NOx emission supervision method and device applied to diesel engine aftertreatment system

Abstract

The invention discloses a NOx emission supervision method and device applied to a diesel engine aftertreatment system, and the method comprises the steps: S1, judging whether the operation condition of an engine is in a reasonable range or not when a urea supply module is in an activated state; s2, when it is judged that the engine runs stably, NOx at an inlet of the SCR catalytic unit is subjected to mass integration, and a set value is accumulated to be X; s3, within the set SCR inlet NOx mass integral, the NOx model conversion efficiency and the NOx actual conversion efficiency of an SCR catalytic unit outlet are calculated; s4, the difference value between the NOx model conversion efficiency and the NOx actual conversion efficiency in one integral window is compared, and the difference value is a scale value for judging whether NOx emission exceeds the limit or not; and S5, the scale value is compared with a preset threshold value, and whether NOx release exceeds the limit value fault or not is judged. According to the method, whether the NOx pollutant level in the tail gas exceeds the limit or not is clearly judged, and whether the NOx emission exceeds the limit or not is accurately judged.

Description

Technical Field

[0002] The present invention relates to the technical field of engine exhaust gas treatment, and in particular to a method and device for NOx emission supervision applied to a diesel engine aftertreatment system. Background Art

[0003] For the off-engine emission reduction technology of internal combustion engines, the aftertreatment technology route for national VI diesel vehicles is mainly DOC+DPF+SCR+ASC. For this set of technology routes, the NOx emission reduction method is to spray the accurately metered urea into the aftertreatment catalyst through a urea supply pump. The urea is hydrolyzed into ammonia and water in the high-temperature exhaust gas. Under the action of the SCR catalyst, ammonia and NOx in the exhaust gas undergo a catalytic reaction to generate harmless nitrogen gas, which is discharged outside the engine to achieve the purpose of reducing NOx emissions.

[0004] According to Appendix F of the national regulation "Limits and Measurement Methods for Pollutant Emissions from Heavy-Duty Diesel Vehicles (China Phase VI)" GB17691-2018, for the vehicle diagnosis system (OBD), when the estimated concentration of Nox pollutants in the exhaust gas exceeds the OTLs limit value, a NOx overlimit fault is released, the fault light on the driver's instrument is lit, and through the induction system, the driver is prompted to perform maintenance.

[0005] Chinese Patent with Application No. 202510044670.1 discloses a diesel engine aftertreatment system based on a urea compensation strategy. It collects the NOx concentration to obtain a collected value, and adjusts the urea injection amount through this collected value, thereby adjusting the efficiency deviation of each component, and correcting the NOx emission pollutants by compensating the urea injection amount. This patent aims at the situation when the SCR system deteriorates and causes the NOx emission to become worse. The system corrects the NOx emission by self-checking means to supplement or reduce the urea injection, so that it is always controlled at a good level. However, for the problem of "worse NOx emission" in this patent, there is a situation where the NOx emission concentration does not exceed the limit value specified by the regulations, and this situation is not clearly described. Summary of the Invention

[0006] The present invention provides a method and device for NOx emission supervision applied to a diesel engine aftertreatment system that can clearly detect the determination of NOx overlimit faults, and can solve at least one of the above technical problems.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions: A method for NOx emission supervision applied to a diesel engine aftertreatment system includes the following steps: S1. When the urea supply module is in an active state, judge whether the engine operating condition is within a reasonable range based on the inlet temperature of the SCR catalytic unit; S2. When the engine is running stably, perform mass integration on the NOx at the inlet of the SCR catalytic unit based on the inlet exhaust gas NOx mass integration mechanism, and accumulate the set value to X; S3. Within the set SCR inlet NOx mass integration, calculate the NOx model conversion efficiency and the actual NOx conversion efficiency at the outlet of the SCR catalytic unit based on the NOx acquisition values at the inlet and outlet of the SCR unit and the SCR catalyst chemical kinetics model algorithm; S4. Compare the difference between the NOx model conversion efficiency and the actual NOx conversion efficiency within an integration window, and this difference is the criterion for judging whether the NOx emission exceeds the limit; S5. Compare the criterion value with the preset threshold value to judge whether to release the NOx over-limit fault; S6. When the SCR inlet NOx mass integration meets the accumulated set value X, reset it to 0 and start accumulating again, and perform cyclic operation supervision during the engine operation stage.

