A method for real-time estimation of ammonia leakage at the downstream end of a diesel engine SCR

Abstract

This application relates to an embodiment in which the method for calculating ammonia leakage under steady-state operating conditions includes: when the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, calculating a first ammonia leakage capacity based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst; when the ammonia coverage of the SCR catalyst exceeds a limit, calculating a second ammonia leakage capacity based on the ammonia coverage of the SCR catalyst; and calculating the ammonia leakage under steady-state operating conditions based on the first ammonia leakage capacity and the second ammonia leakage capacity. By calculating ammonia leakage based on steady-state operating conditions, calculating ammonia leakage based on transient operating conditions, and correcting ammonia leakage based on the post-NOx sensor, and through precise calibration and optimization, the calculation accuracy of NH3 leakage is improved, real-time estimation of NH3 leakage is achieved, closed-loop correction control of SCR ammonia storage control is ensured, and accurate control of urea injection is achieved, thereby achieving the expected emission results.

Description

Technical Field

[0001] This invention relates to the field of engine exhaust gas purification and control, specifically to a method for real-time estimation of ammonia leakage at the downstream end of a diesel engine SCR. Background Technology

[0002] Currently, Urea-SCR technology is widely used in heavy-duty diesel engines. The SCR system uses urea as a reducing agent. Urea, when mixed with water, decomposes into NH3 and CO2 at high temperatures. Its working principle involves injecting the reducing agent NH3 into the exhaust pipe, where nitrogen oxides in the exhaust react with NH3 to be reduced to nitrogen and water, thus reducing the harmful NOx emissions from the diesel engine. To achieve high NOx conversion efficiency in the diesel engine aftertreatment SCR system, excessive urea injection is generally used. However, excessive urea injection can lead to excessive NH3 leakage in the aftertreatment emissions, wasted urea, and urea crystallization in the aftertreatment EGP (Exhaust Gas Grating). While the SCR system uses NH3 as a reducing agent, NH3 leakage often occurs at the exhaust outlet, resulting in the presence of NH3 both before and after the catalyst in the entire SCR system. Therefore, significant errors occur in the measurement of NOx concentration. If the measurement error caused by the cross-sensitivity of the NOx sensor to NH3 is ignored, it will have a significant impact on the precise control of the subsequent SCR system. To address the adverse effects of excessive urea injection, it is necessary to improve the precision of urea injection control, which requires accurate real-time estimation of ammonia leakage. Based on the real-time estimated ammonia leakage, the urea injection quantity is adjusted and optimized in real time, ultimately achieving high NOx conversion efficiency and low NH3 leakage in the diesel engine aftertreatment SCR system.

[0003] Among related technologies, a method for calculating ammonia leakage in an SCR aftertreatment system is disclosed. This method proposes a method for calculating ammonia leakage in an SCR aftertreatment system. In this method, the relationship between the current downstream NOx sensor measurement value and the ammonia leakage value, and the relationship between the downstream NOx sensor measurement value and the ammonia leakage value 1 second ago are obtained. Based on these, the current ammonia leakage value is calculated, and the calculated ammonia leakage value is processed by low-pass filtering. Furthermore, the calculated ammonia leakage value is corrected by observing the changing trends of the calculated and actual ammonia leakage values. When the NOx conversion efficiency obtained from the upstream and downstream NOx sensor measurements is greater than a threshold, the calculated ammonia leakage value is set to 0. In related technologies, an accurate NH3 leakage control method is also disclosed, which proposes a control method for accurately predicting NH3 leakage. This method accurately predicts NH3 leakage based on the current source NOx, the current final emission NOx, the previous source NOx, the previous final emission NOx, the current conversion efficiency, and the previous conversion efficiency. The predicted NH3 leakage is then filtered. This method utilizes the time-delay characteristics of the SCR system to accurately predict NH3 leakage using NOx sensor measurements.

