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CN110657005A - 与活性scr组合的双lnt系统 - Google Patents

与活性scr组合的双lnt系统 Download PDF

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CN110657005A
CN110657005A CN201910572203.0A CN201910572203A CN110657005A CN 110657005 A CN110657005 A CN 110657005A CN 201910572203 A CN201910572203 A CN 201910572203A CN 110657005 A CN110657005 A CN 110657005A
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exhaust
exhaust gas
nitrogen oxide
upstream
oxide storage
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F·D·斯迈特
J·哈姆森
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Ford Global Technologies LLC
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Ford Global Technologies LLC
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F01N13/0093—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are of the same type
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
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    • F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
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    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
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    • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
    • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
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    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
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    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2006—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating
    • F01N3/2013—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating using electric or magnetic heating means
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
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    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
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    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
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    • F02M26/02—EGR systems specially adapted for supercharged engines
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Abstract

本发明涉及与活性SCR组合的双LNT系统。为内燃发动机提供一种具有排气道、排气再循环系统、至少第一和第二氮氧化物储存催化剂以及活性选择性催化还原催化剂的布置，其中第二氮氧化物储存催化剂和选择性催化还原催化剂被布置在排气再循环系统的排气再循环管路的分支点的下游。此外，提供一种用于利用该布置控制排气后处理系统的方法。

