An engine exhaust aftertreatment system and its working method

Abstract

This invention belongs to the field of exhaust emission control technology and discloses an engine exhaust aftertreatment system and its operating method. The system includes a urea tank, a urea supply unit, a compressed air unit, a metering unit, a gas-liquid switching unit, an injection unit, and a control unit. The urea supply unit employs a multi-pump parallel and reflux regulation structure to achieve a stable and cyclical supply of urea solution. The metering unit is equipped with a pressure detection and pulse damping structure to improve injection metering accuracy. The gas-liquid switching unit and the injection unit form a tightly coupled structure to achieve rapid switching between compressed air and urea solution. The control unit performs pre-purge, injection, and delayed purging processes in automatic mode, and allows independent control of each execution unit in manual mode. This invention effectively reduces urea residue and the risk of crystallization blockage through gas-liquid coordinated injection and delayed purging mechanisms, while improving supply stability and injection response performance, thereby improving exhaust gas denitrification efficiency and system operational reliability.

Description

Technical Field

[0001] This invention belongs to the field of engine exhaust gas treatment technology, specifically relating to an engine exhaust gas aftertreatment system and its working method based on gas-liquid coordinated injection control, urea supply pressure regulation and multi-parameter closed-loop control functions. Background Technology

[0002] In the field of exhaust emission control for marine diesel and gas engines, nitrogen oxides (NOx), as one of the main pollutants, are typically treated using selective catalytic reduction (SCR) technology. This technology involves injecting an aqueous urea solution into the exhaust pipe, causing it to decompose at high temperatures to generate ammonia. Ammonia then reacts with nitrogen oxides in the presence of a catalyst, thereby achieving denitrification.

[0003] Existing marine diesel engine exhaust gas treatment systems, such as the one disclosed in Chinese invention patent CN105771649A, are highly efficient systems for simultaneously removing nitrogen oxides, sulfur oxides, and particulate matter from ships. This system places the SCR system behind the turbocharger for flexible SCR device placement. It utilizes high-temperature exhaust gas bypassing the turbine to raise the exhaust gas temperature after the turbine, saving energy. It also employs recirculated exhaust gas for afterburning and heating to remove deposits within the reactor. This aftertreatment system exhibits high removal efficiency for pollutants NOx, SO2, and particulate matter, meeting emission limits set by international organizations such as the IMO, and enabling switching of operating modes when the ship is navigating in the high seas and emission control areas.

[0004] However, in practical applications, the existing technology still has the following shortcomings: 1. In existing technologies, urea solution tends to remain in nozzles and pipelines for extended periods, easily crystallizing and depositing under low temperatures or shutdown conditions. This leads to blockage of the injection channels, affecting the normal operation of the system. The injection system is prone to crystallization and blockage, resulting in insufficient reliability, especially under frequent start-stop or low-load operating conditions. Currently, most systems only mitigate this issue through passive structural optimization or simple evacuation, lacking effective active cleaning or anti-crystallization mechanisms, making it difficult to fundamentally solve the reliability problem of the injection system. Furthermore, while existing systems can achieve basic functions such as start-up, injection, and shutdown, there is a lack of a unified logical coordination mechanism between these operational stages. For example, the shutdown process lacks effective delay processing and channel cleaning strategies, making it difficult to promptly remove residual urea from the system, further exacerbating the crystallization problem and affecting the long-term stable operation of the system.

[0005] 2. Existing urea supply systems mostly employ a single-pump delivery structure, lacking effective pressure stabilization and reflux regulation mechanisms. This results in large flow fluctuations and insufficient metering accuracy. Flow pulsations and pressure fluctuations easily occur under different operating conditions, leading to reduced injection metering accuracy and consequently affecting denitrification efficiency. Furthermore, during dynamic load changes, the supply system's response is lag-dependent, making it difficult to meet precise control requirements.

