CN101646845A - 内燃机的排气净化装置 - Google Patents

内燃机的排气净化装置 Download PDF

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CN101646845A
CN101646845A CN200880010372A CN200880010372A CN101646845A CN 101646845 A CN101646845 A CN 101646845A CN 200880010372 A CN200880010372 A CN 200880010372A CN 200880010372 A CN200880010372 A CN 200880010372A CN 101646845 A CN101646845 A CN 101646845A
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catalyzer
urea
combustion engine
temperature
exhaust gas
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CN101646845B (zh
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利冈俊祐
小田富久
伊藤和浩
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Toyota Motor Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
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Abstract

在内燃机排气通路内配置适合于在氧过剩的条件下利用氨还原排气中的NOx的催化剂(27)。由添加控制阀(32)向催化剂(27)供给尿素水溶液，将供给至催化剂(27)的尿素的一部分贮藏于催化剂(27)内，并且利用由贮藏于催化剂(27)内的尿素产生的氨还原排气中的NOx。判断催化剂(27)的贮藏容量是否大于预定的容许上限容量，在判断为催化剂(27)的贮藏容量大于该容许上限容量时，禁止尿素水溶液的供给。

Description

内燃机的排气净化装置
技术领域
本发明涉及内燃机的排气净化装置。
背景技术
已公知一种内燃机，其在内燃机排气通路内配置适合于在氧过剩的条件下利用氨还原排气中的NOx的催化剂，向该催化剂供给尿素水溶液，将供给至催化剂的尿素的一部分贮藏于催化剂内，并利用由贮藏于催化剂内的尿素产生的氨还原排气中的NOx(参照美国专利第5,628,186号说明书以及国际专利公开第99/67511号)。
对于该内燃机，供给至催化剂的尿素的一部分暂先贮藏于催化剂内，由该所贮藏的尿素生成氨这一由来于(来源于)尿素的物质。该由来于尿素的物质的一部分被用于还原NOx，其余部分并不用于NOx还原而从催化剂排出。该情况下，贮藏于催化剂内的尿素的量越多，从催化剂排出的由来于尿素的物质的量就越多。因此，当催化剂内贮藏大量的尿素时，担心大量的由来于尿素的物质从催化剂不希望地排出。
在该点上，如果只以与从内燃机排出的NOx的量相抵的量向催化剂供给尿素水溶液，则可阻止大量的尿素贮藏于催化剂内，因此可认为能够阻止大量的由来于尿素的物质从催化剂排出。然而，准确地求出从内燃机排出的NOx量或与之相抵的尿素量较困难。或者可以认为，如果控制供给至催化剂中的尿素水溶液的量，使得求出贮藏于催化剂中的尿素的量，且该尿素贮藏量不超过容许上限，则可阻止大量的尿素贮藏于催化剂内。然而，准确地求出贮藏于催化剂中的尿素的量较困难。任一情况下都存在不能切实地阻止从催化剂排出大量的由来于尿素的物质的问题。如果减少向催化剂供给的尿素水溶液的量，则能够阻止大量的尿素贮藏于催化剂内，但是该情况下，担心不能良好地还原NOx。