Description

与活性SCR组合的双LNT系统
技术领域
本发明涉及内燃发动机的布置，其具有排气道、排气再循环系统、至少第一和第二氮氧化物储存催化剂以及活性选择性催化还原催化剂。
背景技术
必须控制氮氧化物排放，以符合严格的法律规范。氮氧化物储存催化剂(也称为稀NOx捕集器，即LNT)用于从内燃发动机的排气中暂时吸附氮氧化物。此外，它们还完成一氧化碳(CO)和碳氢化合物(HC)的氧化后处理任务。在内燃发动机的稀操作中出现的氮氧化物能够被储存在LNT中；为此，LNT将稀排气中包含的一氧化氮(NO)氧化成二氧化氮(NO2)，且然后以硝酸盐的形式储存。LNT涂层中使用的吸附剂是例如氧化钡和/或其他氧化物。
当LNT的储存容量被耗尽时，它必须被再生。在再生事件(净化)中，提供富的亚化学计量的排气状况，例如，通过用相应的燃料-空气混合物操作内燃发动机；储存的氮氧化物被再次解吸并且使用富排气中的成分(CO、HC)在LNT的催化活性组分上被还原成氮。除了为再生执行的净化外，如果排气例如因为内燃发动机的功率需求而变为亚化学计量的，则LNT也自然再生。此外，可以在选择性催化还原催化剂中还原从LNT释放的氮氧化物。
LNT的储存容量受到排气温度以及其他因素的限制。现代LNT能够在约250-550℃的温度范围内以不同的效率储存氮氧化物。两个LNT的顺序布置允许LNT的有用温度范围变宽。然而，具有两个LNT的排气后处理系统具有LNT的高温度的缺点，LNT的高温度例如在高速公路行驶期间的重负荷下发生，增加燃料消耗以保证有效率的氮氧化物转化。一种可能性是在化学计量状况下在400℃和更高的温度状况下操作LNT。然而，在柴油动力内燃发动机中，就燃料消耗而言，化学计量操作是非常不经济的。因此，目的是在高排气温度下更好地控制燃料消耗和排放。
发明内容
该目的通过具有权利要求1的特征的布置来实现。本发明的进一步有利实施例和形式由次级和从属权利要求、附图和示例性实施例产生。
本发明的第一方面涉及一种内燃发动机的布置，其具有排气道，至少一个低压排气再循环管路从所述排气道分支，并且在所述排气道中布置有排气后处理系统，其中所述排气后处理系统包括：
-至少一个第一氮氧化物储存催化剂，
-至少一个第二氮氧化物储存催化剂，其被布置在所述第一氮氧化物储存催化剂的下游，
-至少一个颗粒过滤器，其被布置在所述第一氮氧化物储存催化剂的下游，以及
-至少一个选择性催化还原催化剂，其被布置在所述第二氮氧化物储存催化剂的下游，
其中所述排气再循环管路在所述第一氮氧化物储存催化剂下游和所述第二氮氧化物储存催化剂上游分支，并且其中用于引入还原剂的第一装置被布置在所述第二氮氧化物储存催化剂上游的所述排气道中，且用于引入还原剂的第二装置被布置在所述选择性催化还原催化剂上游的所述排气道中。
该布置是有利的，因为它允许双LNT系统在所有状况下(特别是在重负荷下，例如在高速公路上行驶时)的有效率的操作。具有两个LNT的排气后处理系统中的活性SCR的布置即使在内燃发动机的高负荷下仍允许氮氧化物的有效率的转化而不会在两个LNT的操作期间显著增加燃料消耗。特别是如果第二LNT暴露于高于400℃的温度，则布置在下游的SCR达到其最佳操作温度。此外，有利的是，在排气再循环装置的分支点的上游没有设置用于还原剂(特别是用于尿素或氨)的引入装置。这不包括供应的氨的再循环及其在内燃发动机中转化为其他氮氧化物，这将需要进一步供应氨以还原氮氧化物。
本发明特别适用于具有自点火内燃发动机的布置。因此，颗粒过滤器具体是柴油颗粒过滤器。优选地，为了支持再生，颗粒过滤器被催化涂覆；因此它也被称为cDPF。颗粒过滤器明确没有SCR涂层(sDPF)。有利地，cDPF具有比sDPF更高的烟灰颗粒储存容量，允许更有效地控制过滤器再生，并且由于高温而具有比sDPF更低的破裂或其他损坏的风险。此外，cDPF不需要氨来还原氮氧化物，氮氧化物可以通过滑移而逸出并进入排气再循环管路。颗粒过滤器优选地被布置在排气再循环管路的分支点的上游。
优选地，SCR包括电加热元件。因此，即使在LNT通常不会达到高于400℃的排气温度的城市或乡村道路区域中的内燃发动机的操作中，也能够快速达到SCR的最佳操作温度。
优选地，第一引入装置被构造成将燃料引入排气道中。燃料起还原剂的作用，因为其碳氢化合物也可以用于还原LNT中的氮氧化物。第一引入装置有利地是计量泵和/或喷射泵。理想地，燃料被点燃以提供相应富的排气用于还原。在燃料燃烧时出现的温度有利地用于加热SCR，其中引入的燃料的燃烧可以仅用于加热SCR。
优选地，第二引入装置被构造成将水性尿素溶液引入排气道中。第二引入装置有利地是计量泵和/或喷射泵。通过尿素的水解，产生二氧化碳和氨。所得到的氨与排气中的氮氧化物在SCR催化剂处起反应以成为元素氮(N2)和水。替代地，也可以直接提供气态氨。两个LNT下游的活性SCR的布置有利地允许在高排气温度下的燃料经济操作，以及在还原LNT中的氮氧化物时在高温下可能发生的氨的捕获和储存。
本发明的第二方面涉及一种具有根据本发明的布置的机动车辆。
本发明的第三方面涉及一种利用根据本发明的布置控制用于还原氮氧化物的排气后处理系统的方法，其具有如下步骤：
-操作所述内燃发动机，使得排气被引导通过所述排气道并且具有稀空气-燃料混合物，
-增加所述内燃发动机的负荷，
-确定所述第一氮氧化物储存催化剂上游的温度、所述第二氮氧化物储存催化剂上游的温度和所述选择性催化还原催化剂上游的温度，
-当在所述第一氮氧化物储存催化剂上游超过第一温度阈值时，通过来自所述内燃发动机的富排气提供亚化学计量的排气状况，
