KR20170113357A - Method for monitoring of a methane oxidation catalytic converter and an exhaust aftertreatment device - Google Patents

Abstract

The present invention relates to a method for monitoring a methane-oxide catalytic converter (420) in an exhaust gas train of an internal combustion engine (400), wherein, based on NO ₂ production in the methane-oxide catalytic converter (420) By estimating the methane conversion capacity of the methane oxide catalytic converter 420 based on NO ₂ production in or downstream of the converter, in particular based on the NO ₂ content and / or the NO ₂ / NO _x ratio, Perform activation diagnostics. Estimates the deterioration of the methane conversion capacity of the methane oxide catalytic converter 420 based on the reduction of NO ₂ production in some cases. For the determination of NO ₂ production, an SCR catalytic converter arrangement 460, preferably located in the sub-stream 450 of the exhaust gas train, is used.

Description

METHOD FOR MONITORING OF A METHANE OXIDATION CATALYTIC CONVERTER AND AN EXHAUST AFTERTREATMENT DEVICE,

The present invention relates to a method for monitoring a methane-oxide catalytic converter in an exhaust gas after-treatment system of an internal combustion engine, an exhaust after-treatment apparatus, and a computer program, a machine-readable storage medium and an electronic control apparatus configured to perform the method .

There is known an internal combustion engine capable of being operated also as a methane-containing gas or methane such as, for example, natural gas, or as a mixture of gas and another fuel, for example, diesel fuel. In all deposits caused at least partially by the combustion of the methane-containing gas, there arises a problem of high untreated methane emissions on the engine side. Above all, for reasons of climate protection, methane emissions should be reduced in the category of exhaust gas aftertreatment. A methane oxidation catalytic converter (MOC), which oxidizes the methane contained in the exhaust gas based on the palladium-rich combination, is known. For this purpose, formulations having a weight ratio of palladium (Pd) to platinum (Pt) of, for example, less than or equal to 7: 1 may be used. Other methane oxide catalytic converters are based on so-called palladium singular formulations, such as, for example, palladium / aluminum oxide. However, usually only a given methane conversion can be observed at temperatures above 400 ° C in these formulations. For complete oxidation, it should normally be well above 500 ° C.

The behavior of the methane-oxide catalytic converter, and typically the behavior of the catalytic converter in relation to temperature, can be described by the so-called light-off temperature at which a predetermined proportion of the toxic substances contained in the exhaust gas is converted. In an aged catalytic converter that exhibits deteriorated conversion rates, the required active temperature generally rises. With respect to methane oxidation catalytic converters, the catalytic converter, such as a new one, does not normally exhibit a sharp, The methane conversion rate is often linear rather than in the range of 400 to 550 占 폚.

Many catalytic converter, the functional monitoring based on the temperature value (OBD, O n B oard iagnose D) is carried out. However, this monitoring is generally not easy in the context of methane oxide catalytic converters, because the unsharpened temperature behavior of the methane oxide catalytic converter allows the change in the contribution of the exothermic contribution to methane conversion in methane oxide catalytic converters to be less characteristic It is enemy. More problematic is that the palladium rich methane oxidation catalytic converter is extremely sulfur sensitive and even exhibits vibratory behavior (M. Lyubovski, L. Pfefferle, Catalysis Today 47 (1999): 24-44; R Schwiedernoch, Heidelberg University, 2005).

The present invention provides an improved method for monitoring a methane-oxide catalytic converter (MOC), whereby reliable determination of the deteriorated methane conversion capacity of the MOC can be derived in some cases. This method is provided for the monitoring of MOC in an exhaust gas train of an internal combustion engine (gas or diesel / gas engine), which is provided at least proportionally to the combustion of methane-containing fuel with mainly lean exhaust gases. Indirect monitoring is carried out in a manner in which the active diagnosis of the MOC is carried out, in a predetermined manner, on the basis of measurable NO ₂ (nitrogen oxide) production in the MOC. In this case, the methane conversion capability of the MOC in or downstream of the methane oxide catalytic converter is estimated based on the production of NO ₂ and in particular the NO ₂ content and / or the NO ₂ / NO _x ratio. In comparison with baseline values, the deterioration of methane conversion capacity of MOC is estimated in the case of reduced NO ₂ production. Direct measurement of methane conversion capacity using conventional methods can be very difficult to implement in practice. In contrast, the method according to the present invention can result in a reliable judgment of the functionality of the MOC through indirect monitoring.

