SCR (Selective Catalytic Reduction) double-spraying system and cooperative control method thereof

Abstract

The invention relates to an SCR double-spraying system and a cooperative control method thereof, and relates to the technical field of automobile and engine aftertreatment. The system comprises a first urea nozzle, a first selective catalytic reducer, an ammonia escape catalyst, an oxidation catalyst, a particulate matter trap, a second urea nozzle, a second selective catalytic reducer and another ammonia escape catalyst which are arranged behind an engine and in the airflow direction. The first urea nozzle is arranged at the front end of the first selective catalytic reducer and is of a tight coupling structure with the engine. By combining the ammonia storage capacity and catalytic efficiency of the first selective catalytic reduction device and the second selective catalytic reduction device, the injection proportion of the first urea nozzle and the second urea nozzle is distributed so as to control the urea injection amount. According to the method, the urea injection proportion of the upstream and downstream urea nozzles can be reasonably distributed under different exhaust flow and exhaust temperature conditions, it is ensured that generation of N2O is restrained while the NOx emission target is achieved, cooperative control over NOx and N2O emission is achieved, and the requirements of future emission regulations are met.

Description

Technical Field

[0001] This invention relates to the technical field of automotive and engine aftertreatment, and in particular to a collaborative control strategy and method for an SCR dual-injection system. Background Technology

[0002] In existing technologies, the urea injection rate is determined based on the NOx levels upstream of each stage of the SCR and the ammonia storage capacity of the SCR itself to achieve the goal of reducing NOx. This control strategy has shown excellent market performance in single-injection SCR systems. However, in dual-injection systems, because the NOx sensor is more sensitive to ammonia than NOx, the NOx gas measured by the upstream NOx sensor of SCR2 may contain a certain amount of ammonia. If the downstream urea nozzle then uses the NOx level measured by the upstream NOx sensor of SCR2 as input to determine the urea injection rate target for SCR2, over-injection of urea may occur, leading to excessive ammonia emissions or additional urea consumption, and it also fails to effectively suppress N2O generation. Summary of the Invention

[0003] The purpose of this invention is to provide an SCR dual-injection system and its coordinated control method. By coordinating the control of the SCR dual-injection system, the urea injection ratio of the upstream and downstream urea nozzles is rationally allocated under different exhaust flow and exhaust temperature conditions. This ensures that NOx emission targets are achieved while suppressing N2O generation, thereby achieving coordinated control of NOx and N2O emissions and meeting the requirements of future emission regulations.

[0004] To achieve the above objectives, the present invention provides an SCR dual-injection system, comprising a urea nozzle one, a selective catalytic reduction unit one, an ammonia escape catalyst, an oxidation catalyst, a particulate matter trap, a urea nozzle two, a selective catalytic reduction unit two, and another ammonia escape catalyst, all located behind the engine and arranged along the airflow direction; the urea nozzle one is arranged at the front end of the selective catalytic reduction unit one and is tightly coupled to the engine; by combining the ammonia storage capacity and catalytic efficiency of the selective catalytic reduction unit one and the selective catalytic reduction unit two, the injection ratio of the urea nozzle one and the urea nozzle two is allocated to control the urea injection quantity.

[0005] Preferably, under low-load conditions, NOx is mainly purified by the selective catalytic reducer one; under high-load conditions, NOx is mainly purified by the selective catalytic reducer two and N2O generation is suppressed.

[0006] Preferably, the urea injection ratio is allocated in the following manner: The total amount of base urea injected is calculated based on the amount of NOx upstream of the selective catalytic reducer. The injection ratio of urea nozzle one and urea nozzle two is determined based on the exhaust flow rate and exhaust temperature. At low exhaust temperatures, increase the injection ratio of the urea nozzle one; At high exhaust temperatures, the injection ratio of urea nozzle one is reduced and the injection ratio of urea nozzle two is increased.

[0007] Preferably, a default mode can be used to achieve decoupling control when either urea nozzle one or urea nozzle two fails, in order to reduce NOx emissions.

