Non-road national V diesel engine post-processing system and control method

Abstract

The invention discloses a non-road national V diesel engine post-processing system and a control method, and belongs to the technical field of engine post-processing, the non-road national V diesel engine post-processing system comprises a first exhaust pipeline, a second exhaust pipeline, a third exhaust pipeline, a three-way electromagnetic valve, a heating unit and a cooler, and the heating unit is installed on the second exhaust pipeline and connected with an ECU control unit; the cooler is mounted on the third exhaust pipeline; the first exhaust pipeline, the second exhaust pipeline and the third exhaust pipeline are connected through a three-way electromagnetic valve; the DOC assembly, the DPF assembly, the SCR assembly and the ASC assembly are sequentially arranged on the second exhaust pipeline. The ECU controls opening and closing of the three-way electromagnetic valve branch and the heating unit and controls the temperature of exhaust entering aftertreatment. And the urea injection amount is controlled through the NOX measured value and the SCR average exhaust temperature. The exhaust temperature is stabilized within the exhaust temperature interval of the highest SCR conversion efficiency by heating the tail gas with the low exhaust temperature and cooling the tail gas with the high exhaust temperature, a proper amount of urea is sprayed, it is ensured that emission can be effectively controlled, and the requirements of emission regulations are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of engine after-treatment, and particularly relates to a non-road national V diesel engine after-treatment system and a control method therefor. Background Art

[0002] With the continuous tightening of emission regulations, the non-road Euro V regulations are currently implemented in Europe. When upgrading from national IV to non-road Euro V, the emission pollutant limits are further reduced. In the power range of 56kW - 130kW, the NOx emission limit is reduced by 87.9%. In the power range of 130kW - 560kW, the NOx emission limit is reduced by 80%. The PM emission limit in the range of 56kW - 560kW is reduced by 40%, the PN emission limit in the range of 56kW - 560kW is reduced by 80%, and the ammonia leakage emission limit is reduced by 60%.

[0003] Existing after-treatment systems usually adopt the configuration of DOC + DPF + high-efficiency SCR + ASC. To reduce NOx, it is necessary to close part of the throttle opening at low temperatures to increase the exhaust gas temperature of the engine, thereby increasing the conversion efficiency of SCR. However, closing the throttle causes a reduction in the intake air volume, resulting in deteriorated combustion, which not only severely deteriorates the fuel consumption of the engine, but also increases soot and exacerbates the risk of DPF blockage. At high temperatures, due to the reduced SCR efficiency, more urea needs to be injected to reduce NOx emissions. The catalytic efficiency of ASC decreases at high temperatures, further exacerbating the risk of ammonia leakage. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a non-road national V diesel engine after-treatment system and a control method therefor. By heating the exhaust gas with a relatively low exhaust temperature and cooling the exhaust gas with a relatively high exhaust temperature, the exhaust gas temperature is stabilized within the exhaust temperature range of the highest SCR conversion efficiency, and an appropriate amount of urea is injected to ensure effective emission control and meet the requirements of emission regulations.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A non-road national V diesel engine after-treatment system includes a first exhaust pipe, a second exhaust pipe, a third exhaust pipe, a three-way solenoid valve, a heating unit, a cooler, and an ECU control unit. One end of the first exhaust pipe is connected to the exhaust end of the engine, and the other end is connected to the intake port of the three-way solenoid valve. The two outlet ports of the three-way solenoid valve are respectively connected to the intake ends of the second exhaust pipe and the third exhaust pipe; The heating unit is provided on the second exhaust pipe, and the cooler is provided on the third exhaust pipe. The exhaust end of the third exhaust pipe after passing through the cooler is communicated with the exhaust end of the second exhaust pipe after passing through the heating unit; The described heating unit and the three-way solenoid valve are both electrically connected to the ECU control unit, and the opening and closing of the three-way solenoid valve branch and the heating unit are controlled by the ECU control unit; The liquid inlet end and the liquid return end of the described cooler communicate with the engine cooling system.

