Diesel engine aftertreatment system based on urea difference compensation strategy

Abstract

The invention discloses a diesel engine post-processing system based on a urea difference compensation strategy. The diesel engine post-processing system comprises a control ECU. The urea supply system is used for spraying urea with preset metering into the post-treatment catalyst through a urea nozzle by virtue of a urea supply pump; a first NOx sensor; the NOx sensor is installed at an SCR preceding stage inlet and used for collecting the original NOx concentration in tail gas output by an engine and feeding back the original NOx concentration to the control ECU; the second NOx sensor is mounted at an SCR post-stage outlet and is used for performing feedback monitoring on SCR post-treatment; the control ECU can regulate and control the urea spraying amount according to collection values of the first NOx sensor and the second NOx sensor. The NOx concentration is collected through the first NOx sensor and the second NOx sensor to obtain the collection value, and the urea spraying amount is regulated and controlled through the collection value. Therefore, the efficiency deviation of each part is adjusted, NOx emission pollutants are corrected in a mode of supplementing the urea injection amount, and the accuracy and stability of NOx and NH3 emission control of the SCR system are improved.

Description

[0001] A diesel engine aftertreatment system based on urea supplementation strategy Technical Field

[0002] The invention relates to a diesel engine aftertreatment system based on a urea compensation strategy. Background Art

[0003] Since the Industrial Revolution, environmental degradation has become one of the important factors restricting the speed of human development. As the control of pollutants emitted by internal combustion engines has been widely discussed and studied, the post-treatment technology route of National VI diesel vehicles is mainly DOC+DPF+SCR+ASC.

[0004] This technical route reduces NOx emissions by using a urea supply pump to spray precisely measured urea into the post-treatment catalyst through a urea nozzle. 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 out of the engine, achieving the purpose of reducing NOx emissions.

[0005] The calculation of the necessary NH3 injection amount of the diesel engine SCR system will be affected by system control errors and deviations, such as fluctuations in the original engine emissions, instability of the urea injection system, and deviations between the actual value and the calculated value controlled by the feedback control system, defects in the urea metering calibration strategy and irregular parameter settings, aging of related physical components, and a decrease in the capacity of the SCR catalyst itself. These factors will cause the accuracy and stability of the SCR system's NOx and NH3 emission control to deteriorate, resulting in weak robustness of NOx pollutants in tail emissions, and the inability to effectively control NOx pollutants within the limits required by regulations. Summary of the invention

[0006] The main purpose of the present invention is to provide a diesel engine aftertreatment system based on a urea make-up strategy, aiming to solve the above technical problems.

[0007] To achieve the above object, the present invention proposes a diesel engine aftertreatment system based on a urea compensation strategy, comprising: Control ECU; A urea supply system, wherein the urea supply system sprays a preset amount of urea into the post-treatment catalyst through a urea nozzle via a urea supply pump; The SCR inlet temperature sensor is installed at the SCR front-stage inlet to collect the real-time temperature of the SCR front inlet and feed the collected temperature information back to the control ECU; The first NOx sensor is installed at the inlet of the SCR front stage, which is used to collect the original NOx concentration in the exhaust gas output by the engine and feed it back to the control ECU; The second NOx sensor is installed at the outlet of the SCR post-stage and is used for feedback monitoring of the SCR post-treatment; The control ECU can adjust the urea injection amount according to the collected values ​​of the first NOx sensor and the second NOx sensor.

[0008] In one embodiment, when the engine is running and the temperature information collected by the SCR inlet temperature sensor reaches a certain preset value, the urea supply system is activated so that the urea supply system sprays a preset amount of urea into the post-treatment catalyst through the urea nozzle.

[0009] In one embodiment, the actual NOx conversion efficiency under the engine operating condition is calculated by feedback of the collected value of the second NOx sensor installed in the exhaust gas at the outlet of the SCR catalyst and the collected value of the first NOx sensor at the inlet of the SCR.

[0010] In one embodiment, when the ratio of the collected value collected by the first NOx sensor to the collected value of the second NOx sensor exceeds a preset threshold, the self-learning strategy is started through the self-learning model; First, stop the injection of NH3 to clear the adsorption of NH3 in the SCR catalyst; When both the model efficiency and the actual efficiency drop to the threshold, switch to a fixed ammonia nitrogen ratio of 0.7 for injection.

[0011] In one embodiment, when the efficiency calculated by the model and the actual efficiency fed back by the downstream NOx sensor are stable for a preset time; The model efficiency integral and the actual efficiency integral are calculated separately during the stable time; When the integral of the fixed value injection meets the requirements, calculate the deviation between the two; The urea injection is regulated according to the deviation between the model efficiency integral and the actual efficiency integral.

