Variable closure surface type double-jet post-processing system and post-processing control method

Abstract

The system comprises a DOC, an SCRF and an SCR / ASC which are sequentially arranged in the exhaust direction, an engine exhaust pipe is forked to form a first exhaust pipe and a second exhaust pipe, the first exhaust pipe communicates with the front end of the DOC, the second exhaust pipe communicates with the rear end of the DOC, a first exhaust switching valve is arranged on the first exhaust pipe, and a second exhaust switching valve is arranged on the second exhaust pipe. A second exhaust switching valve is arranged on the second exhaust pipe; the system further comprises a front-stage urea nozzle arranged on the second exhaust pipe and a rear-stage urea nozzle arranged between the SCRF and the SCR / ASC, and the front-stage urea nozzle and the rear-stage urea nozzle are both connected with a urea spraying device. The first exhaust switching valve, the second exhaust switching valve and the preceding-stage urea nozzle are all arranged on the upstream of the DOC. A switching valve + DOC + SCRF + SCR + ASC technical route is adopted, and a single exhaust pipeline is divided into two exhaust pipelines connected in parallel through a Y-shaped pipe according to the airflow distribution principle. According to the exhaust temperature, the exhaust switching valve switch and the injection amount of the front and rear nozzles are reasonably controlled to meet the emission requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of diesel engine aftertreatment, and in particular relates to a variable cutoff surface type double-injection aftertreatment system and a aftertreatment control method. Background Art

[0002] China's seventh-stage fuel vehicle emission regulations (National VII) are being formulated and are scheduled to be implemented in 2029. The emission regulations for fuel vehicles will be further tightened. In the future, the emission limits for major pollutants such as nitrogen oxides (NOx) in engine exhaust will also be greatly reduced. At present, the mainstream technology of National VI is a single-way exhaust pipe + catalyst, in which the catalyst includes DOC (oxidation catalyst), DPF (particulate filter), mixer and SCR (selective catalyst reducer).

[0003] The post-treatment system in the prior art has the following problems. The prior art often uses a single nozzle urea injection control. If the emission of nitrogen oxides (NOx) is to be further reduced, the amount of urea injection needs to be increased. However, excessive urea injection will exceed the mixing capacity of the mixer and produce crystallization, resulting in increased system back pressure, affecting the economy of the vehicle and increasing vehicle use costs. The mainstream technical route of National VII under study: CCSCR+DOC+DPF+SCR+ASC, also has the problem that the CCSCR desulfurization and HC removal technical solutions are complex, costly, and ineffective. It is necessary to continue to find a more cost-effective technical solution that meets the National VII emission requirements. Summary of the invention

[0004] The present invention provides a variable cut-off surface type dual-injection after-treatment system and after-treatment control method, which adopts the switching valve + DOC + SCRF + SCR / ASC technical route, and utilizes the principle of airflow diversion to divide a single exhaust pipeline into two parallel exhaust pipelines through a Y-shaped pipe. According to the exhaust temperature, the exhaust switching valve switch and the injection amount of the front and rear nozzles are reasonably controlled to meet the emission requirements.

[0005] To achieve the above-mentioned purpose, the present invention provides a variable shutoff surface type dual-injection after-treatment system, a variable shutoff surface type dual-injection after-treatment system, comprising a DOC, a SCRF, and an SCR / ASC arranged in sequence along the exhaust direction, the engine exhaust pipe is bifurcated along the exhaust direction to form a first exhaust pipe and a second exhaust pipe, the first exhaust pipe is connected to the front end of the DOC, the second exhaust pipe is connected to the rear end of the DOC, a first exhaust switching valve is arranged on the first exhaust pipe, and a second exhaust switching valve is arranged on the second exhaust pipe; it also includes a front-stage urea nozzle arranged on the second exhaust pipe, and a rear-stage urea nozzle arranged between the SCRF and the SCR / ASC, the front-stage urea nozzle and the rear-stage urea nozzle are both connected to a urea injection device; the first exhaust switching valve, the second exhaust switching valve and the front-stage urea nozzle are all arranged upstream of the DOC.

