CN106168153A - 排放物减少系统 - Google Patents

排放物减少系统 Download PDF

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Publication number
CN106168153A
CN106168153A CN201610326013.7A CN201610326013A CN106168153A CN 106168153 A CN106168153 A CN 106168153A CN 201610326013 A CN201610326013 A CN 201610326013A CN 106168153 A CN106168153 A CN 106168153A
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China
Prior art keywords
pna
nox
doc
exhaust gas
temperature
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CN201610326013.7A
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Inventor
约瑟夫·罗伯特·诺特海斯
克里斯廷·凯·兰伯特
道格拉斯·艾伦·多布森
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Ford Global Technologies LLC
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Ford Global Technologies LLC
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Priority to US14/714,757 priority Critical
Priority to US14/714,757 priority patent/US9657626B2/en
Application filed by Ford Global Technologies LLC filed Critical Ford Global Technologies LLC
Publication of CN106168153A publication Critical patent/CN106168153A/zh
Pending legal-status Critical Current

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    • Y02TCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00Road transport of goods or passengers
    • Y02T10/10Internal combustion engine [ICE] based vehicles
    • Y02T10/12Improving ICE efficiencies

Abstract

公开了一种用于柴油发动机的排气系统。该排气系统可包括被构造成接收来自发动机的排气气体并且使排气气体中的碳氢化合物氧化的柴油氧化催化剂(DOC)、以及位于DOC下游并且被构造成在温度达到150℃时存储来自排气气体的NOx的被动NOx吸附器(PNA)。选择性催化减少(SCR)系统可位于PNA下游并且被构造成减少排气气体中的NOx。PNA可被构造成在温度高于200℃时释放存储的NOx。PNA上游的DOC可通过在N2O到达PNA之前使碳氢化合物氧化而减少由PNA产生的N2O的量。

Description

排放物减少系统
技术领域
[0001 ]本公开涉及例如用于柴油发动机的排放物减少系统。
背景技术