发明内容
因此，本发明的目的在于，提供一种能够阻止大量的产氨化合物从催化剂排出的内燃机的排气净化装置。
根据本发明，提供一种内燃机的排气净化装置，该装置是在内燃机排气通路内配置了适合于在氧过剩的条件下利用氨还原排气中的NOx的催化剂的内燃机的排气净化装置，该装置具备用于向该催化剂供给产氨化合物的供给机构、和用于控制该产氨化合物的供给量的供给控制机构，该催化剂具有将供给至催化剂的该产氨化合物的至少一部分贮藏于催化剂内，并且由贮藏于该催化剂内的产氨化合物生成氨，利用该生成的氨还原排气中的NOx的功能，该装置还具备判断该催化剂的贮藏容量是否大于预定的容许上限容量的判断机构，在判断为该催化剂的贮藏容量大于该容许上限容量时，上述供给控制机构禁止产氨化合物的供给。
附图说明
图1是内燃机的整体图；图2是表示催化剂的贮藏容量的线图；图3是表示贮藏于催化剂内的尿素量与其后从催化剂排出的氨的浓度的关系的一例的线图；图4是表示NOx净化率的线图；图5是用于说明本发明的实施例的时间图；图6是表示尿素水溶液的供给控制程序的流程图；图7是表示贮藏于催化剂内的尿素量与其后从催化剂排出的氰化氢的浓度的关系的一例的线图；图8是表示贮藏于催化剂内的尿素量与其后从催化剂排出的异氰酸的浓度的关系的一例的线图。
具体实施方式
图1表示出将本发明应用于压缩点火式内燃机的情况。另外，本发明也可适用于汽油内燃机。
参照图1，各标号分别表示如下：1-内燃机主体、2-各气缸的燃烧室、3-用于向各燃烧室2内分别喷射燃料的电子控制式燃料喷射阀、4-吸气歧管、5-排气歧管。吸气歧管4借助于吸气导管6与排气涡轮增压器7的压缩机7a的出口连结，压缩机7a的入口借助于空气流量计8与空气滤清器9连结。在吸气导管6内配置电气控制式节气门10，而且在吸气导管6周围配置用于将在吸气导管6内流动的吸入空气冷却的冷却装置11。在图1所示的实施例中，内燃机冷却水被导入冷却装置11内，由内燃机冷却水将吸入空气冷却。另一方面，排气歧管5与排气涡轮增压器7的排气涡轮7b的入口连结，排气涡轮7b的出口与排气后处理装置20连结。
排气歧管5和吸气歧管4，借助于排气再循环(以下称为EGR)通路12相互连结，在EGR通路12内配置电气控制式EGR控制阀13。另外，在EGR通路12周围配置用于将在EGR通路12内流动的EGR气体冷却的冷却装置14。在图1所示的实施例中，内燃机冷却水被导入冷却装置14内，由内燃机冷却水将EGR气体冷却。另一方面，各燃料喷射阀3借助于燃料供给管15与共轨16连结，该共轨16借助于电子控制式的喷出量可变的燃料泵17与燃料箱18连结。燃料箱18内的燃料，利用燃料泵17供给到共轨16内，供给到共轨16内的燃料，借助于各燃料供给管15供给到燃料喷射阀3。
排气后处理装置20具备：借助于排气管21与排气涡轮7b的出口连结的上游侧催化剂转换器22；和借助于排气管23与上游侧催化剂转换器22连结的下游侧催化剂转换器24。在上游侧催化剂转换器22内从上游侧依次配置催化剂25以及催化剂26，在下游侧催化剂转换器24内从上游侧依次配置催化剂27以及催化剂28。催化剂25，26，28由具有氧化功能的催化剂例如氧化催化剂或三元催化剂构成。与此相对，催化剂27由适合于在氧过剩的条件下利用氨还原排气中的NOx的NOx选择还原催化剂构成。另外，催化剂25，27，28担载于蜂窝载体上，催化剂26担载于用于捕集排气中的微粒子的微粒过滤器上。在排气管23上配置用于检测流入下游侧催化剂转换器24内的排气的温度的温度传感器29。流入下游侧催化剂转换器24内的排气的温度表示催化剂27的温度。
