A National VI emission after-treatment system for automobiles

Abstract

The invention discloses a National VI automobile exhaust after-treatment system, belonging to the technical field of automobile exhaust treatment, comprising an exhaust pipe front section, an exhaust pipe rear section, a control system, and an exhaust gas temperature regulator, a DOC, a DPF, an SCR, an ASC ammonia slip catalyst and a pyrolyzer which are sequentially connected in series between the exhaust pipe front section and the exhaust pipe rear section; the control system is composed of a controller, a first temperature sensor installed at an SCR inlet end, a second temperature sensor installed at a DPF inlet end, a first pressure sensor installed at a DPF inlet end and a second pressure sensor installed at a DPF outlet end; the system can control the emission temperature and airspeed of all working conditions, implement high temperature protection for the catalyst of each device, and control the minimum filter layer of the DPF during continuous passive regeneration; the contact opportunity between the exhaust gas and the catalyst is increased, and the maximum efficiency maximization and the back pressure minimization can be achieved at the same time; the catalyst of the patent has a fast cold start, high conversion efficiency in each working condition, small exhaust resistance, stable performance, long service life and low cost.

Description

Technical field:

[0001] This patent relates to the field of automobile exhaust treatment technology, and in particular to an automobile exhaust after-treatment system. Background technology:

[0002] With the advancement of science and technology and the rapid development of the economy, cars have gradually entered more and more user households and are becoming an indispensable means of transportation for people to travel. With the increase in the popularity and use of cars, the environmental pollution caused by car exhaust has become a problem that cannot be ignored.

[0003] As the global automobile emission limits increase, automobile exhaust systems are gradually adding corresponding after-treatment systems, which poses higher challenges to the structure, cost and calibration of exhaust system after-treatment.

[0004] Existing National 5 and below diesel vehicles and GDI gasoline vehicles can meet the standard requirements by relying on only one technical route, that is, optimizing combustion inside the engine to reduce PM + external SCR to reduce NOx, or internal EGR to reduce NOx + external DPF to reduce PM.

[0005] Compared with National V, all indicators of National VI are basically reduced by 50%. Therefore, existing diesel vehicles and GDI gasoline vehicles cannot meet National VI standards by relying on only one technical route. Both routes must be adopted, namely, in-engine (optimized combustion to reduce PM + EGR to reduce NOx) + out-of-engine (DOC + DPF + SCR + ASC).

[0006] It is very difficult to meet the two indicators of NOx and NH3 escaping from SCR under different working conditions by simply relying on the control of SCR. Therefore, the simplest method is that SCR only controls NOx, and the added post-ASC controls NH3 escaping from SCR. In fact, the post-ASC can also assist the front-mounted DOC to complete the work that the front-mounted DOC has not done.

[0007] This is the most mature and effective combination and exhaust post-treatment technology route that is recognized by the world. However, due to different levels of understanding of post-treatment theory and various components, the specific structure and control strategy for implementing this technology route vary greatly, and the actual effects are very different.

[0008] The fatal flaws of the specific structure and control strategy of the existing diesel vehicle National VI emission post-treatment technology route:

[0009] Although the National VI emission standard has not yet been implemented, the National VI emission post-processing technology route has actually been used for a long time, but the control indicators are not so strict.

[0010] The existing post-treatment structures of National IV, National V and National VI are simply composed of DOC, DPF or SCR connected in series. This design has the following major defects:

[0011] (1) In terms of post-processing efficiency: it can only guarantee the highest efficiency under a certain exhaust temperature condition, but cannot guarantee high efficiency under other exhaust temperature conditions;

[0012] (2) In terms of post-processing efficiency: it can only guarantee the highest efficiency at a certain airspeed condition, but cannot guarantee high efficiency at other airspeed conditions;

[0013] (3) The catalysts of each device cannot be protected from high temperatures, which makes the catalysts prone to sintering, volatilization, structural deformation, and shedding, resulting in reduced efficiency, shortened life, and increased secondary pollutants such as N20 and NH3;

[0014] (4) The minimum filter layer of the DPF cannot be guaranteed during continuous passive regeneration, resulting in increased emission of fine particles;

[0015] (5) During cold start, the catalyst startup time is long and the conversion efficiency is very low, causing pollutants to be discharged in large quantities for a long period of time;

[0016] (6) In addition to being uniformly mixed before entering the DOC or SCR, all molecules of the components involved in the redox reaction must have sufficient contact opportunities with the catalyst after entering in order to maximize the conversion efficiency. Under a certain selected design condition, if the existing post-treatment determines the air velocity according to the maximum efficiency, that is, a turbulent flow form is adopted, the exhaust back pressure is very large. If the air velocity is determined according to the minimum back pressure at the highest efficiency, that is, a laminar flow form, the maximum efficiency will be reduced. The existing post-treatment structure cannot simultaneously achieve maximum efficiency maximization and back pressure minimization.