[0008] Furthermore, it is implemented based on the NOx emission supervision system applied to the diesel engine after-treatment system. The NOx emission supervision system includes an ECU control module, a urea supply module, and an exhaust gas after-treatment module; The ECU control module is used to calculate and supervise the NOx pollutants in the exhaust gas, including the engine ECU, the engine, and the CPU chip; The urea supply module is used to input NH 3 into the exhaust gas, and it includes a urea nozzle and a urea supply pump; The exhaust gas after-treatment module is used to sample and collect the NOx pollutants in the exhaust gas, and it includes an SCR inlet NOx sensor, an SCR inlet temperature sensor, an SCR catalytic unit, an SCR outlet NOx sensor, and an exhaust manifold.

[0009] Furthermore, the engine outputs engine exhaust gas, which is diverted to the exhaust gas after-treatment module through the exhaust manifold and flows through the SCR catalytic unit and then is discharged outside the engine; The SCR inlet temperature sensor is installed before the intake direction of the SCR catalytic unit, and is used to sample the exhaust gas temperature in real time, judge whether the engine is running in a stable working condition of medium to high load, and feedback the sampled temperature signal to the ECU control module; The SCR inlet NOx sensor is installed on the exhaust manifold at the front end of the intake direction of the exhaust gas after-treatment module, and is used to sample the NOx concentration value in the most original exhaust gas discharged by the engine, and feedback the sampled concentration signal to the ECU control module; The SCR outlet NOx sensor is installed on the tail pipe at the end of the intake direction of the exhaust gas after-treatment module, and is used to sample the NOx concentration value in the exhaust gas after being converted by the SCR catalytic unit, and feedback the sampled concentration signal to the ECU control module; The SCR catalytic unit is used to catalyze the reaction between the ammonia formed by the hydrolysis of urea and the NOx in the exhaust gas to generate harmless nitrogen gas and discharge it outside the engine.

[0010] Further, the CPU chip is built into the engine ECU, integrated with preset program codes, and is used to implement the supervision, operation and control of signals. The engine ECU is connected to the engine and is used to obtain the signals or data of multiple sensors during the operation of the engine.

[0011] Further, the urea nozzle is installed on the mounting hole before the intake direction of the SCR catalytic unit, and is connected to the urea supply pump through a urea pipeline, and is used to inject the urea aqueous solution obtained by the analysis and calculation of the ECU control module into the SCR catalytic unit.

[0012] Further, in step S3, the NOx model conversion efficiency is calculated by the SCR inlet NOx sensor and the SCR physicochemical kinetic model, and the calculation formula is: (SCR inlet NOx sampling concentration - SCR outlet NOx model predicted concentration) / SCR inlet NOx sampling concentration; The NOx actual conversion efficiency is directly sampled and calculated by the SCR inlet NOx sensor and the SCR outlet NOx sensor, and the calculation formula is: (SCR inlet NOx sampling concentration - SCR outlet NOx sampling concentration) / SCR inlet NOx sampling concentration.

[0013] Further, in step S4, within an integration window, the calculation of the NOx actual conversion efficiency by the SCR catalytic unit is converted to: inlet NOx emission mass / outlet NOx emission mass, and the calculation of the NOx model conversion efficiency by the SCR catalytic unit is converted to: inlet NOx emission mass / outlet NOx model mass.

[0014] Further, in step S5, if the marked value is less than the threshold value, it is evaluated that the outlet NOx pollutant concentration is less than the regulatory limit range at this time, and the NOx over-limit fault is not released; If the marked value is greater than the threshold value, it is evaluated that the outlet NOx pollutant concentration is greater than the regulatory limit range at this time, and the NOx over-limit fault is released.

[0015] Further, in step S5, the setting of the threshold value is determined according to the bench test cycle.

[0016] The computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the above-mentioned NOx emission regulation method applied to a diesel engine aftertreatment system.

[0017] The beneficial effects of the present invention are embodied in: The present invention provides a method that does not require additional components and only relies on components such as the NOx sensor provided in the after-treatment system, and in combination with the monitoring model programmed by the present invention, can achieve the purpose of regulating NOx pollutants in tail emissions, clearly judge whether the NOx pollutant level in the after-treatment outlet tail gas exceeds the limit, and then can accurately judge whether the NOx emission limit exceeding fault is released, effectively solving the problem in the prior art that it is impossible to clearly determine whether the NOx emission concentration in the tail gas exceeds the limit prescribed by regulations. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0019] Figure 1 It is a schematic diagram of the overall process of the NOx emission control method according to an embodiment of the present invention.