[0004] However, the above technical solution can only predict the amount of NH3 leakage if the conditions for NH3 leakage prediction are met. These conditions include: NOx emissions, exhaust flow rate, DOC outlet temperature, SCR inlet temperature, and SCR ammonia storage capacity. The calculation of NH3 leakage prediction can only begin if all of the above prediction conditions meet the relevant measurement thresholds. This makes it impossible to guarantee real-time estimation of NH3 leakage, thereby failing to guarantee closed-loop correction control of SCR ammonia storage, failing to achieve accurate control of urea injection volume, and failing to achieve the expected emission results. Summary of the Invention

[0005] This application provides a real-time estimation method for ammonia leakage at the back end of a diesel engine SCR, which can solve the problems in related technologies that cannot guarantee closed-loop correction control of SCR ammonia storage control, cannot achieve accurate control of urea injection quantity, and cannot achieve the expected emission results.

[0006] In a first aspect, embodiments of this application provide a real-time estimation method for ammonia leakage at the downstream end of a diesel engine SCR, comprising: calculating the ammonia leakage under steady-state operating conditions; calculating the ammonia leakage under transient operating conditions based on the ammonia leakage under the steady-state operating conditions; and calculating the ammonia leakage under transient operating conditions and the downstream NO... X The sensor measurements corrected the ammonia leakage amount, improving the calculation accuracy of NH3 leakage and enabling real-time estimation of NH3 leakage.

[0007] In conjunction with the first aspect, in one embodiment, the method for calculating the ammonia leakage under steady-state conditions includes: when the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, calculating a first ammonia leakage based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst; when the ammonia coverage of the SCR catalyst exceeds a limit, calculating a second ammonia leakage based on the ammonia coverage of the SCR catalyst; and calculating the ammonia leakage under steady-state conditions based on the first ammonia leakage and the second ammonia leakage. By comprehensively considering factors such as the actual ammonia storage capacity inside the SCR catalyst, the maximum ammonia storage capacity of the SCR catalyst, and the ammonia coverage of the SCR catalyst during the calculation process, the calculation accuracy of NH3 leakage is further improved, making the real-time calculation result of NH3 leakage more accurate.

[0008] In conjunction with the first aspect, in one embodiment, the method for calculating the first ammonia leakage includes: calculating the actual ammonia storage inside the SCR catalyst based on the initial value of the NH3 storage within the SCR catalyst and the NH3 storage rate; calculating the maximum ammonia storage of the SCR catalyst based on the maximum ammonia storage of the SCR catalyst, the working volume of the SCR catalyst, and the ammonia storage correction factor for SCR catalyst aging; and calculating the first ammonia leakage based on the actual ammonia storage inside the SCR catalyst and the maximum ammonia storage of the SCR catalyst.

[0009] In conjunction with the first aspect, in one embodiment, the method for calculating the second ammonia leakage includes: calculating the ammonia coverage of the SCR catalyst based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst; and calculating the second ammonia leakage as a function of the ammonia coverage of the SCR catalyst.

[0010] In conjunction with the first aspect, in one embodiment, the method for calculating the ammonia leakage under transient operating conditions includes: calculating the ammonia leakage under transient operating conditions based on the ammonia leakage under steady-state operating conditions, an ammonia leakage correction coefficient related to the catalyst temperature change rate, and a sampling period. By integrating factors such as ammonia leakage, the ammonia leakage correction coefficient related to the catalyst temperature change rate, and the sampling period during the calculation process, the calculation accuracy of NH3 leakage is further improved, making the real-time calculation results of NH3 leakage more accurate.

[0011] In conjunction with the first aspect, in one embodiment, the method for correcting the ammonia leakage includes: based on the subsequent NO... X Sensor measurements are used to identify and calculate the actual amount of NH3 leakage.

[0012] In conjunction with the first aspect, in one implementation, the step according to the subsequent NO... XThe sensor measurement value is used to identify and calculate the actual NH3 leakage amount. This includes: when the post-NOx sensor measurement value is less than a first threshold, the post-NOx sensor measurement value is the NOx concentration at the current moment.

[0013] In conjunction with the first aspect, in one implementation, the step according to the subsequent NO... X The identification and calculation of the actual NH3 leakage amount based on the sensor measurement values ​​includes: when the post-NOx sensor measurement value is greater than a first threshold, the identification and calculation are performed based on the ammonia coverage level.

