Determination of NOx concentration downstream of at least one catalyst of an H2 combustion engine

Abstract

Methods for correcting an initial NOx concentration (r NOx,ds ) an internal combustion engine (10), where the first NOx concentration (r NOx,ds ) is determined by means of a NOx sensor (32) arranged downstream of a catalyst (22), in particular at the outlet of the exhaust system, where the NOx sensor (42) measures an oxygen concentration (r O2,ds ) in the exhaust gas determined, depending on the oxygen concentration (r O2,ds ) a water concentration (r H2O,ds ) is determined in the exhaust gas, where depending on the determined water concentration (r H2O,ds ) in the exhaust gas a correction of the first NOx concentration (r NOx,ds ) is carried out.

Description

State of the art

[0001] DE 10 2014 201 304 A1 concerns a method for operating a catalyst system designed to reduce nitrogen oxide emissions from the exhaust gases of an internal combustion engine, which includes at least one SCR catalyst (150) operated with a reagent that can be stored in the SCR catalyst (150) so that a certain reagent level is present in the SCR catalyst (150), wherein the dose of reagent is based on models (604, 606) using an NH3 level controller (602), modeling errors are compensated using an NH3 level monitor (605). Disclosure of the invention

[0002] In a first aspect, the invention relates to a method for correcting a first NOx concentration of an internal combustion engine, wherein the first NOx concentration is determined by means of a NOx sensor arranged downstream of a catalyst, in particular at the outlet of the exhaust system, wherein the NOx sensor determines an oxygen concentration in the exhaust gas, wherein a water concentration in the exhaust gas is determined depending on the oxygen concentration, and wherein a correction of the first NOx concentration is carried out depending on the determined water concentration in the exhaust gas.

[0003] This method offers the distinct advantage of significantly improving the accuracy of measuring nitrogen oxide (NOx) concentrations in the exhaust gases of internal combustion engines by taking the water concentration in the exhaust gas into account as a correction factor. This innovative method allows for more precise adjustment of NOx measurements under varying operating conditions, leading to more effective emissions control and optimization of exhaust aftertreatment systems. The increased measurement accuracy enables better regulation of internal combustion engines to support compliance with stricter emissions standards, while also providing the flexibility to be applied to various engine types, including those using alternative fuels such as hydrogen.This not only contributes to reducing environmental pollution, but also supports the implementation of on-board monitoring systems (OBM) for continuous emission monitoring during real-world driving.

[0004] In a special configuration, approval is granted for the correction of the first NOx concentration if little to no NOx or NH3 concentration is expected or detected in the exhaust gas.

[0005] This further training has the particular advantage that a conditional approval for the correction of the NOx concentration is provided, based on the expectation or measurement of low to no NOx or NH3 concentrations in the exhaust gas.

[0006] In an advantageous embodiment, a modeled nitrogen oxide conversion is determined using a model calculated on the control unit. If the determined nitrogen oxide conversion exceeds a predefined conversion threshold, the system authorizes the correction of the initial NOx concentration. This embodiment improves emission control through a model-based process running on the control unit that determines the nitrogen oxide conversion. The NOx concentration correction is only authorized if the conversion exceeds a defined threshold. This enables targeted and efficient adjustment of emission values ​​in critical operating conditions, optimizes the accuracy of NOx measurement, and minimizes the consumption of reducing agents as well as the load on exhaust aftertreatment systems. This reduces environmental impact and promotes compliance with emission regulations.

[0007] In a further embodiment, if the gradient of the first NOx concentration falls below a predefinable gradient threshold, the authorization is given to correct the first NOx concentration.

[0008] Furthermore, NOx measurement accuracy is improved by only enabling corrections when the NOx concentration gradient falls below a certain threshold. This demand-based correction activation targets situations with small concentration changes, increasing reliability under stable operating conditions and optimizing the efficiency of exhaust aftertreatment. This prevents false corrections.

[0009] In a special configuration, a map is stored on the control unit, whereby a water concentration in the exhaust gas is determined depending on the measured oxygen concentration and the map.

[0010] This design offers the advantage that storing a map on the control unit and using it to determine the water concentration in the exhaust gas based on the oxygen concentration enables precise and rapid adjustment of the NOx concentration measurement. This method allows for the direct and efficient calculation of the relevant correction factors for NOx measurement, which improves the accuracy of emissions monitoring under various operating conditions. Furthermore, integrating the map into the control unit ensures high flexibility and adaptability to different engine states, increasing the effectiveness of exhaust aftertreatment and contributing to compliance with environmental standards.