[0006] The described after-treatment system further includes a DOC assembly, a DPF assembly, an SCR assembly, an ASC assembly, a first nitrogen oxide sensor, a second nitrogen oxide sensor, a first temperature sensor, a second temperature sensor, a third temperature sensor, a fourth temperature sensor, and a differential pressure sensor; The described DOC assembly, DPF assembly, SCR assembly, and ASC assembly are sequentially arranged on the second exhaust pipe, and the described DOC assembly is arranged at the rear end of the connection between the second exhaust pipe and the third exhaust pipe; The described first nitrogen oxide sensor is arranged at the front end of the intake of the DOC assembly, the described second nitrogen oxide sensor is arranged at the rear end of the exhaust of the ASC assembly, and the first nitrogen oxide sensor and the second nitrogen oxide sensor cooperate to calculate the urea injection amount; The described first temperature sensor is arranged at the front end of the intake of the DOC assembly, the described second temperature sensor is arranged at the rear end of the exhaust of the DOC assembly, and the first temperature sensor and the second temperature sensor cooperate for after-treatment regeneration; The described third temperature sensor is arranged at the front end of the SCR assembly, the described fourth temperature sensor is arranged at the rear end of the exhaust of the ASC assembly, the third temperature sensor is used to detect whether the exhaust temperature is within the range of the SCR maximum conversion efficiency exhaust temperature range, the monitored values of the third temperature sensor and the fourth temperature sensor are used to calculate the average exhaust temperature of the SCR, and according to the SCR efficiency at different temperatures, in cooperation with the first nitrogen oxide sensor and the second nitrogen oxide sensor, the urea injection amount is calculated; The two ends of the described differential pressure sensor are respectively arranged at the front end of the intake and the rear end of the exhaust of the DPF assembly to determine whether the DPF needs regeneration; The described first nitrogen oxide sensor, second nitrogen oxide sensor, first temperature sensor, second temperature sensor, third temperature sensor, fourth temperature sensor, and differential pressure sensor are all electrically connected to the ECU; A urea injection device is arranged at the front end of the described SCR assembly, and a mixer is arranged at the outlet of the urea injection device.

[0007] A control method for an after-treatment system of a non-road national V diesel engine based on the above is used to control the after-treatment system, including: Control the exhaust gas temperature entering the SCR assembly to obtain a higher SCR conversion efficiency.

[0008] Calculate the urea injection amount in the open-loop state based on the original NOx flow rate, the average SCR exhaust temperature, the SCR conversion efficiency, the ammonia-nitrogen ratio, and the ammonia storage compensation amount.

[0009] Calculate the urea injection amount in the closed-loop state according to the NOx closed-loop coefficient, and control the urea injection device to inject urea.

[0010] The beneficial effects of the present invention are as follows: By heating the exhaust gas with a lower exhaust temperature and cooling the exhaust gas with a higher exhaust temperature, the exhaust temperature of the exhaust gas is stabilized within the exhaust temperature range of the highest SCR conversion efficiency. Inject an appropriate amount of urea, and the urea pyrolyzes into ammonia in the SCR, and under the action of the catalyst, the NOx is reduced to nitrogen and water, reducing NOx pollutants. At the same time, the excess ammonia is catalytically oxidized in the ASC, further reducing ammonia pollutants. The present invention can efficiently reduce NOx emissions while ensuring no ammonia leakage, meeting the requirements of emission regulations. Description of the Drawings

[0011] Figure 1 It is a schematic structural diagram of the aftertreatment system of the present invention.

[0012] Figure 2 It is a flowchart of the control method of the aftertreatment system of the present invention.

[0013] Figure 3 It is a flowchart of the exhaust temperature control in the control method of the aftertreatment system of the present invention.

[0014] Markings in the figure: 1. Engine, 2. First exhaust pipe, 3. Three-way solenoid valve, 4. Second exhaust pipe, 5. Heating unit, 6. Third exhaust pipe, 7. Cooler, 8. DOC assembly, 9. DPF assembly, 10. SCR assembly, 11. ASC assembly, 12. First nitrogen oxide sensor, 13. Second nitrogen oxide sensor, 14. First temperature sensor, 15. Second temperature sensor, 16. Third temperature sensor, 17. Fourth temperature sensor, 18. Differential pressure sensor, 19. Urea injection device. Detailed Embodiments