The method according to the invention is based on that the Pd-rich catalytic converter and also the methane-oxide catalytic converter implement the desired NO ₂ production. In this case, a relationship between the NO ₂ generating ability of the MOC and methane conversion performance is formed. As long as the activation temperature of the methane oxide is not significantly exceeded, oxidation from NO (nitrogen monoxide) to NO ₂ hardly occurs. Only at or above the activation temperature a predetermined conversion of NO to NO ₂ in the MOC is effected, depending on the methane conversion capacity, or at an activation temperature or above, an equilibrium concentration for NO ₂ is achieved according to the following equation:

NO conversion or NO ₂ production capacity is used in accordance with the present invention to estimate methane conversion capacity based on measurable NO ₂ production. In this case, preferably, the process is carried out within the temperature range of the MOC where there is a clear correlation between the methane conversion rate and the NO ₂ content and / or the NO ₂ / NO _x ratio downstream of the methane oxide catalytic converter. Depending on the catalytic converter, a particularly suitable temperature range may be, for example, in the range between about 450 ° C and 500 ° C, preferably between 470 ° C and 490 ° C. In an exemplary catalytic converter test, the correlation between NO ₂ production and methane conversion was found to be strongest within this temperature range.

According to the present invention, the NO ₂ producing ability of MOC is used for monitoring of MOC. For this purpose, in principle, NO ₂ / NO _x ratio or NO ₂ content downstream of the MOC can be measured directly. However, particularly preferably, for the measurement of the NO ₂ producing ability of the MOC, an SCR catalytic converter arrangement disposed downstream of the methane oxide catalytic converter is used. This is highly desirable relative to a direct measurement of the NO ₂ / NO _x ratio or NO ₂ content downstream of the MOC, since suitable sensors for this are generally not provided in conventional vehicles.

In using the SCR catalytic converter device to detect the conversion of NO to NO ₂ , the NO _x conversion behavior is dependent on the NO ₂ content of the gas (feed gas) entering the SCR catalytic converter device and / or the NO ₂ / NO _x the NO ₂ sensitivity SCR catalytic converter device that is affected by the ratio is particularly suitable. This type of NO ₂ sensitive SCR catalytic converter device can be used as a sensor for the method according to the invention. For example, several SCR catalytic converter devices are known which exhibit significant dependence of the NO _x conversion to the NO ₂ / NO _x ratio in the feed gas, especially at temperatures below about 250 ° C. As an example, an iron ion-exchanged beta zeolite or VWT (V anadium- W olfram- itanium T) catalytic converter.

In a particularly preferred embodiment of the method according to the invention, a NO ₂ -sensing SCR catalytic converter arrangement is injected into one sub-stream of the exhaust gas train, in which case the SCR catalytic converter arrangement is preferably a sub-SCR catalytic converter arrangement. This sub SCR catalytic converter device preferably has a smaller volume than the main SCR catalytic converter device in the main stream of the exhaust gas train. Because a suitable NO ₂ -sensing SCR catalytic converter device for this purpose exhibits this dependency, especially at temperatures below about 250 ° C, the sub-SCR catalytic converter device is preferably operated at a lower temperature than, for example, the main SCR catalytic converter device in the mainstream, Lt; RTI ID = 0.0 > 170 C < / RTI > For temperature control, depending on the mounting position, for example, electric heating means may be provided in the sub-stream path, and active or passive cooling means may be provided if the temperature level is too high.

At the upstream and downstream of the sub-SCR catalytic converter device, the measurement or calculation of NO _x is carried out for the determination of NO ₂ production in the MOC, preferably for the upstream and / or downstream of the sub SCR catalytic converter device NO _x sensors are used.