[0006] 3. In some existing technologies, the urea injection path and the auxiliary gas path are independent. When the system switches between different operating states, there are problems such as long response time and excessive residual liquid retention. The injection actuator responds slowly, resulting in low gas-liquid switching efficiency and affecting the dynamic performance of the system. Simply superimposing NOx feedback for correction results in a relatively simplistic control strategy that fails to fully consider the coupled effects of multiple factors such as exhaust temperature and system state. The injection control strategy is also simplistic and has poor adaptability. Under low-temperature conditions or large fluctuations in operating conditions, it is prone to over- or under-injection, affecting denitrification efficiency and even causing ammonia escape or crystallization risks. In addition, the dispersed structure of the injection unit and the fluid switching unit leads to poor control coordination, making it difficult to achieve rapid and stable gas-liquid switching control.

[0007] Therefore, developing an intelligent, automated, efficient, and energy-saving engine exhaust aftertreatment system has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] To address the aforementioned shortcomings of existing technologies, this invention aims to solve problems such as easy crystallization and blockage in existing engine exhaust aftertreatment systems, unstable urea supply, insufficient injection control precision, and lag in gas-liquid switching response. This invention provides an exhaust aftertreatment system and its operating method. By constructing a gas-liquid co-injection structure, optimizing the urea supply pressure stabilization mechanism, and introducing a multi-parameter coupling control strategy, it achieves high-precision control of the injection process and active cleaning of the injection channel, thereby improving the system's operational stability and denitrification efficiency.

[0009] To achieve the above objectives, the present invention provides an engine exhaust aftertreatment system, comprising a control unit, a urea supply unit, a compressed air unit, a metering unit, a gas-liquid switching unit, and an injection unit, wherein: The urea supply unit is used to provide a stable urea supply. It is equipped with at least one set of supply pumps, return pipelines and back pressure regulating components to form a circulation supply path, so that the urea solution forms a dynamic pressure stabilization state during the supply process. The compressed air unit is used to provide compressed air at a stable pressure and regulates the output pressure through a pressure reducing component to meet the gas supply requirements under different working conditions. The metering unit is connected to the urea supply unit and the compressed air unit respectively, and is used to quantitatively deliver the urea solution and reduce flow fluctuations through a pulse damping structure. The gas-liquid switching unit and the injection unit are used to selectively switch between the urea channel and the compressed air channel, and form a tightly coupled connection structure with the injection unit to shorten the fluid path and reduce residual liquid retention. The control unit is electrically connected to the urea supply unit, compressed air unit, metering unit, and gas-liquid switching unit, and controls the system operating status based on engine operating parameters.

[0010] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device further includes a urea tank for storing urea solution; a urea supply unit is connected to the urea tank for delivering urea solution to a metering unit; the return pipeline of the urea supply unit is connected to the output end of the supply pump and reconnected to the urea tank so that the urea solution forms a circulating flow and maintains a stable output pressure. The urea tank is equipped with a low level switch and a level sensor to replenish the urea solution; a urea tank temperature sensor is also provided to monitor the urea solution temperature and prevent crystallization.

[0011] According to another embodiment of the present invention or any of the foregoing embodiments of the exhaust gas aftertreatment device, the control unit is electrically connected to the urea supply unit, urea chamber, compressed air unit, metering unit, and gas-liquid switching unit via cables, and is also electrically connected to the injection unit, front-end nitrogen oxide sensor, and rear-end nitrogen oxide sensor, for transmitting control signals to each unit; the front-end nitrogen oxide sensor and the rear-end nitrogen oxide sensor acquire the nitrogen oxide concentration at the inlet and outlet of the SCR reaction chamber. The urea supply unit is connected to the metering unit via two liquid pipelines for transporting and returning urea solution; the compressed air unit is connected to the metering unit via a gas pipeline for transporting compressed air. The output of the metering unit is connected to the gas-liquid switching unit through a liquid pipeline and a gas pipeline. The output of the gas-liquid switching unit delivers compressed air to the injection unit through the gas pipeline and urea solution to the injection unit through the liquid pipeline, and switches between urea solution and compressed air.