[0017] (7) Active regeneration consumes a lot of energy.

[0018] The purpose of this patent is to invent a National VI emission after-treatment system with a catalyst that has a fast cold start, high conversion efficiency in all operating conditions, low exhaust resistance, stable performance, long service life, and low purchase cost. Summary of the invention:

[0019] In order to achieve the above purpose, this patent adopts the following technical route: temperature regulator + DOC + DPF + SCR + ASC + pyrolyzer, and adopts the following technical solutions:

[0020] A vehicle National VI exhaust aftertreatment system comprises an exhaust pipe front section 2, an exhaust pipe rear section 13, a control system, and an exhaust gas cooler 23, a DOC catalyst 4, a DPF particle trap 7, an SCR catalyst 11, an ASC ammonia slip catalyst 12, and a pyrolyzer which are sequentially connected in series between the exhaust pipe front section 2 and the exhaust pipe rear section 13 from front to back; an intake pipe 24 of the exhaust gas cooler 23 is connected to the exhaust pipe front section 2 via a diverter valve 1, and an outlet pipe 22 of the cooler 23 is fixedly connected to the exhaust pipe front section 2 behind the diverter valve 1; the D The OC catalyst 4 is connected in parallel with a bypass pipe 20, the front end of the bypass pipe 20 is connected to the inlet end of the DOC catalyst 4 by a reversing valve 3, and the rear end of the bypass pipe 20 is fixedly connected to the outlet end of the DOC catalyst 4; the SCR catalyst 11 and the ASC ammonia slip catalyst 12 are connected in parallel with a bypass pipe 19, the front end of the bypass pipe 19 is connected to the inlet end of the SCR catalyst 11 by a reversing valve 9, and the rear end of the bypass pipe 19 is divided into two branch pipes 18 and 16, and the two branch pipes 18 and 16 are respectively fixedly connected to the rear section 13 of the exhaust pipe before and after the pyrolyzer.

[0021] In the automobile National VI exhaust after-treatment system described in this patent, the pyrolyzer is composed of three parts: a urea liquid inlet pipe 15, a pyrolysis chamber 17 and an output pipe 14 of the pyrolyzer; the urea liquid inlet pipe 15 and the output pipe 14 of the pyrolyzer are fixedly connected to the pipe of the rear section 13 of the exhaust pipe; the pyrolysis chamber is installed in the pipe of the rear section 13 of the exhaust pipe, isolated from the exhaust gas in the rear section 13 of the exhaust pipe, and absorbs the heat of the exhaust gas in the rear section 13 of the exhaust pipe to heat the urea liquid sprayed into the pyrolysis chamber 17 to pyrolyze it into ammonia; the urea liquid nozzle is installed in the inlet pipe 15.

[0022] In the automobile National VI exhaust after-treatment system described in this patent, the pyrolysis chamber 17 can be a section of spiral tube.

[0023] In the automobile National VI exhaust after-treatment system described in this patent, the outlet end of the output pipe 14 of the pyrolyzer is fixedly connected to the inlet or outlet end of the DPF particulate trap 7.