The present invention also includes an exhaust gas post-treatment apparatus for an exhaust gas train of an internal combustion engine having at least one MOC in a main stream line of an exhaust gas train. According to the invention, a sub-SCR catalytic converter device located within the sub-stream line of the exhaust gas train, which in the present application, the NO _x conversion behavior of the sub of the gas flowing into the SCR catalyst converter device NO ₂ content and / or NO ₂ / the NO ₂ sensitivity SCR catalytic converter device, which is dependent on the NO _x ratio. Using the NO ₂ sensitive SCR catalytic converter device in the manner described above, the NO ₂ content of the exhaust gas outside the MOC can be determined. Based on the NO ₂ content, NO ₂ production in MOC can be estimated, and the methane conversion capacity of MOC can be indirectly estimated based on NO ₂ production in MOC. In order to measure the NO _x conversion rate in the sub SCR catalytic converter device, one or more NO _x sensors may be provided upstream and / or downstream of the sub SCR catalytic converter device. The sub SCR catalytic converter device is preferably an SCR catalytic converter device having a smaller volume than the main SCR catalytic converter device in the main stream line of the exhaust gas train. The sub SCR catalytic converter device is preferably operated at a lower temperature than the main SCR catalytic converter device. For the setting to a lower temperature level, in particular a range between 170 [deg.] C and 250 [deg.] C, heating means and / or cooling means are preferably provided in the region of the sub SCR catalytic converter device.

In one configuration of the exhaust gas after-treatment apparatus according to the present invention, the sub-stream line in which the sub-SCR catalytic converter device is disposed is extended as a bypass from the region of the main SCR catalytic converter device to the main stream line of the exhaust gas train do. In yet another highly preferred arrangement, the sub-stream line with the sub-SCR catalytic converter arrangement branches off downstream of the methane-oxide catalytic converter to form an exhaust gas recycle line upstream of the internal combustion engine or into the internal combustion engine, Line. The present invention also includes the use of an exhaust gas aftertreatment apparatus of this type in a method for monitoring methane oxide catalytic converters. See above for this.

The invention also includes a computer program designed to perform the steps of the method according to the invention. Finally, the present invention relates to a machine-readable storage medium having stored thereon a computer program of this type and to an electronic control device designed to perform the steps of the method according to the invention. The fact that the method according to the invention is embodied as a computer program or as a machine-readable storage medium or as an electronic control means that the advantages of the method according to the invention in this way can be used, for example, , The methane conversion capability of the methane-oxide catalytic converter can be reliably monitored.

Other features and advantages of the invention will be set forth in the description of embodiments with reference to the drawings hereinafter. In this case, the individual features may be implemented individually or in combination with each other.

1 is a diagram showing the relationship between the methane conversion rate and the NO ₂ production capability of a methane oxide catalytic converter, according to temperature.
2 is a graph showing the NO _x conversion of a NO ₂ sensitive SCR catalytic converter device as a function of the NO ₂ / NO _x ratio in the exhaust gas.
Figure 3 is a schematic view of possible arrangements of components in the exhaust aftertreatment system.
Figure 4 is a schematic diagram of another possible arrangement of components within the exhaust aftertreatment system.
Figure 5 is a schematic diagram of another possible arrangement of components in the exhaust aftertreatment system.

Figure 1 shows the relationship between the NO ₂ production capacity and methane conversion of MOC in lean exhaust gas containing NO and methane. Three different catalyst converter states, or methane conversion rates (10, 20, 30) at three different MOCs according to temperatures between about 250 [deg.] C and 550 [deg.] C are shown. Curves 10,20 and 30 represent catalytic converters or catalytic converter operating states at different space velocities, e.g., different degrees of aging and / or inhibited by oxygen to different degrees. The curves 11, 21 and 31 represent NO ₂ / NO _x ratios in the exhaust gases beyond the respective MOC. From this, it can be seen that the MOCs of this type (Pd rich catalytic converters) convert NO to NO ₂ within a certain range. Of course, this NO ₂ production occurs only at the temperature above the activation temperature of each catalytic converter, that is, above the temperature at which methane is converted within the necessary range. As long as the active temperature of the methane oxide is not significantly exceeded, oxidation from NO to NO ₂ hardly occurs. Thus, NO ₂ production depends on the methane conversion capacity. This correlation appears most prominently within a temperature range between about 450 [deg.] C and 500 [deg.] C, in particular between 470 [deg.] C and 490 [deg.] C. This temperature range is well suited for carrying out the process according to the invention. However, since this behavior does not occur in a catalytic converter (Pt / Pd catalytic converter) having a platinum content much higher than that of MOC, such as, for example, a diesel oxide catalytic converter, Or a Pd-rich catalytic converter comprising less than a platinum content of palladium.

