CN116181461A - 用于估计内燃机scr系统中布置在废气道中的至少一个scr催化器下游的氨浓度的方法 - Google Patents
用于估计内燃机scr系统中布置在废气道中的至少一个scr催化器下游的氨浓度的方法 Download PDFInfo
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Abstract
Description
技术领域
本发明涉及一种用于估计在内燃机的SCR系统中布置在废气道中的至少一个SCR催化器下游的氨浓度的方法、一种适合于执行本发明的方法的计算机程序、一种具有计算机程序的电子存储介质和一种用来执行本发明的方法的设备、特别是控制设备。
背景技术
DE 10 2016 201 602 A1公开了一种用于确定在SCR催化器系统(20)中依次布置在废气道(11)中的两个SCR催化器(22,23)之间的氨气质量流量(dm(NH2)_32)的方法,该SCR催化器系统在第一SCR催化器(22)的上游只具有一个还原剂计量单元(21),其中该确定是根据布置在两个SCR催化器之间的NOx传感器(32)的信号和布置在第二SCR催化器(23)下游的NOx传感器(33)的信号进行的。
DE 10 2014 201 304 A1涉及一种运行催化器系统的方法,该催化器系统被提供用于减少内燃机废气中的氮氧化物,该催化器系统包括至少一个SCR催化器(150),该SCR催化器以可储存在SCR催化器(150)中的反应剂运行,从而使得在SCR催化器(150)中存在确定的反应剂水平,其中反应剂的添加是在模型(604,606)的基础上借助于NH3水平控制器(602)进行的,模型误差借助于NH3水平观测器(605)进行补偿。
发明内容
本发明涉及一种用于估计在内燃机的SCR系统中布置在废气道中的至少一个SCR催化器下游的氨浓度的方法,该系统在第一SCR催化器上游具有至少一个还原剂计量单元,在SCR催化器的上游布置第一NOx传感器,该第一NOx传感器确定第一NOx信号,在SCR催化器下游布置第二NOx传感器,该第二NOx传感器确定第二NOx信号,当识别到内燃机的运行状态时准许该方法的释放,并从准许的释放起确定用于估计氨浓度的启动时刻,氨浓度的估计由第一和第二NOx信号以及效率模型确定,并且SCR系统根据估计的氨浓度被调整。
该方法具有特别的优点,即通过估计至少一个SCR催化器下游的氨浓度,所使用的NOx传感器(其对氨气以及氮氧化物具有交叉敏感性)的NOx信号可以被分成氨气(NH3)和氮氧化物(NOx)。这种将第二NOx信号分为氨和氮氧化物的做法使得SCR系统随后能够被更精确地调整或适应,从而改善排放物的转化,提高SCR系统的效率。
此外,内燃机的可预定的运行状态可以对应于这样一个运行状态,在该运行状态下,在至少一个SCR催化器的下游没有氨泄漏或者优选只有微小或低的氨泄漏。
有利的是,该方法可以在这样一个运行状态下启动,在该运行状态下,优选在第二NOx传感器的位置只有氮氧化物排放。从该运行状态出发,该用于估计氨浓度的方法可以稳健且可靠地进行。
此外,内燃机的可预定的运行状态可以对应于内燃机的冷启动。
冷启动是一个有利的运行状态,因为在内燃机的冷启动时,在第二NOx传感器的位置优选很少或没有氨气存在。
在另一个实施方案中,内燃机的可预定的运行状态可以对应于在至少一个SCR催化器下游只存在微小或低NOx排放的运行条件。
有利的是,该方法可以在一种运行状态下启动,在该运行状态下,优选在第二NOx传感器的位置没有氮氧化物排放,而是存在氨泄漏或氨气。从该运行状态出发,所述用于估计氨浓度的方法可以稳健且可靠地进行。
在一个替换的实施方案中,内燃机的可预定的运行状态可以对应于内燃机的推力模式,在该推力模式中,在所述至少一个SCR催化器下游几乎没有或者优选只存在微小或低的氮氧化物排放。
推力模式代表了一种有利的运行状态,因为在内燃机的推力模式下,优选只有氨气(NH3)存在于第二NOx传感器的位置。从该运行状态出发,所述用于估计氨浓度的方法可以稳健且可靠地进行。