[0024] In the automobile National VI exhaust after-treatment system described in this patent, the control system is composed of a controller, a first temperature sensor 10 installed at the inlet end of the SCR catalyst 11, a second temperature sensor 5 installed at the inlet end of the DPF particulate trap 7, a first pressure sensor 6 installed at the inlet end of the DPF particulate trap and a second pressure sensor 8 installed at the outlet end of the DPF particulate trap 7. Each sensor is connected to the controller with wires; the controller detects a pressure difference between the first pressure sensor 6 and the second pressure sensor 8 that exceeds the highest preset value of the current working condition, and the temperature detected by the second temperature sensor 5 is lower than the preset value of the DPF active regeneration. When the temperature reaches the lower limit of the temperature range, the controller takes heating measures under the premise of closing the cooler 23 until the temperature at the inlet of the DPF particulate trap 7 is greater than the lower limit. When the temperature detected by the second temperature sensor 5 is higher than the upper limit of the temperature range of the preset DPF active regeneration, the controller turns on the cooler 23 under the premise of closing the heating measures, and the diverter valve 1 opens the intake pipe 24 of the exhaust gas cooler 23, reducing or even closing the exhaust gas flow directly to the DOC catalyst 4. The exhaust gas cooler 23 starts to work to cool down the high-temperature exhaust gas passing through until the temperature at the inlet of the DPF particulate trap 7 is less than the upper limit, and the DPF is regenerated. The DPF enters a normal active regeneration combustion state to quickly reduce the thickness of the filter layer. At the same time, the reversing valve 9 opens the bypass pipe 19 and closes the pipeline entering the SCR catalyst 11, and the exhaust NOx treatment enters the SNCR mode until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is less than the first low preset value of the current working condition, the controller stops active regeneration, closes the heating measure or the cooler 23, and the DPF enters a passive regeneration combustion state to slowly reduce the thickness of the filter layer. At the same time, the reversing valve 9 closes the bypass pipe 19 and opens the pipeline entering the SCR catalyst 11, and the exhaust NOx treatment is restored to the SCR mode; the controller in the first When the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is less than the second lowest preset value of the current working condition, the reversing valve 3 opens the bypass pipe 20, closes the pipeline entering the DOC catalyst 4, and the exhaust gas bypasses the DOC catalyst 4 and directly enters the DPF particle trap 7, so that the filter layer in the DPF particle trap 7 is rapidly thickened to prevent a large amount of tiny particles from being discharged, until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 by the controller is greater than the third lowest preset value of the current working condition, the reversing valve 3 closes the bypass pipe 20, opens the pipeline entering the DOC catalyst 4, and the exhaust gas re-enters the DPF particle trap 7 through the DOC catalyst 4;After the exhaust gas NOx treatment enters the SCR mode, when the temperature entering the SCR catalyst 11 detected by the first temperature sensor 10 is lower than the low preset value of the SCR high efficiency zone, the controller takes temperature increase measures under the premise of closing the cooler 23 until the temperature entering the SCR catalyst 11 is higher than the low preset value of the SCR high efficiency zone; after the exhaust gas NOx treatment enters the SCR mode, when the temperature entering the SCR catalyst 11 detected by the first temperature sensor 10 is higher than the high preset value of the SCR high efficiency zone, under the premise of closing the temperature increase measures, the controller opens the cooler 23, the diverter valve 1 opens the intake pipe 24 of the exhaust gas cooler 23, reduces or even closes the exhaust gas flow directly to the DOC catalyst 4, and the exhaust gas cooler 23 starts to work to cool the high-temperature exhaust gas passing through until the temperature entering the SCR catalyst 11 is lower than the high preset value of the SCR high efficiency zone. ;

[0025] In the automobile National VI exhaust after-treatment system described in this patent, the temperature increase measure can be carried out inside the engine 25, or a heating device can be provided outside the engine 25.

[0026] In the automobile Country VI exhaust after-treatment system described in this patent, the heating device can be a fuel injector 21 controlled by a controller installed on the front section 2 of the exhaust pipe before the reversing valve 3.

[0027] In the automobile National VI exhaust after-treatment system described in this patent, the structure of the carrier of the DOC catalyst 4, the SCR catalyst 11 and the ASC ammonia slip catalyst 12 can be composed of several sections along the axial direction, and the center lines of the honeycomb holes of each section are parallel to each other or form a wave shape.

[0028] In the automobile National VI exhaust after-treatment system described in this patent, the DOC catalyst 4, DPF particulate trap 7, SCR catalyst 11 and ASC ammonia slip catalyst 12, the structure of their carriers can be composed of several blocks along the radial direction.