2 is a graph schematically illustrating the NO _x conversion behavior of a NO ₂ sensitive SCR catalytic converter device as a function of the NO ₂ / NO _x ratio upstream of the SCR catalytic converter device for temperatures below 250 ° C. Generally, the NO ₂ / NO _x ratio upstream of the SCR catalytic converter device behind the MOC is less than or equal to 0.5 according to FIG. Thus, in practice, the NO _x conversion rate of the NO ₂ sensitive SCR catalytic converter device increases substantially linearly with the increase of the NO ₂ content in the exhaust gas, so that from the NO _x conversion rate of the SCR catalytic converter, NO ₂ production can be estimated.

For purposes of the present invention, NO ₂ -sensing SCR catalytic converters of this type, which are disposed in the substream or partial stream for the main exhaust gas train, are preferably used. This sub SCR catalytic converter device preferably has a smaller volume than the main SCR catalytic converter device in the main stream of the exhaust gas train. In this case, the sub-SCR catalytic converter is preferably operated at a temperature level where the dependence of the NO _x conversion rate on the NO ₂ content of the feed gas occurs in a very prominent manner, in particular at a temperature of 250 ° C or less.

Since the production of NO ₂ in MOC depends on the methane conversion capacity of the MOC, and since these two variables are known as a function of the catalyst converter load (space velocity) and temperature, which can be stored or modeled, for example, as a characteristic map, The methane conversion capacity of the MOC according to the present invention at known boundary conditions (e.g., temperature, space velocity, NO _x content in the sub-stream, etc.) through the NO _x conversion rate that depends on the NO ₂ measured in the sub SCR catalytic converter device Can be estimated.

3 schematically shows an exhaust gas train of an internal combustion engine 300 having a turbocharger 310. As shown in Fig. A methane-oxide catalytic converter (MOC) 320 is provided in the exhaust gas train. A particle filter having a main SCR catalytic converter device 340, for example a conventional SCR catalytic converter or a SCR coating layer, is disposed in the main stream line 330 downstream of the MOC 320. A sub-stream line 350 having a sub-SCR catalytic converter device (small SCR) 360 is disposed in the bypass to the main SCR catalytic converter device 340. There is a supply point 370 of the required reducing agent solution for the SCR catalytic converter devices 340 and 360 upstream of the main SCR catalytic converter device 340 and at the same time upstream of the bifurcation of the sub-stream 350. Between the MOC 320 and the main SCR catalytic converter device 340 is a first NO _x sensor 380, which may also be configured as a lambda / NO _x combination sensor, for example. There is an additional NO _x sensor 390 downstream of the main SCR catalytic converter device 340 and downstream of the summit of the sub-stream 350 into the main stream 330 at the same time. Other known sensors that are required in the system, for example temperature, lambda value, etc., are not shown in detail. When the overall exhaust gas volume flow and the sub-stream volume flow through the small SCR catalytic converter device 360 are known when the sensitivity and accuracy of the two NO _x sensors 380, 390 are sufficient, preferably the main SCR catalytic converter device may 340 be a total NO _x conversion factor is the condition that is predicted, the two NO _x sensors NO _x conversion rate through the sub-stream 350, or a small SCR path directly from the signals (380, 390) calculates at. In this case, the residual amount of NO _{x in} the main exhaust gas train is entirely derived from the sub-stream path 350. Therefore, the NO _x conversion rate in the sub SCR catalytic converter device can be accurately calculated through the absolute volume flow or the mass flow.

Figure 4 shows a comparable exhaust aftertreatment system in which the various components of the exhaust aftertreatment system are designated by the same reference numerals as in Figure 3. [ The difference from FIG. 3 is that in the layout according to FIG. 4, an additional NO _x sensor 391 is disposed downstream of the sub SCR catalytic converter device 360 in the sub-stream 350. This configuration is particularly suitable when the sensitivity and accuracy of the NO _x sensor 390 disposed downstream of the main SCR catalytic converter device 340 is not sufficiently high.