此外,如果优选在启动时刻识别到的运行状态之后重新识别到内燃机的可预定的运行状态,则可以从新的启动时刻开始进行氨浓度的估计。
特别有利的是,当重新识别到可预定的的运行状态之一时,重新设定启动时刻,并且该方法从新识别到的运行状态开始启动。这是特别有利的,因为该方法的稳健性可以因此得到提高。
在一个特别有利的实施方案中,对内燃机的SCR系统中布置在废气道中的至少一个SCR催化器下游的氨浓度的估计是根据以下公式确定的:
该方法具有特别的优点,即通过估计至少一个SCR催化器下游的氨浓度,所使用的NOx传感器(其对氨气以及氮氧化物具有交叉敏感性)的NOx信号可以被分成氨气(NH3)和氮氧化物(NOx)。这种将第二种NOx信号分成氨气和氮氧化物的做法使得SCR系统能够更精确地适应,从而改善排放物的转化,并且提高SCR系统的效率。
在进一步的方面,本发明涉及一种设备、特别是控制设备和一种计算机程序,它们被设置、特别是被编程用于执行所述方法之一。在又一个方面,本发明涉及一种机器可读存储介质,所述计算机程序存储在该机器可读存储介质上。
附图说明
下面根据图中所示的实施例详细阐述本发明。附图中:
图1示出带有内燃机的SCR催化器的SCR系统的示意图;
图2示出本发明的用于估计至少一个SCR催化器下游的氨浓度的方法的示例性方案的流程图。
具体实施方式
内燃机10在其废气道11中具有SCR系统20,如图1所示。该SCR系统具有还原剂计量单元21,用该还原剂计量单元可以将尿素水溶液(AdBlue)注入废气道11。氨在废气的高温下从该尿素水溶液中释放出来。在还原剂计量单元21的下游设置第一SCR催化器22。在第一SCR催化器22的下游可以布置另外的SCR催化器。在废气道11中在还原剂计量单元21的上游和内燃机10的下游设置第一NOx传感器31。在此,第一NOx传感器31测量第一NOx信号xsens,,优选作为NOx浓度或作为NOx质量流量。第二NOx传感器32被布置在第一SCR催化器22的下游并且在此测量第二NOx信号xsens,。所有的NOx传感器31、32都将它们的信号传送给电子控制设备100。由于NOx传感器31、32除了对氮氧化物外还对氨气交叉敏感,所以它们的信号是氮氧化物和氨气的总信号。然而,第一NOx传感器31布置在还原剂计量单元21的上游,因此它可靠地只测量废气中的氮氧化物量。还原剂计量单元21也向控制设备100报告计量到废气道11的氨量。
该方法对带有柴油机或汽油机的内燃机特别有利。由于对氮氧化物和氨的交叉敏感,布置在SCR催化器22下游的NOx传感器32的第二NOx信号xsens,可以表示如下:
xsens,(t)=xNOx,DS(t)+α·xNH3,(t)(1)
xsens,(t)是第二NOx信号,xNOx,DS(t)是NOx浓度,xNH3,(t)是时刻t的NH3浓度,α是氨交叉敏感度的比例系数。在此,变量xi代表废气中考虑的种类i的摩尔分数或体积份额。该比例系数优选取决于物理量,如氧分压或废气温度。
连续函数方程(1),即xsens,(t可以在区间[t,t+Δt]中展开为幂级数(泰勒级数):
为第二NOx信号xsens,DS的第n阶导数。在这种情况下,显然,区间内的函数也是以连续导数为前提。此外,带有运行数n→∞的方程(2)只能被看作是形式上的,在对于实际系统的应用中必须对其进行近似处理,最多为有限阶n-1。在所考虑的函数中,1阶级数为:
在此,是误差系数,其自身以/>的数量级运动和增长,并且/>是布置在SCR催化器22下游的NOx传感器32的一阶时间导数,即第二NOx信号xsens,DS的一阶时间导数。也就是说,该方程可进一步简化为:/>
因为第二NOx信号xsens,DS是基于交叉敏感度作为由氮氧化物份额和NH3份额组成的总信号得出的,所以用方程(4)和方程(1)得到以下关系:
在此,用Δxsens,=xsens,(t+Δt)-xsens,(t)进行缩短。
为了确定SCR催化器22下游估计的NH3信号还对第二NOx信号xNOx,DS的时间变化进行近似。第二NOx信号xNOx,DS的时间变化可以根据第一NOx信号xNOx,DS并借助用于SCR催化器22的效率模型/>如下地近似:
在一个特别的实施方案中,氨浓度的估计可以在确定的初始条件下特别稳健地进行:
在另一个有利的实施方案中,初始条件存在于内燃机10的推力模式中。在推力模式下,内燃机10几乎不产生或仅产生微小或低的NOx排放,因此第二NOx信号xsens,DS近似为所需的导数可以用数字方式近似为差商。
由于测量误差对这种方法有直接影响,所以可能有必要对所考虑的测量信号进行过滤(例如用移动平均法等)。另一种可能性是对相应信号进行多项式插值或多项式均衡回归。后者的优点是,多项式及其系数不需要对导数进行数字近似。
在第一步骤200中,当识别到内燃机10的可预定的运行条件时,通过控制设备100准许该方法的释放。
在第一实施方案中,如果识别到内燃机10的这样一个运行状态,在该运行状态中在至少一个SCR催化器(22)下游在第二NOx传感器(32)处没有或者优选几乎没有氨气泄漏(Ammoniakschlupf),则准许该方法的释放。
在此,优选通过第二NOx信号32和/或通过内燃机10的运行变量组合例如SCR催化器22的温度、SCR催化器的填充度来确定所述运行状态的存在。优选地,在较长的时间段上对这些运行变量进行过滤,并且如果没有超过可预定的阈值,则准许该方法的释放。
这种在SCR催化器22下游几乎没有或只有很少的氨气存在的运行状态例如是内燃机10的冷启动。
在一个有利的第二实施方案中,当对于内燃机10识别到在SCR催化器22的下游只存在微小或低的NOx排放的运行状态时,该方法可以被释放。这种运行状态可以通过内燃机10的已知的运行变量来确定,这些运行变量允许得出关于氮氧化物的产生的推论。有利的是,它们是以下运行变量,如内燃机的速度和负荷、废气再循环率、喷射量、第二NOx信号32。
有利的是,这些运行变量在较长的时间段上被过滤,并且如果没有超过可预定的阈值,则准许该方法的释放。
在一个有利的实施方案中,当内燃机10处于推力模式时,则存在这种运行状态。该运行状态可以通过内燃机10的运行协调器以已知方式确定。
然后在步骤210中继续该方法。
随后,可以在步骤220中继续该方法。
因此,第n个时间步长是tn=t0+n·Δt。
随后,在下一步骤230中继续该方法。
然后可以在步骤240中继续该方法。
随后,该方法可以在步骤210中从头开始,其中,对于氨浓度的下一次估计设定t0=t1。替换地,该方法可以被终止。
Claims (10)
1.一种用于估计在内燃机的(10)的SCR系统(20)中布置在废气道(11)中的至少一个SCR催化器(22)下游的氨浓度的方法,该系统在第一SCR催化器(22)上游具有至少一个还原剂计量单元(21),其中,
在SCR催化器(22)上游布置第一NOx传感器(31),该第一NOx传感器确定第一NOx信号(xsens,US),
在SCR催化器(22)下游布置第二NOx传感器(32),该第二NOx传感器确定第二NOx信号(xsens,DS),其中当识别到内燃机(10)的运行状态时准许该方法的释放,并且从准许的释放开始确定用于估计氨浓度的启动时刻(t0),
2.根据权利要求1所述的方法,其特征是,内燃机(10)的可预定的运行状态对应于在所述至少一个SCR催化器(22)下游没有氨泄漏或优选只有微小氨泄漏的运行状态。
3.根据权利要求2所述的方法,其特征是,内燃机(10)的可预定的运行状态对应于内燃机(10)的冷启动。
4.根据权利要求1所述的方法,其特征是,内燃机(10)的可预定的运行状态对应于在所述至少一个SCR催化器(22)下游只存在微小NOx排放的运行状态。
5.根据权利要求4所述的方法,其特征是,内燃机(10)的可预定的运行状态对应于内燃机(10)的推力运行,在该推力运行中,在所述至少一个SCR催化器(22)下游几乎没有或者优选只有微小的NOx排放。
8.一种计算机程序,其被设置用于执行根据权利要求1至7中任一项所述的方法。
9.一种电子存储介质,其具有根据权利要求8所述的计算机程序。
10.一种设备,特别是控制设备(100),其被设置用于执行根据权利要求1至7中任一项所述的方法。
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