[0020] Figure 2 It is a specific flow chart of the NOx emission control method according to an embodiment of the present invention.

[0021] Figure 3 Schematic diagram of a NOx emission monitoring system according to an embodiment of the present invention.

[0022] Figure 4 It is a diagram showing the MATLAB Simulink logic code framework of an embodiment of the present invention.

[0023] Figure 5 It is a structural block diagram of a computer device according to an embodiment of the present invention.

[0024] The components in the attached figure are marked as follows: 1. Engine ECU; 2. Engine; 3. SCR inlet NOx sensor; 4. Urea nozzle; 5. SCR inlet temperature sensor; 6. SCR catalytic unit; 7. SCR outlet NOx sensor; 8. CPU chip; 9. Urea supply pump; 10. Exhaust branch pipe. DETAILED DESCRIPTION

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0026] It should be noted that the meaning of "and / or" appearing throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, or solution B, or the solution where A and B are satisfied simultaneously. In addition, "a plurality" means two or more. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0027] See Figure 1 - Figure 2 , the embodiments of the present invention provide a NOx emission supervision method and device applied to a diesel engine after-treatment system, including the following steps: S1. When the urea supply module is in an active state, determine whether the engine operating condition is within a reasonable range based on the inlet temperature of the SCR catalytic unit; S2. When it is determined that the engine is in a stable operating state, perform mass integration on the NOx at the inlet of the SCR catalytic unit based on the inlet exhaust gas NOx mass integration mechanism, and accumulate a set value of X, generally set to 15 g; S3. Within the set SCR inlet NOx mass integration, calculate the NOx model conversion efficiency and the NOx actual conversion efficiency at the outlet of the SCR catalytic unit based on the NOx acquisition values at the inlet and outlet of the SCR unit and the SCR catalyst chemical kinetic model algorithm; S4. Compare the difference between the NOx model conversion efficiency and the NOx actual conversion efficiency within an integration window, and this difference is the criterion value for judging whether the NOx emission exceeds the limit; S5. Compare the criterion value with a preset threshold value to judge whether to release the NOx over-limit value fault; S6. When the SCR inlet NOx mass integration satisfies the cumulative set value X, reset it to 0 and accumulate again, and perform cyclic operation supervision during the engine operation stage.

[0028] See Figure 3 , in this embodiment, it is implemented based on a NOx emission supervision system applied to a diesel engine after-treatment system, and the NOx emission supervision system includes an ECU control module, a urea supply module, and an exhaust gas after-treatment module; The ECU control module is used to calculate and monitor NOx pollutants in the exhaust gas, including the engine ECU1, engine 2, and CPU chip 8; The urea supply module is used for the direct source of NH 3 in the exhaust gas, including the urea nozzle 4 and the urea supply pump 9. The accurately metered urea is sprayed into the post-treatment catalyst through the urea supply pump 9 and the urea nozzle 4. The urea is hydrolyzed into ammonia and water in the high-temperature exhaust gas. Under the action of the SCR catalyst, ammonia and NOx in the exhaust gas undergo a catalytic reaction to generate harmless nitrogen, which is discharged outside the engine to achieve the purpose of reducing NOx emissions; The exhaust gas post-treatment module is used to sample and collect NOx pollutants in the exhaust gas, including the SCR inlet NOx sensor 3, the SCR inlet temperature sensor 5, the SCR catalytic unit 6, the SCR outlet NOx sensor 7, and the exhaust manifold 10.