另一方面，含有产生氨的产氨化合物的液体贮存于罐30内，贮存于罐30内的含有产氨化合物的液体，借助于供给泵31以及电磁控制式添加控制阀32供给到排气管23内。
电子控制单元40包括数字计算机，具备由双向性总线41相互连接的ROM(只读存储器)42、RAM(随机读取存储器)43、CPU(微处理器)44、输入端口45以及输出端口46。空气流量计8产生与吸入空气量成比例的输出电压，该输出电压通过相对应的AD转换器47输入到输入端口45。另一方面，温度传感器29的输出信号，通过各自对应的AD转换器47输入到输入端口45。在油门踏板49上连接产生与油门踏板49的踏下量成比例的输出电压的负荷传感器50，负荷传感器50的输出电压通过对应的AD转换器47输入到输入端口45。而且，在输入端口45上连接每当曲轴旋转例如30°就产生输出脉冲的曲轴转角传感器51。另一方面，输出端口46借助于对应的驱动电路48与燃料喷射阀3、节气门10驱动装置、EGR控制阀13、燃料泵17、供给泵31以及添加控制阀32连接。
如上所述，向催化剂27上游的排气管23内供给含有产氨化合物的液体。关于可产生氨的产氨化合物，存在各种的化合物，因此，作为产氨化合物，可使用各种的化合物。在本发明的实施例中，作为产氨化合物，使用了尿素，作为含有产氨化合物的液体，使用了尿素水溶液。因此，以下以向催化剂27上游的排气管23内供给尿素水溶液的情况为例来说明本发明。
另一方面，如上所述，催化剂27由NOx选择还原催化剂形成，在图1所示的实施例中，作为该NOx选择还原催化剂，使用了以二氧化钛为载体并在该载体上担载了氧化钒的催化剂V2O5/TiO2(以下称为钒·二氧化钛催化剂。)、或以沸石为载体并在该载体上担载了铜的催化剂Cu/ZSM5(以下称为铜沸石催化剂。)。
当向含有过剩氧的排气中供给尿素水溶液时，排气中所含的NO在催化剂27上被由尿素CO(NH2)2产生的氨NH3还原(例如，2NH3+2NO+1/2O2→2N2+3H2O)。
即，供给的尿素水溶液中的尿素首先附着于催化剂27上。此时，如果催化剂27的温度高达例如约350℃以上，则尿素一下子热分解，从而产生氨。
另一方面，在催化剂27的温度为约132℃～约350℃时，尿素暂先贮藏于催化剂27内，接着由贮藏于催化剂27内的尿素一点一点地产生、放出氨。该情况下的氨产生，可以认为是因为在催化剂27上，尿素产生形态变化的缘故。即，尿素在约132℃下变化为缩二脲(双缩脲；biuret)，缩二脲在约190℃下变化为氰尿酸，氰尿酸在约360℃下变化为氰酸或异氰酸。或者可以认为，贮藏于催化剂27内之后随着经过的时间变长，尿素变化为缩二脲，缩二脲变化为氰尿酸，氰尿酸变化为氰酸或异氰酸。在这样的形态变化的过程中，一点一点地产生氨。
在催化剂27的温度在作为尿素的热分解温度的约132℃以下时，若向催化剂27供给尿素水溶液，则尿素水溶液中的尿素贮藏于催化剂27内，此时，基本不由贮藏的尿素产生氨。
然而，当其后进行例如内燃机加速运行，催化剂27的温度增高时，就由贮藏于催化剂27内的尿素生成上述的氨、缩二脲、氰尿酸、氰酸或异氰酸等，而且有时这些生成物与排气中的氢HC反应，生成氰化氢。这样由尿素生成的由来于尿素的物质的一部分，被用于还原排气中的NOx，但其余部分并不还原NOx而从催化剂27排出。
贮藏于催化剂27内的尿素的量越多，从催化剂27排出的由来于尿素的物质的量就越多。因此，当在催化剂27内贮藏大量的尿素时，担心大量的由来于尿素的物质从催化剂27并不希望地排出。