[0012] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device includes a central processing module and an input / output module electrically connected thereto. The input / output module includes: Digital input / output module, used to acquire switch signals and output control signals; Analog input module, used to acquire temperature and pressure; Analog output module, used to output analog signals to control the metering pump; The digital input / output module has 8 inputs and 8 outputs, the analog input module has 8 channels, and the analog output module has 2 channels.

[0013] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device is wherein the gas-liquid switching component is a three-way valve structure, and its switching end is connected to the urea channel and the compressed air channel respectively.

[0014] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device includes a metering unit comprising a metering pump, a pressure detection element and a pulse damping assembly, for accurately metering and stably outputting urea solution.

[0015] According to another embodiment of the present invention or any of the foregoing embodiments of the exhaust gas aftertreatment device, the urea supply unit includes at least two supply pumps, which are connected to a filter before being connected in parallel, and the urea outlet of the urea tank is connected to the filter; in addition to being connected to a metering unit through a liquid pipeline, the supply pumps are also connected to a vent valve and a safety valve connected in parallel, and then connected to the urea return port of the urea tank to achieve redundant supply or staged supply.

[0016] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust aftertreatment device, wherein the control unit determines the injection conditions based on at least two parameters selected from engine load, reactor temperature and nitrogen oxide concentration; The control unit adopts a combination of open-loop and closed-loop control. The open-loop control determines the urea injection quantity based on the engine load, while the closed-loop control corrects the injection quantity based on the nitrogen oxide concentration.

[0017] Accordingly, the present invention also provides a method for exhaust gas aftertreatment, including an automatic mode, the automatic mode comprising the following steps: After the system is powered on, the system status is checked, and when there is no fault in the system, it enters standby mode. When the engine load is detected to reach the first threshold, the control gas-liquid switching unit switches to the compressed air channel so that the compressed air pre-purges the injection channel. When the reactor temperature is detected to have reached the preset temperature threshold, the gas-liquid switching unit is controlled to switch to the urea channel, and the metering unit is controlled to output urea solution for injection. The urea injection baseline quantity is determined based on engine load, and the injection quantity of the injection unit is adjusted in a closed loop based on the nitrogen oxide concentration. When the engine load is below the second threshold or the injection conditions are not met, urea injection is stopped, and the gas-liquid switching unit is controlled to switch to the compressed air channel. After stopping urea injection, maintain continuous compressed air output for a preset time to clean the injection channel.

[0018] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device operation method is provided, wherein a first threshold of the engine is used to determine whether to enter the injection preparation state, and when the engine load is higher than the first threshold, the system is allowed to enter the flushing or injection preparation stage. The second threshold is used to determine whether to exit the injection state. When the engine load is lower than the second threshold, the system stops urea injection and enters the shutdown process. The first threshold is greater than or equal to the second threshold to form a load hysteresis interval, thereby avoiding frequent switching of the system's operating state near the critical load.

[0019] According to another embodiment of the present invention or any of the foregoing embodiments, the method of operating the exhaust gas aftertreatment device includes: the control unit coordinating the gas-liquid switching state and the injection state based on the urea tank level signal and temperature signal, including: When the temperature in the urea tank is below the crystallization risk threshold, compressed air purging should be maintained first. When the urea tank level is below the preset value, it is forbidden to enter the urea injection mode and the gas channel must be kept open. Switching to the urea injection path is only permitted after the urea tank temperature recovers or the liquid level meets the requirements.

[0020] According to another embodiment of the present invention or any of the foregoing embodiments, the operating method of the exhaust gas aftertreatment device is wherein, after the urea injection is stopped, the preset time for maintaining continuous output of compressed air is 15 minutes.

[0021] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device operation method includes closed-loop adjustment of the injection quantity of the injection unit based on the nitrogen oxide concentration, with the nitrogen oxide conversion rate as the control target, so that the conversion rate is maintained within a preset range.

[0022] According to another embodiment of the present invention or any of the foregoing embodiments, the exhaust gas aftertreatment device operation method further includes a manual / test mode: The control unit receives manually input commands and performs at least one of the following operations based on the commands: The solenoid valve controls the opening and closing of the compressed air unit; Receives a set engine load signal and controls the operating status of the metering unit based on the load signal; Control the start and stop of the supply pump in the urea supply unit; Adjust the urea output flow rate of the metering unit.

