A two-stage SCR system HC and S poisoning recovery control method

Abstract

The application discloses a kind of two-stage SCR system HC and S poisoning recovery control method, it is related to engine exhaust treatment technology.The conversion efficiency of front-stage SCR catalyst and rear-stage SCR catalyst is obtained, if the conversion efficiency of front-stage SCR catalyst is lower than the set efficiency threshold one, then trigger active regeneration strategy two, to make in-cylinder temperature keep at a set target temperature value;If the conversion efficiency of rear-stage SCR catalyst is lower than the set efficiency threshold two, then trigger active regeneration strategy one, to improve exhaust temperature to target temperature value;If the conversion efficiency of two-stage SCR catalyst is lower than the set efficiency threshold three, then trigger active regeneration strategy one, to improve exhaust temperature to target temperature value.The application can accurately determine which level SCR catalyst appears poisoning phenomenon, also can effectively and accurately restore the conversion efficiency of corresponding SCR catalyst, avoid SCR catalyst poisoning deepening influence engine system normal work, make engine emission meet emission requirements.

Description

Technical Field

[0001] This invention relates to engine exhaust gas treatment technology, and more specifically, to a method for restoring control of HC and S poisoning in a two-stage SCR system. Background Technology

[0002] The basic principle of selective catalytic reduction (SCR) technology is to add a reducing agent to the exhaust gas and use a suitable catalyst to promote the reaction between the reducing agent and NOx, while inhibiting the non-selective oxidation reaction between the reducing agent and oxygen. SCR systems can effectively reduce NOx emissions, and dual-stage SCR systems can further reduce NOx emissions, especially during cold starts. Dual-stage SCR systems help engines improve exhaust performance, reduce the need for thermal management, decrease soot generation rates, and reduce the frequency of DPF active regeneration, thereby reducing fuel consumption and CO2 emissions. However, engine component failure or damage leading to increased HC levels in the exhaust gas, or excessive sulfur content in the fuel, can poison the SCR catalyst. Both HC and sulfur poisoning in the engine's aftertreatment catalyst significantly weaken the SCR's ability to convert NOx. However, as the SCR carrier temperature increases, the inhibitory effect of HC poisoning weakens significantly, while the desulfurization effect of sulfur poisoning is positively correlated with temperature and time. HC-poisoned samples can achieve normal SCR conversion efficiency after being treated at 400℃; S-poisoned samples require high-temperature treatment above 550℃ for the SCR catalyst conversion efficiency to approach normal levels. When diesel fuel has a high sulfur content, a large amount of SO2 is produced after combustion in the engine. Under low-temperature conditions, SO2 reacts with NH3 to form ammonium sulfate, which deposits on the catalyst surface and hinders the contact between the reacting gases and the active centers, leading to catalyst deactivation. At the same time, SO2 reacts with the active metals in the SCR catalyst to form stable sulfates, which also lead to catalyst deactivation, causing emissions to exceed emission limits. Ammonium sulfate and sulfates require temperatures of 450℃ or even higher to decompose.

[0003] When SCR catalysts experience low SCR efficiency due to sulfur poisoning, the vehicle's aftertreatment system needs to be triggered to enter driving regeneration or parking mode to actively increase the aftertreatment system temperature and promptly remove deposited sulfides from the SCR catalyst surface to restore SCR performance. For two-stage SCR systems, determining which stage of the SCR catalyst is poisoned by sulfur (S) or chloroform (HC), and the regeneration control methods after S poisoning of each stage of the SCR catalyst, are ongoing research directions in this field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method for the recovery and control of HC and S poisoning in a two-stage SCR system. This method can accurately determine which stage of the SCR catalyst is poisoned and effectively and accurately restore the conversion efficiency of the corresponding SCR catalyst, thereby preventing the SCR catalyst poisoning from worsening and affecting the normal operation of the engine system, and ensuring that the engine emissions meet the emission requirements.

[0005] The present invention discloses a method for controlling the recovery of HC and S poisoning in a two-stage SCR system. This method obtains the conversion efficiency of the pre-stage SCR catalyst and the post-stage SCR catalyst. If the conversion efficiency of the pre-stage SCR catalyst is lower than a set efficiency threshold one, an active regeneration strategy two is triggered to maintain the in-cylinder temperature at a set target temperature value. If the conversion efficiency of the post-stage SCR catalyst is lower than the set efficiency threshold two, an active regeneration strategy one is triggered to increase the exhaust temperature to the target temperature value. If the conversion efficiency of the two-stage SCR catalyst is lower than a set efficiency threshold three, an active regeneration strategy one is triggered to increase the exhaust temperature to the target temperature value.