[0002]相比于常见的汽油发动机,柴油发动机通常在更低温度下操作并且更稀地运行。尽管汽油发动机由于更高的燃烧温度在百万分之一基础上可放出更多的NOx,但是当A/F比率为理想配比时三元催化剂可高效地减少该NOx。因此,来自装备有催化剂的汽油发动机的NOx排放物能够低于来自柴油发动机的NOx排放物。由于柴油稀操作,三元催化剂可能不会减少NOx JOx排放物的减少因此成为对柴油发动机的独特挑战。一种减少柴油发动机的NOx排放的方法是选择性催化还原(SCR)系统的使用。一旦SCR催化剂的温度高于最小操作水平(例如,150 °C或200°C),则通过尿素喷射的SCR系统对于在稀条件下减少NOx是非常有效的。然而,在SCR催化剂已经达到此操作温度之前,排气中的许多NOx在没有被减少的情况下通过SCR催化剂并且被从车辆排放。
发明内容
[0003]在至少一个实施例中,提供一种用于柴油发动机的排气系统。该系统可包括被构造成接收来自发动机的排气气体并且使排气气体中的碳氢化合物氧化的柴油氧化催化剂(DOC)、以及位于DOC下游并且被构造成在温度达到150°C时存储来自排气气体的NOx的被动NOx吸附器(PNA)。选择性催化减少(SCR)系统可位于PNA下游并且可被构造成减少NOx。
[0004]在一个实施例中,PNA被构造成在温度达到180 °C时存储来自排气气体的NOx。在另一个实施例中,PNA被构造成在温度高于2000C时释放存储的NOx JNA可被构造成在350°C或更低的温度时释放基本上所有存储的NOx JOC可具有大于1:1的钯比铂的含量比,诸如至少为3:1JNA可具有至少为3:1的钯比铂的含量比。排气系统在发动机启动之后的第一个2000秒期间可排放小于I Oppm的N2O。
[0005] 在一个实施例中,DOC可通过排气导管连接至PNA。在另一个实施例中,DOC和PNA可被包含在单一壳体中。DOC和PNA可作为层形成在单一基板上。PNA可基本上不包含碱金属或碱土金属,诸如钡。PNA可包含一种或多种稀土元素,诸如铈。
[0006]在至少一个实施例中,提供一种处理来自柴油发动机的排气的方法。该方法可包括将第一排气气体(FEG)从发动机引导至柴油氧化催化剂(DOC)以产生第二排气气体(SEG),以及将SEG从DOC引导至被动NOx吸附器(PNA)以产生第三排气气体(TEG) INA在温度达到150 °C时可存储来自SEG的NOx。TEG可从PNA被弓丨导至NOx减少系统。
[0007] 在一个实施例中,在温度高于200°C时PNA将存储的NOx释放到TEG中。在400°C或更低的温度下,PNA可将基本上所有的存储的NOx释放至IjTEG中。在一个实施例中,在启动柴油发动机之后的第一个2000秒期间,来自NOx减少系统的输出排气气体(OEG)包括小于1ppm的N20。柴油发动机可基本上总是通过稀空气燃料比运行。
[0008]在至少一个实施例中,提供一种用于处理来自柴油发动机的排气气体的排气系统。该系统可包括设置在基板上并且被构造成在温度达到150°C时存储来自排气气体的NOx的被动NOx吸附器(PNA)层、以及设置在PNA层上并且被构造成使排气气体中的碳氢化合物氧化的柴油氧化催化剂(DOC)层。选择性催化减少(SCR)系统可位于PNA和DOC层下游并且被构造成减少排气气体中的NOx。在一个实施例中,PNA层和DOC层可具有至少为3:1的钯比铂的含量比并且PNA层可基本上不包括碱金属或碱土金属。
附图说明
[0009] 图1示出了当在原料气中具有10ppm的NO和250ppm的C2H4的测试时在实验室测试期间随时间过去的从被动NOx吸附器(PNA)排放的N2O的水平;
[0010]图2示出了在实验室测试期间随时间过去的来自单独的柴油氧化催化剂(DOC)、单独的PNA、以及DOC和PNA的组合的碳氢化合物、C2H4的水平;
[0011]图3示出了在实验室测试期间随时间过去的从单独的DOC、单独的PNA、以及DOC和PNA的组合排放的N2O的水平;
[0012]图4为根据一个实施例的包括单独的DOC和PNA的排气系统的示意图;