Fig. 5 shows another highly preferred configuration of the exhaust gas post-treatment apparatus according to the present invention. An MOC 420 is disposed in an exhaust gas train of an internal combustion engine 400 having a turbocharger 410. In the main stream 430 of the exhaust gas train, there is a main SCR catalytic converter device 440 connected upstream of a supply device 470 for the required reducing agent. There are one NO _x sensor 480 and 490 respectively upstream and downstream of the main SCR catalytic converter device 440. In this layout, sub-SCR catalytic converter device 460 is located in sub-stream 450 of the exhaust gas train, and sub-stream 450 branches between supply point 470 and main SCR catalytic converter device 440 . The sub-stream 450 is a low pressure exhaust gas recirculation line with an exhaust flap 453 for the internal combustion engine 400. It is highly desirable to place the sub SCR catalytic converter device 460 in the low pressure exhaust gas recirculation line because the exhaust gas recirculation coolers 451 and 452 provided in the exhaust gas recirculation line 450 are (optionally) This is because the temperature level suitable for the method according to the invention can be set very precisely in such a way that an optimum temperature level between 170 DEG C and 250 DEG C can be set. Further, the exhaust gas volume flow or the exhaust gas mass flow in the exhaust gas recirculation line 450 is very accurately known for other reasons, so that the NO _x conversion rate in the sub SCR catalytic converter device 460 can be controlled by using the NO _x sensor 491 to serve Can be calculated very accurately downstream of the SCR catalytic converter device 460. The sub SCR catalytic converter device 460 and the exhaust gas recirculation coolers 451 and 452 can be assembled or integrated into one component.

For performing the monitoring method according to the invention or for MOC diagnosis, the following steps can be carried out: Firstly, the current exhaust gas temperature at the MOC is checked for diagnosis and an engine operating point suitable for diagnosis is set For example T = 460 ° C). A suitable operating point can be derived from the reference behavior (expected value). Subsequently, the current temperature in the sub SCR catalytic converter device is checked, and conditions suitable for diagnosis are set (e.g., T = 180 ° C through cooling performance, corresponding setting of the sub-stream mass flow, etc.). Subsequently, the NO _x conversion rate through the sub SCR catalytic converter device is determined, and the corresponding NO ₂ / NO _x ratio is calculated and compared with a reference value (expected value) as occasion demands (for example, the corresponding NO ₂ / NO _x ratio is 0.25 NO _x conversion is 60%). If the NO _x conversion rate is sufficiently high compared to the preset threshold value, the methane conversion performance of the MOC is also sufficient. Where it is determined that the methane conversion performance is insufficient, there may be variously introduced known reactivation measures for MOC.

Additionally or alternatively, the degree of deactivation of the MOC can be quantified by repeating the process at another temperature in the MOC. To this end, the exhaust gas temperature at the MOC may rise to another, e.g., higher, temperature level (e.g., T = 500 ° C) through the setting of another engine operating point. Then, the temperature in the sub SCR catalytic converter device is again checked, and a condition suitable for diagnosis (for example, T = 180 DEG C) is set. The NO _x conversion rate through the sub-SCR catalytic converter device is determined and, in some cases, the associated NO ₂ / NO _x ratio is calculated and compared with the new expected value (threshold value). If the NO _x conversion rate is not sufficiently high even at the elevated MOC temperature, that is, if it is below the threshold value, the methane conversion performance is no longer sufficient and, in some cases, a reactivation measure for the MOC can be introduced.

This configuration of the method according to the invention is particularly preferred when a sufficiently good methane-oxidized MOC is selected as the reference state. In this case, even if the methane conversion rate is slightly reduced (here, for example, 90% at 470 캜 instead of 98% at 500 캜 as a reference state), NO ₂ production can be significantly reduced. That is, for example, diagnostics can be performed at 470 ° C, but the MOC operates at 500 ° C rather than in actual operation or the reference condition. In this case, at 470 ° C, the MOC may be incorrectly rated as being too poor for methane oxidation, due to the very low NO ₂ content. It is therefore desirable to perform NO ₂ generation diagnostics again at one or more higher temperatures where better activation of the MOC may be expected to correlate the methane conversion at one or more other NO ₂ thresholds. If NO ₂ production is too low even at higher temperatures, the MOC can be diagnosed as being very precisely insufficient or "inactive ". Through the temperature rise in this manner in the diagnosis according to the present invention, the active temperature curve for methane conversion can be scanned (multi-point determination), so that the degree of methane oxide inactivity can be (more) accurately quantified, ₂ behavior is detected over a larger temperature range.