[0008] The technical solution of the present invention also provides a collaborative control method for an SCR dual-injection system, comprising the following steps: Detect the status of urea nozzle one and urea nozzle two; If both urea nozzle one and urea nozzle two are functioning normally, the system enters normal mode and distributes the urea injection volume through a dual-injection coordinated control strategy. If urea nozzle one is normal but urea nozzle two is faulty, then default mode 1 is entered, and all urea injection needs are met by urea nozzle one. If urea nozzle one malfunctions while urea nozzle two is functioning normally, then default mode 2 is entered, and all urea injection needs are met by urea nozzle two.

[0009] Preferably, in normal mode, the following steps are included: The total amount of basic urea injection is calculated based on the NOx content at the inlet of the selective catalytic reducer. The injection ratio of urea nozzle one and urea nozzle two is determined based on the exhaust flow rate and exhaust temperature. Based on the catalytic efficiency models of the selective catalytic reducer one and the selective catalytic reducer two, and the ammonia storage capacity, the urea injection rate is adjusted. The urea injection is controlled by the urea nozzle one and the urea nozzle two according to the corrected urea injection volume.

[0010] Preferably, in the default mode 1, the following steps are included: The basic urea injection rate is calculated based on the NOx content at the inlet of the selective catalytic reducer. Based on the efficiency models of the selective catalytic reducer one and the selective catalytic reducer two, and the ammonia storage target, the urea injection rate is adjusted. The final urea injection rate is obtained by performing closed-loop correction based on the downstream NOx level. Control the urea nozzle to spray urea at the final urea injection volume.

[0011] Preferably, in default mode 2, the following steps are included: The base urea injection rate is calculated based on the NOx content at the second inlet of the selective catalytic reducer. Based on the efficiency model of the selective catalytic reducer II and the ammonia storage target, the urea injection rate is adjusted. The final urea injection rate is obtained by performing closed-loop correction based on the downstream NOx level. Control the urea nozzle two to spray urea according to the final urea injection volume.

[0012] Preferably, it also includes nozzle diagnostic testing, specifically including: The presence of a short circuit or open circuit is determined based on the voltage signal fed back from the urea nozzle. Check if the urea pump pressure drops to the set threshold to determine if the nozzle is stuck or blocked.

[0013] Preferably, it also includes correction logic based on the SCR efficiency model and ammonia storage capacity for precise control of urea injection volume, which includes: The first revision based on the SCR efficiency model; The second revision based on the ammonia storage capacity of SCR; The third correction is based on closed-loop injection.

[0014] In summary, the present invention has the following beneficial technical effects: This invention enables the coordinated control of the SCR dual-injection system to rationally allocate the urea injection ratio between upstream and downstream urea nozzles. This effectively reduces NOx emissions while suppressing N2O formation, achieving coordinated control of NOx and N2O emissions to meet future emission regulations. Simultaneously, it avoids the over-injection of urea by the upstream NOx sensor in SCR2, which might cause ammonia to be mistaken for NOx, thus reducing urea consumption and the risk of urea crystallization. Even when a single nozzle in the upstream or downstream urea system malfunctions, the SCR dual-injection system can still be decoupled using the default mode, minimizing NOx emissions during the malfunction.

[0015] This invention, by tightly coupling the upstream urea nozzle to the engine, reduces the dissipation of engine exhaust heat and achieves rapid warm-up during the cold start phase. The Selective Catalytic Reduction Unit (SCR1) can reach its injection temperature in a short time, thereby shortening the NOx emission time during the cold start phase and significantly reducing emissions pollution during cold starts.

[0016] The system dynamically adjusts the injection ratio of upstream and downstream urea nozzles based on exhaust flow rate, exhaust temperature, and NOx levels. At low exhaust temperatures, the injection ratio of the upstream urea nozzle is increased to leverage the higher temperature of the SCR1 carrier and improve catalytic efficiency. At high exhaust temperatures, the upstream injection ratio is decreased while the downstream injection ratio is increased to suppress the reaction of NH3 with NO2 and O2 to generate N2O during the high-temperature stage. This dynamic adjustment strategy achieves synergistic control of NOx and N2O.