[0013]图5为根据一个实施例的包括连接的DOC和PNA的排气系统的示意图;
[0014]图6为根据一个实施例的包括组合的DOC和PNA的排气系统的示意图;以及
[0015]图7为图6中的组合的DOC和PNA的示意性横截面,其示出了在PNA层上方的DOC层。
具体实施方式
[0016]根据需要,此处公开了本发明的详细实施例;然而应当理解,所公开的实施例仅仅是本发明的可以各种可替代形式实施的实例。附图不一定按比例绘制;一些特征可被放大或缩小以展示特定部件的细节。因此,本文公开的具体的结构性和功能性的细节不应被解释为限制,而仅仅是作为用于教导本领域中的技术人员多方面地实施本发明的代表性基础。
[0017]在SCR催化剂还未达到其最小操作水平期间的时间周期可称为“冷启动”时间周期。该冷启动周期可持续多达几分钟,例如,多达200秒。从柴油发动机排放的主要污染物是碳氢化合物(HC)、一氧化碳(CO)、氮氧化物(NOx)、以及颗粒物(例如,烟灰)。如在背景技术中所描述的,在冷启动周期期间,排气温度对于SCR催化剂来说太低而不能减少NOx,因此NOx被释放到大气中。可将被动NOx吸附器(PNA)添加至排气系统以在该冷启动周期期间吸收和存储至少发动机排放的NOx的一些。PNA可包含铂(Pt)和/或钯(Pd)和NOx存储材料(例如,二氧化铈)。不像SCR系统,PNA的目标是存储NOx并且然后在之后的时间将其释放,而不是减少或氧化NOx本身。PNA可存储NOx直到在尿素喷射系统是可操作的并且下游SCR催化剂已经达到其操作温度(例如,至少150 °C或200 °C )之后,在那时NOx被从PNA释放。PNA因此存储那些否则将未反应地通过SCR系统直到SCR催化剂已经达到允许其减少从PNA释放的NOx的温度的NOx。
[0018] PNA被设计成替代通常已经为柴油后处理系统中的第一催化剂砖的柴油氧化催化剂(DOC)。因此,除了在冷启动周期期间存储和释放NOx,PNA也被构造成提供氧化HC和一氧化碳(CO)的DOC功能。此外,一旦排气系统热起来(例如,大约2000C),PNA中的Pt就可将发动机排出的NO的一部分氧化成NO2并且因此向SCR催化剂提供NO和NO2的混合物,SCR催化剂在低温时提高其NOx减少能力。
[0019]然而,当PNA被用作排气系统中的第一砖时,其持续地暴露于从发动机排放的NOx和HC的全浓度。在冷启动周期结束(例如,大约200秒)并且排气系统达到全操作温度之后,研究发现由于在约200 °C的温度下碳氢化合物与NOx之间的反应PNA能够产生N20。这种反应可被称为稀NOx催化或碳氢化合物-SCR。研究发现该反应对于铂而言比钯更显著。N2O的产物是不合需要的,因为N2O是非常有效的温室气体。例如,N2O在捕获热量方面比二氧化碳有效几百倍。
[0020]图1示出了在实验室反应器上的几个温度斜坡测试期间来自被动NOx吸附器的N2O形成,其中烘箱温度从70°C以10°C/min倾斜至175°C,保温10分钟,并且然后从175°C以10°C/min倾斜至300°C并且在那保温5分钟。该测试使PNA暴露于其在联邦测试程序(FTP)的阶段I和阶段2期间以及在US06测试(一种补充联邦测试程序(SFTP))期间将暴露于的温度的子集。排气包含250ppm乙烯(C2H4)、10ppmNO, 10 %O2、5 % CO2和H2O、以及平衡N2。除了N2O排放物,图1还示出原料气NO、排气管NOx、排气管C2H4、以及来自其中一个测试的床温度。
[0021]如在图1中所示,在测试的第一个100秒到120秒期间PNA有效地存储NOx并且然后在150秒与300秒之间释放一些存储的NOx。其还有效地存储C2H4大约100秒。在第一个180秒期间N2O形成非常慢。然而,在180秒之后,PNA开始产生显著水平的N2O;当床温度在180°C与230°C之间时N2O在15ppm与20ppm之间并且当床温度增加到接近250°C的温度时减少到约lOppm。当温度在靠近测试结束接近300°C时,犯0形成下降到大约5ppm。当测试在具有NO但无C2H4的情况下运行时,无N2O形成。这表明N2O起因于NOx与HC之间的反应。研究发现这种反应在PNA的钯和铂中发生,但是铂比钯引起更多的N2O产生。
