柴油机DOC+SCR系统数值仿真与结构优化
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摘要
为降低柴油机污染物排放,提出DOC+SCR直筒型催化器系统,利用计算流体动力学(CFD)建立DOC+SCR直筒型催化器的三维数值仿真模型,该模型包括尿素水溶液的蒸发和分解,但忽略催化剂表面的催化还原反应,基于简化模型提出一种NO_x转换效率的计算方法,根据试验结果对数值模型和NO_x转换效率计算方法进行验证.分析计算得到的催化器系统内部流场分布情况,提出多种结构优化方案,结果表明:优化后,特定工况下催化器系统压降由9.98,kPa减小至8.60,kPa,催化器结构因素引起的压降由2.98,kPa降低至1.60,kPa;SCR入口截面还原剂NH_3均匀性指数可提高到93.45%,,在特定工况下NO_x转换效率可达92.87%,.
In order to reduce the pollutant emissions from diesel engines,a DOC+SCR catalytic converter system was proposed.A three-dimensional numerical simulation model of the DOC+SCR catalytic converter was established by using computational fluid dynamics(CFD).The model includes evaporation and decomposition of urea aqueous solution,but ignores the catalytic reduction reaction on the catalyst surface.Based on the simplified model,a calculation method of NO_x conversion efficiency was proposed.The numerical model and the NO_x conversion efficiency calculation method were verified by test results.Through the numerical simulation of the model,the flow field distribution of the catalytic converter was obtained and several optimization scheme were put forward.The results show that after optimization,in certain conditions,the pressure drop of the catalytic converter system is reduced from 9.98,kPa to 8.60,kPa.Also,the pressure drop caused by the catalyst structure factor is decreased from 2.98,kPa to 1.60,kPa.In addition,the NH_3 uniformity index of the SCR can be increased to 93.45%,.The conversion efficiency of NO_x can reach up to 92.87%, in certain conditions.
In order to reduce the pollutant emissions from diesel engines,a DOC+SCR catalytic converter system was proposed.A three-dimensional numerical simulation model of the DOC+SCR catalytic converter was established by using computational fluid dynamics(CFD).The model includes evaporation and decomposition of urea aqueous solution,but ignores the catalytic reduction reaction on the catalyst surface.Based on the simplified model,a calculation method of NO_x conversion efficiency was proposed.The numerical model and the NO_x conversion efficiency calculation method were verified by test results.Through the numerical simulation of the model,the flow field distribution of the catalytic converter was obtained and several optimization scheme were put forward.The results show that after optimization,in certain conditions,the pressure drop of the catalytic converter system is reduced from 9.98,kPa to 8.60,kPa.Also,the pressure drop caused by the catalyst structure factor is decreased from 2.98,kPa to 1.60,kPa.In addition,the NH_3 uniformity index of the SCR can be increased to 93.45%,.The conversion efficiency of NO_x can reach up to 92.87%, in certain conditions.
引文
[1]周敏.柴油车排放控制技术路线选择[EB/OL].http://mp.weixin.qq.com/s?__biz=Mj M5NDU4Njcy MQ%3D%3D&idx=1&mid=400237980&scene=21&sn=f2b1f22d717364271a24ffcf4e9cdc5a,2015.
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[10]Birkhold F,Meingast U,Wassermann P,et al.Modeling and simulation of the injection of urea-water-solution for automotive SCR DeNOx-systems[J].Applied Catalysis B:Environmental,2007,70(1-4):119-127.
[11]蔡忆昔,唐炜,王军,等.基于NOx传感器NH3交叉感应的柴油机Urea-SCR的试验[J].内燃机学报,2015,33(5):461-465.
[12]刘文坤,张翠平,王鹏,等.紧凑型DOC-混合器-SCR后处理系统数值模拟[J].车用发动机,2015,5:57-62.
[13]赵彦光,胡静,陈镇,等.混合器对车用柴油机尿素SCR系统性能影响的试验研究[J].汽车工程,2011,33(4):303-308.
[14]Clark N,Mckain D L,Wayne W,et al.Chassis dynamometer emissions characterization of a urea-SCRtransit bus[C]//SAE Paper.Detroit,Michigan,USA,2011,2011-01-2469.
[2]Cho Y S,Lee S W,Choi W C,et al.Urea-SCR system optimization with various combinations of mixer types and decomposition pipe lengths[J].International Journal of Automotive Technology,2014,15(5):723-731.
[3]尹和俭,季振林.SCR催化转化器结构对流场及压力损失的影响[C]//中国内燃机学会2009年学术年会暨中小功率柴油机分会、基础件分会联合学术年会.广西,南宁,2009:502-505.
[4]温苗苗.尿素选择性催化还原系统的仿真与优化[D].武汉:武汉理工大学能源与动力工程学院,2009.
[5]Yim S D,Kim S J,Baik J H,et al.Decomposition of urea into NH3 for the SCR process[J].Industrial and Engineering Chemistry Research,2004,43(16):4856-4863.
[6]王谦,张铎,何志霞,等.柴油机Urea-SCR系统数值模拟与混合器结构优化[J].内燃机工程,2015,36(3):50-57.
[7]陶建忠.利用选择性催化还原反应(SCR)降低车用柴油机氮氧化物的技术研究[D].济南:山东大学能源与动力工程学院,2008.
[8]Loveday P.CFD simulations of pollution control systems:DPF and SCR[R].2011.
[9]胡杰,张磊,李敏,等.SCR催化器热失活数值仿真[J].内燃机学报,2015,33(5):446-452.
[10]Birkhold F,Meingast U,Wassermann P,et al.Modeling and simulation of the injection of urea-water-solution for automotive SCR DeNOx-systems[J].Applied Catalysis B:Environmental,2007,70(1-4):119-127.
[11]蔡忆昔,唐炜,王军,等.基于NOx传感器NH3交叉感应的柴油机Urea-SCR的试验[J].内燃机学报,2015,33(5):461-465.
[12]刘文坤,张翠平,王鹏,等.紧凑型DOC-混合器-SCR后处理系统数值模拟[J].车用发动机,2015,5:57-62.
[13]赵彦光,胡静,陈镇,等.混合器对车用柴油机尿素SCR系统性能影响的试验研究[J].汽车工程,2011,33(4):303-308.
[14]Clark N,Mckain D L,Wayne W,et al.Chassis dynamometer emissions characterization of a urea-SCRtransit bus[C]//SAE Paper.Detroit,Michigan,USA,2011,2011-01-2469.