[0017] The system achieves precise control of urea injection quantity through basic urea injection quantity calculation, efficiency model correction, ammonia storage correction, and closed-loop injection correction. This multi-level correction logic can effectively address differences in component production consistency and SCR aging issues, ensuring long-term stable operation of the system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the system layout in an SCR dual-injection system and its collaborative control method according to the present invention; Figure 2 This is a schematic diagram of the control flow of the SCR dual-injection system in the SCR dual-injection system and its collaborative control method of the present invention; Figure 3 This is a schematic diagram of the normal mode control logic in an SCR dual-injection system and its collaborative control method according to the present invention. Figure 4 This is a schematic diagram of the default mode 1 control logic in an SCR dual-injection system and its collaborative control method of the present invention; Figure 5 This is a schematic diagram of the default mode 2 control logic in an SCR dual-injection system and its collaborative control method of the present invention.

[0019] Reference numerals in the attached diagram: 1. Engine; 2. Urea nozzle one; 3. Selective catalytic reduction one; 4. Ammonia escape catalyst; 5. Oxidation catalyst; 6. Particulate matter collector; 7. Urea nozzle two; 8. Selective catalytic reduction two. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: This invention discloses a dual-injection SCR system and its coordinated control method, aiming to optimize NOx and N2O emission control in engine aftertreatment systems. The system includes, in sequence along the airflow direction, an engine 1, a urea nozzle 2 (Urea1), a selective catalytic reduction 1 (SCR1), an ammonia slip catalyst 4 (ASC), an oxidation catalyst 5 (DOC), a particulate filter 6 (DPF), a second urea nozzle 7 (Urea2), a second selective catalytic reduction 2 (SCR2), and a separately arranged ammonia slip catalyst 4 (ASC). The system precisely controls the urea injection quantity by rationally allocating the injection ratio of upstream and downstream urea nozzles, combined with the ammonia storage capacity and catalytic efficiency model of the SCR, and provides a default mode to reduce NOx emissions in case of nozzle failure.

[0022] System layout as follows Figure 1 As shown, selective catalytic reduction (SCR) 3 is positioned upstream of oxidation catalyst 5, with upstream urea nozzle 2 positioned at the front end of SCR 3, forming a tight coupling with engine 1. This arrangement reduces heat dissipation from engine 1 exhaust, enabling rapid warm-up during cold starts and helping SCR 3 quickly reach its injection temperature, thus shortening NOx emission time during cold starts. Oxidation catalyst 5 and particulate filter 6 are positioned downstream of SCR 3. The main function of oxidation catalyst 5 is to purify CO / HC and SOF (soluble organic matter) in exhaust gas, while increasing the proportion of NO2 to improve the passive regeneration efficiency of particulate filter 6. The passive regeneration reaction inside particulate filter 6 reduces the NO2 concentration entering SCR 8, thereby inhibiting N2O formation in SCR 8. SCR 8 is positioned downstream of particulate filter 6, with downstream urea nozzle 7 positioned at the front end of SCR 8. Under low to medium load conditions, the system mainly relies on selective catalytic reduction unit 3 to purify NOx; under medium to high load conditions, it mainly relies on selective catalytic reduction unit 8 to purify NOx and suppress the generation of N2O.

[0023] During system operation, the basic total urea injection amount is calculated based on the NOx level upstream of the selective catalytic reduction unit (SCR) 3 according to the equivalent ammonia-nitrogen ratio. Then, the urea injection ratio of the upstream and downstream urea nozzles is rationally allocated based on exhaust flow rate and exhaust temperature. At low exhaust temperatures, the injection ratio of the upstream urea nozzle 2 is increased to utilize the higher carrier temperature of the SCR 3, improving catalytic efficiency and reducing NOx emissions during cold and low-load stages. At high exhaust temperatures, the injection ratio of the upstream urea nozzle 2 and the ammonia storage capacity of the SCR 3 are reduced to suppress the reaction of NH3 with NO2 and O2 to generate N2O during the high-temperature stage, while simultaneously reducing ammonia leakage from the SCR 3. During this stage, the carrier temperature of the selective catalytic reduction unit (SCR 8) is in the high-efficiency catalytic zone, allowing for an increase in the injection ratio of the downstream urea nozzles, thus achieving synergistic control of NOx and N2O. In addition to the basic urea injection ratio allocation, the injection amount is also corrected based on the ammonia storage capacity of the SCR and the SCR efficiency model under different conditions to achieve precise control of urea injection. If a single nozzle in the upstream or downstream urea nozzles fails, the SCR dual-injection system can still be decoupled using the default mode to minimize NOx emissions under fault conditions.