[0006] To further improve the process, the amount of NOx between the pre-stage SCR catalyst and the post-stage SCR catalyst is obtained and denoted as NOx1; the amount of NOx at the end of the post-stage SCR catalyst furthest from the pre-stage SCR catalyst is obtained and denoted as NOx2; the amount of NOx at the end of the pre-stage SCR catalyst furthest from the post-stage SCR catalyst is obtained and denoted as NOx3; and the conversion efficiency of the SCR catalyst is determined based on the correlation between NOx1, NOx2, and NOx3.

[0007] Furthermore, the conversion efficiency of the SCR catalyst is expressed as follows:

[0008] (NOx3-NOx1) / NOx3 represents the conversion efficiency of the pre-SCR catalyst;

[0009] (NOx1-NOx2) / NOx1 represents the conversion efficiency of the subsequent SCR catalyst;

[0010] (NOx3-NOx2) / NOx3 represents the conversion efficiency of a two-stage SCR catalyst.

[0011] Furthermore, the first efficiency threshold is 50%-70%; the second efficiency threshold is 75%-95%; and the third efficiency threshold is 85%-95%.

[0012] As a further improvement, the active regeneration strategy one is to start in-cylinder remote injection and divide the exhaust gas from the engine into two parts: one part is discharged to the rear pipe of the front-stage SCR catalytic converter, and the other part is directly discharged to the rear pipe of the front-stage SCR catalytic converter; at the same time, exhaust throttling treatment is performed.

[0013] As a further improvement, the second active regeneration strategy is to perform cylinder deactivation on the engine, and after cylinder deactivation, obtain the second post-injection quantity based on the temperature difference between the target temperature and the actual measured temperature; and activate in-cylinder remote post-injection based on the second post-injection quantity, while simultaneously performing exhaust throttling.

[0014] Furthermore, the second post-injection quantity is calculated using the following formula:

[0015]

[0016] In the formula, u2(t) is the control parameter for the second injection quantity; K p The control proportional coefficient for the second injection quantity is denoted as e(t); the temperature deviation is denoted as T. i The two-integral control time for the post-injection quantity; d t t is the double integral time of the post-injection quantity; de(t) is the double derivative time of the post-injection quantity; and T is the derivative correction time of the fuel quantity deviation.

[0017] Further improvements include real-time monitoring of the SCR catalyst conversion efficiency after the active regeneration strategy is triggered.

[0018] If the regeneration time interval or regeneration mileage interval is greater than the set time threshold or mileage threshold, and the current conversion efficiency of the SCR catalyst is less than the corresponding efficiency threshold, an OBD alarm will be activated to remind you to check the urea injection system or urea solution.

[0019] If the regeneration time interval or regeneration mileage interval is less than the set time threshold or mileage threshold, and the current conversion efficiency of the SCR catalyst is greater than the corresponding efficiency threshold, then the OBD alarm will be activated to remind the user to add qualified fuel.

[0020] Beneficial effects

[0021] The advantages of this invention are as follows: by monitoring the NOx concentration values ​​of the engine's primary and exhaust gases, the overall conversion efficiency of the two-stage SCR system and the conversion efficiency of each stage of the SCR catalyst can be determined. Then, by comparing the conversion efficiency with the corresponding efficiency threshold, the corresponding active regeneration strategy is triggered based on the comparison results. This can accurately determine which stage of the SCR catalyst is poisoned and effectively and accurately restore the conversion efficiency of the corresponding SCR catalyst, avoiding the deepening of SCR catalyst poisoning and its impact on the normal operation of the engine system, so that the engine emissions meet the emission requirements. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the two-stage SCR system structure of the present invention;

[0023] Figure 2This is a schematic diagram of the recovery control method for HC and S poisoning in the two-stage SCR system of the present invention.

[0024] Figure 3 This is a logic diagram of the active regeneration strategy of the present invention;

[0025] Figure 4 This is a schematic diagram of the active regeneration strategy two of the present invention;

[0026] Figure 5 This is a comparison chart of the conversion efficiency of the SCR catalyst at 200℃ before and after regeneration at different regeneration temperatures. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0028] See Figures 1-5 This invention discloses a method for restoring control of HC and S poisoning in a two-stage SCR system. Before implementing this method, some structural modifications to the two-stage SCR system are required. For example, in the pre-stage SCR catalyst (i.e....) Figure 1 A bypass pipe is provided at both ends of the tightly coupled SCR, and a reversing valve is installed in the pipe. This structural improvement is mainly used to implement the active regeneration strategy.

