基于模型的DPF再生温度控制策略开发及验证

为精确控制柴油机颗粒捕集器(diesel particulate filter, DPF)的再生温度,避免因再生失控引起的DPF失效风险,在柴油机氧化催化器(diesel oxidation catalyst, DOC)和DPF组成的后处理系统上建立基于化学反应动力学原理的DOC温度模型,在温度模型和再生温度控制算法的基础上设计DPF再生温度前馈及反馈控制策略;利用发动机台架测试数据进行控制策略联合仿真,对控制参数进行系统整定及优化;通过发动机台架瞬态及稳态工况测试,验证控制策略的实际应用效果。仿真和台架试验结果表明：DPF再生温度控制策略具有很好的动态性能及稳态性能,最大峰值温度及燃油喷射量均控制在限定范围,可确保DPF实现高效可靠的再生。     

DOC+DPF+SCR后处理系统对小型柴油机性能及排放的影响

对比无后处理的小型柴油机原机和氧化催化器(diesel oxidation catalyst,DOC)+颗粒物捕集器(diesel particulate filter,DPF)+选择性催化还原(selective catalytic reduction,SCR)后处理技术的柴油机性能和排放状态,测试排气管和DPF出口处NO_x排放中NO的体积分数。试验结果表明:与搭载DOC+DPF+SCR后处理的柴油机相比,原机的扭矩提高5～10 N·m,油耗无明显变化;原机NO_x排放中全部为NO,搭载DOC+DPF+SCR后,NO的体积分数随温度的升高逐渐降低,排温在500℃时,体积分数降至84%左右;相比于原机,搭载DOC+DPF+SCR后处理系统的小型柴油机在非道路稳态循环(non-road steady cycle,NRSC)试验中CO的比排放降低了97%,HC的比排放下降了86%,NO_x的比排放下降了70%,PM的比排放下降了80%。     

柴油机DPF驻车再生排气热管理策略试验研究

在一台非道路国四高压共轨柴油机上,利用试验台架研究颗粒捕集器(diesel particulate filter,DPF)驻车再生过程中不同排气热管理策略对氧化型催化器(diesel oxidation catalyst,DOC)入口温度及排放的影响。结果表明,合适的再生转速、节气门关闭角度及喷油参数对提升DOC入口温度、降低DOC入口未燃HC效果显著。研究结果可以对柴油机DPF驻车再生排气热管理策略的制定和优化提供指导。     

微粒捕集器喷油率对再生温度影响的仿真分析与优化

对于柴油机微粒排放后处理问题,可通过喷油助燃再生的方法来实现。再生温度对柴油机微粒过滤器(DPF)内部冲击造成过滤器内部温度受热很难达到均匀,易造成热应力破坏。结果表明:在微粒过滤器(DPF)喷油助燃再生过程中,不同的喷油率值对DPF内部峰值温度的影响也不同。提高喷油率可以增加燃烧功率,但喷油率提高后,排气中氧含量减少,燃烧效率下降导致再生速率下降。因此对于排气中氧含量的增加尤为必要。     

不同后处理装置生物柴油发动机颗粒多环芳烃排放

基于一台高压共轨柴油机,利用台架试验采样和离线分析,研究了燃用生物柴油混合燃料BD20使用不同后处理装置(DOC、DPF和CDPF)对柴油机的颗粒多环芳烃(PAHs)排放特性、成分和毒性的影响。研究结果表明:燃用生物柴油混合燃料BD20引起了柴油机颗粒物中PAHs质量比升高和颗粒物毒性增强;不同后处理装置均降低了柴油机的颗粒PAHs排放和毒性,DOC可降低颗粒PAHs排放约30%,使颗粒物毒性降低约20%;DPF和CDPF可去除排气中大部分颗粒PAHs,使颗粒物毒性降低60%以上,使排气毒性降低85%以上,可有效地实现对生物柴油发动机颗粒PAHs排放和毒性的控制。     

基于仿真与试验的SCR混合器开发及验证

为解决国Ⅵ排放法规下柴油机后处理系统尿素结晶风险过高的问题，提出了一种选择性催化还原(SCR)系统混合器设计优化及性能验证方法．首先，借助计算流体动力学(CFD)，对建立的后处理系统模型进行了4种典型工况条件下速度场和氨(NH₃)分布均匀性等性能的数值仿真，然后通过台架进行NH₃分布均匀性试验对仿真过程进行优化，基于对优化后仿真结果的分析，提出了一种结合破碎格栅、导流装置和微孔整流板等设计元素的混合器优化方案．高温高速工况下，该方案可在基本不影响排气背压情况下将SCR₁载体内部的速度分布均匀性从0.951提升至0.976,NH₃分布均匀性从0.947提升至0.979，瞬态尿素结晶风险试验结果表明：该方案具备优异的混合性能与抗结晶性能．     