[0029] See Figure 3 , in this embodiment, the engine 2 outputs engine exhaust gas, which is diverted to the exhaust gas post-treatment module through the exhaust manifold 10 and flows through the SCR catalytic unit 6 and is discharged outside the engine; The SCR inlet temperature sensor 5 is installed before the intake direction of the SCR catalytic unit 6 and is used to sample the exhaust gas temperature in real time, determine whether the engine 2 is operating in a stable condition of medium to high load, and feedback the sampled temperature signal to the ECU control module; According to regulatory requirements, NOx monitoring must be real-time. As long as the urea supply module is in the activated state and the feedback of the inlet temperature acquisition value of the SCR catalytic unit 6 exceeds 220 degrees Celsius, it is necessary to run the monitoring strategy; It must be explained here that due to the physical limitations of the SCR catalyst itself at low temperatures, when the inlet temperature of the SCR catalytic unit 6 is less than 220 degrees Celsius, the conversion efficiency is not high, the chemical molecular activity is not strong, and the fluctuations are large. The calculated results are not robust. Therefore, the calculated results in this stage are not credible. In order to make the estimated NOx in the exhaust gas by this monitoring strategy reasonable and credible, this working condition must be deliberately excluded; The SCR inlet NOx sensor 3 is installed on the exhaust manifold 10 at the front end of the intake direction of the exhaust gas post-treatment module and is used to sample the NOx concentration value in the most original exhaust gas discharged by the engine 2. The sampling unit is ppm, and the sampled concentration signal is feedback to the ECU control module. It can be used for the calculation of urea demand and can also be used as the actual sampled value of the NOx actual conversion efficiency and the NOx actual conversion efficiency; The SCR outlet NOx sensor 7 is installed on the tail pipe at the end of the intake direction of the exhaust gas after-treatment module, and is used to sample the NOx concentration value in the exhaust gas after being converted by the SCR catalytic unit 6. The sampling unit is ppm, and the sampled concentration signal is fed back to the ECU control module. In this method, this sensor undertakes an important feedback control function, and its feedback value ultimately affects the estimation of the outlet NOx level; The SCR catalytic unit 6 is used to catalyze the reaction between the ammonia formed by the hydrolysis of urea and the NOx in the exhaust gas to generate harmless nitrogen gas and discharge it outside the engine.

[0030] See Figure 3 - Figure 4 , in this embodiment, the CPU chip 8 is built into the engine ECU1, integrated with preset program codes, and is used to implement the supervision, operation and control of signals. The engine ECU1 is connected to the engine 2 and is used to obtain the signals or data of multiple sensors during the operation of the engine 2.

[0031] See Figure 3 , in this embodiment, the urea nozzle 4 is installed on the mounting hole before the intake direction of the SCR catalytic unit 6, and is connected to the urea supply pump 9 through a urea pipeline, and is used to inject the urea aqueous solution obtained by the analysis and calculation of the ECU control module into the SCR catalytic unit 6.

[0032] See Figure 2 - Figure 3 , in this embodiment, in S3, the NOx model conversion efficiency is calculated by the SCR inlet NOx sensor 3 and the SCR physical and chemical kinetic model. The calculation formula is: (SCR inlet NOx sampling concentration - SCR outlet NOx model predicted concentration) / SCR inlet NOx sampling concentration; The NOx actual conversion efficiency is directly sampled and calculated by the SCR inlet NOx sensor 3 and the SCR outlet NOx sensor 7. The calculation formula is: (SCR inlet NOx sampling concentration - SCR outlet NOx sampling concentration) / SCR inlet NOx sampling concentration.

[0033] NOx model conversion efficiency: According to the SCR chemical kinetic reaction principle and the molar ratio of NH 3 to the NOx reaction, this value should conform to the initial feedforward calibration trend of the project, and theoretically exceed 95%.

[0034] NOx actual conversion efficiency: According to factors such as the deterioration state of each component, injection accuracy, and SCR catalyst aging, this value intuitively shows the current NOx pollutant level in the exhaust gas.

[0035] See Figure 2 - Figure 3, in this embodiment, in S4, within an integration window, the actual NOx conversion efficiency calculation of the SCR catalytic unit 6 is transformed into: inlet NOx emission mass / outlet NOx emission mass, and the model NOx conversion efficiency calculation of the SCR catalytic unit 6 is transformed into: inlet NOx emission mass / outlet NOx model mass.

[0036] When the set inlet NOx mass integration is satisfied, the difference between the calculated model NOx conversion efficiency and the actual NOx conversion efficiency is the regulated value of this method.

[0037] See Figure 2 - Figure 3 , in this embodiment, in S5, if the regulated value is less than the threshold value, it is evaluated that the outlet NOx pollutant concentration is less than the regulatory limit range at this time, and the NOx overlimit fault is not released; If the regulated value is greater than the threshold value, it is evaluated that the outlet NOx pollutant concentration is greater than the regulatory limit range at this time, and the NOx overlimit fault is released.