[0022] 研究发现,通过PNA的N2O形成能够通过在PNA的前部放置富Pd DOC而减少。DOC—旦处于其操作温度,则可将PNA上游的碳氢化合物氧化成二氧化碳和水,因而消除或减少可用于在PNA上与NOx(例如,NO)反应以形成N2O的HC的量。参照图2,具有175gpcf铂族金属(PGM)(具有I至4的铂/钯比率)的老化DOC被放置在PNA的前部,并且执行另一个斜坡测试。图2示出了原料气C2H4、在单独DOC之后的C2H4、在单独PNA之后的C2H4、以及在D0C+PNA组合之后的C2H4。在没有DOC的情况下,进入单独PNA的C2H4浓度是267ppm的全原料气水平。但是在PNA的前部具有DOC的情况中,进入PNA的C2H4浓度从600秒到以后都在O到10ppm之间(S卩,由标记“单独D0C”的曲线指示)。值得注意的是,来自D0C+PNA组合的C2H4在超过600秒之后非常低,这是将DOC放置在PNA前部的附加优势。
[0023]图3将无DOC的N20(类似于图1中的数据)与带有在PNA前面的DOC的N2O进行了比较。图3也示出了由单独DOC形成的N2O,这是非常少的。D0C+PNA组合比单独PNA产生少得多的N20。尽管此处未示出,但是DOC对进入PNA的NOx浓度本质上没有影响。因此,N2O的下降仅归因于DOC氧化了一些C2H4并且因此减少了 NOx与C2H4之间在PNA上形成N2O的反应。因此研究发现,与其将PNA作为第一催化剂放置到后处理系统中,不如将富Pd DOC放置到PNA的前部以使N2O形成最小化并且以提高HC转化。所公开的布置对于PNA的耐久性而言也是有益的。在预热操作期间DOC可执行许多放热氧化反应,尤其是在柴油颗粒过滤器(DPF)的再生期间。取决于应用,DPF可位于SCR系统的下游或上游。在DPF再生期间DOC可产生热排气,并且该热排气可在进入DPF之前(如果在SCR下游)通过PNA和SCR JOC可保护PNA因为DOC代替PNA执行放热反应。放热反应能够在PGM位置处产生高温,这会损坏它们。照此,DOC可保护PNA使其免受这种放热反应的侵害。
[0024]参照图4至图7,公开了排气系统10的若干实施例。在至少一个实施例中,该排气系统1是柴油发动机排气系统。排气系统1可连接至发动机12 (可为柴油发动机)的出气口。系统1可包括柴油氧化催化剂(DOC) 14和被动NOx吸附器(PNA) 16。在所示实施例中,系统1也可包括在D0C14和PNA16下游的选择性催化减少(SCR)系统18 ACR系统18可包括还原剂喷射系统和该还原剂喷射系统下游的SCR催化剂。还原剂喷射系统可将还原剂引入排气气体中。还原剂可为流体,诸如无水氨、氨水、或尿素。可替代地,可使用固体还原剂,固体还原剂可不需要喷射系统。SCR催化剂可减少NOx以形成氮气、水、和/或二氧化碳,这取决于还原剂。尽管未示出,但是SCR系统18可被替换或补充有稀NOx捕获器(LNT),或其他已知的NOx减少装置。LNT是被设计成在升高温度下(例如,高于200°C)吸收和减少NOx的装置。LNT通常通过在稀发动机操作期间吸收NOx并且在富发动机操作期间减少NOx操作。因而,LNT可通过在稀发动机操作与富发动机操作之间交替而被“再生”。LNT可吸收NOx作为硝酸盐,硝酸盐是相对稳定的并且要求富循环来减少硝酸盐。LNT通常为铂和/或钡重的。LNT直到系统预热之后才开始操作,并且因此对冷启动排放物具有很小影响或没有影响。