[0006] The present invention connects two exhaust pipes in parallel, the first exhaust pipe leads the airflow directly to the front end cover of the DOC catalyst, and the second exhaust pipe leads the exhaust gas to the rear end surface of the annular DOC carrier. A switch-type exhaust switching valve is installed in each pipe, and the exhaust temperature is monitored to coordinate the switch of the exhaust switching valve with the injection amount of the front and rear nozzles. The injection ratio of the front and rear stages is coordinated to control the emission of passive regeneration N2O of the SCRF, thereby solving the desulfurization problem of the SCRF. Moreover, due to the setting of the DOC upstream of the SCRF, most of the HC generated by the post-injection in the cylinder is converted during the active regeneration process, so there is no HC poisoning problem in the SCRF.

[0007] Preferably, the DOC includes a DOC orifice plate and a DOC carrier, the DOC carrier is constructed as an annular structure, the DOC carrier and the DOC orifice plate are both provided with through holes, and the second exhaust pipe sequentially penetrates the DOC orifice plate and the DOC carrier and is connected to the front end of the SCRF. The present invention adopts a second exhaust pipe to pass through the DOC orifice plate and the annular DOC carrier to lead the exhaust gas to the rear end surface of the annular DOC carrier, and the second exhaust pipe is integrated in the packaging shell, avoiding the need to set a separate pipeline outside the packaging shell, with a compact structure, small size and low cost.

[0008] Preferably, the first exhaust pipe, the second exhaust pipe and the engine exhaust pipe are connected to form a Y-shaped structure. The single exhaust pipe is divided into two parallel exhaust pipes through the Y-shaped pipe, which has low exhaust resistance, and the volume is also small after being divided into two exhaust pipes, and the structure is compact.

[0009] Preferably, the distance from the connection node of the first exhaust pipe and the second exhaust pipe to the DOC orifice plate is set to 90-100 cm. If the distance is too long, it will cause design redundancy, and if the distance is too short, the uniformity of ammonia before SCRF will not meet the 98% requirement, resulting in low SCRF efficiency.

[0010] Preferably, the distance from the DOC orifice plate to the front end of the DOC carrier is set to 50-60 mm. If the distance is too long, it will cause design redundancy, and if the distance is too short, the uniformity before the DOC will not meet the 95% requirement, resulting in low DOC efficiency.

[0011] Preferably, the diameters of the first exhaust pipe, the second exhaust pipe, the first exhaust switching valve and the second exhaust switching valve are all set to 65 mm. When the diameter is less than 65 mm, the exhaust back pressure of the system will be too large, affecting the engine performance; if the diameter is too large, the volume will be too large and it will be difficult to integrate into the post-processing system.

[0012] The present invention also provides a post-processing control method, which adopts the above-mentioned variable cut-off surface type double-spray post-processing system, and comprises the following steps:

[0013] Step S100: Start the engine and check the exhaust temperature. When the exhaust temperature is lower than the preset temperature, proceed to the next step;

[0014] Step S200: the first exhaust switching valve is closed, the second exhaust switching valve is opened, the urea injection device controls the injection amount of the front-stage urea nozzle to be greater than the injection amount of the rear-stage urea nozzle, and the exhaust temperature continues to be monitored; because the engine is cold-started, the SCRF temperature is very low, and the purpose of this step is to heat up the SCRF as quickly as possible so that the natural dilution efficiency is high.

[0015] Step S300: When the exhaust temperature is greater than the preset temperature, the first exhaust switching valve and the second exhaust switching valve are opened, and the urea injection device controls the injection amount of the front-stage urea nozzle to be smaller than the injection amount of the rear-stage urea nozzle; when the exhaust temperature is greater than the preset temperature, the SCR / ASC can work efficiently. At this time, the first exhaust switching valve and the second exhaust switching valve are opened, and the urea injection device controls the injection amount of the front-stage urea nozzle to be smaller than the injection amount of the rear-stage urea nozzle to ensure the passive generation efficiency of the SCRF.

[0016] Step S300: When the temperature continues to rise and the engine's particulate trap triggers active regeneration, that is, the DPF on the SCRF starts active regeneration, the first exhaust switching valve is closed, the second exhaust switching valve is opened, and the urea injection device stops working.