[0023] The beneficial effects of this invention are: 1. The engine exhaust aftertreatment system and its working method described in this invention introduce a multi-parameter coupled control strategy based on temperature, load, and nitrogen oxide concentration to combine open-loop and closed-loop control, thereby reducing the fluctuation range of denitrification efficiency by more than 30% and effectively avoiding ammonia escape. By constructing a multi-mode operation system including start-up, flushing, metering, and shutdown, and combining it with state switching logic, the system achieves automatic connection between various operating stages, improving the continuity and stability of system operation.

[0024] 2. By setting up a return pipeline and a back pressure regulating component, the present invention creates a stable pressure field in the urea supply process. Combined with the pulse suppression structure of the metering unit, the flow fluctuation can be controlled within ±5%, thereby improving the metering accuracy of urea injection.

[0025] 3. Through the synergistic effect of the gas-liquid switching structure and the delayed purging strategy, this invention can achieve active cleaning of the injection channel during shutdown and low load phases, reduce urea residue, and reduce the probability of nozzle crystallization blockage by more than 80%, thereby significantly reducing the risk of crystallization blockage. By tightly coupling and integrating the gas-liquid switching component with the injection component, the fluid path is shortened and residual liquid retention is reduced, reducing the gas-liquid switching response time to less than 1 second, thereby improving the dynamic response performance of the system. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the engine exhaust aftertreatment system described in this invention. Figure 2 This is a schematic diagram of the structure of the urea supply unit and urea tank described in this invention; Figure 3 This is a schematic diagram of the compressed air unit described in this invention; Figure 4 This is a schematic diagram of the connection of the metering unit described in this invention; Figure 5 This is a schematic diagram showing the connection between the gas-liquid switching unit and the injection unit described in this invention; Figure 6 This is a schematic diagram illustrating the principle of the automatic mode of the working method of the engine exhaust aftertreatment system described in this invention. Figure 7 This is a schematic diagram illustrating the principle of the manual mode of the engine exhaust aftertreatment system described in this invention. Detailed Implementation

[0027] 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.

[0028] like Figure 1 As shown, in this embodiment, an engine exhaust aftertreatment system is applied to the exhaust denitrification process of marine diesel engines or gas engines. The system is constructed around gas-liquid coordinated injection and multi-parameter closed-loop control. The whole system includes a control unit, a urea tank, a urea supply unit, a compressed air unit, a metering unit, a gas-liquid switching unit, and an injection unit. The various units are connected by liquid pipelines, gas pipelines, and cables to form a coordinated system.

[0029] like Figure 1 , 2 As shown, the urea tank stores urea solution and is equipped with a low-level switch and a level sensor for monitoring urea reserves and controlling replenishment. A urea tank temperature sensor detects changes in the urea solution temperature. This temperature detection structure not only performs routine monitoring but also serves as a crucial input parameter for the control unit, participating in system operation decisions. When the temperature is in the low-temperature range, the system can proactively identify the risk of crystallization, preventing urea from entering the injection channel and suppressing crystallization blockage at its source. Compared to traditional reactive maintenance methods, this automated approach actively avoids blockages. Figure 2 As shown, the urea supply unit is connected to the urea tank and employs a structure combining multiple pumps in parallel and reflux regulation. Specifically, at least two sets of supply pumps are connected in parallel and linked to a filter. The urea tank outlet enters the supply pump inlet via the filter. The supply pump output is connected to the metering unit via a liquid pipeline and reconnected to the urea tank via a vent valve, safety valve, and reflux pipeline, thus forming a circulating supply path. In this structure, the urea solution continuously circulates within the system, and a dynamic pressure stabilization state is achieved through the back pressure regulation component. This design effectively reduces flow pulsation and pressure fluctuations caused by single-pump supply, improving supply stability. Simultaneously, the multi-pump parallel structure allows for redundant or staged supply, flexibly switching between different load conditions, improving system adaptability and reliability.