[0029] In the automobile National VI exhaust after-treatment system described in this patent, a flow valve with an adjustable carrier intake geometric cross-section size can be installed at each inlet of the DOC catalyst 4, DPF particulate trap 7, SCR catalyst 11 and ASC ammonia slip catalyst 12, or, for the SCR catalyst 11 and the ASC ammonia slip catalyst 12, only a flow valve with an adjustable carrier intake geometric cross-section size can be installed at the inlet of the SCR catalyst 11; the controller adjusts the geometric cross-section size of each flow valve according to the change in the exhaust volume of the engine 25 to ensure that the time for the exhaust gas to flow through each device reaches a preset value.

[0030] In the automobile National VI exhaust after-treatment system described in this patent, the flow valve with adjustable carrier intake geometric cross-sectional size has the following structure: two valve plates 27 and 28 that rotate synchronously but in opposite directions are hinged on the exhaust pipe 26 at the inlet of the carrier 29, and an actuator is connected to the valve plate rotating shaft 30. The actuator is controlled by a controller to adjust the cross-sectional size between the two valve plates that allows exhaust gas to flow through.

[0031] In the automobile National VI exhaust after-treatment system described in this patent, the flow valve with adjustable carrier intake geometric cross-section size can also have the following structure: in the exhaust pipe 31 at the inlet of the carrier 35, several guide vanes 32 are fixedly connected to evenly distribute the exhaust gas to the entire inlet cross-section of the carrier; in the flow channel 34 between every two guide vanes, a valve plate 33 is hinged; the valve plates rotate synchronously; the rotating shaft 36 of each valve plate is hinged on the exhaust pipe 31; on the valve plate rotating shaft 36, an actuator is connected, and the actuator is controlled by a controller to adjust the cross-sectional size between each valve plate and the guide vane on one side that allows the exhaust gas to flow through.

[0032] The effects of this patent are:

[0033] (1) In terms of post-treatment efficiency, the exhaust temperature under all operating conditions is controlled to achieve the highest efficiency of each catalyst under all operating conditions;

[0034] (2) In terms of post-treatment efficiency, the space velocity under all operating conditions is controlled to achieve the highest efficiency of each catalyst under all operating conditions;

[0035] (3) Implement high temperature protection for the catalysts of each device to prevent sintering, volatilization, structural deformation, and shedding of the catalyst, so as to avoid a decrease in efficiency, shortened service life, and an increase in secondary pollutants such as N20 and NH3;

[0036] (4) Implement high temperature protection for DPF to prevent overheating and carrier burning;

[0037] (5) Control the presence of the minimum filter layer of the DPF during continuous passive regeneration to ensure that fine particulate matter emissions do not increase significantly;

[0038] (6) During cold start, the catalyst startup time is greatly shortened so that it can enter a high conversion efficiency state as soon as possible to avoid large-scale discharge of pollutants for a long time;

[0039] (7) All molecules of the redox reaction components have sufficient contact opportunities with the catalysts when entering the DOC, SCR and ASC in a low-speed impingement mixing flow form, so as to achieve the highest efficiency maximization and back pressure minimization at the same time;

[0040] (8) Urea thermal decomposition makes full use of the heat of the after-treatment system, which not only saves engine energy but also reduces the temperature of the exhaust pipe outlet;

[0041] (9) The DOC is always in the high-efficiency temperature range of the reduction reaction, and also in the high-efficiency temperature range of the NO oxidation reaction. A large amount of NO2 can continuously eliminate the thickness of the filter layer in the DPF, which can not only reduce the number of active regenerations and save the energy consumption of active regeneration, but also extend the life of each component. Description of the drawings:

[0042] Figure 1 This is a schematic diagram of the structure of the automobile National VI exhaust after-treatment system of this patent;

[0043] Figure 2 It is a schematic diagram of the structure of a flow valve with adjustable carrier air intake geometric cross-section size without a guide vane;

[0044] Figure 3 It is a structural schematic diagram of a flow valve with an adjustable carrier air intake geometric cross-section size having a guide vane. Specific implementation method:

[0045] This patent is further explained in conjunction with the accompanying drawings and embodiments.