[0011] In an advantageous embodiment, the water concentration in the exhaust gas is determined using a Pischinger formula as a function of an air-fuel ratio, a fresh air mass, and / or an exhaust gas mass. This approach enables a highly precise and dynamic calculation of the water concentration, which is crucial for correcting the NOx concentration. By directly considering these specific engine operating parameters, the accuracy of emission measurement under varying operating conditions is significantly improved. The application of the Pischinger formula thus contributes to more effective exhaust aftertreatment, optimizes emission control, and supports compliance with stringent environmental regulations through a more precise adjustment of NOx emission values.

[0012] In a further embodiment, offset values ​​are determined to compensate for the first NOx concentration from discretized areas, whereby the discretized areas are created depending on the water concentration, and a minimum value is determined for each discretized area from the current first NOx concentration.

[0013] This method improves the precision of NOx concentration measurement by determining offset values ​​from discretized ranges defined based on water concentration. For each of these ranges, a minimum NOx concentration value is determined, which is used for compensation. This approach enables finely tuned correction of NOx values ​​that responds specifically to the respective water concentration in the exhaust gas. By adapting the correction values ​​to the actual operating conditions, the accuracy of emissions measurement is significantly improved under a wide variety of engine states. This methodological approach contributes to increasing the effectiveness of exhaust aftertreatment and supporting compliance with environmental standards through more precise emissions controls.

[0014] In an advantageous embodiment, the minimum value is used as a valid value for the correction of the first NOx concentration if the NOx concentration is determined for a minimum time within the discretized range.

[0015] This design increases the precision of NOx emission measurement by selectively choosing the minimum value as a correction value, provided the NOx concentration remains within a specifically discretized range for a defined minimum duration. This defined minimum duration can, for example, correspond to a predefined minimum time or a time interval. This methodological approach enables a finely tuned correction based on stable measurement data, thus improving the reliability of emission monitoring. By eliminating short-term spikes or outliers in the measured values, this design significantly contributes to a more accurate and reliable adjustment of the NOx concentration, which increases the effectiveness of exhaust aftertreatment and supports compliance with strict environmental regulations.

[0016] In a special embodiment, interpolated offset values ​​are determined depending on the determined offset values ​​for the discretized areas, whereby the correction of the first NOx concentration is carried out using the interpolated offset values.

[0017] In a special configuration, the internal combustion engine is an H2 internal combustion engine. This modification extends the applicability of the method specifically to hydrogen combustion engines, addressing the particular challenges of emission measurement and correction in hydrogen-powered vehicles. Since hydrogen engines exhibit a significantly higher water concentration in their exhaust gas compared to conventional gasoline or diesel engines, this specific adaptation of the method enables more precise correction of the NOx concentration under these unique operating conditions. This contributes significantly to improving emission monitoring and control in hydrogen vehicles, supports compliance with environmental standards, and promotes the acceptance and widespread adoption of environmentally friendly hydrogen combustion engines as an alternative to fossil fuels.

[0018] In further aspects, the invention relates to a device, in particular a control unit, and a computer program, which are configured, in particular programmed, to execute one of the methods. In yet another aspect, the invention relates to a machine-readable storage medium on which the computer program is stored. Brief description of the drawings

[0019] The invention will be explained in more detail below with reference to an embodiment illustrated in the figures. The figures show: Fig. 1 in a schematic representation an SCR system with an SCR catalyst of an H2 internal combustion engine, Fig. 2 a) an exemplary measurement of a status bit for a valid measurement for the procedure, b) an exemplary measurement of an H2O concentration r H2O,ds downstream of at least one SCR catalyst 22, c) an exemplary measurement of a NOx concentration r NOx,dsdownstream of at least one SCR catalyst 22, Fig. 3 A schematic flowchart of an exemplary embodiment of the inventive method for correcting a NOx concentration r NOx,ds downstream of at least one SCR catalyst 22 of an internal combustion engine. Exemplary embodiments of the invention