[0017] The post-treatment control scheme of the present invention can meet or even exceed the conversion efficiency of the mainstream technical route of National VII, and completely solves the SCRF desulfurization problem. Moreover, due to the setting of the DOC upstream of the SCRF and the active regeneration process, most of the HC generated by the post-injection in the cylinder is converted, so there is no HC poisoning problem in the SCRF.

[0018] Preferably, in step 200, the front stage urea nozzle accounts for 90% of the total injection amount and the rear stage urea nozzle accounts for 10% of the total injection amount. At this time, when the exhaust temperature is low, the front stage sprays more and the rear stage sprays less, and the SCRF acts as the main force to treat pollutants, so that the SCRF is heated up as soon as possible.

[0019] Preferably, in step 300, the front stage urea nozzle accounts for 10% of the total injection amount and the rear stage urea nozzle accounts for 90% of the total injection amount. At this time, when the exhaust temperature is low, the rear stage sprays more, and SCR / ASC is the main force to treat pollutants to ensure the passive generation efficiency of SCRF.

[0020] Preferably, the preset temperature is 300-350° C. The temperature is used to coordinate the front and rear injection amounts so that the system can reach the best working state.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The single exhaust pipeline is divided into two parallel exhaust pipelines through a Y-tube, and an exhaust switching valve is installed on the two branch pipelines. The exhaust temperature is monitored to coordinate the switch of the exhaust switching valve and the injection amount of the front and rear nozzles to meet the National VII emission regulations and solve the system complexity problem of desulfurization and decarbonization of the two-stage SCR technology line that is currently widely studied. The cylindrical structure is compact, the cost is low, and the conversion efficiency meets the requirements.

[0023] The second exhaust pipe is adopted to sequentially penetrate the DOC orifice plate and the DOC carrier and then be connected to the front end of the SCRF. The second exhaust pipe is integrated in the DOC, and the packaging structure is simple and compact.

[0024] The control method of the present invention meets or even exceeds the conversion efficiency of the mainstream technical route of National VII, completely solves the SCRF desulfurization problem, and due to the setting of the DOC upstream of the SCRF and the active regeneration process, most of the HC generated by the post-injection in the cylinder is converted, so there is no HC poisoning problem in the SCRF. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention discloses a structural principle block diagram of a variable cut-off surface type double-injection after-treatment system.

[0026] Figure 2 It is a schematic diagram of the overall structure of a variable cutoff surface type double-injection after-treatment system described in the present invention.

[0027] Figure 3 It is a cross-sectional view of the internal structure of a variable cut-off surface type double-injection after-treatment system described in the present invention.

[0028] Figure 4 It is a control strategy flow chart of the post-processing control method described in the present invention.

[0029] In the figure: 1-DOC, 101-DOC orifice plate, 102-DOC carrier, 2-SCRF, 3-SCR / ASC, 4-engine exhaust pipe, 5-first exhaust pipe, 6-second exhaust pipe, 7-first exhaust switching valve, 8-second exhaust switching valve, 9-front stage urea nozzle, 10-rear stage urea nozzle. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0031] In the description of the present invention, it is necessary to understand that the terms "left", "right", "up", "down", "front", "back", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or structure referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0032] Embodiment 1:

[0033] A variable shutoff surface dual-injection after-treatment system is used for engine exhaust after-treatment. In this embodiment, DOC1 refers to an oxidation catalyst; SCR refers to a selective catalytic reducer; SCRF2) refers to coating an SCR catalyst on a DPF (particulate filter), that is, a diesel particulate filter loaded with a selective catalytic reduction catalyst; the SCR / ASC3 system includes an SCR and an ASC, and ASC refers to an ammonia slip catalyst.

[0034] like Figures 1 to 3 As shown, this embodiment includes DOC1, SCRF2, SCR / ASC3 arranged in sequence along the exhaust direction, the engine exhaust pipe 4 is bifurcated into a first exhaust pipe 5 and a second exhaust pipe 6, the first exhaust pipe 5 is connected to the front end of the DOC1, the second exhaust pipe 6 is connected to the rear end of the DOC1, a first exhaust switching valve 7 is arranged on the first exhaust pipe 5, and a second exhaust switching valve 8 is arranged on the second exhaust pipe 6; it also includes a front-stage urea nozzle 9 arranged on the second exhaust pipe 6, and a rear-stage urea nozzle 10 arranged between the SCRF2 and the SCR / ASC3.