[0024] System control flow as follows Figure 2 As shown, the urea injection strategy is determined based on the status of the upstream and downstream urea nozzles. Before the urea injection system enters the metering injection stage after urea pressure build-up, a diagnostic test is performed on the urea nozzles. The diagnostic test includes real-time electrical diagnostics and urea injection testing. Electrical diagnostics determines whether there is a short circuit or open circuit based on the voltage signal fed back from the urea nozzle. Urea injection testing is performed under the premise of no nozzle electrical faults. Urea injection testing involves opening the nozzle valve and detecting whether the urea pump pressure drops to a set threshold to determine whether the nozzle is stuck or blocked. Only when there are no electrical faults and no sticking or blockage in the nozzle is the system determined that the nozzle is normal and fault-free.

[0025] When both upstream and downstream urea nozzles are functioning normally, the system operates in normal mode, determining the urea injection volume of each nozzle through a dual-injection coordinated control strategy. When the upstream nozzle is functioning normally but the downstream nozzle malfunctions, the system operates in default mode 1, with all urea injection requests handled by the upstream nozzle. When the upstream nozzle malfunctions but the downstream nozzle is functioning normally, the system operates in default mode 2, with all urea injection requests handled by the downstream nozzle. In normal operating mode, the system achieves coordinated control of NOx and N2O through the dual-injection coordinated control strategy. Even if a single nozzle malfunctions, the dual-injection system can be decoupled through the default mode, ensuring the system continues to operate in its optimal mode.

[0026] The control logic in normal mode is as follows Figure 3As shown, the system first calculates the basic total urea injection amount based on the NOx quantity at the inlet of the selective catalytic reducer-3 multiplied by the equivalent ammonia-nitrogen ratio, and then determines the urea injection ratio distribution based on the carrier temperature and exhaust flow rate of the selective catalytic reducer-3. Specifically, it includes the following steps: The NOx amount at the inlet of the selective catalytic reducer-3 is the basic input parameter measured by the NOx sensor. The theoretical urea injection amount required for the reaction with NOx is obtained by multiplying the NOx amount at the inlet of the selective catalytic reducer-3 by the equivalent ammonia-nitrogen ratio, which serves as the basic total urea injection amount. To facilitate subsequent calibration and development, the equivalent ammonia-nitrogen ratio is designed as a calibrable MAP.

[0027] The exhaust flow rate and the carrier temperature of the selective catalytic reduction (SCR) unit 3 are used as the basis for determining the urea injection ratio of the SCR unit 3. The urea injection ratio of the SCR unit 3 is determined by referring to the MAP table. The urea injection ratio of the SCR unit 3 is multiplied by the basic urea injection total to obtain the basic urea injection amount of the SCR unit 3. Then, the basic urea injection amount of the SCR unit 3 is corrected for the first time according to the catalytic efficiency of the SCR unit 3 under different conditions. Considering that the ammonia storage capacity of the SCR unit 3 is limited, a second correction is made based on the ammonia storage target of the SCR unit 3. The ammonia storage correction target can be flexibly set according to the ammonia storage capacity and the synergistic control requirements of NOx and N2O. After the second correction, the urea injection amount of the SCR unit 3 under open-loop control is obtained. Considering the production consistency of components and SCR aging, an additional closed-loop injection correction is made based on the downstream NOx amount. After the closed-loop injection correction, the final urea injection amount of the SCR unit 3 is obtained.