[0020] An internal combustion engine 10, in particular an H2 internal combustion engine, has an SCR system 20 in its exhaust stream 11, which is located in Fig. Figure 1 shows the system. This system has a reducing agent dosing unit 21, with which a urea-water solution (AdBlue) can be injected into the exhaust stream 11. Ammonia is released from this solution at the high temperatures of the exhaust gas. A first SCR catalyst 22 is arranged downstream of the reducing agent dosing unit 21. Further SCR catalysts can be arranged downstream of the first SCR catalyst 22. An optional second NOx sensor 31 and a temperature sensor 12 are arranged upstream of the reducing agent dosing unit 21 and downstream of an H2 combustion engine 10 in the exhaust stream 11. The second NOx sensor 31 measures a second NOx concentration value r. NOx,usUpstream of the at least one SCR catalyst 22, preferably as NOx concentration or as a NOx mass flow rate. A first NOx sensor 32 is arranged downstream of the at least one SCR catalyst 22 and measures a first NOx concentration sensor value r. NOx,ds , preferably as NOx concentration or as a NOx mass flow rate. The NOx concentration values ​​refer in particular to the NOx concentration signal of the corresponding NOx sensor 31;32.

[0021] All NOx sensors 31 and 32 transmit their signals to an electronic control unit 100, primarily via wired connections. Since the NOx sensors 31 and 32 are also cross-sensitive to ammonia in addition to nitrogen oxides, their signals are sum signals of nitrogen oxides and ammonia. Furthermore, the first and second NOx sensors 31 and 32 can each determine the air-fuel ratio and the oxygen concentration. The reducing agent dosing unit 21 also reports the amount of ammonia injected into the exhaust stream 11 to the control unit 100.

[0022] The control unit 100 still has a model M stored, which depends on the first NOx concentration sensor value r. NOx,us and the second NOx concentration sensor value r NOX,ds a modeled NOx concentration r Nox,ds,mod downstream of the SCR catalyst 22, the exhaust gas temperature from temperature sensor 12 and the exhaust gas mass flow rate (dm) can optionally be determined.exh can be used as an input variable for modeling.

[0023] It should be noted that the present model M cannot represent, or can represent too inaccurately, the absorption and desorption of emissions in the catalyst 22, especially of NOx molecules, so that the model M cannot be used permanently for determining the first NOx concentration r. NOx,ds The model M can be used downstream of the SCR catalyst 22. Furthermore, the model M offers the possibility of determining a modeled nitrogen oxide conversion of the SCR catalyst 22, and if the determined nitrogen oxide conversion exceeds a predefinable conversion threshold S U exceeds the release for compensation of the first NOx sensor signal r NOx,ds is granted.

[0024] In the Fig. Figure 2 shows an example measurement for the presented method. The time axis t, represented as the abscissa, applies to all three diagrams shown: a), b), and c).

[0025] Diagram a) above shows an example measurement for a status bit determined on control unit 100. The status bit changes from a value of 0 to a value of 1 when an operating point for the procedure exists such that the procedure can provide valid values ​​for correcting the initial NOx concentration r. NOx,ds can determine.

[0026] In Fig. 2 b) is a measurement of the water concentration r H2O,ds The graph shows the process downstream of at least one SCR catalyst 22 over time t. Six discretized regions B are shown on the ordinate. i shown between H2O concentrations of 0 to 14%. In the present example, the release for the procedure for valid values ​​to determine the offset values ​​O i only in the discretized area B1 with 0 to 2% H2O concentration r H2O given.

[0027] In Fig. 2 c) is a measurement of the first NOx concentration r NOX,dsdownstream of at least one SCR catalyst 22 over time t, an operating condition can be observed in which only low to no high values ​​for the first NOx concentration r are observed. NOx,ds is present. In the time interval between time t1 and t2, the values ​​of the first NOx concentration r are determined. NOx,ds for the corresponding water concentration r H2O,ds Determined by control unit 100 and offset values ​​O i determined for the procedure.

[0028] In the Fig. Figure 3 is an example of the procedure for correcting a NOx sensor signal r NOx of an internal combustion engine 10, shown using a flowchart.

[0029] In a first step 200, the control unit 100 checks for the release of the first NOx sensor 32. The control unit 100 grants the release for the first NOx sensor 32 when the NOx sensor 32 has completed its measurement readiness, in particular a heating process. In a preferred embodiment, the temperature of the sensor is continuously determined by means of the temperature sensor 12.

[0030] For this purpose, the control unit 100 determines the temperature at the location of the first NOx sensor 32, preferably using the temperature sensor 12 in the exhaust system 11. This is preferably done using a temperature model that models the temperature at the location of the first NOx sensor 32 based on the temperature sensor 12. Alternatively, another temperature sensor, which is located close to the installation location of the first NOx sensor 32, can also be used to enable the NOx sensor 32. The first NOx sensor 32 is enabled when a predefined temperature threshold is exceeded by the temperature at the location of the NOx sensor or the temperature sensor 12.

