupled mixer; SCR crystallization prediction model; Fluent