[0028] The urea injection ratio of Selective Catalytic Reduction Unit 1 (SCR 2) is obtained by multiplying the urea injection ratio of SCR 2 by the total base urea injection. This yields the base urea injection amount of SCR 2. The base urea injection amount is then corrected for the first time based on the catalytic efficiency of SCR 2 under different conditions. Similarly, since the ammonia storage capacity of SCR 2 is limited, a second correction is made based on the ammonia storage target of SCR 2. The ammonia storage correction target can be flexibly set according to the ammonia storage capacity and the synergistic control requirements of NOx and N2O. After the second correction, the open-loop controlled urea injection amount of SCR 2 is obtained. Considering the production consistency of components and SCR aging, a closed-loop injection correction is further performed based on the downstream NOx level. The final urea injection amount of SCR 2 is obtained after the closed-loop injection correction.

[0029] Control the upstream urea nozzle to inject urea at the urea injection rate of selective catalytic reduction unit 3, and control the downstream urea nozzle to inject urea at the urea injection rate of selective catalytic reduction unit 28.

[0030] It should be noted that the above efficiency model correction coefficients are based on the measured conversion efficiency calibration of SCR under different exhaust temperatures, exhaust flow rates, and ammonia storage conditions; the ammonia storage correction is determined based on the deviation between the target ammonia storage amount and the current ammonia storage model value to determine the urea injection amount or reduction amount; the closed-loop injection correction is a final supplement, which is based on the deviation between the downstream NOx amount model value calculated in the aforementioned steps and the downstream NOx amount measured by the sensor to determine the urea injection amount or reduction amount, and the specific calculation is as follows: 1. (Urea injection rate - ammonia storage) * equivalent nitrogen-ammonia ratio = theoretical NOx purification capacity; 2. Upstream NOx amount - Theoretical NOx purification value = Downstream NOx amount (model value); 3. (Downstream NOx model value - Downstream NOx amount) * Equivalent ammonia-nitrogen ratio * Correction slope = Closed-loop injection correction amount; To facilitate later development, all parameters involved in the correction calculations are designed as calibrated values, and the same applies to the correction calculations mentioned below.

[0031] The default mode 1 control logic is as follows: Figure 4 As shown, the basic urea injection rate of selective catalytic reduction (SCR) 3 is obtained by multiplying the NOx inlet quantity of SCR 3 by the equivalent ammonia-nitrogen ratio. Then, based on the efficiency models of SCR 3 and SCR 2 8 and the ammonia storage target, the injection rate is corrected and additional closed-loop corrections are performed to obtain the final urea injection rate of SCR 3. This includes the following steps: The theoretical urea injection rate required for the reaction with NOx is obtained by multiplying the NOx inlet amount of the selective catalytic reducer-3 by the equivalent ammonia-nitrogen ratio. This is used as the basic urea injection rate for the selective catalytic reducer-3. To facilitate later calibration and development, the equivalent ammonia-nitrogen ratio is designed as a calibrable MAP.

[0032] The basic urea injection quantity of selective catalytic reducer 3 and selective catalytic reducer 2 under different conditions is then corrected for the first time. The urea injection quantity of selective catalytic reducer 3 is then corrected for the second time based on the ammonia storage target of selective catalytic reducer 3 and selective catalytic reducer 2 to obtain the open-loop controlled urea injection quantity. Considering the production consistency of components and SCR aging, the closed-loop injection correction is further performed based on the downstream NOx content. After the closed-loop injection correction, the final urea injection quantity of selective catalytic reducer 3 is obtained. The upstream urea nozzle is then controlled to inject urea based on the final urea injection quantity of selective catalytic reducer 3.

[0033] The default mode 2 control logic is as follows: Figure 5As shown, the basic urea injection rate of the selective catalytic reduction unit (SCR) 8 is obtained by multiplying the NOx inlet quantity of SCR 8 by the equivalent ammonia-nitrogen ratio. Then, based on the efficiency model of SCR 8 and the ammonia storage target, the injection rate is corrected and additional closed-loop corrections are performed to obtain the final urea injection rate of SCR 8. This includes the following steps: The theoretical urea injection rate required for the reaction with NOx is obtained by multiplying the NOx inlet amount of selective catalytic reducer 28 by the equivalent ammonia-nitrogen ratio. This is used as the basic urea injection rate for selective catalytic reducer 28. To facilitate later calibration and development, the equivalent ammonia-nitrogen ratio is designed as a calibrable MAP.