[0031] The process then continues in step 210.

[0032] In step 210, the NOx conversion capacity η of the at least one SCR catalyst 22 is determined by the control unit 100. Furthermore, the first and second NOx concentrations r are continuously measured.NOx,ds ; r NOx,us Received and stored by control unit 100.

[0033] Based on the temperature of the temperature sensor 12, modeled temperatures are determined for several partial volumes or locations as sections within the at least one SCR catalyst 22. For example, these partial volumes can represent axially arranged discs, so-called bricks. A physical model can be used for this purpose, incorporating, in particular, the fluid-mechanical properties of the at least one SCR catalyst 22 as well as thermal properties such as heat capacity, thermal conductivity, etc., of the SCR catalyst 22, the H2 combustion engine 10, and the exhaust gas. These properties can be permanently stored in a data memory of the control unit 100, for example, in the form of one or more maps, lookup tables, parameter sets, or similar.

[0034] Furthermore, the local conversion capacities are determined from the local temperatures thus ascertained, using dependencies of the conversion rate on the local temperature that are valid for the respective location or corresponding partial volume (e.g., the aforementioned light-off curve). This dependency depends in particular on the type of at least one

[0035] The efficiency of the SCR catalyst 22 depends on its age, as different conversion reactions to be catalyzed require different temperatures, and the conversion efficiency generally decreases with increasing catalyst aging. The aging of the SCR catalyst 22 can be determined, for example, as part of a diagnostic function and taken into account in the form of an aging parameter. This aging parameter can apply globally to the entire SCR catalyst 22 or be determined location-dependently, since, for example, temperatures in a peripheral zone of the catalyst are generally lower than in a core zone, and thus the core zone ages faster than the peripheral zone.

[0036] Each brick can have its own individual NOx conversion capacity η. i, where i is the number of bricks, or an average value for the total NOx conversion capacity η of the SCR catalyst 22 can be determined. In the further course of the exemplary embodiment, the average value for the total NOx conversion capacity η is used.

[0037] If the NOx conversion capacity η exceeds a predefinable sales threshold S U The process continues in step 220, particularly for a predetermined period. The reason for this is that the process requires an operating state in which little to no cross-influence from nitrogen oxide and / or ammonia emissions affects the signal of the first NOx concentration r. NOx,ds This can impair the performance of the exhaust gas mass flow in these operating conditions. Therefore, the influence of water (H2O) in the exhaust gas mass flow on the signal of the first NOx concentration r can be affected. NOx,ds can be identified and corrected particularly well.

[0038] In a preferred embodiment, the process for determining the first NOx concentration r is released upon the occurrence of the operating state described above. Nox,ds granted.

[0039] In an alternative embodiment, a gradient G of the first NOx concentration r is used. NOx,ds Determined by control unit 100. If the gradient G falls below a predefined gradient threshold S G , in particular for a specified period of time, the procedure will continue in step 220.'

[0040] In a preferred embodiment, the process for determining the first NOx concentration r is released upon the occurrence of the operating state described above. Nox,ds granted.

[0041] In step 220, an oxygen concentration r is continuously increased. O2,usThe first NOx sensor 32 determines the water concentration r based on a characteristic map K stored on the control unit 100 or using the Pischinger formula. H2O,ds determined in the exhaust gas.

[0042] The process is then continued in step 230.

[0043] In step 230, the determined water concentrations r H2O,ds discretised areas B i assigns the discretized areas B. i was stored on control unit 100 during an application phase.

[0044] In a preferred embodiment, the discretised areas B i Divided into 2% increments. Basically, all divisions into areas with i >= 2 areas are possible.

[0045] The determined water concentration values ​​r H2O,ds The discretized areas B now pass through i, whereby the first NOx concentration values ​​are continuously determined. NOX,ds These settings are received and stored by control unit 100. Advantageously, these assignments are stored in an array, specifically in a map, on control unit 100.

[0046] In a first embodiment, these determined initial NOx concentration values ​​can be used to... NOx,ds,i A correction to the initial NOx concentration signal is performed directly. These initial NOx concentration values ​​are then used to... NOX,ds,i The data is continuously stored on control unit 100 and used for correction. This is advantageously carried out using an offset correction, whereby the correction does not affect NOx concentration values. NOx,ds allows values ​​smaller than 0.