[0014] In conjunction with the first aspect, in one embodiment, the identification calculation based on the ammonia coverage level includes: when the ammonia coverage is less than a second threshold, the NOx sensor measurement value is the NOx concentration at the current moment.

[0015] In conjunction with the first aspect, in one embodiment, the identification calculation based on the ammonia coverage level includes: when the ammonia coverage is greater than a second threshold, the measured value of the post-NOx sensor is the NH3 leakage value at the current moment; and the actual NH3 leakage is calculated based on the ammonia leakage under the transient condition, the measured value of the post-NOx sensor, and the weight correction coefficient.

[0016] The real-time estimation method for accurately calculating the ammonia leakage at the back end of an SCR system, provided by this invention, is performed according to the following steps:

[0017] 1. Calculation of ammonia leakage under steady-state operating conditions

[0018] The ammonia leakage under steady-state operating conditions can be mainly divided into the following two parts:

[0019] 1) When the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, the ammonia leakage rate is calculated as follows:

[0020] m NH3_slip_base1 =m NH3_Store -m NH3_Capacity

[0021]

[0022] m NH3_Capacity =m NH3_Capacity_base (T)×V SCR ×f SCR_aging

[0023] in:

[0024] m NH3Int The initial value for the calculated NH3 content within the SCR catalyst;

[0025] The calculated NH3 storage rate;

[0026] m NH3_Capacity_base The maximum ammonia storage capacity is related to the temperature of the SCR catalyst. The maximum ammonia storage capacity is mainly related to the characteristics of the support, the temperature of the support, and the degree of aging of the support.

[0027] V SCR This refers to the working volume of the SCR catalyst.

[0028] f SCR_aging This is the SCR catalyst aging correction factor.

[0029] 2) Calculation of ammonia leakage when the ammonia coverage of the SCR catalyst exceeds the limit.

[0030] Only NH3 adsorbed on the SCR catalyst can react with NOx in engine emissions. Unadsorbed or desorbed NH3 will escape, ultimately causing ammonia leakage. SCR catalysts typically use ammonia coverage ratio to indicate the amount of NH3 adsorbed. A higher ammonia coverage ratio results in higher NOx conversion efficiency, but also increases ammonia leakage.

[0031]

[0032] m NH3_slip_base2 =f(θ) NH3 )

[0033] Based on the above, the steady-state ammonia leakage rate is calculated as follows:

[0034] m NH3_slip_Steady =m NH3_slip_base1 +m NH3_slip_base2

[0035] 2. Calculation of ammonia leakage under transient operating conditions

[0036] The change in ammonia leakage under transient operating conditions is mainly related to the SCR catalyst temperature. The more drastic the change in SCR catalyst temperature, the greater the ammonia leakage. The ammonia leakage under transient operating conditions is as follows:

[0037] m NH3_slip ={m NH3_slip_Steady (t)+m NH3_slip_Steady (t-1)×[1-f NH3_slip (t-1)]}×f NH3_slip (t)

[0038] Where t is the sampling period, f NH3_slip This is a correction factor for ammonia leakage related to the rate of change of catalyst temperature.

[0039] 3. Correction of ammonia leakage based on post-NOx sensor

[0040] To account for the calculation error of ammonia leakage, it is necessary to introduce the measurement value of the post-NOx sensor for correction to ensure the accuracy of the final calculated ammonia leakage. At the same time, considering the cross-sensitivity of NH3 measurements by the post-NOx sensor, it is necessary to identify and calculate the actual NH3 corresponding to the post-NOx sensor measurement value.

[0041] a) When the post-NOx sensor measurement is less than the threshold, the emissions of both NOx and NH3 are low, and the SCR is in the stage of just complete reaction. At this time, the post-NOx measurement value is considered to be the NOx concentration at the current moment.

[0042] b) When the NOx sensor measurement value is higher than a certain threshold and the ammonia coverage level is low, the SCR still has ammonia storage capacity, NH3 escape will be less, and the cross-sensitivity of NH3 to the NOx sensor will be less. At this time, the NOx sensor measurement value is considered to be the NOx concentration at the current time.