另一方面，可贮藏于催化剂27内的尿素的量存在极限，即在催化剂27内只能贮藏尿素直到贮藏容量。该贮藏容量相应于催化剂27的气氛例如催化剂27的温度而变动，因此在催化剂27的贮藏容量大时，催化剂27内能够贮藏大量的尿素，在催化剂27的贮藏容量小时，催化剂27内只能贮藏少量的尿素。
于是，如果在催化剂27的贮藏容量大时，禁止向催化剂27供给尿素水溶液，则能够阻止在催化剂27内贮藏大量的尿素。这是本发明的基本的想法。
即在本发明的实施例中，判断催化剂27的贮藏容量是否大于预定的容许上限容量，在判断为催化剂27的贮藏容量大于容许上限容量时，禁止尿素水溶液的供给。该场合下，直接求出催化剂27的贮藏容量是困难的。另一方面，如图2所示，在催化剂27的温度TC低时，与催化剂27的温度TC高时相比，催化剂27的贮藏容量SC大，在催化剂27的温度TC为TCX时，催化剂27的贮藏容量SC变为容许上限量SCU。
因此在本发明的实施例中，将催化剂27的贮藏容量SC变为容许上限容量SCU的温度TC设定为设定温度TCX，在催化剂27的温度TC低于该设定温度TCX时，判断为催化剂27的贮藏容量SC大于容许上限容量SCU，此时，禁止尿素水溶液的供给。另一方面，在催化剂27的温度高于设定温度TCX时，判断为催化剂27的贮藏容量SC小于容许上限容量SCU，此时，容许尿素水溶液的供给。即，例如只以与从内燃机排出的NOx量相应的量向催化剂27供给尿素水溶液。这样一来，贮藏于催化剂27内的尿素的量不会超过容许上限容量SCU。因此，即使不求出实际贮藏于催化剂27内的尿素量，也能够阻止大量的尿素贮藏于催化剂27内。
容许上限容量SCU怎样地设定都可以。在本发明的实施例中，容许上限容量SCU如下地设定。
如上所述，贮藏于催化剂27内的尿素的量越多，从催化剂27排出的由来于尿素的物质的量就越多。图3表示出催化剂27内贮藏的尿素量Q与在其后的例如内燃机加速时从催化剂27排出的氨的浓度CA的关系的一例。由图3可知，在贮藏尿素量Q多时，与贮藏尿素量Q少时相比，高浓度的氨从催化剂27排出。
在此，为了避免氨排出浓度CA超过预定的其容许上限值CAU，由图3可知，必须使在催化剂27内贮藏的尿素量Q不超过其上限量QAU。
另一方面，如上所述，在催化剂27内贮藏的尿素量不会超过容许上限容量SCU。因此在本发明的实施例中，将容许上限容量SCU设定为用于氨的上限量QAU。其结果，可阻止其后从催化剂27排出的氨浓度超过其容许上限值CAU。
另外，也可设定容许上限容量SCU使其比用于氨的上限量QAU少。然而，如果将容许上限容量SCU设定为该上限量QAU，则可在向催化剂27供给对于NOx还原足够的量的尿素的同时，降低从催化剂27排出的氨量。
可是，如图4所示，当催化剂27的温度TC低于下限温度TCEL或高于上限温度TCEH时，催化剂27的NOx净化率EFF低于容许下限率EFFL，当催化剂27的温度TC为下限温度TCEL～上限温度TCEH时，其高于容许下限率EFFL。上述的设定温度TCX高于该下限温度TCEL。
在此，对于例如内燃机起动后的尿素水溶液的供给开始时机进行考虑。在图5中，如由X所示那样，内燃机一起动，催化剂27的温度TC就慢慢地上升。此时，停止尿素水溶液的供给。接着，如图5中由Y所示那样，即使催化剂27的温度TC达到下限温度TCEL，也没有开始尿素水溶液的供给。接着，如图5中由Z所示那样，当催化剂27的温度TC达到设定温度TCX时，开始尿素水溶液的供给。即，在本发明的实施例中，即使催化剂27为了NOx还原而充分地活化，也没有开始尿素水溶液的供给，当催化剂27的温度TC上升到能够阻止大量的由来于尿素的物质排出的温度时，终于开始尿素水溶液的供给。
图6表示出本发明的实施例的用于执行尿素水溶液的供给控制的程序，该程序通过每隔一定时间的中断来执行。