[0047] In an alternative configuration, the data in the discretized area B are used. i determined values ​​a minimum value M iThe control unit 100 determines and stores the value. Advantageously, a correction of the initial NOx concentration is performed. NOx,ds using the minimum values ​​M i as offset values.

[0048] In a preferred version, the minimum value M i then as a valid value for the correction of the first NOx concentration r NOx,ds used when the NOx concentration r NOx,ds for a predefinable minimum time t min within the discretized area B i is determined.

[0049] In a further embodiment, preferably an exponentially weighted moving average (EWMA), or an average value, can be applied to the determined values. Alternatively, it can also be applied to the minimum values ​​M. i That is, one receives B for each of the areas. i a filtered offset value O i to correct the first NOx concentration r NOx,ds .

[0050] In an alternative configuration, the following can be used from areas B i determined offset values ​​O i A characteristic curve or a functional rule can be determined by means of interpolation, so that over the entire area B i or depending on the water concentration values ​​r H2O,ds Interpolated offset values ​​are calculated and used to correct the initial NOx concentration r NOx,ds be used.

[0051] The procedure can then be continued or terminated in step 210. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 201 304 A1

[0001]

Claims

[1] Methods for correcting an initial NOx concentration (r NOx,ds ) an internal combustion engine (10), where the first NOx concentration (r NOx,ds ) is determined by means of a NOx sensor (32) arranged downstream of a catalyst (22), in particular at the outlet of the exhaust system, where the NOx sensor (42) measures an oxygen concentration (r O2,ds ) determined in the exhaust gas, where depending on the oxygen concentration (r O2,ds ) a water concentration (r H2O,ds ) is determined in the exhaust gas, characterized by , that depending on the determined water concentration (r H2O,ds ) in the exhaust gas a correction of the first NOx concentration (r NOx,ds ) is carried out. [2] Method according to claim 1, characterized by , that a release for the correction of the first NOx concentration (r NOx,ds ) is granted when little to no NOx or NH3 concentration is expected or detected in the exhaust gas. [3] Method according to claim 2, characterized by , that a modeled nitrogen oxide turnover is determined by means of a model calculated on the control unit (100), and if the determined nitrogen oxide turnover exceeds a predefinable turnover threshold (S U ) exceeds, the release for the correction of the first NOx concentration (r) NOx,ds ) is granted. [4] Method according to claim 2, characterized by , that if a gradient of the first NOx concentration (r NOx,ds ) a predefinable gradient threshold (S G ) falls below the threshold for the release of the first NOx concentration correction (r). NOx,ds ) is granted. [5] Method according to claim 1, characterized by , that a map (K) is stored on the control unit (100), whereby depending on the determined oxygen concentration (r O2,ds ) and the characteristic curve (K) a water concentration (r H2O,ds ) is determined in the exhaust gas. [6] Method according to claim 1, characterized by , that the water concentration (r H2O,ds ) in the exhaust gas using a Pischinger formula as a function of an air-fuel ratio (λ), a fresh air mass (m air ) and / or an exhaust gas mass (m exh ) is determined. [7] Method according to claim 1, characterized by , that offset values ​​(O i ) to compensate for the initial NOx concentration (r NOx,ds ) from discretized areas (B i ) are determined, whereby the discretized areas (B i ) depending on the water concentration (r H2O,ds ) are created, where for each discretized area (B i ) a minimum value (M i ) from the current first NOx concentration (r NOx,ds ) is determined. [8] Method according to claim 7, characterized by , that the minimum value (M i ) as a valid value for the correction of the first NOx concentration (r NOx,ds ) is used when the NOx concentration (r NOx,ds) for a minimum time (t min ) within the discretized domain (B i ) is determined. [9] Method according to any one of the preceding claims, wherein depending on the determined offset values ​​(O i ) for the discretized areas (B i ) interpolated offset values ​​were determined, whereby the correction of the first NOx concentration (r) NOx,ds ) is carried out using the interpolated offset values. [10] Method according to claim 1, characterized by , that the internal combustion engine (10) is an H2 internal combustion engine. [11] Computer program configured to perform a method according to any one of claims 1 to 10. [12] Electronic storage medium with a computer program according to claim 11. [13] Device, in particular control unit (100), which is configured to perform a method according to any one of claims 1 to 10.

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