用HRTEM研究DOC和DPF对柴油机颗粒排放的影响

利用高分辨率透射电镜(HRTEM)对安装了排气后处理装置的CY4102-CE4B柴油机排放的颗粒进行观察,对比了ESC循环中工况7与工况10后处理装置中,柴油氧化催化器(DOC)与颗粒捕集器(DPF)前后颗粒的微观形貌与结构。研究结果表明:组成颗粒的基本粒子均呈近似球形,与发动机工况和后处理装置无关;经DOC后组成颗粒的基本粒子的轮廓比在DOC前更清晰,次级粒子由葡萄状结构向链状结构转化,但经DPF后,又向葡萄型结构转化;低速低负荷时,组成基本粒子的内核与外壳不甚明晰,呈无定型结构,基本结构单元的尺寸较小,薄层呈波浪状;而高速高负荷时,组成基本粒子的内核与外壳更加清晰,呈石墨结构,层状结构也更加明显,薄层几乎呈直线段。     

低温等离子体降低柴油机排放的研究进展

简要介绍了当前柴油机排气后处理所采用的DPF和SCR技术,并指出了其应用难点。详细分析了两种低温等离子体技术各自的技术特点,阐述了D/I NTP技术在降低柴油机有害排放方面最新的研究进展及发展趋势,指出对D/I NTP系统分解柴油机排气中PM、再生DPF的微观机理进行分析将成为今后研究的重点。     

满足国V以上排放的轿车柴油机关键技术的研究

对肖今世界轿车柴油机满足国V以上排放的技术路线进行了剖析,拟定了史适合我旧轿车柴油机发展的“EGR＋DPF”技术路线;基于“EGR＋DPF”技术路线,设计了目标机型Yc4W110—40轿车柴油机的电控管理系统,包括电控高压共轨燃油喷射技术、电控空气管理技术以及“DOC＋DPF”后处理技术。指出在轿车柴油机管理系统的开发中町综合考虑各种因素,充分发挥各种技术措施的作用。     

DOC/POC/SCR组合后处理技术在非电控柴油机排放上的应用研究

在一台经典非电控柴油机上进行了氧化催化剂(diesel oxidation catalyst,DOC)/颗粒氧化转化器(particle oxidation catalyst,POC)/选择性催化还原转化器(selective catalytic reduction,SCR)组合后处理排放控制研究以使其达到国-Ⅴ标准要求,对后处理单元的选择及排布进行了考察。试验结果表明:DOC+POC及SCR单后处理系统仅能使试验发动机排放污染物中颗粒物(PM)或NOx达到国-Ⅴ标准;而DOC/POC/SCR组合后处理系统则可使两种污染物排放均满足标准要求。SCR与DOC+POC排布顺序对污染物去除效率无明显影响。对POC的被动再生研究表明:DOC+POC系统需置于SCR系统前以使排气中NO2量满足POC的连续再生要求,且SCR系统后置也可降低其入口温度,减小温度对涂层的热老化影响。通过陶瓷POC的应用及结构优化设计使得组合后处理系统排气背压控制在25kPa之内,可减少对发动机性能影响。     

柴油发动机尾气后处理技术的发展

综述柴油发动机尾气后处理技术的主要发展。实验表明,在SCR前加DOC后,NOx在低温下的转化率明显提高,沸石催化剂性能好于钒基催化剂;LNT中采用碱土金属（如钡）或碱金属（如钾）作为吸附剂来提高储藏NOx的能力,采用贵金属不均匀分布法可降低成本;在LNC中小量的H2（〈2%）,就能在很宽的温度范围显著地提高银基LNC的NOx的转化率。分析了DPF载体新材料（基于钛酸铝的化合物等）的特点,总结了DPF再生及灰烬处理技术。     

采用不同后处理装置的柴油机减排效果分析

对分别安装DOC+ DPF和DOC+ POC后处理装置的两台柴油机进行了排放试验.在有/无后处理装置两种状态下,通过ESC试验对两台发动机常规污染物CO、HC、NOx和PM以及非常规污染物NO2和SO2的排放水平进行检测和对比分析,此外对全负荷烟度水平也进行了检测.试验结果表明:DOC+ DPF后处理装置对常规污染物的...     

Effects of a DOC+DPF system on emission characteristics of China Π engineering vehicle diesel engine and influence factors of trapping efficiency of PM for DOC+DPF system

To evaluate the emission characteristics of engineering vehicle diesel engine effectively and find a suitable emission control strategy, the emission characteristics experiment of China ?? engineering vehicle diesel engine was conducted with and without DOC+ DPF. The experiment took high-idling, low-idling, and free-acceleration as testing conditions, and used NanoMet3 particulate analysis system to measure PM mass concentration, number concentration and mean particle size. The gaseous emissions (NOx, NO₂, CO, HC) were analyzed by flue gas analyzer Testo350. The results showed that the PM emission characteristics of engineering vehicle diesel engine improved observably under three different conditions With DOC+ DPF. PM mass emissions reduced by over 85%, and PM number emissions were more than reduce of 90%. The metabolic characteristics of PM mean particle size were sample A < sample B < sample C and high-idling < low-idling < free-acceleration. NOx concentration was not influenced obviously by DOC+ DPF, but NO₂/NOx value increased. Besides, DOC+ DPF made CO emissions decreased by 85% and HC emissions decrement between 50%~80% under different conditions. DOC + DPF could improve the emission characteristics of engineering vehicle diesel engine efficiently, which was easily affected by diesel quality and equipment working hours.     