[0015] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the drawings of this specification. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] As Figure 1As shown in the figure: A post-treatment system for a non-road national V diesel engine according to the present invention includes a first exhaust pipe 2, a second exhaust pipe 4, a third exhaust pipe 6, a three-way solenoid valve 3, a heating unit 5, a cooler 7 and an ECU control unit. One end of the first exhaust pipe 2 is connected to the exhaust end of the engine 1, and the other end is connected to the intake port of the three-way solenoid valve 3. The two outlet ports of the three-way solenoid valve 3 are respectively connected to the intake end of the second exhaust pipe 4 and the intake end of the third exhaust pipe 6. The heating unit 5 is provided on the second exhaust pipe 4, and the cooler 7 is provided on the third exhaust pipe 6. The exhaust end of the third exhaust pipe 6 after passing through the cooler 7 is communicated with the exhaust end of the second exhaust pipe 4 after passing through the heating unit 5. The heating unit 5 and the three-way solenoid valve 3 are both electrically connected to the ECU control unit, and the opening and closing of the three-way solenoid valve 3 branch and the heating unit 5 are controlled by the ECU control unit. The liquid inlet end and the liquid return end of the cooler 7 are communicated with the cooling system of the engine 1.The post-treatment system further includes a DOC assembly 8, a DPF assembly 9, an SCR assembly 10, an ASC assembly 11, a first nitrogen oxide sensor 12, a second nitrogen oxide sensor 13, a first temperature sensor 14, a second temperature sensor 15, a third temperature sensor 16, a fourth temperature sensor 17, a differential pressure sensor 18, and a urea injection device 19. The DOC assembly 8, DPF assembly 9, SCR assembly 10, and ASC assembly 11 are sequentially arranged on the second exhaust pipe 4. The DOC assembly 8 is arranged at the rear end of the connection between the second exhaust pipe 4 and the third exhaust pipe 6. The first nitrogen oxide sensor 12 is arranged at the front end of the intake of the DOC assembly 8. The second nitrogen oxide sensor 13 is arranged at the rear end of the exhaust of the ASC assembly 11. The first nitrogen oxide sensor 12 and the second nitrogen oxide sensor 13 cooperate to calculate the urea injection amount. The first temperature sensor 14 is arranged at the front end of the intake of the DOC assembly 8. The second temperature sensor 15 is arranged at the rear end of the exhaust of the DOC assembly 8. The first temperature sensor 14 and the second temperature sensor 15 cooperate for post-treatment regeneration. The third temperature sensor 16 is arranged at the front end of the SCR assembly 10. The fourth temperature sensor 17 is arranged at the rear end of the exhaust of the ASC assembly 11. The third temperature sensor 16 is used to detect whether the exhaust temperature is within the SCR maximum conversion efficiency exhaust temperature range. The monitored values of the third temperature sensor 16 and the fourth temperature sensor 17 are used to calculate the average exhaust temperature of the SCR. According to the SCR efficiency at different temperatures, the urea injection amount is calculated in cooperation with the first nitrogen oxide sensor 12 and the second nitrogen oxide sensor 13. The two ends of the differential pressure sensor 18 are respectively arranged at the front end of the intake and the rear end of the exhaust of the DPF assembly 9 to determine whether the DPF needs regeneration. The first nitrogen oxide sensor 12, the second nitrogen oxide sensor 13, the first temperature sensor 14, the second temperature sensor 15, the third temperature sensor 16, the fourth temperature sensor 17, and the differential pressure sensor 18 are all electrically connected to the ECU. A urea injection device 19 is provided at the front end of the SCR assembly 10, and a mixer is provided at the outlet of the urea injection device 19.