[0043] c) When the NOx sensor reading exceeds the threshold and the ammonia coverage exceeds the threshold, the SCR's internal ammonia storage capacity has reached its limit, resulting in a large escape of NH3 and near-complete NOx reaction. In this case, the NOx sensor reading is considered to represent the NH3 leakage amount. Based on the NOx sensor reading obtained at this point, the estimated NH3 leakage amount is corrected.

[0044] m NH3_slip_final =m NH3_slip +k×(NO X_measure -m NH3_slip )

[0045] The aforementioned related sensors, ammonia coverage threshold, and calculation weight correction coefficient K are derived from multiple qualitative adjustments and tunings during simulation testing and experiments.

[0046] The beneficial effects of the technical solutions provided in this application include at least the following:

[0047] By calculating ammonia leakage based on steady-state conditions, calculating ammonia leakage based on transient conditions, and correcting ammonia leakage based on post-NOx sensors, the accuracy of NH3 leakage calculation was improved through precise calibration and optimization. This enabled real-time estimation of NH3 leakage, ensured closed-loop correction control of SCR ammonia storage control, and achieved accurate control of urea injection, thereby achieving the expected emission results. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 A flowchart illustrating a method for real-time estimation of ammonia leakage at the SCR end of a diesel engine provided in an embodiment of the present invention;

[0050] Figure 2 A flowchart illustrating the calculation of ammonia leakage based on steady-state conditions in the real-time estimation method for ammonia leakage at the SCR back end of a diesel engine provided in this embodiment of the invention.

[0051] Figure 3 A flowchart illustrating the calculation of ammonia leakage based on transient operating conditions in the real-time estimation method for ammonia leakage at the SCR back end of a diesel engine provided in this embodiment of the invention.

[0052] Figure 4 A flowchart illustrating the ammonia leakage correction based on a post-NOx sensor in the real-time estimation method for ammonia leakage at the SCR end of a diesel engine provided in this embodiment of the invention. Detailed Implementation

[0053] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0054] This application provides a real-time estimation method for ammonia leakage at the SCR back end of a diesel engine. It can solve the problems in related technologies that cannot guarantee real-time closed-loop correction control of SCR ammonia storage control, cannot achieve accurate control of urea injection quantity, and cannot achieve the expected emission results.

[0055] Figure 1 This invention provides a real-time estimation method for ammonia leakage at the downstream end of a diesel engine SCR, which may include: calculating the ammonia leakage under steady-state operating conditions; calculating the ammonia leakage under transient operating conditions based on the ammonia leakage under steady-state operating conditions; and calculating the ammonia leakage under transient operating conditions and the downstream NO... XThe ammonia leakage amount is corrected by the sensor measurement value. In this embodiment, the ammonia leakage amount is calculated based on steady-state conditions, ammonia leakage amount calculated based on transient conditions, and ammonia leakage amount corrected based on the post-NOx sensor. Through precise calibration and optimization, the calculation accuracy of NH3 leakage amount is improved, real-time estimation of NH3 leakage amount is realized, closed-loop correction control of SCR ammonia storage control is guaranteed, and accurate control of urea injection amount is achieved, thereby achieving the expected emission results.

[0056] See Figure 2 As shown, in some embodiments, the method for calculating the ammonia leakage under steady-state conditions may include: when the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, calculating a first ammonia leakage based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst; when the ammonia coverage of the SCR catalyst exceeds a limit, calculating a second ammonia leakage based on the ammonia coverage of the SCR catalyst; and calculating the ammonia leakage under steady-state conditions based on the first ammonia leakage and the second ammonia leakage.

[0057] In this embodiment, NH3 leakage occurs when the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst. The first ammonia leakage amount is calculated based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst, enabling real-time calculation of ammonia leakage under steady-state conditions. Similarly, NH3 leakage also occurs when the ammonia coverage of the SCR catalyst exceeds a limit. The second ammonia leakage amount is calculated based on the ammonia coverage of the SCR catalyst, enabling real-time calculation of ammonia leakage under steady-state conditions. The total ammonia leakage amount under steady-state conditions is obtained by adding the first and second ammonia leakage amounts. By integrating factors such as the actual ammonia storage capacity inside the SCR catalyst, the maximum ammonia storage capacity of the SCR catalyst, and the ammonia coverage of the SCR catalyst during the calculation process, the accuracy of the NH3 leakage calculation is further improved, making the real-time calculation result of the NH3 leakage amount more precise.