[0012] In one embodiment, the step of controlling the urea injection according to the deviation between the model efficiency integral and the actual efficiency integral is specifically as follows: The actual efficiency integral is greater than the model efficiency integral. Through the normalized curve, the proportional factor is calculated by self-learning to be a value less than 1, which is fed back to the feedforward urea-ammonia-nitrogen ratio to achieve urea injection reduction.

[0013] In one embodiment, the step of controlling the urea injection according to the deviation between the model efficiency integral and the actual efficiency integral is specifically as follows: The actual efficiency integral is less than the model efficiency integral. Through the normalized curve, the proportional factor is calculated by self-learning to be a value greater than 1, which is fed back to the feedforward urea-ammonia-nitrogen ratio to achieve urea injection.

[0014] In the technical solution of the present invention, the diesel engine aftertreatment system based on the urea compensation strategy includes: Control ECU; A urea supply system, wherein the urea supply system sprays a preset amount of urea into the post-treatment catalyst through a urea nozzle via a urea supply pump; The SCR inlet temperature sensor is installed at the SCR front-stage inlet to collect the real-time temperature of the SCR front inlet and feed the collected temperature information back to the control ECU; The first NOx sensor is installed at the inlet of the SCR front stage, which is used to collect the original NOx concentration in the exhaust gas output by the engine and feed it back to the control ECU; The second NOx sensor is installed at the outlet of the SCR post-stage and is used for feedback monitoring of the SCR post-treatment; The control ECU can adjust the urea injection amount according to the collected values ​​of the first NOx sensor and the second NOx sensor.

[0015] In the present application, the NOx concentration is collected by the first NOx sensor and the second NOx sensor to obtain a collection value, and the urea injection amount is regulated by the collection value, so as to adjust the efficiency deviation of each component, correct the NOx emission pollutants by compensating the urea injection amount, and improve the accuracy and stability of the NOx and NH3 emission control of the SCR system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0017] Figure 1 It is a structural schematic diagram of a diesel engine aftertreatment system based on a urea compensation strategy according to an embodiment of the present invention; Figure 2 A schematic diagram briefly illustrating the software logic in the present invention; Figure 3 This is a schematic diagram showing the data of the test process in the present invention; Figure 4 The schematic diagram shows the MATLAB Simulink logic code framework in the present invention.

[0018] Description of the accompanying drawings: 01. Control EUC; 02. Engine; 03. First NOx sensor; 04. Urea nozzle; 05. SCR inlet temperature sensor; 06. SCR catalyst; 07. Second NOx sensor; 09. Urea supply pump; 10. Exhaust branch pipe; 11. Urea post-treatment system.

[0019] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0022] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0023] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0024] Please refer to Figure 1-4 The present invention provides a diesel engine aftertreatment system based on a urea compensation strategy, comprising: Urea supply system: It is the direct source of NH3 in the exhaust gas. The urea supply pump sprays the precisely measured urea into the post-treatment catalyst through the urea nozzle. The urea is hydrolyzed into ammonia and water in the high-temperature exhaust gas. Under the action of the SCR catalyst, the ammonia and NOx in the exhaust gas undergo a catalytic reaction to generate harmless nitrogen, which is discharged out of the engine to achieve the purpose of reducing NOx emissions.

[0025] SCR inlet temperature sensor: Installed at the SCR front inlet, used to collect real-time SCR front inlet temperature and feed back the collected temperature information to the ECU control strategy The first NOx sensor: installed at the entrance of the SCR pre-stage, used to collect the original NOx concentration in the exhaust gas output by the engine. Feedback to the control system ECU can be used for the calculation of urea demand and the reset control of the closed-loop feedback system.

[0026] The second NOx sensor: installed at the outlet of the SCR rear stage, used for feedback monitoring of the SCR post-treatment. If the ratio of NOx pollutants to the model is too large, the self-learning monitoring strategy is activated. In the strategy, the sensor assumes an important feedback control function, which ultimately affects the self-learning operation results of the post-treatment system.

[0027] Urea nozzle: responsible for injecting the urea aqueous solution calculated by ECU into the exhaust after-treatment system.

[0028] like Figure 1 As shown, the exhaust gas output by the engine is guided to the after-treatment system through the exhaust branch pipe, and finally the exhaust gas flows through the SCR catalyst and is discharged outside the engine.

[0029] When the engine is running at medium to high load and under relatively stable working conditions, the SCR inlet temperature sensor is installed in front of the SCR catalyst to sample the exhaust gas. When the sampling temperature exceeds, the urea supply pump can work and provide a higher and more stable efficiency range, generally exceeding 250 degrees Celsius.

[0030] The urea nozzle is installed on the special mounting hole in front of the SCR catalyst, connected by the urea pipeline and the urea supply pump, and is responsible for injecting the urea aqueous solution calculated by the ECU into the exhaust after-treatment system.