[0038] See Figure 2 - Figure 3 , in this embodiment, in S5, the setting of the threshold value is determined according to the bench test cycle. The setting of the threshold value is the benchmark of this regulatory method. According to engineering experience, the answer can be found in the bench test cycle. Replace the normal SCR test piece with a deteriorated SCR catalyst, run the WHTC test cycle, check that the final result of the WHTC is about 1000 mg / Kwh, which is less than the regulatory limit of 1200 mg / Kwh, record the difference between the model NOx conversion efficiency and the actual NOx conversion efficiency within this cycle, and fill in the threshold value.

[0039] The embodiment of the present invention also provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, the processor is caused to execute the steps of the above-mentioned NOx emission regulation method applied to a diesel engine aftertreatment system.

[0040] See Figure 5 , the embodiment of the present invention also provides a computer device including a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor is caused to execute the steps of the above-mentioned NOx emission regulation method applied to a diesel engine aftertreatment system.

[0041] The embodiment of the present invention also provides a computer program product containing instructions, and when it runs on a computer, the computer is caused to execute the steps of the above-mentioned NOx emission regulation method applied to a diesel engine aftertreatment system.

[0042] It is understandable that the system, device and storage medium provided in the embodiments of the present invention correspond to the method provided in the embodiments of the present invention, and the explanation, examples and beneficial effects of the relevant contents can refer to the corresponding parts of the above-mentioned NOx emission control method applied to the diesel engine aftertreatment system.

[0043] It should be noted that those skilled in the art can understand that all or part of the steps implemented in the embodiments of the present invention can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using hardware, it can be implemented in whole or in part in the form of purchased standard parts or modified parts. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website, computer, server or data center to another website, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.). The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a DVD), or a semiconductor medium (eg, a solid state disk (SSD)).

[0044] In summary, in view of the situation in the prior art where it is impossible to clearly determine whether the NOx emission concentration in the exhaust gas exceeds the limit prescribed by regulations, the present invention provides a method that does not require additional components and only relies on the NOx sensor and other components of the after-treatment system, and is combined with the monitoring model programmed by the present invention to achieve the purpose of regulating NOx pollutants in the exhaust, clearly determine whether the NOx pollutant level in the exhaust gas at the after-treatment outlet exceeds the limit, and further accurately determine whether the NOx emission limit exceeding fault is released.

[0045] It should be understood that the examples and implementation modes described herein are for illustrative purposes only and are not intended to limit the present invention. Those skilled in the art may make various modifications or changes based on the examples and implementation modes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A NOx emission control method for a diesel engine aftertreatment system, characterized in that: The following steps are involved: S1: The urea supply module is in an activated state, and the engine operating condition is judged whether it is within a reasonable range based on the inlet temperature of the SCR catalytic unit; S2. Determine that the engine is in a stable operating state, perform mass integration of NOx at the inlet of the SCR catalytic unit based on the inlet exhaust NOx mass integration mechanism, and set the cumulative value to X; S3. Calculate the NOx model conversion efficiency and the actual NOx conversion efficiency at the outlet of the SCR catalytic unit based on the NOx collection value at the inlet / outlet of the SCR unit and the SCR catalyst chemical kinetic model algorithm within the set SCR inlet NOx mass integral; S4, comparing the difference between the NOx model conversion efficiency and the NOx actual conversion efficiency within an integral window, the difference being a standard value for determining whether NOx emissions exceed the limit; S5, comparing the marked value with the preset threshold value to determine whether a NOx over-limit fault is released; S6. When the SCR inlet NOx mass integral meets the cumulative set value X, it is reset to 0 and accumulated again, and the supervision is cyclically calculated during the engine operation stage.

2. The NOx emission monitoring method for a diesel engine aftertreatment system according to claim 1, characterized in that: The NOx emission monitoring system is implemented based on the NOx emission monitoring system applied to the diesel engine after-treatment system, and the NOx emission monitoring system includes an ECU control module, a urea supply module and an exhaust gas after-treatment module; The ECU control module is used for calculating and monitoring NOx pollutants in exhaust gas, and comprises an engine ECU (1), an engine (2) and a CPU chip (8); The urea supply module is used as a direct source of NH3 input into the exhaust gas, and comprises a urea nozzle (4) and a urea supply pump (9); The exhaust gas post-treatment module is used to sample and collect NOx pollutants in the exhaust gas, and comprises an SCR inlet NOx sensor (3), an SCR inlet temperature sensor (5), an SCR catalytic unit (6), an SCR outlet NOx sensor (7) and an exhaust branch pipe (10).