[0017] As Figure 2 and Figure 3 shown: A control method for a post-treatment system of a non-road National V diesel engine based on the above, used to control the post-treatment system, includes the following: S301: Control the exhaust gas temperature entering the SCR assembly 10. According to the exhaust gas flow rate entering the SCR, and the monitored exhaust gas temperatures of the third temperature sensor 16 and the fourth temperature sensor 17, obtain the average SCR exhaust gas temperature and a higher SCR conversion efficiency. In the embodiment, controlling the exhaust gas temperature of the SCR assembly 10 specifically includes: When the exhaust gas temperature at the front end of the SCR assembly 10 monitored by the third temperature sensor 16 is between the first temperature threshold and the second temperature threshold, the ECU control unit controls the three-way solenoid valve 3 to open the branch connected to the second exhaust pipe 4 and close the branch connected to the third exhaust pipe 6; When the exhaust gas temperature at the front end of the SCR assembly 10 monitored by the third temperature sensor 16 is lower than the first temperature threshold, the ECU control unit controls the heating unit 5 to start working to heat the exhaust gas temperature until the exhaust gas temperature rises to the first temperature threshold, and then the heating unit 5 stops working; When the exhaust gas temperature at the front end of the SCR assembly 10 monitored by the third temperature sensor 16 is higher than the second temperature threshold, the ECU controls the three-way solenoid valve 3 to open the branch connected to the third exhaust pipe 6 and close the branch connected to the second exhaust pipe 4, and the cooler 7 provided in the third exhaust pipe 6 cools the exhaust gas temperature until the exhaust gas temperature drops below the second temperature threshold. At this time, the ECU control unit controls the three-way solenoid valve 3 to open the branch connected to the second exhaust pipe 4 and close the branch connected to the third exhaust pipe 6; The first temperature threshold is lower than the second temperature threshold; S302: Obtain the exhaust gas flow rate entering the aftertreatment, the first nitrogen oxide concentration monitored by the first nitrogen oxide sensor 12, the average SCR exhaust gas temperature, the SCR conversion efficiency, and the ammonia-nitrogen ratio, and determine the ammonia required to convert the first nitrogen oxide; S303: Calibrate the ammonia storage amount at different efficiencies according to the exhaust gas flow rate and the average SCR exhaust gas temperature, and determine the ammonia compensation amount according to the calibrated ammonia storage amount and the target ammonia storage amount; S304: Determine the urea injection amount in the open-loop state according to the ammonia required to convert the first nitrogen oxide and the ammonia compensation amount; S305: Obtain the nitrogen oxide concentration, SCR conversion efficiency, and exhaust gas flow rate monitored by the first nitrogen oxide sensor 12 and the second nitrogen oxide sensor 13, calculate the theoretical mass flow rate of nitrogen oxides at the outlet of the aftertreatment, and determine the NOx closed-loop coefficient through PI adjustment of the mass flow rate difference between the actual mass flow rate of nitrogen oxides obtained from the concentration monitored by the second nitrogen oxide sensor 13; S306: Control the urea injection device 19 to inject urea according to the urea injection amount in the open-loop state and the NOx closed-loop coefficient; In the above implementation, the urea injection amount Dosing is calculated according to the following formula, including: Dosing = 5.425×(1.587× NO X × m exh × NSR ×eff + mNH3 Ld)×SCRFBC fac Where: NOx is the concentration value of nitrogen oxides monitored by the first nitrogen oxide sensor 12; m exh is the exhaust gas mass flow; NSR is the ammonia-nitrogen ratio; eff is the conversion efficiency of SCR; mNH3 Ld is the ammonia storage compensation amount; SCRFBC fac is the NOx closed-loop coefficient.

[0018] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0019] The parts not detailed in the present invention are prior art.

Claims

1. A non-road national stage V diesel engine aftertreatment system, comprising a first exhaust pipe (2), a second exhaust pipe (4), a third exhaust pipe (6), a three-way solenoid valve (3), a warming-up unit (5), a cooler (7) and an ECU control unit, characterized in that: One end of the first exhaust pipe (2) is connected to the exhaust end of the engine (1), and the other end is connected to the intake port of the three-way solenoid valve (3). The two outlet ports of the three-way solenoid valve (3) are respectively connected to the intake end of the second exhaust pipe (4) and the intake end of the third exhaust pipe (6); A heating unit (5) is provided on the second exhaust pipe (4), and a cooler (7) is provided on the third exhaust pipe (6). The exhaust end of the third exhaust pipe (6) after passing through the cooler (7) is communicated with the exhaust end of the second exhaust pipe (4) after passing through the heating unit (5); Both the heating unit (5) and the three-way solenoid valve (3) are electrically connected to the ECU control unit, and the opening and closing of the three-way solenoid valve (3) branch and the heating unit (5) are controlled by the ECU control unit; The liquid inlet end and the liquid return end of the cooler (7) communicate with the engine (1) cooling system; 2. The aftertreatment system for a non-road national stage V diesel engine according to claim 1, wherein The after-treatment system further includes a DOC assembly (8), a DPF assembly (9), an SCR assembly (10), an ASC assembly (11), a first nitrogen oxide sensor (12), a second nitrogen oxide sensor (13), a first temperature sensor (14), a second temperature sensor (15), a third temperature sensor (16), a fourth temperature sensor (17), and a differential pressure sensor (18); The DOC assembly (8), the DPF assembly (9), the SCR assembly (10), and the ASC assembly (11) are sequentially arranged on the second exhaust pipe (4), and the DOC assembly (8) is arranged at the rear end of the connection between the second exhaust pipe (4) and the third exhaust pipe (6); The first nitrogen oxide sensor (12) is arranged at the front end of the intake of the DOC assembly (8), and the second nitrogen oxide sensor (13) is arranged at the rear end of the outlet of the ASC assembly (11). The first nitrogen oxide sensor (12) and the second nitrogen oxide sensor (13) cooperate to calculate the urea injection amount; The first temperature sensor (14) is arranged at the front end of the intake of the DOC assembly (8), and the second temperature sensor (15) is arranged at the rear end of the outlet of the DOC assembly (8). The first temperature sensor (14) and the second temperature sensor (15) cooperate for after-treatment regeneration; The third temperature sensor (16) is arranged at the front end of the SCR assembly (10), and the fourth temperature sensor (17) is arranged at the rear end of the outlet of the ASC assembly (11). The third temperature sensor (16) is used to detect whether the exhaust temperature is within the SCR maximum conversion efficiency exhaust temperature range. The monitoring values of the third temperature sensor (16) and the fourth temperature sensor (17) are used to calculate the average exhaust temperature of the SCR. According to the SCR efficiency at different temperatures, the urea injection amount is calculated in cooperation with the first nitrogen oxide sensor (12) and the second nitrogen oxide sensor (13); The differential pressure sensor (18) is arranged at the front end of the intake and the rear end of the outlet of the DPF assembly (9) respectively to judge whether the DPF needs regeneration.