[0029] The recovery control method in this embodiment is to obtain the pre-stage SCR catalyst and the post-stage SCR catalyst (i.e., Figure 1 The conversion efficiency of the SCR (Sequencing Catalyst Catalyst) in the chassis is mainly determined by the relationship between NOx on both sides of the catalyst.

[0030] Specifically, the amount of NOx between the pre-stage SCR catalyst and the post-stage SCR catalyst is recorded as NOx1; the amount of NOx at the end of the post-stage SCR catalyst furthest from the pre-stage SCR catalyst is recorded as NOx2; and the amount of NOx at the end of the pre-stage SCR catalyst furthest from the post-stage SCR catalyst is recorded as NOx3.

[0031] (NOx3-NOx1) / NOx3 represents the conversion efficiency of the pre-stage SCR catalyst; (NOx1-NOx2) / NOx1 represents the conversion efficiency of the post-stage SCR catalyst; and (NOx3-NOx2) / NOx3 represents the conversion efficiency of the two-stage SCR catalyst.

[0032] If the conversion efficiency of the pre-stage SCR catalytic converter is lower than the set efficiency threshold one, active regeneration strategy two is triggered to maintain the in-cylinder temperature at a set target temperature value, such as above 550°C, thus achieving regeneration. If the conversion efficiency of the post-stage SCR catalytic converter is lower than the set efficiency threshold two, active regeneration strategy one is triggered to raise the exhaust temperature to the target temperature value. If the conversion efficiency of the two-stage SCR catalytic converter is lower than the set efficiency threshold three, active regeneration strategy one is triggered to raise the exhaust temperature to the target temperature value.

[0033] This invention monitors the NOx concentrations in the engine's primary and secondary exhaust gases to determine the overall conversion efficiency of the two-stage SCR system and the conversion efficiency of each stage of the SCR catalyst. By comparing the conversion efficiency with corresponding efficiency thresholds, it triggers an active regeneration strategy based on the comparison results. This approach can accurately identify which stage of the SCR catalyst is poisoned and effectively and accurately restore the conversion efficiency of the corresponding SCR catalyst, preventing further poisoning of the SCR catalyst from affecting the normal operation of the engine system and ensuring that engine emissions meet emission requirements.

[0034] In this embodiment, the first efficiency threshold is 50%-70%; the second efficiency threshold is 75%-95%; and the third efficiency threshold is 85%-95%.

[0035] For the first active regeneration strategy, specifically, after determining the post-injection quantity, in-cylinder remote post-injection is initiated. Simultaneously, the reversing valve is controlled to divide the engine exhaust gas into two parts: one part is discharged through the pre-stage SCR catalytic converter to its rear-end pipe, and the other part is directly discharged to the rear-end pipe of the pre-stage SCR catalytic converter. Exhaust gas throttling is also performed concurrently.

[0036] The rear injection quantity and the opening degree of the reversing valve are expressed by the following formulas:

[0037]

[0038] In the above formula, u(t1) is the control parameter for the in-cylinder remote and rear fuel injection quantity; K p1 The post-injection quantity is the control proportional coefficient; e(t) is the temperature deviation; K i1 T is the integral control coefficient for the post-injection quantity. i1 The integral control time for the post-injection quantity; d t1 K is the integral time of the subsequent fuel injection quantity; d1 T is the differential control coefficient for the post-injection quantity. d1 Here, de(t1) is the derivative control time of the post-injection quantity; t1 is the post-injection quantity time based on regeneration temperature correction; u(t2) is the control parameter for the opening degree of the bypass valve; K p2 K is the proportional coefficient for controlling the opening degree of the bypass valve.i2 T is the integral control coefficient for the bypass valve opening. i2 The integral control time for the bypass valve opening; d t2 K is the integral time for the bypass valve opening. d2 T is the differential control coefficient for the bypass valve opening; d2 t1 is the differential control time of the bypass valve opening; de(t2) is the differential time of the bypass valve; t2 is the time of the bypass valve opening based on the regeneration temperature correction; t1 is the time of the post-injection quantity based on the regeneration temperature correction; t2 is the time of the bypass valve opening based on the regeneration temperature correction; t is the regeneration temperature correction time, t=t1+t2.

[0039] The second active regeneration strategy involves performing cylinder deactivation on the engine. After cylinder deactivation, the second post-injection quantity is obtained based on the temperature difference between the target temperature and the actual measured temperature. Based on this second post-injection quantity, in-cylinder remote post-injection is initiated, while simultaneously performing exhaust throttling.

[0040] The second post-injection quantity is calculated using the following formula.