3. The NOx emission monitoring method applied to a diesel engine aftertreatment system as claimed in claim 2, characterized in that: The engine (2) outputs engine exhaust gas, which is directed to the exhaust gas post-processing module through the exhaust branch pipe (10), and flows through the SCR catalytic unit (6) to be discharged outside the engine; The SCR inlet temperature sensor (5) is installed in front of the air intake direction of the SCR catalytic unit (6) and is used to sample the exhaust gas temperature in real time, determine whether the engine (2) is running in a stable working state with medium or high load, and feed back the sampled temperature signal to the ECU control module; The SCR inlet NOx sensor (3) is mounted on the exhaust branch pipe (10) located at the front end of the exhaust post-treatment module in the air intake direction, and is used to sample the NOx concentration value in the original exhaust gas discharged by the engine (2), and feed back the sampled concentration signal to the ECU control module; The SCR outlet NOx sensor (7) is mounted on the tail pipe at the end of the exhaust gas after-treatment module in the air intake direction, and is used to sample the NOx concentration value in the exhaust gas after conversion by the SCR catalytic unit (6), and feed back the sampled concentration signal to the ECU control module; The SCR catalytic unit (6) is used to catalyze ammonia formed by hydrolysis of urea and NOx in the exhaust gas to generate harmless nitrogen and discharge it outside the engine.

4. The NOx emission monitoring method for a diesel engine aftertreatment system according to claim 2, characterized in that: The CPU chip (8) is built into the engine ECU (1) and is integrated with a preset program code for realizing the supervision, operation and control of signals. The engine ECU (1) is connected to the engine (2) and is used to obtain signals or data from multiple sensors during the operation phase of the engine (2).

5. The NOx emission monitoring method applied to a diesel engine aftertreatment system as claimed in claim 2, characterized in that: The urea nozzle (4) is mounted on a mounting hole located in front of the air intake direction of the SCR catalytic unit (6), and is connected to the urea supply pump (9) via a urea pipeline, and is used to inject the urea aqueous solution obtained by analysis and calculation by the ECU control module into the SCR catalytic unit (6).

6. The NOx emission monitoring method applied to a diesel engine aftertreatment system as claimed in claim 2, characterized in that: In S3, the NOx model conversion efficiency is calculated by the SCR inlet NOx sensor (3) and the SCR physical and chemical dynamic model, and the calculation formula is: (SCR inlet NOx sampling concentration - SCR outlet NOx model predicted concentration) / SCR inlet NOx sampling concentration; The actual NOx conversion efficiency is calculated by directly sampling the SCR inlet NOx sensor (3) and the SCR outlet NOx sensor (7), and the calculation formula is: (SCR inlet NOx sampling concentration - SCR outlet NOx sampling concentration) / SCR inlet NOx sampling concentration.

7. The NOx emission control method for a diesel engine aftertreatment system as claimed in claim 2, characterized in that: In S4, within an integral window, the actual NOx conversion efficiency calculated by the SCR catalytic unit (6) is converted into: inlet NOx emission mass / outlet NOx emission mass, and the NOx model conversion efficiency calculated by the SCR catalytic unit (6) is converted into: inlet NOx emission mass / outlet NOx model mass.

8. The NOx emission monitoring method applied to a diesel engine aftertreatment system as claimed in claim 1, characterized in that: In S5, if the standard value is less than the threshold value, it is evaluated that the NOx pollutant concentration at the outlet is less than the regulatory limit range, and the NOx over-limit fault is not released; If the standard value is greater than the threshold value, it is assessed that the outlet NOx pollutant concentration at this time is greater than the regulatory limit range, and the NOx limit fault is released.

9. The NOx emission monitoring method applied to a diesel engine aftertreatment system as claimed in claim 1, characterized in that: In S5, the setting of the threshold is determined according to a bench test cycle.

10. A computer device, characterized in that It comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the NOx emission control method applied to a diesel engine aftertreatment system as claimed in any one of claims 1 to 9.

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