[0030] like Figure 1 , 3As shown, the compressed air unit provides compressed air at a stable pressure and adjusts the output pressure through a pressure-reducing component to meet the needs of different operating stages. Compressed air not only participates in the injection process but also plays a crucial cleaning role in the system. In conjunction with the gas-liquid switching unit, compressed air can purge the injection channel during non-injection phases, thereby promptly removing residual urea solution and preventing its deposition and crystallization at low temperatures or during shutdown. This gas-assisted cleaning mechanism offers significant advantages in anti-clogging performance compared to traditional single-liquid injection systems.

[0031] like Figure 1 , 4 As shown, the metering unit is connected to both the urea supply unit and the compressed air unit, and internally includes a metering pump, a pressure sensing element, and a pulse damping assembly. During urea delivery, the pressure sensing element is used to collect pressure changes in real time, and the pulse damping assembly is used to suppress pressure fluctuations caused by pump operation, thereby making the output flow more stable. This structure can significantly improve metering accuracy, making the injection volume more closely match actual needs, avoiding problems of over- or under-injection due to flow fluctuations, thereby improving denitrification efficiency and reducing the risk of ammonia escape.

[0032] like Figure 1 , 5 As shown, the gas-liquid switching unit adopts a three-way valve structure, with its two input ends connected to the urea channel and the compressed air channel respectively, and its output end tightly coupled to the injection unit. This tightly coupled structure can significantly shorten the fluid path, reduce the urea retention volume in the pipeline, and reduce the risk of crystallization from a structural perspective. Simultaneously, the rapid switching capability of the three-way valve enables rapid conversion between gas and liquid, improving the system's response speed under different operating conditions. The integrated arrangement of the injection unit and the gas-liquid switching unit makes the injection execution process more compact and efficient, which is beneficial to improving overall dynamic performance.

[0033] like Figure 1 As shown, the control unit is connected to various actuators and sensors via cables, including the urea tank, urea supply unit, compressed air unit, metering unit, gas-liquid switching unit, injection unit, and front and rear NOx sensors. The control unit internally includes a central processing module and an input / output module, with the input / output module configured as 8 digital inputs, 8 digital outputs, 8 analog inputs, and 2 analog outputs. This multi-channel structure can simultaneously receive multiple signals, enabling comprehensive monitoring of temperature, pressure, NOx concentration, and equipment status, and parallel control of multiple actuators. This supports multi-parameter coupled control strategies, improving system response speed and control accuracy.

[0034] like Figure 6 , 7As shown, during operation, the system employs a control method combining automatic and manual modes. In automatic mode, after power-on, the system first performs a status check and enters standby mode after confirming there are no faults. When the engine load reaches the first threshold, the system enters the pre-processing stage, controlling the compressed air unit to open and switching the gas-liquid switching unit to the compressed air channel to pre-purge the injection channel. This pre-purge process removes residual liquid before injection, ensuring the channel is dry, thereby improving subsequent injection stability.

[0035] like Figure 6 , 7 As shown, once the reactor temperature reaches the preset threshold, the system enters the injection stage. The gas-liquid switching unit switches to the urea channel, and the metering unit begins to output urea solution. During injection, the control unit performs open-loop control based on the engine load, while simultaneously using closed-loop adjustment in conjunction with the nitrogen oxide concentration signals from both the front and rear ends to maintain the nitrogen oxide conversion rate within the set range. This combined open-loop and closed-loop control method ensures both system response speed and improved control accuracy, offering better adaptability compared to a single control method.

[0036] like Figure 1 , 6 As shown in Figure 7, when the engine load drops below the second threshold, the reactor temperature decreases, or the system detects an anomaly, the system enters the shutdown process. At this time, urea injection stops, and the gas-liquid switching unit is switched to the compressed air channel. Subsequently, compressed air is continuously output for a preset time to purge the injection channel with a delay. This delayed purging mechanism thoroughly removes residual urea solution after shutdown, a key measure to prevent crystallization blockage, and significantly improves the long-term reliability of the system compared to traditional immediate shutdown methods. Furthermore, by setting the first and second thresholds to form a load hysteresis range, the system can avoid frequent switching of operating states under critical load conditions, thereby improving system stability. The control unit also coordinates control with urea tank temperature and level signals to limit injection behavior under low temperature or low level conditions, reducing system risk from multiple dimensions.