-当在所述第二氮氧化物储存催化剂上游超过第二温度阈值时，通过借助于第一引入装置将燃料引入所述排气道中，提供亚化学计量的排气状况，
-当在所述选择性催化还原催化剂上游超过第三温度阈值时，借助于第二引入装置将还原剂引入所述排气道中。
该方法的优点对应于根据本发明的布置的优点。
在每个LNT和SCR的上游确定温度。温度可以借助于布置在排气道中的相应传感器和/或基于模型来确定。低于250℃，LNT仅用于储存氮氧化物。因此，第一和第二阈值优选为250℃。第三阈值优选为200℃，在该温度以上SCR达到其操作温度。低于该值，不引入尿素。在任何情况下，在富排气阶段期间氮氧化物被还原，由此尿素消耗保持较低。储存在LNT中的氮氧化物量和储存在SCR中的氨量基于模型确定。而且，排气中包含的氮氧化物的量可以基于模型确定。
优选地，在该方法中，借助于第一引入装置引入还原剂，以便通过放热反应达到第三温度阈值。在这种情况下，还原剂是燃料，其除了提高温度外，还用于提供用于还原氮氧化物的富排气状况。
优选地，在颗粒过滤器的再生期间借助于第二引入装置引入还原剂。在这种情况下，还原剂是氨或水性尿素溶液。在颗粒过滤器的再生期间，由于出现高温，极有可能发生氮氧化物从LNT被释放并且然后能够在SCR中被还原。
除了温度外，还可以根据质量流量执行通过第二引入装置引入还原剂。可以基于模型或传感器确定排气的质量流量。优选地，仅当排气的温度和质量流量二者都超过阈值时，借助于第二引入装置引入还原剂。
附图说明
参考附图更详细地解释本发明。附图示出：
图1是根据本发明的布置的实施例的示意图。
图2是根据本发明的方法的实施例的流程图。
具体实施方式
根据本发明的布置1在图1所示的实施例中包括内燃发动机2。内燃发动机2是自点火内燃发动机，但是替代地也可以是外部点火的内燃发动机。在该描述中，内燃发动机2具有四个汽缸，但是也可具有不同数量的汽缸。
内燃发动机2被连接到排气道3。第一氮氧化物储存催化剂(LNT)4被布置在排气道3中。柴油颗粒过滤器(DPF)5被布置在第一LNT 4的下游。DPF 5具有催化活性涂层。
低压排气再循环系统的排气再循环管路6从DPF 5下游的排气道3分支出来。排气再循环管路6将排气道3流体地连接到进气道(未示出)。为了控制再循环排气的量，排气再循环管路6包括阀。
第二LNT 7被布置在排气再循环管路6的分支点的下游。第一引入装置8被直接布置在第二LNT 7的上游。第一引入装置8具体是用于燃料的喷射装置。为了点燃燃料，在第一引入装置8的区域中在排气道3中布置点火装置(未示出)。
选择性催化还原催化剂(SCR)9被布置在第二LNT 7的下游。第二引入装置10被布置在SCR 9的直接上游。第二引入装置10具体是用于水性尿素溶液(例如，)的喷射装置，该水性尿素溶液由为此目的提供的容器提供。尿素溶液被水解成氨和二氧化碳，且氨被储存在SCR 9中以便以后用于还原氮氧化物，或直接用于还原氮氧化物。SCR 9可以具有电加热装置，以便在需要时使SCR达到最佳操作温度，而与排气温度无关。
此外，布置1可以包括传感器(未示出)，例如，用于氮氧化物、氨、λ和/或温度的传感器，所述传感器可以被布置在布置1中的任意点处。温度传感器具体布置在LNT 4、7上游的区域中。传感器被连接到控制装置(未示出)。替代地，可以基于模型确定温度值和其他值。控制装置进而被连接到第一引入装置8和第二引入装置10，第一引入装置8和第二引入装置10可以根据需要被致动，以便将还原剂引入排气道3中。控制装置被更进一步地连接到内燃发动机2，以便基于对测量值的分析发出有关富或稀空气-燃料混合物的控制命令。
在图2所示的用于借助于具有图1的特征的布置来控制排气后处理的方法中，在第一步骤S1中，操作内燃发动机2，使得排气被引导通过排气道。内燃发动机2利用稀空气-燃料混合物操作。在第二步骤S2中，增加内燃发动机2上的负荷。因此，排气温度升高。
在第三步骤S3中，在第一LNT 4和第二LNT 7的上游以及SCR 9的上游确定排气温度。这可以通过布置在那里的温度传感器或基于模型来进行。关于第一LNT 4上游的第一温度阈值TL1、第二LNT 7上游的第二温度阈值TL2和SCR 9上游的第三阈值TS1观察温度。第一阈值TL1和第二阈值TL2被设定为250℃。第三阈值TS1被设定为200℃。
当达到或超过第一阈值TL1和/或第二阈值TL2时，为LNT 4、7提供亚化学计量的状况。这通过为第一LNT 4设定内燃发动机2的富空气-燃料混合物，以及通过为第二LNT 7借助于第一引入装置8将燃料引入排气道3中来实现。
当达到或超过SCR 9上游的第三阈值TS1时，借助于第二引入装置10将还原剂引入排气道3中。也可以通过燃烧通过第一引入装置8引入的燃料有意地提供温度TS1，以便开始还原SCR 9中的氮氧化物。
在该方法的实施例中，还可以根据排气的质量流量执行还原剂通过第二引入装置10的引入。为此，本领域技术人员建立另一阈值M1。在该实施例中，当达到或超过阈值TS1并且也达到或超过阈值M1时，经由第二引入装置10引入还原剂。替代地，也可以仅根据排气的质量流量借助于第二引入装置10引入还原剂。当在该实施例中达到或超过阈值M1时，借助于第二引入装置10引入还原剂。
参考标记的列表
1 布置
2 内燃发动机
3 排气道
4 第一氮氧化物储存催化剂
5 颗粒过滤器
6 排气再循环管路
7 第二氮氧化物储存催化剂
8 第一引入装置
9 选择性催化还原催化剂
10 第二引入装置