[0034] The basic urea injection quantity of the selective catalytic reducer 28 is then corrected for the first time based on the catalytic efficiency of the selective catalytic reducer 28 under different conditions. Then, a second correction is made based on the ammonia storage target of the selective catalytic reducer 28 to obtain the open-loop controlled urea injection quantity. Considering the production consistency of components and the aging of the selective catalytic reducer, a closed-loop injection correction is further made based on the downstream NOx content. After the closed-loop injection correction, the final urea injection quantity of the selective catalytic reducer 28 is obtained. Then, the downstream urea nozzle is controlled to inject urea based on the final urea injection quantity of the selective catalytic reducer 28.

[0035] Example 2: To facilitate understanding of the present invention, this embodiment, based on Embodiment 1, further illustrates the specific implementation details of the present invention using a practical application scenario.

[0036] 1. When a vehicle / engine 1 is started from cold, if selective catalytic reduction (CCR) 3 reaches its injection temperature while CCR 2 has not, the injection rate of the upstream urea nozzle is set based on the base total injection rate, the efficiency model correction of CCR 3, and the maximum ammonia storage capacity to ensure effective reduction of NOx emissions during the cold start phase. When the exhaust temperature rises to the point where both CCR 3 and CCR 2 reach their injection temperatures simultaneously, and the carrier temperature of CCR 3 is below 400°C, CCR 3 is in its high-efficiency operating temperature range. In this case, injection is still primarily from the upstream urea nozzle, while CCR 2 mainly functions to convert NOx escaping from CCR 3 and appropriately increase its own ammonia storage capacity. As the exhaust temperature continues to rise... When the carrier temperature of selective catalytic reduction unit 3 reaches above 400℃, ammonia and O2 inside the selective catalytic reduction unit 3 easily react with NO2 to generate N2O, and the selective catalytic reduction unit 3 is no longer in the high-efficiency operating temperature range. At this time, reducing the upstream urea injection ratio consumes NO2 through rapid reaction and gradually reduces the ammonia storage in the selective catalytic reduction unit 3 to 0, thereby reducing the ammonia storage inside the selective catalytic reduction unit 3. This achieves the purpose of converting some NOx and inhibiting N2O generation. At this time, the temperature of selective catalytic reduction unit 8 is still in the high-efficiency operating temperature range. Increasing the injection ratio of the downstream urea nozzle ensures that NOx emissions can be effectively reduced while inhibiting N2O generation, achieving synergistic control of NOx and N2O emissions, and ultimately meeting the requirements of future emission regulations.

[0037] 2. A malfunction in the downstream urea nozzle of a certain vehicle / engine 1 triggers the default mode 1 control strategy. The upstream nozzle is responsible for the total urea injection volume required by selective catalytic reduction unit 1 3 and selective catalytic reduction unit 2 8. When the total urea injection volume demand is within the maximum injection volume limit of the upstream urea nozzle, the injection is performed according to the demand volume. If the demand injection volume is greater than the maximum injection volume limit of the upstream urea nozzle, the injection is performed according to the maximum injection volume limit of the upstream urea nozzle. Within the limits allowed by the hardware, the NOx emissions in the malfunction state are reduced to the minimum.

[0038] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An SCR dual-injection system, characterized in that, It includes a urea nozzle 1 (2) located behind the engine (1) and arranged along the airflow direction, a selective catalytic reducer 1 (3), an ammonia escape catalyst (4), an oxidation catalyst (5), a particulate matter trap (6), a urea nozzle 2 (7), a selective catalytic reducer 2 (8), and another ammonia escape catalyst (4); the urea nozzle 1 (2) is arranged at the front end of the selective catalytic reducer 1 (3) and is tightly coupled with the engine (1); by combining the ammonia storage capacity and catalytic efficiency of the selective catalytic reducer 1 (3) and the selective catalytic reducer 2 (8), the injection ratio of the urea nozzle 1 (2) and the urea nozzle 2 (7) is allocated to control the urea injection amount.