[0025] 与LNT相反,PNA被构造成或适于在低温下操作,诸如达到150°C、180°C或200°C。此夕卜,PNA不减少NOx;它们仅仅在冷启动温度期间存储NOx并且在更高温度时释放NOx。通过在低温时存储NOx,PNA给予SCR系统18 (或其他下游系统)时间来预热。一旦下游系统已经达到它们的操作温度,PNA就释放存储的NOx并且允许下游系统减少NOx、使NOx氧化或另外地使NOx反应成危害性更低的物质。PNA16可为被动的,因为它不需要任何能量输入,燃料组分的改变、或其他主动步骤来操作。这与需要在稀操作与富操作之间交替以再生上述捕集器的LNT相反。此外,PNA16可吸收NOx作为亚硝酸盐,而不是硝酸盐(像LNT—样)。亚硝酸盐可为不太稳定的,从而允许它们在没有富燃料循环的情况下被释放。通过在低温操作,在发动机冷启动之后,诸如第一个100秒、150秒或200秒,PNA可对NOx排放物具有直接的显著影响。尽管这看起来似乎是短暂的时间段,但是由于在冷启动期间其他排放物系统的相对无效,在此时间周期期间相对大量的有害排放物可被释放到大气中。由于在冷启动周期期间来自车辆的大部分的排气管排放物可被排放,因此在满足严格排放标准方面减少冷启动排放物是重要的。
[0026]参照图4,公开了系统10的实施例,在该实施例中D0C14位于发动机12的下游,并且PNA16位于D0C14的下游。在该实施例中,D0C14和PNA16是单独的部件,其可通过排气管、管道、导管或软管20连接。D0C14可被称为第一或前部砖,PNA16可被称为第二或后部砖。PNA16的下游是SCR系统18,尽管也可包括额外的或其他的系统(例如,LNT和/或DPF)。
[0027]参照图5,公开了系统10的实施例,在该实施例中D0C14位于发动机12的下游,并且PNA位于D0C14的下游。在该实施例中,D0C14和PNA16是单独的部件但是被直接地端部对端部地连接在相同的催化转化器中,使得在它们之间不存在排气管。D0C14和PNA16可位于单独基板上或被区域涂层至单一基板上。D0C14可被称为前部或第一区,PNA16可被称为砖的第二或后部区。PNA16的下游是SCR系统18,尽管也可包括额外的或其他的系统(例如,LNT和/^DPF) ο
[0028]参照图6和图7,公开了系统10的实施例,在该实施例中D0C14和PNA16被结合到单一部件或砖中。在此实施例中,D0C14可形成为设置在PNA层24上方、顶部或覆盖PNA层24的层22,其中PNA层24设置在基板26的上方、顶部或覆盖基板26。相应地,D0C14可仍然被认为在PNA16的“上游”,因为排气气体将遇到并且首先与DOC层22反应然后与PNA层24反应。图7示出了基板26、PNA层24和DOC层22的示意性横截面。基板26可类似于公开的用于D0C14和PNA16的基板。DOC层22和PNA层24可由与D0C14和PNA16相似的部件形成,如下文所述(例如,载体涂料和催化剂)。尽管示出上述层是平坦的并且在厚度上是一致的,但是该层也可具有粗糙表面和/或具有自始至终不同的厚度。
[0029] DOC在本技术中是熟知的因此将不再详细描述。D0C14可为被构造成使碳氢化合物(HC)和一氧化碳(CO)氧化以形成二氧化碳(CO2)和水(H2O)的任意装置。D0C14可为具有基板和包括一种或多种催化剂材料的主动层的通过装置。D0C14可不包含存储NOx的材料,诸如铈。基板可具有排气气体可通过的多个通道或开口。基板可为整块石料或挤压材料,诸如堇青石。可使用载体涂料将主动层施加至基板。尽管DOCs通常包括作为主要催化材料的铂和钯,但是在至少一个实施例中,D0C14可具有比铂更多的钯(例如,Pd: Pt比率>1)。例如,00〇14可具有至少2:1、3:1、4:1或更大的?(1:?丨比率。在另一个实施例中,00(:可不包括铂,或基本上不包括铂(例如,小于总催化剂材料重量的1%)。如前所述,研究发现,铂的使用相比于其他催化剂导致更大的N2O产量。相应地,通过减少D0C14中的Pt的量,可减少总N2O产量。