Claims (11)

1.一种内燃发动机(2)的布置(1)，其具有排气道(3)，至少一个低压排气再循环管路(6)从所述排气道分支，并且在所述排气道中布置有排气后处理系统，其中所述排气后处理系统包括：
-至少一个第一氮氧化物储存催化剂(4)，
-至少一个第二氮氧化物储存催化剂(7)，其被布置在所述第一氮氧化物储存催化剂(4)的下游，
-至少一个颗粒过滤器(5)，其被布置在所述第一氮氧化物储存催化剂(4)的下游，和
-至少一个选择性催化还原催化剂(9)，其被布置在所述第二氮氧化物储存催化剂(7)的下游，
其中所述排气再循环管路(6)在所述第一氮氧化物储存催化剂(4)下游和所述第二氮氧化物储存催化剂(7)上游分支，并且其中用于引入还原剂(8)的第一装置被布置在所述第二氮氧化物储存催化剂(7)上游的所述排气道(3)中，且用于引入还原剂(10)的第二装置被布置在所述选择性催化还原催化剂(9)上游的所述排气道(3)中。
2.根据权利要求1所述的布置(1)，其中所述颗粒过滤器(5)被催化涂覆以支持再生。
3.根据权利要求1或2所述的布置(1)，其中所述颗粒过滤器(5)被布置在所述排气再循环管路(6)的分支点的上游。
4.根据前述权利要求中任一项所述的布置(1)，其中所述选择性催化还原催化剂(9)包括电加热元件。
5.根据前述权利要求中任一项所述的布置(1)，其中所述第一引入装置(8)被构造成将燃料引入所述排气道(3)中。
6.根据前述权利要求中任一项所述的布置(1)，其中所述第二引入装置(10)被构造成将尿素引入所述排气道中。
7.一种机动车辆，其具有根据权利要求1-6中任一项所述的布置。
8.一种用于利用根据权利要求1-6中任一项所述的布置控制用于还原氮氧化物的排气后处理系统的方法，其具有如下步骤：
-操作所述内燃发动机(2)，使得排气被引导通过所述排气道(3)并且具有稀空气-燃料混合物，
-增加所述内燃发动机(2)的负荷，
-确定所述第一氮氧化物储存催化剂(4)上游的温度、所述第二氮氧化物储存催化剂(7)上游的温度和所述选择性催化还原催化剂(9)上游的温度，
-当在所述第一氮氧化物储存催化剂(4)上游超过第一温度阈值时，通过来自所述内燃发动机(2)的富排气提供亚化学计量的排气状况，
-当在所述第二氮氧化物储存催化剂(7)上游超过第二温度阈值时，通过借助于所述第一引入装置(8)将燃料引入所述排气道(3)中，提供亚化学计量的排气状况，
-当在所述选择性催化还原催化剂(9)上游超过第三温度阈值时，借助于所述第二引入装置(10)将还原剂引入所述排气道(3)中。
9.根据权利要求8所述的方法，其中借助于所述第一引入装置(8)将燃料引入所述排气道(3)中，以便通过放热反应达到所述第三温度阈值。
10.根据权利要求8或9所述的方法，其中在所述颗粒过滤器(5)的再生期间，借助于所述第二引入装置(10)将还原剂引入所述排气道中。
11.根据权利要求8、9或10所述的方法，其中当除了达到所述第二温度阈值之外还达到或超过所述排气的质量流量的阈值时，借助于所述第二引入装置(10)将还原剂引入所述排气道(3)中。
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