[0046] like Figure 1 As shown, a National VI exhaust aftertreatment system for automobiles includes an exhaust pipe front section 2, an exhaust pipe rear section 13, a control system, and an exhaust gas cooler 23, a DOC catalyst 4, a DPF particulate trap 7, an SCR catalyst 11, an ASC ammonia slip catalyst 12, and a pyrolyzer which are sequentially connected in series between the exhaust pipe front section 2 and the exhaust pipe rear section 13 from front to back; an air inlet pipe 24 of the exhaust gas cooler 23 is connected to the exhaust pipe front section 2 via a diverter valve 1, and an air outlet pipe 22 of the cooler 23 is fixedly connected to the exhaust pipe front section 2 behind the diverter valve 1; The DOC catalyst 4 is connected in parallel with a bypass pipe 20, the front end of the bypass pipe 20 is connected to the inlet end of the DOC catalyst 4 by a reversing valve 3, and the rear end of the bypass pipe 20 is fixedly connected to the outlet end of the DOC catalyst 4; the SCR catalyst 11 and the ASC ammonia slip catalyst 12 are connected in parallel with a bypass pipe 19, the front end of the bypass pipe 19 is connected to the inlet end of the SCR catalyst 11 by a reversing valve 9, and the rear end of the bypass pipe 19 is divided into two branch pipes 18 and 16, and the two branch pipes 18 and 16 are respectively fixedly connected to the rear section 13 of the exhaust pipe before and after the pyrolyzer.

[0047] The pyrolyzer is composed of three parts, namely, a urea liquid input pipe 15, a pyrolysis chamber 17 and an output pipe 14 of the pyrolyzer, which are fixedly connected; the urea liquid input pipe 15 and the output pipe 14 of the pyrolyzer are fixedly connected to the pipe of the rear section 13 of the exhaust pipe; the pyrolysis chamber is installed in the pipe of the rear section 13 of the exhaust pipe, isolated from the exhaust gas in the rear section 13 of the exhaust pipe, and absorbs the heat of the exhaust gas in the rear section 13 of the exhaust pipe to heat the urea liquid sprayed into the pyrolysis chamber to pyrolyze it into ammonia; the urea liquid nozzle is installed in the input pipe 15.

[0048] The pyrolysis chamber is a section of spiral tube.

[0049] The outlet end of the output pipe 14 of the pyrolyzer is fixedly connected to the inlet end of the DPF particle trap 7 .

[0050] The control system is composed of a controller, a first temperature sensor 10 installed at the inlet end of the SCR catalyst 11, a second temperature sensor 5 installed at the inlet end of the DPF particle trap 7, a first pressure sensor 6 installed at the inlet end of the DPF particle trap, and a second pressure sensor 8 installed at the outlet end of the DPF particle trap 7. Each sensor is connected to the controller by wires. When the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 exceeds the highest preset value of 1kpa under the current working condition, and the temperature detected by the second temperature sensor 5 is lower than the lower limit of the preset DPF active regeneration temperature range of 550°, the controller turns off the cooler. Under the premise of 23, the controller turns on the fuel injector 21 to increase the temperature until the temperature at the inlet end of the DPF particle trap 7 is greater than the lower limit value. When the temperature detected by the second temperature sensor 5 is higher than the upper limit value of the preset DPF active regeneration temperature range of 600°, under the premise of closing the fuel injector 21, the controller turns on the cooler 23, the diverter valve 1 opens the intake pipe 24 of the exhaust gas cooler 23, reduces or even closes the exhaust gas flow directly to the DOC catalyst 4, and the exhaust gas cooler 23 starts to work to cool the high-temperature exhaust gas passing through until the temperature at the inlet end of the DPF particle trap 7 is less than the upper limit value, and the DPF enters the normal active regeneration fuel. The DPF is in a state of passive regeneration and combustion to quickly reduce the thickness of the filter layer. At the same time, the reversing valve 9 opens the bypass pipe 19 and closes the pipeline entering the SCR catalyst 11, and the exhaust NOx treatment enters the SNCR mode until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is less than the first low preset value 250pa of the current working condition, the controller stops active regeneration, closes the fuel injector 21 and the cooler 23, and the DPF enters a state of passive regeneration and combustion to slowly reduce the thickness of the filter layer. At the same time, the reversing valve 9 closes the bypass pipe 19 and opens the pipeline entering the SCR catalyst 11, and the exhaust NOx treatment is restored to the SCR mode. The controller detects that the pressure difference between the first pressure sensor 6 and the second pressure sensor 8 is less than the first low preset value 250pa of the current working condition, and then stops active regeneration, closes the fuel injector 21 and the cooler 23, and the DPF enters a state of passive regeneration and combustion to slowly reduce the thickness of the filter layer. At the same time, the reversing valve 9 closes the bypass pipe 19 and opens the pipeline entering the SCR catalyst 11, and the exhaust NOx treatment is restored to the SCR mode. When the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 is less than the second lowest preset value of 100 Pa of the current working condition, the reversing valve 3 opens the bypass pipe 20, closes the pipeline entering the DOC catalyst 4, and the exhaust gas bypasses the DOC catalyst 4 and directly enters the DPF particle trap 7, so that the filter layer in the DPF particle trap 7 is rapidly thickened to prevent a large amount of tiny particles from being discharged, until the pressure difference detected by the first pressure sensor 6 and the second pressure sensor 8 by the controller is greater than the third lowest preset value of 120 Pa of the current working condition, the reversing valve 3 closes the bypass pipe 20, opens the pipeline entering the DOC catalyst 4, and the exhaust gas re-enters the DPF particle trap 7 through the DOC catalyst 4;After the exhaust NOx treatment enters the SCR mode, when the temperature entering the SCR catalyst 11 detected by the first temperature sensor 10 is less than the low preset value of 280° in the SCR high efficiency zone, the controller opens the fuel injector 21 on the premise of closing the cooler 23 until the temperature entering the SCR catalyst 11 is greater than the low preset value of the SCR high efficiency zone; after the exhaust NOx treatment enters the SCR mode, when the temperature entering the SCR catalyst 11 detected by the first temperature sensor 10 is greater than the high preset value of 420° in the SCR high efficiency zone, the controller opens the cooler 23 on the premise of closing the fuel injector 21, and the diverter valve 1 opens the intake pipe 24 of the exhaust gas cooler 23, reducing or even closing the exhaust gas flow directly to the DOC catalyst 4, and the exhaust gas cooler 23 starts to work to cool the high-temperature exhaust gas passing through until the temperature entering the SCR catalyst 11 is less than the high preset value of the SCR high efficiency zone. ;