[0041]

[0042] In the formula, u2(t) is the control parameter for the second injection quantity; K p The control proportional coefficient for the second injection quantity is denoted as e(t); the temperature deviation is denoted as T. i The two-integral control time for the post-injection quantity; d t t is the double integral time of the post-injection quantity; de(t) is the double derivative time of the post-injection quantity; and T is the derivative correction time of the fuel quantity deviation.

[0043] Once the active regeneration strategy is triggered, the SCR catalyst conversion efficiency is monitored in real time. If the regeneration time interval or regeneration mileage interval is greater than the set time threshold or mileage threshold, and the current conversion efficiency of the SCR catalyst is less than the corresponding efficiency threshold, an OBD alarm is activated to remind the user to check the urea injection system or urea solution. If the regeneration time interval or regeneration mileage interval is less than the set time threshold or mileage threshold, and the current conversion efficiency of the SCR catalyst is greater than the corresponding efficiency threshold, an OBD alarm is activated to remind the user to add qualified fuel. This setup accurately and promptly alerts the user to take appropriate measures when the SCR catalyst is poisoned or regeneration is abnormal, ensuring normal engine operation.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention, and these will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for recovery control of HC and S poisoning in a two-stage SCR system, characterized in that, The conversion efficiency of the pre-stage SCR catalyst and the post-stage SCR catalyst is obtained. If the conversion efficiency of the pre-stage SCR catalyst is lower than the set efficiency threshold one, the active regeneration strategy two is triggered to keep the in-cylinder temperature at a set target temperature value. If the conversion efficiency of the post-stage SCR catalyst is lower than the set efficiency threshold two, the active regeneration strategy one is triggered to increase the exhaust temperature to the target temperature value. If the conversion efficiency of the two-stage SCR catalyst is lower than the set efficiency threshold three, then the active regeneration strategy one is triggered to increase the exhaust temperature to the target temperature value. The amount of NOx between the pre-stage SCR catalyst and the post-stage SCR catalyst is obtained and denoted as NOx1. The amount of NOx at the end of the downstream SCR catalyst furthest from the upstream SCR catalyst is recorded as NOx2; the amount of NOx at the end of the upstream SCR catalyst furthest from the downstream SCR catalyst is recorded as NOx3; the conversion efficiency of the SCR catalyst is determined based on the correlation between NOx1, NOx2 and NOx3. The conversion efficiency of an SCR catalyst is expressed as: (NOx3-NOx1) / NOx3 represents the conversion efficiency of the pre-SCR catalyst; (NOx1-NOx2) / NOx1 represents the conversion efficiency of the subsequent SCR catalyst; (NOx3-NOx2) / NOx3 represents the conversion efficiency of a two-stage SCR catalyst; The active regeneration strategy one is to start in-cylinder remote injection and divide the exhaust gas from the engine into two parts. One part is discharged to the rear pipe of the front-stage SCR catalytic converter, and the other part is directly discharged to the rear pipe of the front-stage SCR catalytic converter; at the same time, exhaust throttling treatment is performed. The second active regeneration strategy involves performing cylinder deactivation on the engine, obtaining the second post-injection quantity based on the temperature difference between the target temperature and the actual measured temperature after cylinder deactivation, and activating in-cylinder remote post-injection based on the second post-injection quantity while simultaneously performing exhaust throttling.

2. The recovery control method for HC and S poisoning in a two-stage SCR system according to claim 1, characterized in that, The first efficiency threshold is 50%-70%; the second efficiency threshold is 75%-95%; and the third efficiency threshold is 85%-95%.

3. The recovery control method for HC and S poisoning in a two-stage SCR system according to claim 1, characterized in that, The second post-injection quantity is calculated using the following formula. ； In the formula, u2(t) is the control parameter for the second injection quantity; K p The control proportional coefficient for the second injection quantity is denoted as e(t); the temperature deviation is denoted as T. i The two-integral control time for the post-injection quantity; d t t is the double integral time of the post-injection quantity; de(t) is the double derivative time of the post-injection quantity; and T is the derivative correction time of the fuel quantity deviation.

4. The recovery control method for HC and S poisoning in a two-stage SCR system according to claim 1, characterized in that, After the active regeneration strategy is triggered, the conversion efficiency of the SCR catalyst is monitored in real time. If the regeneration time interval or regeneration mileage interval is greater than the set time threshold or mileage threshold, and the current conversion efficiency of the SCR catalyst is less than the corresponding efficiency threshold, an OBD alarm will be activated to remind you to check the urea injection system or urea solution. If the regeneration time interval or regeneration mileage interval is less than the set time threshold or mileage threshold, and the current conversion efficiency of the SCR catalyst is greater than the corresponding efficiency threshold, then the OBD alarm will be activated to remind the user to add qualified fuel.

Images