[0031] The first NOx sensor is installed on the exhaust branch pipe at the front end of the exhaust aftertreatment system. It is responsible for sampling the original NOx concentration value in the engine exhaust gas in ppm.

[0032] The second NOx sensor is installed on the tail pipe at the rear end of the exhaust after-treatment system. It is responsible for sampling the NOx value in the exhaust gas after conversion by the SCR catalyst. The sampling unit is PPM.

[0033] The program code files required by this patent design are stored in the ECU main control unit CPU, and the following function operations are performed on each signal.

[0034] The actual NOx efficiency is calculated by directly sampling the first NOx sensor and the second NOx sensor. The formula is (first NOx sensor - second NOx sensor) / first NOx sensor. Figure 1 As shown in the reference number 11.

[0035] The NOx model efficiency is calculated by the first NOx sensor and the SCR outlet model concentration calculated by the SCR physical and chemical dynamic model. The formula is (first NOx sensor-second NOx model concentration) / SCR inlet NOx sensor, such as Figure 1 As shown in the reference number 12.

[0036] When the prerequisite engine running time timer or NH3 injection amount reaches the set value, the model efficiency and actual efficiency exceed 95% according to the engine operating conditions at this time, and the self-learning function begins to intervene.

[0037] After the self-learning function of the post-treatment system is activated, the urea injection function will be stopped first. As the adsorbed NH3 in the SCR catalyst is cleared and the amount of NH3 adsorbed decreases, the model efficiency and the actual efficiency will begin to decrease. The decline rates of the two values ​​may be inconsistent. This is caused by inaccurate calculation of NH3 adsorbed in the SCR catalyst. When both efficiency values ​​drop to the set drop threshold of 70%, an AND gate circuit is designed in the logic circuit.

[0038] The program code of this strategy is integrated into the CPU of the engine ECU control chip, and the calculation process of the self-learning urea compensation strategy for NOx in exhaust gas is as follows: Trigger NH3 detection strategy software function enable: ScrAdpMgr_enaNh3AdapFct_C& ScrAdpMgr_enaSpecAdv_C (the name of the calibration quantity programmed in this strategy) is calibrated to 1, and the strategy module is activated for use.

[0039] In order to prevent the self-learning function from being triggered multiple times in a short period of time, two preconditions are designed and exist in the logic in the form of an OR gate.

[0040] When ScrAdpMgr_enaTiSpecAdvReq_C is 1, the self-learning request function based on the engine running time is activated. As long as the engine is not idling and the SCR system is operating normally, the self-learning trigger timer starts running. According to the vehicle application and system layout, based on the experience of field tests, the time is in hours, such as 20h. This value is stored in the EEP every time the power is turned off, and is extracted during the initialization process of each power-on to continue timing.

[0041] When ScrAdpMgr_enaMNh3SpecAdvReq_C is 1, the self-learning request function based on the cumulative NH3 injection amount is activated. The relevant path is consistent with the engine running time. The ECU will accumulate and calculate the amount of injected urea and store it. When the value exceeds the threshold value, such as 2kg, the self-learning function can be triggered.

[0042] After the self-learning enabling condition is triggered and allowed to be activated, the engine runs to medium and high loads, when the SCR inlet temperature collection value feedback exceeds 250 degrees Celsius.

[0043] The urea supply system is activated and begins to inject precisely measured urea aqueous solution into the exhaust gas to reduce NOx emissions.

[0044] The feedback value collected by the NOx sensor installed in the exhaust gas at the outlet of the SCR catalyst can be compared with the value collected by the NOx sensor at the inlet of the SCR to calculate the actual NOx conversion efficiency under the engine operating conditions at this time.

[0045] The ECU software can deduce the ideal NOx model conversion efficiency under the current engine operating conditions through the SCR catalyst physical model algorithm strategy.

[0046] In the set ideal SCR theoretical conversion efficiency range, when the model efficiency and actual efficiency reach more than 95% simultaneously, self-learning detection begins.

[0047] After the self-learning strategy is started, NH3 injection will be stopped first to clear the amount of NH3 adsorbed in the SCR catalyst. As the amount of NH3 adsorbed decreases, the model efficiency and actual efficiency will begin to decrease. The rate of decrease of the two values ​​may be inconsistent. This is caused by inaccurate calculation of NH3 adsorbed in the SCR catalyst. When both efficiency values ​​drop to the set falling edge threshold, 70%, the AND gate logic is designed here.

[0048] After both the model efficiency and the actual efficiency reach the falling edge threshold, the system switches to a fixed ammonia nitrogen ratio of 0.7 for injection.

[0049] Wait for a period of time for the efficiency calculated by the model and the actual efficiency fed back by the downstream NOx sensor to stabilize. This stabilization time can be determined by the integral of the NH3 injected at a fixed value, generally 10g.