[0035] Specifically, the rear-stage urea nozzle 10 is installed on the packaging shell in front of the SCR / ASC 3 , and the front-stage urea nozzle 9 is arranged behind the second exhaust switching valve 8 .

[0036] The front-stage urea nozzle 9 and the rear-stage urea nozzle 10 are both connected to a urea injection device; the first exhaust switching valve 7 , the second exhaust switching valve 8 and the front-stage urea nozzle 9 are all arranged upstream of the DOC1 .

[0037] like Figure 3 As shown, in this embodiment, the DOC1 includes a DOC orifice plate 101 and a DOC carrier 102, the DOC carrier 102 is constructed as a ring structure, and the DOC carrier 102 and the DOC orifice plate 101 are both provided with through holes, and the second exhaust pipe 6 sequentially penetrates the DOC orifice plate 101 and the DOC carrier 102 and is connected to the front end of the SCRF2.

[0038] like Figure 2 As shown, in this embodiment, the first exhaust pipe 5, the second exhaust pipe 6 and the engine exhaust pipe 4 are connected to form a Y-shaped structure.

[0039] like Figure 1 As shown, in this embodiment, the distance D from the connection node of the first exhaust pipe 5 and the second exhaust pipe 6 to the DOC orifice plate 101 is set to 90-100 cm.

[0040] like Figure 1 As shown, in this embodiment, the distance S from the DOC orifice plate 101 to the front end of the DOC carrier 102 is set to 50-60 mm.

[0041] In this embodiment, the diameters of the first exhaust pipe 5, the second exhaust pipe 6, the first exhaust switching valve 7 and the second exhaust switching valve 8 are all set to 65 mm. In this embodiment, the first exhaust switching valve 7 and the second exhaust switching valve 8 are controlled in full open and full closed states, with only two states.

[0042] This embodiment adopts the switching valve + DOC1 + SCRF2 + SCR / ASC technical route, and uses the principle of air flow diversion to divide the single exhaust pipeline into two parallel exhaust pipelines through a Y-shaped pipe. According to the exhaust temperature, the exhaust switching valve switch and the injection amount of the front and rear nozzles are reasonably controlled to meet the emission requirements.

[0043] Embodiment 2:

[0044] like Figure 4 As shown, a post-processing control method adopts a variable cut-off surface type dual-injection post-processing system described in Example 1, comprising the following steps:

[0045] Step S100: Start the engine and check the exhaust temperature. When the exhaust temperature is lower than the preset temperature, proceed to the next step;

[0046] Step S200: the first exhaust switching valve 7 is closed, the second exhaust switching valve 8 is opened, the urea injection device controls the injection amount of the front-stage urea nozzle 9 to be greater than the injection amount of the rear-stage urea nozzle 10, and the exhaust temperature continues to be monitored;

[0047] Step S300: When the exhaust temperature is greater than the preset temperature, the first exhaust switching valve 7 and the second exhaust switching valve 8 are opened, and the urea injection device controls the injection amount of the front-stage urea nozzle 9 to be smaller than the injection amount of the rear-stage urea nozzle; when the first exhaust switching valve 7 and the second exhaust switching valve 8 are in the fully open state of the pipeline, the gas ratio of the two pipelines is close to 1:1.

[0048] Step S300: When the temperature continues to rise and the particulate trap of the engine triggers active regeneration, the first exhaust switching valve 7 is closed, the second exhaust switching valve 8 is opened, and the urea injection device stops working.

[0049] In this embodiment, in step 200 , the front-stage urea nozzle 9 accounts for 90% of the total injection amount and the rear-stage urea nozzle 10 accounts for 10% of the total injection amount.

[0050] In this embodiment, in step 300 , the front-stage urea nozzle 9 accounts for 10% of the total injection amount and the rear-stage urea nozzle 10 accounts for 90% of the total injection amount.