参照图6，首先起初在步骤100中判别催化剂27的温度TC是否低于设定温度TCX。在TC≥TCX时，接着进入步骤101，容许尿素水溶液的供给。与此相对，在TC＜TCX时，接着进入步骤102，禁止尿素水溶液的供给。
容许上限容量SCU也可如下地设定。
图7表示出催化剂27内贮藏的尿素量Q与其后的例如内燃机加速时从催化剂27排出的氰化氢的浓度CC的关系的一例，图8表示出催化剂27内贮藏的尿素量Q与其后的例如内燃机加速时从催化剂27排出的异氰酸的浓度CI的关系的一例。由图7和图8可知，为了避免氰化氢排出浓度CC超过预定的其容许上限值CCU，只要催化剂27内贮藏的尿素量Q不超过其上限量QCU即可，为了避免异氰酸排出浓度CI超过预定的其容许上限值CIU，只要催化剂27内贮藏的尿素量Q不超过其上限量QIU即可。
因此，可以将容许上限容量SCU设定为用于氰化氢的上限量QCU，或者设定为用于异氰酸的上限量QIU。
或者，也可以将容许上限容量SCU设定为用于氨、氰化氢、异氰酸的上限量QAU、QCU、QIU之中的最少的量。如果这样的话，则能够阻止氨、氰化氢、异氰酸全部超过各自的容许上限值CAU、CCU、CIU。

Claims (7)

1、一种内燃机的排气净化装置，该装置是在内燃机排气通路内配置了下述催化剂的内燃机的排气净化装置，所述催化剂适合于在氧过剩的条件下利用氨还原排气中的NOx，
该装置具备：用于向该催化剂供给产氨化合物的供给机构；和用于控制该产氨化合物的供给量的供给控制机构，
该催化剂具有下述功能，即将供给至催化剂的该产氨化合物的至少一部分贮藏于催化剂内，并且由贮藏于该催化剂内的产氨化合物生成氨，利用该生成的氨还原排气中的NOx，
该装置还具备判断该催化剂的贮藏容量是否大于预定的容许上限容量的判断机构，
在判断为该催化剂的贮藏容量大于该容许上限容量时，所述供给控制机构禁止产氨化合物的供给。
2、根据权利要求1所述的内燃机的排气净化装置，其中，设定所述容许上限容量，以使在其后从所述催化剂排出的由来于产氨化合物的物质的量不超过其容许上限量。
3、根据权利要求2所述的内燃机的排气净化装置，其中，所述由来于产氨化合物的物质是选自氨、氰化氢和异氰酸之中的至少一种。
4、根据权利要求2所述的内燃机的排气净化装置，其中，设定所述容许上限容量，以使在其后从所述催化剂排出的氨、氰化氢以及异氰酸全部不超过各自的容许上限量。
5、根据权利要求1所述的内燃机的排气净化装置，其中，与该催化剂的温度高时相比，该催化剂的温度低时，所述催化剂的贮藏容量大，在该催化剂的温度低于设定温度时，所述判断机构判断为该催化剂的贮藏容量大于该容许上限容量，所述设定温度被设定为该催化剂的贮藏容量为所述容许上限容量的温度。
6、根据权利要求5所述的内燃机的排气净化装置，其中，与该催化剂的温度低时相比，该催化剂的温度高时，所述催化剂的NOx还原率高，所述设定温度被设定为高于该催化剂的NOx净化率为预定的容许下限率的温度。
7、根据权利要求1所述的内燃机的排气净化装置，其中，在判断为所述催化剂的贮藏容量小于所述容许上限容量时，所述供给控制机构容许产氨化合物的供给。
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CN105736094A (zh) * 2016-04-12 2016-07-06 苏州水木康桥环境工程技术有限公司 一种用于船用尾气净化装置的气态氨生成系统

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US20100050610A1 (en) 2010-03-04
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