[0058] See Figure 2 As shown, in some embodiments, the method for calculating the first ammonia leakage amount may include: calculating the actual ammonia storage amount inside the SCR catalyst based on the initial value of the NH3 storage amount and the NH3 storage rate inside the SCR catalyst; calculating the maximum ammonia storage amount of the SCR catalyst based on the maximum ammonia storage amount of the SCR catalyst, the working volume of the SCR catalyst, and the ammonia storage amount correction factor for SCR catalyst aging; and calculating the first ammonia leakage amount based on the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst.

[0059] In this embodiment, the actual ammonia storage capacity inside the SCR catalyst is related to the initial value of NH3 storage capacity and the NH3 storage rate inside the SCR catalyst. The maximum ammonia storage capacity of the SCR catalyst is related to the basic maximum ammonia storage capacity of the SCR catalyst, the working volume of the SCR catalyst, and the ammonia storage correction coefficient due to SCR catalyst aging. After calculating the actual ammonia storage capacity and the maximum ammonia storage capacity inside the SCR catalyst, when the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, the ammonia leakage is equal to the ammonia leakage within the SCR catalyst. By comprehensively considering factors such as the initial value of NH3 storage capacity, the NH3 storage rate, the basic maximum ammonia storage capacity of the SCR catalyst, the working volume of the SCR catalyst, and the ammonia storage correction coefficient due to SCR catalyst aging during the calculation process, the calculation accuracy of NH3 leakage is further improved, making the real-time calculation result of NH3 leakage more accurate.

[0060] In other embodiments, the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst can also be obtained by other means, such as by measurement, experimentation or from the product manual.

[0061] See Figure 2 As shown, in some embodiments, the method for calculating the second ammonia leakage amount may include: calculating the ammonia coverage of the SCR catalyst based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst; and calculating the second ammonia leakage amount as a function of the ammonia coverage of the SCR catalyst.

[0062] In this embodiment, only NH3 adsorbed on the SCR catalyst can react with NOx emitted from the engine. Unadsorbed and desorbed NH3 will escape, ultimately causing ammonia leakage. The amount of NH3 adsorbed by the SCR catalyst is generally expressed by its ammonia coverage ratio. A higher ammonia coverage ratio results in higher NOx conversion efficiency, but also increases ammonia leakage. The ammonia coverage ratio of the SCR catalyst is related to the actual ammonia storage capacity and the maximum ammonia storage capacity within the SCR catalyst. After calculating the ammonia coverage ratio, the linear relationship between the ammonia coverage ratio and the second ammonia leakage rate is used to calculate the real-time ammonia leakage rate under steady-state conditions when the ammonia coverage ratio exceeds the limit. By integrating factors such as the actual ammonia storage capacity and the maximum ammonia storage capacity within the SCR catalyst during the calculation process, the accuracy of the NH3 leakage calculation is further improved, making the real-time calculation result of the NH3 leakage rate more precise.

[0063] See Figure 3As shown, in some embodiments, the method for calculating the ammonia leakage under transient conditions may include: calculating the ammonia leakage under transient conditions based on the ammonia leakage under steady-state conditions, an ammonia leakage correction coefficient related to the catalyst temperature change rate, and a sampling period.

[0064] In this embodiment, the ammonia leakage change under transient conditions is mainly related to the SCR catalyst temperature; the more drastic the SCR catalyst temperature change, the greater the ammonia leakage. The ammonia leakage under transient conditions is calculated using the ammonia leakage rate under steady-state conditions, the ammonia leakage correction factor related to the catalyst temperature change rate, and the sampling period. By integrating factors such as the ammonia leakage rate, the ammonia leakage correction factor related to the catalyst temperature change rate, and the sampling period during the calculation process, the accuracy of the NH3 leakage calculation is further improved, making the real-time calculation results of the NH3 leakage more precise.