[0051] The fuel injector 21 controlled by the controller is installed on the front section 2 of the exhaust pipe before the reversing valve 3 .

[0052] The carrier structure of the DOC catalyst 4, SCR catalyst 11 and ASC ammonia slip catalyst 12 is composed of four sections along the axial direction, and the center lines of the honeycomb holes of each section form a wave shape with each other.

[0053] The carrier structure of the DOC catalyst 4, DPF particle trap 7, SCR catalyst 11 and ASC ammonia slip catalyst 12 is composed of 5 pieces in the radial direction.

[0054] A flow valve with an adjustable carrier intake geometric cross-section size is installed at each inlet of the DOC catalyst 4, DPF particle trap 7, and SCR catalyst 11; the controller adjusts the geometric cross-section size of each flow valve according to the change in the exhaust volume of the engine 25 to ensure that the time for the exhaust gas to flow through each device reaches the preset value of 0.1 second.

[0055] The flow valve with adjustable carrier intake geometric cross-sectional size has the following structure: two valve plates 27 and 28 that rotate synchronously but in opposite directions are hinged on the exhaust pipe 26 at the inlet of the carrier 29, and an actuator is connected to the valve plate rotating shaft 30. The actuator is controlled by a controller to adjust the cross-sectional size between the two valve plates that allows exhaust gas to flow through.