[0030] PNA16可为被构造成在相对低温时(诸如达到150°C、180°C或200°C)存储NOx并且在其他排放物系统开始操作的温度时(诸如180°C或200°C)开始释放NOx的装置。例如,PNA16可被构造成在从0°C或20°C至150°C、180°C或200°C的温度时存储N0XJNA16可通过吸收和解吸存储和释放NOx。在一个实施例中,所有的或基本上所有的(例如,至少95%)存储的NOx在达到450 0C时(诸如达到400 V、或达到350 V)可被PNAl6释放。PNAl6可存储NOx作为亚硝酸盐或硝酸盐。PNA16可为具有基板和包括一种或多种催化剂材料的主动层的通过装置。基板可具有排气气体可通过的多个通道或开口。基板可为整块石料或挤压材料。合适的基板材料的非限制性实例包括堇青石、钛酸铝、以及碳化硅。可使用载体涂料将主动层施加至基板。
[0031 ] PNA16可包括催化剂材料,催化剂材料可包括铂、钯以及铑。在至少一个实施例中,卩嫩16可具有比铂更多的钯(例如,?(1:?计|:率>1)。例如,?嫩16可具有至少2:1、3:1、4:1或更大的Pd:Pt比率。在另一个实施例中,PNA16可不包括铂,或基本上不包括铂。用于施加主动材料的载体涂料可包括诸如氧化铝(例如,AL2O3)和/或二氧化铈(例如,CeO2)、或其他稀土元素或其氧化物。在至少一个实施例中,载体涂料可包括很少的或不包括碱金属或碱土金属,诸如钡。例如,载体涂料可包括比碱金属或碱土金属(例如,钡)更多的氧化铝和/或二氧化铈。在一个实施例中,载体涂料包括少于5%重量的碱金属或碱土金属(例如,钡),诸如少于I %重量或无碱金属或碱土金属(例如,O %重量),诸如钡。碱金属或碱土金属可存储NOx,但是要求高温来释放NOx,这使得它们不适合在PNA中使用。如上所述,研究发现,铂的使用相比于其他催化剂导致更大的N2O产量。相应地,通过减少PNA16中的Pt的量,可减少总N2O产量。
[0032]如上所述,SCR系统18在本领域中是熟知的因此将不详细描述。通常,SCR系统使用催化剂或还原剂将NOx转化成氮气、水和二氧化碳,这取决于系统。还原剂通常为无水氨、氨水或尿素并且可被添加至烟道或排气气体流中。SCR催化剂可包括沸石或碱金属的氧化物。例如,可使用包括铜或铁或钒的氧化物的沸石、钼和钨。如上所述,系统10可包括D0C14和PNA16下游的SCR系统18A0C14和PNA16下游、SCR系统18上游或下游可包括额外的NOx减少系统。可替代地,SCR系统18可被一个或多个其他NOx减少系统替代,例如,LNT。
[0033]已经公开了用于减少NOx (尤其是N2O )、排放物的系统1的实施例。该系统1可包括PNA16上游的D0C14,PNA16位于NOx减少装置(诸如,SCR系统18)上游。研究发现,当PNA从发动机12接收碳氢化合物和NOx时,PNA能够产生N20,N2O是一种强大的温室气体。当PNA铂含量大时,Ν2θ产量可更大。
[0034] 公开的系统10通过包含在ΡΝΑ16的下游的D0C14而不是用PNA替代DOC解决了这个问题。D0C14—旦在其操作温度,则在大部分或所有的HC到达ΡΝΑ16之前氧化大部分或所有的HC,从而大大地减少在ΡΝΑ16上形成N2O的反应中的其中一个还原剂的量。系统10因此解决面对柴油发动机排气系统的若干挑战。如刚才所述,通过提供DOC和PNA的组合,其中DOC减少由PNA接收的碳氢化合物的量,系统10极大地减少了产生并且排放到大气中的N2O的量。一旦DOC加热到其操作温度,诸如200 °C和以上的温度,其就氧化HC。这包括当PNA处于在N2O产量最大时的大约200到250 0C的温度范围中时DOC减少由PNA接收的HC。
[0035]此外,PNAl 6极大地有助于在冷启动周期期间(例如,第一个200秒)从系统1的减少的NOx排放。PNAl 6在低温时(诸如达到150 °C、180 °C或200 °C)吸收NOx。此段时间是关键的,因为下游系统(诸如SCR系统18)在达到最小操作温度(例如,大约200 °C)之前在减少NOx方面是无效的。因此,在冷启动期间通过SCR系统18的任何NOx将不减少并且将从车辆排放。PNA16在此冷启动周期期间吸收和保持NOx并且一旦系统的温度已经达到下游部件是有效的水平就将NOx释放。相应地,所公开的系统10在“7令”和“热”发动机操作期间提供NOx减少,同时还通过PNA16极大地减少产生的N2O JOC也可保护PNA免受高温的侵害并且帮助其耐久性。例如,PNA可位于离DOC的远程位置(例如,通过导管连接),这可降低PNA经历的温度。非常高的温度,诸如高于700 °C或800 0C会损坏或减小PNA中的贵金属催化剂的耐久性。