Analysis of reformed EGR on the performance of a diesel particulate filter

The use of a diesel particulate filter (DPF) in combination with an upstream diesel oxidation catalyst (DOC) has been successfully implemented and shown to reduce carbon monoxide (CO), hydrocarbon (HC) and Particulate Matter (PM) diesel exhaust gas emissions. However issues including cost, size and uncontrolled active regeneration under a low temperature window still require attention. This study therefore primarily focuses on the potential benefits of using a single catalytic coated DPF (cDPF) and a combined DOC-cDPF instead of the DOC-DPF aftertreatment system utilising a passive, low temperature regeneration method. Comparisons were made through monitoring exhaust gas compositions from an experimental single cylinder diesel engine as well as measuring the pressure drop across the filters to analyse the accumulation of soot particles. The influence of reformed EGR (REGR), enriched simulated hydrogen (H₂) and CO, on DPF and cDPF soot loading was of interest as H₂ promotes the NO to NO₂ oxidation. Similarly the addition of simulated reformate (added either directly into the engine intake or exhaust manifold) for optimal performance of the aftertreatment systems was examined.The effects of adding REGR resulted in a significant decrease in total engine-out NO_x emissions, as well as an increase in both NO₂ concentration and NO₂/NO_x ratio. This resulted in improved filter efficiency and overall loading, especially under a DOC-cDPF aftertreatment configuration system. As a whole, a simultaneous NO_x and PM reduction was achieved.     

Soot deposition effects and microwave regeneration modelling of diesel particulate filtration system

Regeneration of accumulated soot particles in the substrate walls of the diesel particulate filtration system is one of the major challenges faced by the automotive industry. This study investigated the conversion efficiency and filtration behaviour of the after treatment system comprising of diesel oxidation catalysis (DOC) and diesel particulate filtration (DPF) system. The average conversion efficiency of hydrocarbons was close to 54% and filtration efficiency of the particle number emissions was around 92%. Characterization of the DOC and DPF substrate were conducted using microscopic imaging, Fourier transform infrared spectroscopy (FTIR) and particle size analysis (PSA). The results of FTIR study indicated the presence of carcinogenic agents trapped in the porous walls of the filter substrate. A model for microwave based regeneration system is proposed in this article and CFD analysis were conducted to determine the temperature and electric field distribution in the DPF substrate for a regeneration time of 180 s. Results of simulation showed that the microwave radiations raise the temperature close to soot oxidation temperature (873 K), ensuring effective regeneration.     

基于燃烧器的柴油机颗粒过滤器再生试验研究

介绍了DPF的颗粒捕集机理和再生原理,并对基于燃烧器再生的SiC过滤器再生开展了试验研究。试验表明,燃烧器能够提供比较均匀稳定的温度场供DPF再生,整个再生过程中DPF的内部温度能够保证再生完全,又不至导致DPF的热损坏,同时采取新的控制策略达到节能和延长DPF寿命的目的,有利于进一步优化DPF再生控制策略,完善DPF后处理系统。     

机动车后处理系统快速老化技术研究

介绍了机动车不同排放后处理系统的老化机理,指出:影响TWC、DOC、SCR老化的主要因素为热老化,而影响GPF和DPF老化的主要因素为灰分积聚。介绍了汽油机TWC、GPF快速老化技术以及柴油机后处理装置快速老化技术,包括小样台架快速老化、马弗炉快速老化、DOC前喷油快速老化、DPF灰分加载快速老化、燃烧器快速老化等,并比较分析了各种快速老化技术的特点及应用情况。     

掺混PODE对DOC+CDPF氧化及再生特性的影响

在高压共轨柴油机上研究了使用掺混20%聚甲氧基二甲醚的柴油(D80P20)对搭载柴油氧化型催化器(DOC)和催化型颗粒捕集器(CDPF)的后处理装置(DOC+CDPF)的影响,包括小负荷时的低温氧化特性和大负荷时的颗粒物加载和再生特性.研究表明:小负荷工况下在1400~2000 r/min内,DOC和DOC+CDPF对柴油排放的CO转化效率平均分别高达70%和90%,而对D80P20排放的CO转化效率则仅近19%和36%,燃用柴油时DOC和CDPF后端的排气升温现象较为明显,低温氧化特性优于D80P20;在大负荷低速工况下,燃用D80P20时,DOC前/后两端排气氧质量分数以及NO2排放均明显高于柴油,但CO原始排放和不透光烟度显著低于柴油.因而DOC+CDPF对D80P20的CO、PM氧化放热量较低,DOC后端温升明显低于柴油.此外,大负荷下DOC+CDPF对D80P20排放的CO净化效率和PM氧化再生效率高达近100%,DOC+CDPF前/后端压差峰值仅是柴油的1/3,其可显著降低CDPF的堵塞风险,减少主动再生频率.