Claims

1. An automobile National VI exhaust after-treatment system, characterized in that: It includes an exhaust pipe front section, an exhaust pipe rear section, a control system, and an exhaust gas cooler, a DOC catalyst, a DPF particulate trap, an SCR catalyst, an ASC ammonia slip catalyst, and a pyrolyzer which are sequentially connected in series between the exhaust pipe front section and the exhaust pipe rear section from front to back; the exhaust gas cooler's air inlet pipe is connected to the exhaust pipe front section by a diverter valve, and the cooler's air outlet pipe is fixedly connected to the exhaust pipe front section behind the diverter valve; the DOC catalyst is connected in parallel with a first bypass pipe, the front end of the first bypass pipe is connected to the inlet end of the DOC catalyst by a reversing valve, and the rear end of the first bypass pipe is fixedly connected to the outlet end of the DOC catalyst; the SCR catalyst and the ASC ammonia slip catalyst are connected in parallel with a second bypass pipe, the front end of the second bypass pipe is connected to the inlet end of the SCR catalyst by a reversing valve, and the rear end of the second bypass pipe is divided into two branch pipes, and the two branch pipes are respectively fixedly connected to the exhaust pipe rear section before and after the pyrolyzer, The pyrolyzer is composed of three parts: a urea liquid input pipe, a pyrolysis chamber and an output pipe of the pyrolyzer. The urea liquid input pipe and the output pipe of the pyrolyzer are fixedly connected to the pipe at the rear section of the exhaust pipe. The pyrolysis chamber is installed in the pipe at the rear section of the exhaust pipe, isolated from the exhaust gas in the rear section of the exhaust pipe, and absorbs the heat of the exhaust gas in the rear section of the exhaust pipe to heat the urea liquid sprayed into the pyrolysis chamber to pyrolyze it into ammonia. The urea liquid nozzle is installed in the input pipe. The pyrolysis chamber is a section of spiral tube. The outlet end of the output pipe of the pyrolyzer is fixedly connected to the inlet end or the outlet end of the DPF particle trap. The control system is composed of a controller, a first temperature sensor installed at the inlet end of the SCR catalyst, a second temperature sensor installed at the inlet end of the DPF particle trap, a first pressure sensor installed at the inlet end of the DPF particle trap, and a second pressure sensor installed at the outlet end of the DPF particle trap. Each sensor is connected to the controller by wires. When the pressure difference detected by the first pressure sensor and the second pressure sensor exceeds the highest preset value of the current working condition, and the temperature detected by the second temperature sensor is lower than the lower limit of the preset DPF active regeneration temperature range, the controller takes temperature increase measures under the premise of turning off the cooler until the DPF particle trap enters the regeneration process. When the temperature at the outlet is greater than the lower limit, and the temperature detected by the second temperature sensor is higher than the upper limit of the preset DPF active regeneration temperature range, under the premise of closing the heating measures, the controller turns on the cooler, and the diverter valve opens the intake pipe of the exhaust gas cooler to reduce or even close the exhaust gas flow directly to the DOC catalyst. The exhaust gas cooler starts to work to cool the high-temperature exhaust gas passing through until the temperature at the inlet of the DPF particulate trap is less than the upper limit, and the DPF enters a normal active regeneration combustion state to quickly reduce the thickness of the filter layer. At the same time, the reversing valve opens the second bypass pipe, closes the pipeline entering the SCR catalyst, and the exhaust NOx treatment enters the SNCR mode. When the pressure difference detected by the first pressure sensor and the second pressure sensor is less than the first low preset value of the current working condition, the controller stops active regeneration, turns off the heating measures or the cooler, and the DPF enters a passive regeneration combustion state to slowly reduce the thickness of the filter layer. At the same time, the reversing valve closes the second bypass pipe and opens the pipeline entering the SCR catalyst, and the exhaust gas NOx treatment is restored to the SCR mode; when the pressure difference detected by the first pressure sensor and the second pressure sensor is less than the second low preset value of the current working condition, the reversing valve opens the first bypass pipe and closes the pipeline entering the DOC catalyst, and the exhaust gas bypasses the DOC catalyst and directly enters the DPF particulate trap, so that the D The filter layer in the DPF particle trap thickens rapidly to prevent a large amount of tiny particles from being discharged until the pressure difference detected by the first pressure sensor and the second pressure sensor of the controller is greater than the third lowest preset value of the current working condition, the reversing valve closes the first bypass pipe, opens the pipeline entering the DOC catalyst, and the exhaust gas re-enters the DPF particle trap through the DOC catalyst; after the exhaust gas NOx treatment enters the SCR mode, when the temperature entering the SCR catalyst detected by the first temperature sensor is less than the low preset value of the SCR high-efficiency zone, the controller takes heating measures on the premise of closing the cooler until the temperature entering the SCR catalyst is greater than the low preset value of the SCR high-efficiency zone;After the exhaust gas NOx treatment enters the SCR mode, when the temperature entering the SCR catalyst detected by the first temperature sensor is greater than the high preset value of the SCR high efficiency zone, the controller turns on the cooler and the diverter valve opens the intake pipe of the exhaust gas cooler, reducing or even closing the exhaust gas flow directly to the DOC catalyst, and the exhaust gas cooler starts to work to cool the high-temperature exhaust gas passing through until the temperature entering the SCR catalyst is less than the high preset value of the SCR high efficiency zone. ;

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