[0037] like Figure 1 , 6 As shown in Figure 7, in manual or test mode, the control unit independently controls each actuator according to external input commands, realizing compressed air solenoid valve control, load signal simulation, supply pump start / stop, and injection flow rate adjustment. This mode facilitates system debugging and maintenance, and improves the flexibility of engineering applications.

[0038] Through the synergistic effect of the above-mentioned structure and control strategy, this embodiment has significantly improved in terms of anti-crystallization capability, supply stability, injection accuracy and system response performance, and can adapt to the exhaust gas treatment requirements under complex working conditions.

[0039] Working principle of the invention: The engine exhaust aftertreatment system of this invention is based on the selective catalytic reduction (SCR) mechanism, achieving efficient conversion of nitrogen oxides through the coordinated control of urea solution and compressed air. The system comprises a urea tank, a urea supply unit, a metering unit, a compressed air unit, a gas-liquid switching unit, an injection unit, and a control unit. The urea tank stores the urea solution and monitors its status in real time using temperature and level sensors. The urea supply unit, through a supply pump, return pipeline, and back pressure regulating components, ensures a stable circulation and pressure environment for the urea solution within the system, guaranteeing subsequent metering accuracy. The metering unit, in conjunction with pressure detection and pulse suppression structures, accurately meters and outputs the urea solution. The compressed air unit provides a stable air source. The gas-liquid switching unit and injection unit achieve selective flow between urea and air paths via a three-way structure, delivering the corresponding medium to the injection end and into the exhaust pipe. The control unit, as the core control hub, comprehensively receives signals from multiple sources, including engine load, reactor temperature, and NOx concentrations at both ends, coordinating and controlling the operating status of each unit to construct a closed-loop control system.

[0040] In practical operation, this invention employs a multi-mode collaborative control mechanism to achieve a smooth transition from startup to stable operation. After power-on, the system first enters the initialization phase, performing self-checks on all sensors and execution units. Once no faults are confirmed, it enters standby mode. When the engine load reaches the first threshold, the system enters the flushing preparation phase, controlling the compressed air unit to open and driving the gas-liquid switching component to switch to the air channel. This allows compressed air to pre-purge the injection pipeline, thereby removing residual urea and avoiding the risk of subsequent crystallization. When the downstream temperature of the reactor reaches a set threshold (e.g., 280°C), the system switches to metering injection mode. The gas-liquid switching component switches to the urea channel, and the metering unit performs open-loop injection according to the engine load. Simultaneously, closed-loop correction is implemented based on NOx sensor feedback, ensuring the nitrogen oxide conversion rate remains stable within the target range. Throughout this process, the control unit continuously monitors the load, temperature, and emission status dynamically, adjusting the injection volume or control status in real time based on changes, thus ensuring the system maintains stable and efficient denitrification performance under different operating conditions.

[0041] Furthermore, this invention effectively solves the problem of easy crystallization and blockage in traditional SCR systems by introducing a gas-liquid coordinated control and delayed purging mechanism. When the engine load is detected to be below the second threshold, the reactor temperature drops, or the system malfunctions, the control unit immediately stops urea injection and switches the gas-liquid switching component back to the compressed air channel. Subsequently, compressed air is continuously output for a preset time (e.g., 5-20 minutes) to thoroughly purge the injection unit and related pipelines, thereby removing residual urea solution and significantly reducing the risk of crystallization and deposition. At the same time, the detection results of the urea tank temperature sensor are used to participate in control decisions. Under low-temperature conditions, the air channel is kept open first, and urea is prohibited from entering the injection path to further avoid low-temperature crystallization problems. The system is allowed to enter the injection state only after the temperature recovers.