2. The SCR dual-injection system according to claim 1, characterized in that, Under low load conditions, NOx is mainly purified by the selective catalytic reducer one (3); under high load conditions, NOx is mainly purified by the selective catalytic reducer two (8) and the generation of N2O is suppressed.

3. The SCR dual-injection system according to claim 2, characterized in that, The urea injection ratio shall be allocated in the following manner: The total amount of basic urea injection is calculated based on the amount of NOx upstream of the selective catalytic reducer (3); The injection ratio of the urea nozzle one (2) and the urea nozzle two (7) is determined based on the exhaust flow rate and exhaust temperature; At low exhaust temperature, increase the injection ratio of the urea nozzle 1 (2); At high exhaust temperature, the injection ratio of urea nozzle one (2) is reduced and the injection ratio of urea nozzle two (7) is increased.

4. The SCR dual-injection system according to claim 3, characterized in that, The default mode can be used to achieve decoupling control in the event of a failure of either urea nozzle one (2) or urea nozzle two (7) in order to reduce NOx emissions.

5. A collaborative control method for the SCR dual-injection system according to any one of claims 1-4, characterized in that, Includes the following steps: Detect the status of the urea nozzle one (2) and the urea nozzle two (7); If both the urea nozzle one (2) and the urea nozzle two (7) are normal, then the normal mode is entered, and the urea injection volume is allocated through the dual-injection collaborative control strategy. If the urea nozzle one (2) is normal but the urea nozzle two (7) is faulty, then the default mode 1 is entered, and all urea injection needs are met by the urea nozzle one (2). If the urea nozzle 1 (2) malfunctions while the urea nozzle 2 (7) is normal, then the default mode 2 is entered, and all urea injection needs are met by the urea nozzle 2 (7).

6. The SCR dual-injection system collaborative control method according to claim 5, characterized in that, In normal mode, the following steps are included: The total amount of basic urea injected is calculated based on the NOx content at the inlet of the selective catalytic reducer (3); The injection ratio of the urea nozzle one (2) and the urea nozzle two (7) is determined based on the exhaust flow rate and exhaust temperature; Based on the catalytic efficiency model of the selective catalytic reducer one (3) and the selective catalytic reducer two (8) and the ammonia storage capacity, the urea injection amount is corrected; The urea nozzles 1 (2) and 2 (7) are controlled to spray urea according to the modified urea injection volume.

7. The SCR dual-injection system collaborative control method according to claim 6, characterized in that, In the default mode 1, the following steps are included: The basic urea injection rate is calculated based on the NOx content at the inlet of the selective catalytic reducer (3); Based on the efficiency models of the selective catalytic reducer one (3) and the selective catalytic reducer two (8) and the ammonia storage target, the urea injection rate is corrected; The final urea injection rate is obtained by performing closed-loop correction based on the downstream NOx level. Control the urea nozzle (2) to spray urea according to the final urea injection amount.

8. The SCR dual-injection system collaborative control method according to claim 7, characterized in that, In the default mode 2, the following steps are included: The basic urea injection rate is calculated based on the NOx content at the inlet of the selective catalytic reducer II (8); Based on the efficiency model of the selective catalytic reducer 2 (8) and the ammonia storage target, the urea injection rate is adjusted; The final urea injection rate is obtained by performing closed-loop correction based on the downstream NOx level. Control the urea nozzle two (7) to spray urea according to the final urea injection amount.

9. The SCR dual-injection system collaborative control method according to claim 8, characterized in that, It also includes nozzle diagnostic tests, specifically: The presence of a short circuit or open circuit is determined based on the voltage signal fed back from the urea nozzle. Check if the urea pump pressure drops to the set threshold to determine if the nozzle is stuck or blocked.

10. The SCR dual-injection system collaborative control method according to claim 9, characterized in that, It also includes correction logic based on the SCR efficiency model and ammonia storage capacity for precise control of urea injection volume, which includes: The first revision based on the SCR efficiency model; The second revision based on the ammonia storage capacity of SCR; The third correction is based on closed-loop injection.

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