3. The aftertreatment system for a non-road national stage V diesel engine according to claim 2, wherein: The described first nitrogen oxide sensor (12), second nitrogen oxide sensor (13), first temperature sensor (14), second temperature sensor (15), third temperature sensor (16), fourth temperature sensor (17), and differential pressure sensor (18) are all electrically connected to the ECU control unit.

4. The aftertreatment system for a non-road national stage V diesel engine according to claim 2, wherein: A urea injection device (19) is provided at the front end of the SCR assembly (10), and a mixer is provided at the outlet of the urea injection device (19).

5. A control method for a post-treatment system of a non-road national stage V diesel engine according to any one of claims 1 to 4, characterized in that: It includes the following: Control the exhaust gas temperature entering the SCR assembly (10) to obtain a higher SCR conversion efficiency; Calculate the urea injection amount in the open-loop state based on the original exhaust NOx flow rate, SCR average exhaust temperature, SCR conversion efficiency, ammonia-nitrogen ratio, and ammonia storage compensation amount; Calculate the urea injection amount in the closed-loop state according to the NOx closed-loop coefficient, and control the urea injection device (19) to inject urea.

6. The control method of a non-road national stage V diesel engine after-treatment system according to claim 5, characterized in that: Control the exhaust gas temperature of the SCR assembly (10), specifically including: When the third temperature sensor (16) monitors that the exhaust gas temperature at the front end of the SCR assembly (10) is between the first temperature threshold and the second temperature threshold, the ECU control unit controls the three-way solenoid valve (3) to open the branch connected to the second exhaust pipe (4), and the branch connected to the third exhaust pipe (6) is closed; When the third temperature sensor (16) monitors that the exhaust gas temperature at the front end of the SCR assembly (10) is lower than the first temperature threshold, the ECU control unit controls the heating unit (5) to start working to heat the exhaust gas temperature until the exhaust gas temperature rises to the first temperature threshold, and then the heating unit (5) stops working; When the third temperature sensor (16) monitors that the exhaust gas temperature at the front end of the SCR assembly (10) is higher than the second temperature threshold, the ECU controls the three-way solenoid valve (3) to open the branch connected to the third exhaust pipe (6), and the branch connected to the second exhaust pipe (4) is closed. The exhaust gas temperature is cooled by the cooler (7) provided in the third exhaust pipe (6) until the exhaust gas temperature drops below the second temperature threshold. At this time, the ECU control unit controls the three-way solenoid valve (3) to open the branch connected to the second exhaust pipe (4), and the branch connected to the third exhaust pipe (6) is closed.

7. The control method of a non-road national stage V diesel engine aftertreatment system according to claim 6, characterized in that: The described first temperature threshold is lower than the second temperature threshold.

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