【摘要】：我國(guó)于2016年開(kāi)始逐步實(shí)行第五階段機(jī)動(dòng)車(chē)排放標(biāo)準(zhǔn),機(jī)外凈化成為柴油機(jī)不可或缺的一部分。SCR(Selective Catalytic Reduction)技術(shù)被認(rèn)為是應(yīng)用最為廣泛的柴油機(jī)后處理技術(shù)。SCR催化消聲器將SCR催化轉(zhuǎn)化器和排氣消聲器的功能整合在一起,實(shí)現(xiàn)尾氣凈化和降低排氣噪聲的雙重效果,同時(shí)節(jié)省了布置空間。本文以某款SCR催化消聲器為研究對(duì)象,研究了其內(nèi)部結(jié)構(gòu)參數(shù)對(duì)聲學(xué)性能和流場(chǎng)性能的影響,最后對(duì)用于提高排氣中尿素混合和蒸發(fā)性能的混合器進(jìn)行改進(jìn)設(shè)計(jì),使排放滿(mǎn)足第五階段排放要求。具體內(nèi)容如下:1、基于聲學(xué)有限元法的催化消聲器聲學(xué)性能研究。在Hypermesh中創(chuàng)建催化消聲器聲學(xué)有限元計(jì)算模型,采用Virtual.Lab中Acoustic模塊進(jìn)行聲學(xué)仿真計(jì)算,重點(diǎn)研究了混合器和載體結(jié)構(gòu)參數(shù)對(duì)催化消聲器傳遞損失的影響,為催化消聲器的聲學(xué)設(shè)計(jì)提供指導(dǎo)。2、基于試驗(yàn)?zāi)Ｐ偷拇呋暺骰旌辖�。為提高催化消聲器流�?chǎng)仿真的準(zhǔn)確度,采用混合建模方法建立噴嘴和載體在FLUENT中的數(shù)學(xué)模型。將載體簡(jiǎn)化為多孔介質(zhì),通過(guò)冷流背壓試驗(yàn),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(xué)模型。在尿素水溶液霧化試驗(yàn)臺(tái)架上,通過(guò)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(jì)算的催化消聲器流場(chǎng)性能研究。在ICEM中創(chuàng)建催化消聲器有限元模型并導(dǎo)入FLUENT中,通過(guò)單流場(chǎng)的計(jì)算以及帶尿素噴射的離散相耦合計(jì)算,分析了混合器和載體的結(jié)構(gòu)參數(shù)對(duì)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(shè)計(jì)。混合器結(jié)構(gòu)影響尿素液滴的混合、蒸發(fā)以及結(jié)晶的產(chǎn)生,與催化消聲器的凈化性能密切相關(guān)。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(jié)構(gòu)組成的混合器,使排放滿(mǎn)足第五階段排放要求。5、改進(jìn)前后催化消聲器聲學(xué)與流場(chǎng)性能仿真分析。分析結(jié)果表明:改進(jìn)后催化消聲器的壓力損失較改進(jìn)前略有增加,其聲學(xué)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(jìn)前結(jié)構(gòu)。6、試驗(yàn)驗(yàn)證。在發(fā)動(dòng)機(jī)臺(tái)架上進(jìn)行噪聲試驗(yàn)、排放試驗(yàn)以及結(jié)晶試驗(yàn),試驗(yàn)結(jié)果表明:額定工況下,催化消聲器的插入損失較改進(jìn)前提高了11.9%,背壓從8kPa上升至9.5kPa,滿(mǎn)足背壓要求;ESC和ETC試驗(yàn)中,NOx排放較改進(jìn)前分別降低了20.6%和16.6%,滿(mǎn)足第五階段排放要求;20000空速下,NOx單點(diǎn)轉(zhuǎn)化率較改進(jìn)前明顯提高,尤其在265℃以下的低溫工況,單點(diǎn)轉(zhuǎn)化率平均提高了7.3%;改進(jìn)后催化消聲器的抗結(jié)晶性能滿(mǎn)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(hào)：2240862