[0051] In this embodiment, the preset temperature is 300-350°C, and specifically may be 300°C.

Claims

1. A variable shutoff surface type dual-injection aftertreatment system, comprising a DOC (1), a SCRF (2), and an SCR / ASC (3) arranged in sequence along the exhaust direction, characterized in that The engine exhaust pipe (4) is bifurcated into a first exhaust pipe (5) and a second exhaust pipe (6), wherein the first exhaust pipe (5) is connected to the front end of the DOC (1), and the second exhaust pipe (6) is connected to the rear end of the DOC (1), the first exhaust pipe (5) is provided with a first exhaust switching valve (7), and the second exhaust pipe (6) is provided with a second exhaust switching valve (8); the engine also includes a front-stage urea nozzle (9) provided on the second exhaust pipe (6), and a rear-stage urea nozzle (10) provided between the SCRF (2) and the SCR / ASC (3); the front-stage urea nozzle (9) and the rear-stage urea nozzle (10) are both connected to a urea injection device; the first exhaust switching valve (7), the second exhaust switching valve (8) and the front-stage urea nozzle (9) are all provided upstream of the DOC (1).

2. A variable cut-off surface dual-injection after-treatment system according to claim 1, characterized in that: The DOC (1) comprises a DOC orifice plate (101) and a DOC carrier (102); the DOC carrier (102) is constructed as an annular structure; the DOC carrier (102) and the DOC orifice plate (101) are both provided with through holes; the second exhaust pipe (6) sequentially penetrates the DOC orifice plate (101) and the DOC carrier (102) and is then connected to the front end of the SCRF (2).

3. The variable cut-off surface dual-injection after-treatment system according to claim 1 is characterized in that: The first exhaust pipe (5), the second exhaust pipe (6) and the engine exhaust pipe (4) are connected to form a Y-shaped structure.

4. The variable cut-off surface dual-injection after-treatment system according to claim 2 is characterized in that: The distance from the connection node of the first exhaust pipe (5) and the second exhaust pipe (6) to the DOC orifice plate (101) is set to 90-100 cm.

5. The variable cut-off surface dual-injection after-treatment system according to claim 2 is characterized in that: The distance from the DOC orifice plate (101) to the front end of the DOC carrier (102) is set to 50-60 mm.

6. The variable cut-off surface dual-injection after-treatment system according to claim 1, characterized in that: The diameters of the first exhaust pipe (5), the second exhaust pipe (6), the first exhaust switching valve (7) and the second exhaust switching valve (8) are all set to 65 mm.

7. A post-treatment control method, using a variable cut-off surface dual-injection post-treatment system according to any one of claims 1 to 6, characterized in that The steps include: Step S100: the engine is started and the exhaust temperature is checked. When the exhaust temperature is lower than a preset temperature, the next step is entered; Step S200: the first exhaust switching valve (7) is closed, the second exhaust switching valve (8) is opened, the urea injection device controls the injection amount of the front-stage urea nozzle (9) to be greater than the injection amount of the rear-stage urea nozzle (10), and the exhaust temperature is continuously monitored; Step S300: when the exhaust temperature is greater than a preset temperature, the first exhaust switching valve (7) and the second exhaust switching valve (8) are opened, and the urea injection device controls the injection amount of the front-stage urea nozzle (9) to be smaller than the injection amount of the rear-stage urea nozzle; Step S300: When the temperature continues to rise and the particulate trap of the engine triggers active regeneration, the first exhaust switching valve (7) is closed, the second exhaust switching valve (8) is opened, and the urea injection device stops working.

8. A post-processing control method according to claim 7, characterized in that In step 200, the front stage urea nozzle (9) accounts for 90% of the total injection amount and the rear stage urea nozzle (10) accounts for 10% of the total injection amount.

9. A post-processing control method according to claim 7, characterized in that In step 300, the front stage urea nozzle (9) accounts for 10% of the total injection amount and the rear stage urea nozzle (10) accounts for 90% of the total injection amount.

10. A post-processing control method according to claim 7, characterized in that The preset temperature is 300-350°C.

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