[0050] The model efficiency integral and the actual efficiency integral are calculated separately within the stable integral time. When the NH3 integral of the fixed value injection meets the requirements, the deviation between the two is calculated.

[0051] Model efficiency: Based on the SCR chemical kinetic reaction principle and the molar ratio of NH3 to NOx reaction, this value should conform to the initial feedforward calibration trend of the project.

[0052] Actual efficiency: Depending on the degradation status of each component, injection accuracy, SCR aging and other factors, there may be deviations between the integral trend and the model, and this deviation occurs in two states.

[0053] State 1: Positive deviation means that the actual efficiency integral is greater than the model efficiency integral. Through the normalized curve, the proportional factor is calculated by self-learning to be a value less than 1, which is fed back to the feedforward urea-ammonia-nitrogen ratio to achieve urea injection reduction.

[0054] State 2: Negative deviation means that the actual efficiency integral is less than the model efficiency integral. Through the normalized curve, the proportional factor is calculated by self-learning to be a value greater than 1, which is fed back to the feedforward urea-ammonia-nitrogen ratio to achieve urea injection.

[0055] After the self-learning factor calculation is completed, the system immediately performs closed-loop injection according to the new injection factor, and finally realizes the entire self-learning process. In addition, the timer and the cumulative NH3 integrator are reset to 0 and then accumulated.

[0056] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A diesel engine aftertreatment system based on urea compensation strategy, characterized in that: The diesel engine aftertreatment system based on urea make-up strategy includes: Control ECU; A urea supply system, wherein the urea supply system sprays a preset amount of urea into the post-treatment catalyst through a urea nozzle via a urea supply pump; The SCR inlet temperature sensor is installed at the SCR front-stage inlet to collect the real-time temperature of the SCR front inlet and feed the collected temperature information back to the control ECU; The first NOx sensor is installed at the inlet of the SCR front stage, which is used to collect the original NOx concentration in the exhaust gas output by the engine and feed it back to the control ECU; The second NOx sensor is installed at the outlet of the SCR post-stage and is used for feedback monitoring of the SCR post-treatment; The control ECU can adjust the urea injection amount according to the collected values ​​of the first NOx sensor and the second NOx sensor.

2. The diesel engine aftertreatment system based on urea compensation strategy according to claim 1, characterized in that: When the engine is running and the temperature information collected by the SCR inlet temperature sensor reaches a certain preset value, the urea supply system is activated so that the urea supply system sprays a preset amount of urea into the post-treatment catalyst through the urea nozzle.

3. The diesel engine aftertreatment system based on urea compensation strategy according to claim 2, characterized in that: The actual NOx conversion efficiency under the engine operating condition is calculated by the feedback of the collected value of the second NOx sensor installed in the exhaust gas at the outlet of the SCR catalyst and the collected value of the first NOx sensor at the inlet of the SCR.

4. The diesel engine aftertreatment system based on urea compensation strategy according to claim 3, characterized in that: When the ratio of the collected value collected by the first NOx sensor to the collected value of the second NOx sensor exceeds a preset threshold, a self-learning strategy is started through a self-learning model; First, stop the injection of NH3 to clear the adsorption of NH3 in the SCR catalyst; When both the model efficiency and the actual efficiency drop to the threshold, switch to a fixed ammonia nitrogen ratio of 0.7 for injection.

5. The diesel engine aftertreatment system based on urea compensation strategy according to claim 4, characterized in that: When the efficiency calculated by the model and the actual efficiency fed back by the downstream NOx sensor are stable for a preset time; The model efficiency integral and the actual efficiency integral are calculated separately during the stable time; When the integral of the fixed value injection meets the requirements, calculate the deviation between the two; The urea injection is regulated according to the deviation between the model efficiency integral and the actual efficiency integral.

6. The diesel engine aftertreatment system based on urea compensation strategy according to claim 5, characterized in that: The steps of controlling the urea injection according to the deviation between the model efficiency integral and the actual efficiency integral are specifically as follows: The actual efficiency integral is greater than the model efficiency integral. Through the normalized curve, the proportional factor is calculated by self-learning to be a value less than 1, which is fed back to the feedforward urea-ammonia-nitrogen ratio to achieve urea injection reduction.

7. The diesel engine aftertreatment system based on urea compensation strategy according to claim 6, characterized in that: The steps of controlling the urea injection according to the deviation between the model efficiency integral and the actual efficiency integral are specifically as follows: The actual efficiency integral is less than the model efficiency integral. Through the normalized curve, the proportional factor is calculated by self-learning to be a value greater than 1, which is fed back to the feedforward urea-ammonia-nitrogen ratio to achieve urea injection.

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