【摘要】：我國于2016年開始逐步實行第五階段機動車排放標準,機外凈化成為柴油機不可或缺的一部分。SCR(Selective Catalytic Reduction)技術被認為是應用最為廣泛的柴油機后處理技術。SCR催化消聲器將SCR催化轉化器和排氣消聲器的功能整合在一起,實現(xiàn)尾氣凈化和降低排氣噪聲的雙重效果,同時節(jié)省了布置空間。本文以某款SCR催化消聲器為研究對象,研究了其內部結構參數(shù)對聲學性能和流場性能的影響,最后對用于提高排氣中尿素混合和蒸發(fā)性能的混合器進行改進設計,使排放滿足第五階段排放要求。具體內容如下:1、基于聲學有限元法的催化消聲器聲學性能研究。在Hypermesh中創(chuàng)建催化消聲器聲學有限元計算模型,采用Virtual.Lab中Acoustic模塊進行聲學仿真計算,重點研究了混合器和載體結構參數(shù)對催化消聲器傳遞損失的影響,為催化消聲器的聲學設計提供指導。2、基于試驗模型的催化消聲器混合建模。為提高催化消聲器流場仿真的準確度,采用混合建模方法建立噴嘴和載體在FLUENT中的數(shù)學模型。將載體簡化為多孔介質,通過冷流背壓試驗,獲得載體慣性阻力系數(shù)和粘性阻力系數(shù),并作為仿真輸入建立載體的數(shù)學模型。在尿素水溶液霧化試驗臺架上,通過激光粒度分析儀獲取噴嘴的霧化特性,根據(jù)尿素液滴的分布指數(shù)和分布直徑建立噴嘴的霧化模型。3、基于連續(xù)相與離散相耦合計算的催化消聲器流場性能研究。在ICEM中創(chuàng)建催化消聲器有限元模型并導入FLUENT中,通過單流場的計算以及帶尿素噴射的離散相耦合計算,分析了混合器和載體的結構參數(shù)對催化消聲器壓力損失、載體前的速度均勻性和氨蒸汽均勻性的影響。4、改善尿素溶液蒸發(fā)性能的混合器設計�；旌掀鹘Y構影響尿素液滴的混合、蒸發(fā)以及結晶的產(chǎn)生,與催化消聲器的凈化性能密切相關。從提高尿素液滴蒸發(fā)速率入手,創(chuàng)新性的提出了一種由半球面與百葉窗結構組成的混合器,使排放滿足第五階段排放要求。5、改進前后催化消聲器聲學與流場性能仿真分析。分析結果表明:改進后催化消聲器的壓力損失較改進前略有增加,其聲學性能、速度均勻性、氨蒸汽均勻性以及尿素液滴的蒸發(fā)性能均明顯優(yōu)于改進前結構。6、試驗驗證。在發(fā)動機臺架上進行噪聲試驗、排放試驗以及結晶試驗,試驗結果表明:額定工況下,催化消聲器的插入損失較改進前提高了11.9%,背壓從8kPa上升至9.5kPa,滿足背壓要求;ESC和ETC試驗中,NOx排放較改進前分別降低了20.6%和16.6%,滿足第五階段排放要求;20000空速下,NOx單點轉化率較改進前明顯提高,尤其在265℃以下的低溫工況,單點轉化率平均提高了7.3%;改進后催化消聲器的抗結晶性能滿足要求。
[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，

本文編號：2240862