[0065] See Figure 4 As shown, in some embodiments, the method for correcting the ammonia leakage amount may include: based on the subsequent NO... X Sensor measurements are used to identify and calculate the actual amount of NH3 leakage.

[0066] In this embodiment, considering the calculation error of ammonia leakage, it is necessary to introduce the measurement value of the post-NOx sensor for correction to ensure the accuracy of the final calculated ammonia leakage. Simultaneously, considering the cross-sensitivity of NH3 measurements by the post-NOx sensor, it is necessary to identify and calculate the actual NH3 corresponding to the post-NOx sensor measurement value. Through precise calibration and optimization, the calculation accuracy of NH3 leakage is improved, enabling real-time estimation of NH3 leakage, ensuring closed-loop correction control of SCR ammonia storage control, and achieving accurate control of urea injection quantity, thereby achieving the expected emission results.

[0067] See Figure 4 As shown, in some embodiments, the step of proceeding according to the subsequent NO... X The identification and calculation of the actual NH3 leakage amount based on sensor measurements can include: when the post-NOx sensor measurement value is less than a first threshold, the post-NOx sensor measurement value is considered the NOx concentration at the current moment. In this embodiment, when the post-NOx sensor measurement value is less than the threshold, both NOx and NH3 emissions are low, and the SCR is in the stage of just-complete reaction; at this time, the post-NOx measurement value is considered the NOx concentration at the current moment. By considering the cross-sensitivity of NH3 measurements from the post-NOx sensor, further identification and calculation of the actual NH3 corresponding to the post-NOx sensor measurement value is performed, further improving the accuracy of NH3 leakage calculation.

[0068] See Figure 4 As shown, in some embodiments, the step of proceeding according to the subsequent NO... XThe identification and calculation of the actual NH3 leakage amount based on sensor measurements may include: when the post-NOx sensor measurement is greater than a first threshold, identification and calculation are performed based on the ammonia coverage level. In this embodiment, when the post-NOx sensor measurement is greater than the first threshold, identification and calculation based on the ammonia coverage level can determine whether the ammonia storage capacity inside the SCR has reached its upper limit, thereby determining whether a large amount of NH3 has escaped and whether NOx has been basically completely reacted, and thus determining the cross-sensitivity effect of NH3 on the NOx sensor.

[0069] See Figure 4 As shown, in some embodiments, the identification calculation based on the ammonia coverage level may include: when the ammonia coverage is less than a second threshold, the measured value of the post-NOx sensor is the NOx concentration at the current moment. In this embodiment, when the measured value of the post-NOx sensor is higher than the first threshold and the ammonia coverage level is low, the SCR still has ammonia storage capacity, NH3 escape will be relatively small, and the cross-sensitivity of NH3 to the NOx sensor will have less impact. In this case, the measured value of the NOx sensor is considered to be the NOx concentration at the current moment. By considering the cross-sensitivity of NH3 measurement by the post-NOx sensor, the actual NH3 corresponding to the measured value of the post-NOx sensor is further identified and calculated, which further improves the accuracy of NH3 leakage calculation.

[0070] See Figure 4 As shown, in some embodiments, the identification calculation based on the ammonia coverage level may include: when the ammonia coverage is greater than a second threshold, calculating the actual NH3 leakage based on the ammonia leakage under the transient operating condition, the post-NOx sensor measurement value, and a weighted correction coefficient. In this embodiment, when the post-NOx sensor measurement value is greater than a first threshold and the ammonia coverage is greater than a second threshold, the SCR's internal ammonia storage capacity has reached its limit, a large amount of NH3 escapes, and NOx is almost completely reacted. At this time, the NOx sensor measurement value is considered to be essentially the NH3 leakage value. Based on the post-NOx sensor measurement value obtained at this time, the estimated NH3 leakage value is corrected. Then, the actual NH3 leakage value is calculated based on the ammonia leakage under the transient operating condition, the post-NOx sensor measurement value, and the weighted correction coefficient. By taking into account the calculation error of ammonia leakage, the measurement value of the post-NOx sensor is introduced for correction, which further ensures the accuracy of the final calculated ammonia leakage. At the same time, considering the cross-sensitivity of NH3 measurement of the post-NOx sensor, the actual NH3 corresponding to the measurement value of the post-NOx sensor is further identified and calculated, which further improves the calculation accuracy of NH3 leakage, realizes real-time estimation of NH3 leakage, and ensures the closed-loop correction control of SCR ammonia storage control.