[0036]尽管以上公开了示例性的实施例,但是并不意在这些实施例描述本发明的所有可能形式。此外,在说明书中使用的文字是描述性文字而非限制性,并且应当理解,在不背离本发明的精神和范围的情况下可进行各种改变。额外地,可将各种实施的实施例的特征进行组合以形成本发明的进一步的实施例。

Claims (20)

1.一种用于柴油发动机的排气系统,包括: 被构造成接收来自所述发动机的排气气体并且使所述排气气体中的碳氢化合物氧化的柴油氧化催化剂(DOC); 位于所述DOC下游并且被构造成在温度达到150°C时存储来自所述排气气体的NOx的被动NOx吸附器(PNA);以及 位于所述PNA下游并且被构造成减少所述排气气体中的NOx的选择性催化减少(SCR)系统。
2.根据权利要求1所述的系统,其中,所述PNA被构造成在温度达到180°C时存储来自所述排气气体的NOx。
3.根据权利要求1所述的系统,其中,所述PNA被构造成在温度高于200°C时释放所述存储的NOx。
4.根据权利要求1所述的系统,其中,所述DOC具有大于1:1的钯与铂的含量比。
5.根据权利要求1所述的系统,其中,所述DOC具有至少为3:1的钯与铂的含量比。
6.根据权利要求1所述的系统,其中,所述排气系统在所述发动机启动之后的第一个2000秒期间排放少于1ppm的N2O。
7.根据权利要求1所述的系统,其中,所述DOC通过排气导管连接至所述PM。
8.根据权利要求1所述的系统,其中,所述DOC和所述PNA被包含在单一壳体中。
9.根据权利要求1所述的系统,其中,所述DOC和所述PNA作为层成型在单一基板上。
10.根据权利要求1所述的系统,其中,所述PNA被构造成在350°C或更低的温度时释放基本上所有存储的NOx。
11.根据权利要求1所述的系统,其中,所述PNA具有至少为3:1的钯与铂的含量比。
12.根据权利要求1所述的系统,其中,所述PNA基本上不包含碱金属或碱土金属。
13.根据权利要求1所述的系统,其中,所述PNA包含一种或多种稀土元素。
14.一种处理来自柴油发动机的排气的方法,包括: 将第一排气气体(FEG)从所述发动机引导至柴油氧化催化剂(DOC)以产生第二排气气体(SEG); 将所述SEG从所述DOC引导至被动NOx吸附器(PNA)以产生第三排气气体(TEG),所述PNA在温度达到150 0C时存储来自所述SEG的NOx;以及 将所述TEG从所述PNA引导至NOx减少系统。
15.根据权利要求14所述的方法,其中,在温度高于200°C时所述PNA将存储的NOx释放到所述TEG中。
16.根据权利要求14所述的方法,其中,在400°C或更低温度时,所述PNA将基本上所有存储的NOx释放到所述TEG中。
17.根据权利要求14所述的方法,其中,在启动所述柴油发动机之后的第一个2000秒期间,来自所述NOx减少系统的输出排气气体(OEG)包括小于I Oppm的N2O。
18.根据权利要求14所述的方法,其中,所述柴油发动机基本上一直通过稀空气燃料比运行。
19.一种用于处理来自柴油发动机的排气气体的排气系统,包括: 设置在基板上并且被构造成在温度达到150 °C时存储来自所述排气气体的NOx的被动NOx吸附器(PNA)层; 设置在所述PNA层上并且被构造成使所述排气气体中的碳氢化合物氧化的柴油氧化催化剂(DOC)层;以及 位于所述PNA层和所述DOC层下游并且被构造成减少所述排气气体中的NOx的选择性催化减少(SCR)系统。
20.根据权利要求19所述的系统,其中,所述PNA层和所述DOC层均具有至少为3:1的钯比铂的含量比,并且所述PNA层基本上不包括碱金属或碱土金属。
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Application publication date: 20161130