SCR催化消声器声学特性与流场特性研究
发布时间：2018-09-13 10:02
【摘要】：我国于2016年开始逐步实行第五阶段机动车排放标准,机外净化成为柴油机不可或缺的一部分。SCR(Selective Catalytic Reduction)技术被认为是应用最为广泛的柴油机后处理技术。SCR催化消声器将SCR催化转化器和排气消声器的功能整合在一起,实现尾气净化和降低排气噪声的双重效果,同时节省了布置空间。本文以某款SCR催化消声器为研究对象,研究了其内部结构参数对声学性能和流场性能的影响,最后对用于提高排气中尿素混合和蒸发性能的混合器进行改进设计,使排放满足第五阶段排放要求。具体内容如下:1、基于声学有限元法的催化消声器声学性能研究。在Hypermesh中创建催化消声器声学有限元计算模型,采用Virtual.Lab中Acoustic模块进行声学仿真计算,重点研究了混合器和载体结构参数对催化消声器传递损失的影响,为催化消声器的声学设计提供指导。2、基于试验模型的催化消声器混合建模。为提高催化消声器流场仿真的准确度,采用混合建模方法建立喷嘴和载体在FLUENT中的数学模型。将载体简化为多孔介质,通过冷流背压试验,获得载体惯性阻力系数和粘性阻力系数,并作为仿真输入建立载体的数学模型。在尿素水溶液雾化试验台架上,通过激光粒度分析仪获取喷嘴的雾化特性,根据尿素液滴的分布指数和分布直径建立喷嘴的雾化模型。3、基于连续相与离散相耦合计算的催化消声器流场性能研究。在ICEM中创建催化消声器有限元模型并导入FLUENT中,通过单流场的计算以及带尿素喷射的离散相耦合计算,分析了混合器和载体的结构参数对催化消声器压力损失、载体前的速度均匀性和氨蒸汽均匀性的影响。4、改善尿素溶液蒸发性能的混合器设计。混合器结构影响尿素液滴的混合、蒸发以及结晶的产生,与催化消声器的净化性能密切相关。从提高尿素液滴蒸发速率入手,创新性的提出了一种由半球面与百叶窗结构组成的混合器,使排放满足第五阶段排放要求。5、改进前后催化消声器声学与流场性能仿真分析。分析结果表明:改进后催化消声器的压力损失较改进前略有增加,其声学性能、速度均匀性、氨蒸汽均匀性以及尿素液滴的蒸发性能均明显优于改进前结构。6、试验验证。在发动机台架上进行噪声试验、排放试验以及结晶试验,试验结果表明:额定工况下,催化消声器的插入损失较改进前提高了11.9%,背压从8kPa上升至9.5kPa,满足背压要求;ESC和ETC试验中,NOx排放较改进前分别降低了20.6%和16.6%,满足第五阶段排放要求;20000空速下,NOx单点转化率较改进前明显提高,尤其在265℃以下的低温工况,单点转化率平均提高了7.3%;改进后催化消声器的抗结晶性能满足要求。
[Abstract]:In 2016, China began to gradually implement the fifth stage motor vehicle emission standards. External purification is an indispensable part of diesel engine. SCR (Selective Catalytic Reduction) technology is considered to be the most widely used diesel engine aftertreatment technology. SCR catalytic muffler integrates the functions of SCR catalytic converter and exhaust muffler. The dual effect of purifying exhaust gas and reducing exhaust noise is realized, and the layout space is saved at the same time. In this paper, the influence of internal structure parameters on acoustic performance and flow field performance of a SCR catalytic muffler is studied. At last, an improved mixer is designed to improve the mixing and evaporation performance of urea in exhaust. Make emissions meet stage V emission requirements. The specific contents are as follows: 1. Acoustic performance of catalytic muffler based on acoustic finite element method. The acoustic finite element model of catalytic muffler was established in Hypermesh, and the acoustic simulation was carried out by Acoustic module in Virtual.Lab. The influence of the structure parameters of mixer and carrier on the transfer loss of catalytic muffler was studied. Provide guidance for acoustical design of catalytic muffler. 2. Hybrid modeling of catalytic muffler based on experimental model. In order to improve the accuracy of flow field simulation of catalytic muffler, the mathematical model of nozzle and carrier in FLUENT was established by mixed modeling method. The carrier is simplified to porous medium, and the inertial resistance coefficient and viscous resistance coefficient are obtained by cold flow backpressure test, and the mathematical model of the carrier is established as the simulation input. The atomization characteristics of the nozzle were obtained by laser particle size analyzer on the test bench of urea aqueous solution atomization. According to the distribution index and diameter of urea droplet, the atomization model of nozzle. 3 was established. The flow field performance of catalytic muffler was studied based on the coupling calculation of continuous phase and discrete phase. The finite element model of catalytic muffler was established in ICEM and introduced into FLUENT. The pressure loss of catalytic muffler was analyzed by the calculation of single flow field and discrete phase coupling calculation with urea injection. The influence of velocity uniformity in front of carrier and ammonia vapor uniformity. 4. Design of mixer to improve evaporation performance of urea solution. The structure of the mixer affects the mixing, evaporation and crystallization of urea droplets, which is closely related to the purification performance of the catalytic silencer. In order to improve the evaporation rate of urea droplet, an innovative mixer composed of semi-sphere and shutter is proposed, which makes the discharge meet the requirement of the fifth stage, and simulates the acoustics and flow field performance of catalytic muffler before and after improvement. The results show that the pressure loss of the modified catalytic muffler is slightly higher than that before the improvement, and its acoustic performance, velocity uniformity, ammonia vapor uniformity and evaporation performance of urea droplet are obviously better than that of the modified structure .6. the experimental results show that the pressure loss of the modified catalytic muffler is better than that of the former. Noise test, emission test and crystallization test are carried out on the engine bench. The test results show that: under rated working conditions, The insertion loss of catalytic muffler was increased by 11.9%, and the back pressure increased from 8kPa to 9.5 KPA. The emission of no x in ESC and ETC tests was reduced by 20.6% and 16.6A respectively compared with that before the improvement. The conversion rate was significantly higher than that before the improvement. Especially at the low temperature below 265 鈩，