[0071] The real-time estimation method for accurately calculating the ammonia leakage at the back end of an SCR system, provided by this invention, is performed according to the following steps:

[0072] 1. Calculation of ammonia leakage under steady-state operating conditions

[0073] The ammonia leakage under steady-state operating conditions can be mainly divided into the following two parts:

[0074] 1) When the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, the ammonia leakage rate is calculated as follows:

[0075] m NH3_slip_base1 =m NH3_Store -m NH3_Capacity

[0076]

[0077] m NH3_Capacity =m NH3_Capacity_base (T)×V SCR ×f SCR_aging

[0078] in:

[0079] m NH3Int The initial value for the calculated NH3 content within the SCR catalyst;

[0080] The calculated NH3 storage rate;

[0081] m NH3_Capacity_base The maximum ammonia storage capacity is related to the temperature of the SCR catalyst. The maximum ammonia storage capacity is mainly related to the characteristics of the support, the temperature of the support, and the degree of aging of the support.

[0082] V SCR This refers to the working volume of the SCR catalyst.

[0083] f SCR_aging This is the SCR catalyst aging correction factor.

[0084] 2) Calculation of ammonia leakage when the ammonia coverage of the SCR catalyst exceeds the limit.

[0085] Only NH3 adsorbed on the SCR catalyst can react with NOx in engine emissions. Unadsorbed or desorbed NH3 will escape, ultimately causing ammonia leakage. SCR catalysts typically use ammonia coverage ratio to indicate the amount of NH3 adsorbed. A higher ammonia coverage ratio results in higher NOx conversion efficiency, but also increases ammonia leakage.

[0086]

[0087] m NH3_slip_base2 =f(θ) NH3 )

[0088] Based on the above, the steady-state ammonia leakage rate is calculated as follows:

[0089] m NH3_slip_Steady =m NH3_slip_base1 +m NH3_slip_base2

[0090] 2. Calculation of ammonia leakage under transient operating conditions

[0091] The change in ammonia leakage under transient operating conditions is mainly related to the SCR catalyst temperature. The more drastic the change in SCR catalyst temperature, the greater the ammonia leakage. The ammonia leakage under transient operating conditions is as follows:

[0092] m NH3_slip ={m NH3_slip_Steady (t)+m NH3_slip_Steady (t-1)×[1-f NH3_slip (t-1)]}×f NH3_slip (t)

[0093] Where t is the sampling period, f NH3_slip This is a correction factor for ammonia leakage related to the rate of change of catalyst temperature.

[0094] 3. Correction of ammonia leakage based on post-NOx sensor

[0095] To account for the calculation error of ammonia leakage, it is necessary to introduce the measurement value of the post-NOx sensor for correction to ensure the accuracy of the final calculated ammonia leakage. At the same time, considering the cross-sensitivity of NH3 measurements by the post-NOx sensor, it is necessary to identify and calculate the actual NH3 corresponding to the post-NOx sensor measurement value.

[0096] a) When the post-NOx sensor measurement is less than the threshold, the emissions of both NOx and NH3 are low, and the SCR is in the stage of just complete reaction. At this time, the post-NOx measurement value is considered to be the NOx concentration at the current moment.

[0097] b) When the NOx sensor measurement value is higher than a certain threshold and the ammonia coverage level is low, the SCR still has ammonia storage capacity, NH3 escape will be less, and the cross-sensitivity of NH3 to the NOx sensor will be less. At this time, the NOx sensor measurement value is considered to be the NOx concentration at the current time.

[0098] c) When the NOx sensor reading exceeds the threshold and the ammonia coverage exceeds the threshold, the SCR's internal ammonia storage capacity has reached its limit, resulting in a large escape of NH3 and near-complete NOx reaction. In this case, the NOx sensor reading is considered to represent the NH3 leakage amount. Based on the NOx sensor reading obtained at this point, the estimated NH3 leakage amount is corrected.