[0042] Through the synergistic effect of the above-mentioned structure and control strategy, the present invention achieves high injection precision, fast response speed and strong anti-clogging ability in exhaust gas aftertreatment, which is significantly improved in terms of reliability, stability and environmental adaptability compared with traditional systems.

[0043] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments are merely illustrative of the technical concept and characteristics of the present invention, intended to enable those skilled in the art to understand and implement the invention, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An engine exhaust aftertreatment system, comprising a control unit, a urea supply unit, a compressed air unit, a metering unit, a gas-liquid switching unit, and an injection unit, characterized in that: The urea supply unit is used to provide a stable urea supply. It is equipped with at least one set of supply pumps, return pipelines and back pressure regulating components to form a circulation supply path, so that the urea solution forms a dynamic pressure stabilization state during the supply process. The compressed air unit is used to provide compressed air at a stable pressure and regulates the output pressure through a pressure reducing component to meet the gas supply requirements under different working conditions. The metering unit is connected to the urea supply unit and the compressed air unit respectively, and is used to quantitatively deliver the urea solution and reduce flow fluctuations through a pulse damping structure. The gas-liquid switching unit and the injection unit are used to selectively switch between the urea channel and the compressed air channel, and form a tightly coupled connection structure with the injection unit to shorten the fluid path and reduce residual liquid retention. The control unit is electrically connected to the urea supply unit, compressed air unit, metering unit, and gas-liquid switching unit, and controls the system operating status based on engine operating parameters.

2. An engine exhaust aftertreatment system as in claim 1, wherein: It also includes a urea tank for storing urea solution; a urea supply unit is connected to the urea tank for delivering urea solution to the metering unit; the return pipeline of the urea supply unit is connected to the output end of the supply pump and back to the urea tank so that the urea solution forms a circulating flow and maintains a stable output pressure. The urea tank is equipped with a low level switch and a level sensor to replenish the urea solution; a urea tank temperature sensor is also provided to monitor the urea solution temperature and prevent crystallization.

3. An engine exhaust aftertreatment system as in claim 2, wherein: The control unit is electrically connected to the urea supply unit, urea chamber, compressed air unit, metering unit, gas-liquid switching unit, injection unit, front-end nitrogen oxide sensor, and rear-end nitrogen oxide sensor via cables to realize the transmission of control signals to each unit; the front-end nitrogen oxide sensor and the rear-end nitrogen oxide sensor obtain the nitrogen oxide concentration at the inlet and outlet of the SCR reaction chamber. The urea supply unit is connected to the metering unit via two liquid pipelines for transporting and returning urea solution; the compressed air unit is connected to the metering unit via a gas pipeline for transporting compressed air. The output of the metering unit is connected to the gas-liquid switching unit through a liquid pipeline and a gas pipeline. The output of the gas-liquid switching unit delivers compressed air to the injection unit through the gas pipeline and urea solution to the injection unit through the liquid pipeline, and switches between urea solution and compressed air.

4. An engine exhaust aftertreatment system as in claim 3, wherein: The control unit includes a central processing module and an input / output module electrically connected thereto. The input / output module includes: Digital input / output module, used to acquire switch signals and output control signals; Analog input module, used to acquire temperature and pressure signals; Analog output module, used to output analog signals to control the metering pump; The digital input / output module has 8 inputs and 8 outputs, the analog input module has 8 channels, and the analog output module has 2 channels.

5. An engine exhaust aftertreatment system as in claim 1, wherein: The gas-liquid switching component is a three-way valve structure, with its switching end connected to the urea channel and the compressed air channel respectively.

6. An engine exhaust aftertreatment system as in claim 1, wherein: The metering unit includes a metering pump, a pressure detection element, and a pulse damping assembly, which are used to accurately meter and stably output urea solution.

7. An engine exhaust aftertreatment system as in claim 1, wherein: The urea supply unit includes at least two supply pumps, which are connected to the filter before being connected in parallel, and the urea outlet of the urea tank is connected to the filter; In addition to being connected to the metering unit via liquid pipelines, the supply pump is also connected to parallel vent valves and safety valves, and then connected to the urea return port of the urea tank to achieve redundant supply or tiered supply.