Claims (15)

A method for monitoring a methane-oxide catalytic converter (320; 420) in an exhaust gas train of an internal combustion engine (300; 400)
Methane oxide catalyst converter; on the basis of the generation of NO ₂ in the (320 420), on the basis of the NO ₂ generation and, NO ₂ content and / or the NO ₂ / NO _x ratio at or downstream in the methane oxide catalyst converter by estimating the methane conversion capability of; (420 320), methane oxide catalyst converter methane oxide catalyst converter (320; 420) performs an active diagnosis, in accordance NO methane oxide catalyst converter based on a decrease in the _second generation (320 in; 420) in the methane conversion catalytic converter is estimated to be deteriorated. The method of claim 1, wherein the method, the methane conversion rate of methane oxide catalytic converter downstream of the NO ₂ content and / or the NO ₂ / NO _x ratio of methane oxide catalyst converter of correlation exists between; temperatures (320 420) Wherein the catalytic converter is performed within a range of < RTI ID = 0.0 > 100 < / RTI > The catalytic converter system of claim 1 or 2, wherein at least one SCR catalytic converter device (360; 460) is disposed downstream of the methane oxide catalytic converter (320; 420) NO2 < / RTI &_gt; is determined. ≪ Desc / Clms Page number 20 > 4. The method of claim 3, wherein the SCR catalytic converter device (360; 460) is configured such that its NO _x conversion behavior is dependent on the NO ₂ content and / or the NO ₂ / NO _x ratio of the gas entering the SCR catalytic converter device Wherein the catalytic converter is a NO ₂ sensitive SCR catalytic converter device. 4. A method according to claim 3, characterized in that the SCR catalytic converter arrangement (360; 460) is a sub SCR catalytic converter arrangement disposed in the sub-stream (350; 450) of the exhaust gas train. The method of claim 5, wherein the sub SCR catalytic converter device (360; 460) has a smaller volume than the main SCR catalytic converter device (340; 440) in the main stream (330; 430) Is operated at a temperature lower than that of the device (340; 440). 4. A method according to claim 3, characterized in that a measurement of NO _x is made upstream and / or downstream of the SCR catalytic converter arrangement (360; 460) to determine NO ₂ production. An exhaust gas aftertreatment apparatus for an exhaust gas train of an internal combustion engine (300; 400) having one or more methane oxide catalytic converters (320, 420) in a main stream line (330; 430) of an exhaust gas train,
The sub-SCR catalytic converter device 360 (460) is disposed in the sub-stream line 350 (450) of the exhaust gas train and the NO _x conversion behavior of the sub-SCR catalytic converter device 360 (460) NO ₂ content of the gas flowing into and / or NO ₂ / NO _x ratio NO ₂ sensitive SCR catalytic converter device in the exhaust gas treatment device, characterized in that the right and left on. 9. The method according to claim 8, characterized in that heating means and / or cooling means (451, 452) are provided for setting the temperature within the range of 170 DEG C to 250 DEG C for the sub SCR catalytic converter device (460) , An exhaust gas aftertreatment device. 10. A method according to claim 8 or 9, characterized in that the sub-stream line (350) of the exhaust gas train is arranged in the area of the main SCR catalytic converter arrangement (340) in the bypass to the main stream line (330) , An exhaust gas aftertreatment device. The exhaust aftertreatment apparatus according to claim 8 or 9, characterized in that the sub-stream line (450) of the exhaust gas train is an exhaust gas recirculation line branching downstream of the methane-oxide catalytic converter (420). The exhaust aftertreatment apparatus according to claim 8 or 9, wherein the exhaust gas after-treatment apparatus used in the method for monitoring the methane-oxide catalytic converter (320; 420) according to claim 1 or 2. A computer program designed to carry out the steps of the method according to any one of the preceding claims and stored in a machine-readable storage medium. 14. A machine-readable storage medium having stored thereon a computer program according to claim 13. An electronic control device designed to perform the steps of the method according to claim 1 or 2.

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