[0099] m NH3_slip_final =m NH3_slip +k×(NO X_measure -m NH3_slip )

[0100] The aforementioned related sensors, ammonia coverage threshold, and calculation weight correction coefficient K are derived from multiple qualitative adjustments and tunings during simulation testing and experiments.

[0101] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0102] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0103] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for real-time estimation of ammonia leakage at the downstream end of a diesel engine SCR, characterized in that, It includes: Calculate the ammonia leakage rate under steady-state conditions; Calculate the ammonia leakage rate under transient conditions based on the ammonia leakage rate under steady-state conditions. Based on the ammonia leakage and subsequent NO under the transient operating conditions X The sensor measurement value was corrected to adjust for the ammonia leakage amount; The method for calculating ammonia leakage under steady-state operating conditions includes: When the actual ammonia storage capacity inside the SCR catalyst exceeds the maximum ammonia storage capacity of the SCR catalyst, the first ammonia leakage amount is calculated based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst. When the ammonia coverage of the SCR catalyst exceeds the limit, a second ammonia leakage amount is calculated based on the ammonia coverage of the SCR catalyst. Calculate the ammonia leakage under steady-state conditions based on the first ammonia leakage rate and the second ammonia leakage rate; The method for calculating ammonia leakage under transient conditions includes: calculating ammonia leakage under transient conditions based on ammonia leakage under steady-state conditions, an ammonia leakage correction coefficient related to the catalyst temperature change rate, and a sampling period; The method for correcting the ammonia leakage includes: based on the subsequent NO... X Sensor measurements are used to identify and calculate the actual amount of NH3 leakage.

2. The real-time estimation method for ammonia leakage at the SCR downstream end of a diesel engine as described in claim 1, characterized in that, The calculation method for the first ammonia leakage amount includes: The actual ammonia storage capacity inside the SCR catalyst is calculated based on the initial value of NH3 storage capacity and the NH3 storage rate within the SCR catalyst. The maximum ammonia storage capacity of the SCR catalyst is calculated based on the maximum ammonia storage capacity of the SCR catalyst, the working volume of the SCR catalyst, and the ammonia storage capacity correction factor for SCR catalyst aging. The first ammonia leakage amount is calculated based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst.

3. The real-time estimation method for ammonia leakage at the SCR downstream end of a diesel engine as described in claim 1, characterized in that, The calculation method for the second ammonia leakage includes: The ammonia coverage of the SCR catalyst is calculated based on the actual ammonia storage capacity inside the SCR catalyst and the maximum ammonia storage capacity of the SCR catalyst. The second ammonia leakage amount is calculated as a function of the ammonia coverage of the SCR catalyst.

4. The real-time estimation method for ammonia leakage at the SCR downstream end of a diesel engine as described in claim 1, characterized in that, According to the subsequent NO X The sensor measurements are used to identify and calculate the actual NH3 leakage amount, including: When the measured value of the post-NOx sensor is less than the first threshold, the measured value of the post-NOx sensor is the NOx concentration at the current moment.

5. The real-time estimation method for ammonia leakage at the SCR downstream end of a diesel engine as described in claim 1, characterized in that, According to the subsequent NO X The sensor measurements are used to identify and calculate the actual NH3 leakage amount, including: When the measured value of the post-NOx sensor is greater than the first threshold, identification calculation is performed based on the ammonia coverage level.

6. The real-time estimation method for ammonia leakage at the SCR downstream end of a diesel engine as described in claim 5, characterized in that, The identification calculation based on ammonia coverage level includes: When the ammonia coverage is less than the second threshold, the NOx concentration measured by the post-NOx sensor is the NOx concentration at the current moment.

7. The real-time estimation method for ammonia leakage at the downstream end of a diesel engine SCR as described in claim 5, characterized in that, The identification calculation based on ammonia coverage level includes: When the ammonia coverage rate is greater than the second threshold, the measurement value of the post-NOx sensor is the NH3 leakage value at the current moment; the actual NH3 leakage is calculated based on the ammonia leakage under the transient condition, the measurement value of the post-NOx sensor, and the weight correction coefficient.

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