本文编号：2240862
[Abstract]:In 2016, China began to gradually implement the fifth stage motor vehicle emission standards. External purification is an indispensable part of diesel engine. SCR (Selective Catalytic Reduction) technology is considered to be the most widely used diesel engine aftertreatment technology. SCR catalytic muffler integrates the functions of SCR catalytic converter and exhaust muffler. The dual effect of purifying exhaust gas and reducing exhaust noise is realized, and the layout space is saved at the same time. In this paper, the influence of internal structure parameters on acoustic performance and flow field performance of a SCR catalytic muffler is studied. At last, an improved mixer is designed to improve the mixing and evaporation performance of urea in exhaust. Make emissions meet stage V emission requirements. The specific contents are as follows: 1. Acoustic performance of catalytic muffler based on acoustic finite element method. The acoustic finite element model of catalytic muffler was established in Hypermesh, and the acoustic simulation was carried out by Acoustic module in Virtual.Lab. The influence of the structure parameters of mixer and carrier on the transfer loss of catalytic muffler was studied. Provide guidance for acoustical design of catalytic muffler. 2. Hybrid modeling of catalytic muffler based on experimental model. In order to improve the accuracy of flow field simulation of catalytic muffler, the mathematical model of nozzle and carrier in FLUENT was established by mixed modeling method. The carrier is simplified to porous medium, and the inertial resistance coefficient and viscous resistance coefficient are obtained by cold flow backpressure test, and the mathematical model of the carrier is established as the simulation input. The atomization characteristics of the nozzle were obtained by laser particle size analyzer on the test bench of urea aqueous solution atomization. According to the distribution index and diameter of urea droplet, the atomization model of nozzle. 3 was established. The flow field performance of catalytic muffler was studied based on the coupling calculation of continuous phase and discrete phase. The finite element model of catalytic muffler was established in ICEM and introduced into FLUENT. The pressure loss of catalytic muffler was analyzed by the calculation of single flow field and discrete phase coupling calculation with urea injection. The influence of velocity uniformity in front of carrier and ammonia vapor uniformity. 4. Design of mixer to improve evaporation performance of urea solution. The structure of the mixer affects the mixing, evaporation and crystallization of urea droplets, which is closely related to the purification performance of the catalytic silencer. In order to improve the evaporation rate of urea droplet, an innovative mixer composed of semi-sphere and shutter is proposed, which makes the discharge meet the requirement of the fifth stage, and simulates the acoustics and flow field performance of catalytic muffler before and after improvement. The results show that the pressure loss of the modified catalytic muffler is slightly higher than that before the improvement, and its acoustic performance, velocity uniformity, ammonia vapor uniformity and evaporation performance of urea droplet are obviously better than that of the modified structure .6. the experimental results show that the pressure loss of the modified catalytic muffler is better than that of the former. Noise test, emission test and crystallization test are carried out on the engine bench. The test results show that: under rated working conditions, The insertion loss of catalytic muffler was increased by 11.9%, and the back pressure increased from 8kPa to 9.5 KPA. The emission of no x in ESC and ETC tests was reduced by 20.6% and 16.6A respectively compared with that before the improvement. The conversion rate was significantly higher than that before the improvement. Especially at the low temperature below 265 鈩，
本文编号：2240862
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