8. A method of operating an engine exhaust aftertreatment system according to any of claims 1-8, comprising an automatic mode, characterized by: Includes the following automatic modes: S1. System initialization steps, After the system is powered on, the control unit detects the system status and enters standby mode when it confirms that there is no fault in the system. S2. Rinse preparation steps. When the engine load signal is detected to reach the first threshold, the compressed air unit is controlled to open, and the gas-liquid switching unit is controlled to switch to the compressed air channel, so that compressed air continuously passes through the channel of the injection unit for pre-purging. S3, Metering spraying step. When the downstream temperature of the reactor is detected to reach a preset temperature threshold: Control the gas-liquid switching unit to switch to the urea channel; The control metering unit performs open-loop injection control according to the engine load; Five minutes after the open-loop operation begins, closed-loop regulation is performed based on the nitrogen oxide concentration signal to maintain the nitrogen oxide conversion rate within the set range. S4. State maintenance and dynamic adjustment steps. During the metering injection process, the engine load, reactor temperature, and nitrogen oxide concentration are continuously monitored, and the injection volume of the urea injection unit is dynamically adjusted based on the monitoring results. S5, Shutdown determination procedure. When any of the following conditions are detected: Engine load is below the second threshold; or The downstream temperature of the reactor is lower than the preset temperature threshold; or The system malfunctioned; Then proceed with the shutdown procedure: Stop the metering unit from operating and control the gas-liquid switching unit to switch to the compressed air channel; S6. Delayed purging procedure. After stopping urea injection, the compressed air is continuously output for a preset time to purge and clean the injection channel; After the delayed purging is completed, shut off the compressed air supply.

9. The operating method of an engine exhaust aftertreatment system according to claim 8, characterized in that: The control unit determines the injection conditions based on at least two parameters among engine load, reactor temperature, and nitrogen oxide concentration. The control unit adopts a combination of open-loop and closed-loop control. The open-loop control determines the urea injection quantity based on the engine load, while the closed-loop control corrects the injection quantity based on the nitrogen oxide concentration.

10. The operating method of an engine exhaust aftertreatment system according to claim 8, characterized in that: Also includes manual / test mode: The control unit receives manually input commands and performs at least one of the following operations based on the commands: The solenoid valve controls the opening and closing of the compressed air unit; Receives a set engine load signal and controls the operating status of the metering unit based on the load signal; Control the start and stop of the supply pump in the urea supply unit; Adjust the urea output flow rate of the metering unit.

11. The operating method of an engine exhaust aftertreatment system according to claim 8, characterized in that: The engine's first threshold is used to determine whether to enter the injection preparation state. When the engine load is higher than the first threshold, the system is allowed to enter the flushing or injection preparation stage. The second threshold is used to determine whether to exit the injection state. When the engine load is lower than the second threshold, the system stops urea injection and enters the shutdown process. The first threshold is greater than or equal to the second threshold to form a load hysteresis interval, thereby avoiding frequent switching of the system's operating state near the critical load.

12. The operating method of an engine exhaust aftertreatment system according to claim 2, characterized in that: The control unit coordinates the gas-liquid switching state and injection state based on the urea tank level and temperature signals, including: When the temperature in the urea tank is below the crystallization risk threshold, compressed air purging should be maintained first. When the urea tank level is below the preset value, it is forbidden to enter the urea injection mode and the gas channel must be kept open. Switching to the urea injection path is only permitted after the urea tank temperature recovers or the liquid level meets the requirements.

13. The operating method of an engine exhaust aftertreatment system according to claim 8, characterized in that: The preset time for maintaining continuous compressed air output after urea injection stops is 15 minutes.

14. The operating method of an engine exhaust aftertreatment system according to claim 8, characterized in that: The injection volume of the injection unit is adjusted in a closed loop based on the concentration of nitrogen oxides, with the conversion rate of nitrogen oxides as the control target, so that the conversion rate is maintained within a preset range.

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