A composite dual-stage SCR system, control method, post-processing system and vehicle

Abstract

The present invention belongs to the field of engine aftertreatment system, and provides a composite two-stage SCR system, control method, aftertreatment system and vehicle, wherein the system includes a first SCR, a first ASC, a DOC, a DPF, a second SCR, a second ASC, a calculation control unit, an electric heating device, a gas concentration detection unit and an exhaust temperature unit, and determines the urea injection control strategy of the first SCR and the second SCR and the working strategy of the electric heating device according to the nitrogen oxide concentration and nitrogen dioxide ratio detected by the gas concentration detection unit and the temperature obtained by the exhaust temperature unit, and controls the first SCR, the second SCR and the electric heating device to work respectively according to the determined strategy. The present invention can meet the coordinated control requirements of ultra-low nitrogen oxide emissions and nitrous oxide gas emission restrictions of diesel engines.

Description

Technical Field

[0001] The present invention belongs to the field of engine after-treatment systems, and in particular relates to a composite two-stage SCR system, a control method, a after-treatment system and a vehicle. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, the requirements for diesel engine post-treatment emission control technology have been continuously updated. The current diesel engine post-treatment technology route is the combination of oxidation catalyst DOC (Diesel Oxidation Catalyst), diesel carbon particulate filter DPF (Diesel Particulate Filter), selective catalytic reduction system SCR (Selective Catalytic Reduction) and ammonia slip catalyst ASC (Ammonia Slip Catalyst). Referring to the latest research trends at home and abroad, the emission restrictions on nitrogen oxides will be further tightened in the future, and new requirements for nitrous oxide N2O gas emissions will be added, so new post-treatment technologies need to be proposed.

[0004] The dual-stage SCR is widely favored among many new post-treatment technology routes for further reducing nitrogen oxide NOx emissions. In this technology, two upstream and downstream SCRs are arranged after the turbine and after the DPF, and corresponding urea injection devices are configured to achieve NOx emission control under all working conditions. However, the urea injection strategy for the dual-stage SCR is still under study. At the same time, considering the generation of N2O in the copper-based SCR, the effects of exhaust temperature, NO2 ratio, ammonia nitrogen ratio and other factors on the coordinated control process of NOx and N2O need to be further considered during the urea injection process. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a composite two-stage SCR system, a control method, a post-treatment system and a vehicle. The present invention can meet the requirements of ultra-low NO x The need for coordinated control of emissions and nitrous oxide (N2O) gas emission limits.

[0006] According to some embodiments, the present invention adopts the following technical solutions:

[0007] A composite two-stage SCR system includes a first SCR, a first ASC, a DOC, a DPF, a second SCR, a second ASC, a calculation control unit, an electric heating device, a gas concentration detection unit and an exhaust temperature unit, wherein:

[0008] The first SCR is arranged upstream, and an electric heating device is arranged at the front end thereof; the second SCR is arranged downstream, and a first ASC, a DOC and a DPF are arranged in sequence between the first SCR and the second SCR;

[0009] A second ASC is disposed at the rear end of the second SCR;

[0010] The gas concentration detection unit is used to detect the nitrogen oxide concentration and nitrogen dioxide ratio at the first SCR and the second SCR, and feed back to the calculation control unit;

[0011] The exhaust temperature unit is used to obtain the exhaust temperature after the turbine, the temperature at the first SCR and the second SCR, and feed them back to the calculation control unit;

[0012] The calculation control unit is used to determine the urea injection control strategy of the first SCR and the second SCR and the working strategy of the electric heating device according to the nitrogen oxide concentration and the nitrogen dioxide ratio detected by the gas concentration detection unit and the temperature obtained by the exhaust temperature unit, and control the operation of the first SCR, the second SCR and the electric heating device respectively according to the determined strategies.

[0013] As an optional implementation, the first SCR is a copper-based LO-SCR (Light-Off Selective Catalytic Reduction), and the distance between the first SCR and the turbine is less than a set value.

[0014] That is, the first SCR is arranged close to the turbine.

[0015] As an optional embodiment, the second SCR is a copper-iron composite-based SCR. In setting the SCR length, the first part adopts a copper-based SCR and the second part adopts an iron-based SCR.

[0016] And the length of the first part is greater than the length of the second part.

[0017] As an optional embodiment, the exhaust temperature unit includes a post-turbine exhaust temperature sensor, a first SCR temperature sensor, and a second SCR temperature sensor. The post-turbine exhaust temperature sensor is arranged at the rear end of the turbine and at the front end of the electric heating device; the first SCR temperature sensor is arranged at the inlet end of the first SCR, and the second SCR temperature sensor is arranged at the inlet end of the second SCR.

[0018] As an optional embodiment, the gas concentration detection unit includes a first nitrogen oxide concentration sensor, a first nitric oxide concentration sensor, a second nitrogen oxide concentration sensor and a second nitric oxide concentration sensor, wherein the first nitrogen oxide concentration sensor and the first nitric oxide concentration sensor are arranged at the inlet end of the first SCR, and the second nitrogen oxide concentration sensor and the second nitric oxide concentration sensor are arranged at the inlet end of the second SCR.

[0019] As an optional implementation, the computing control unit is configured as follows:

[0020] When the temperature at the first SCR is less than the set value, the electric heating device is started until the exhaust temperature is greater than or equal to the set value. At the same time, the second SCR does not inject urea during this stage, and the first SCR adopts the first injection strategy;

[0021] When the temperature at the inlet of the first SCR is greater than the set value, the first SCR adopts the second injection strategy and determines the temperature at the inlet of the second SCR at the same time:

[0022] When the temperature at the second SCR is less than or equal to the set value, and the nitrogen dioxide ratio of the second SCR is less than the set threshold, the second SCR adopts the first injection strategy; when the nitrogen dioxide ratio is greater than or equal to the set threshold, the second SCR adopts the second injection strategy;

[0023] When the second SCR temperature is greater than a set value, the second SCR adopts a second injection strategy.

[0024] As a further step, the first injection strategy is to set the ammonia nitrogen ratio to 1;

[0025] The second injection strategy is: when the corresponding SCR inlet temperature is lower than a predetermined value, the ammonia nitrogen ratio is set to 1.1; when the corresponding SCR inlet temperature is greater than or equal to a predetermined value, the ammonia nitrogen ratio is set to 1.2, and the predetermined value is greater than the set value.

[0026] As an optional implementation, the nitrogen dioxide ratio is calculated based on the corresponding nitrogen oxide concentration and nitrogen monoxide concentration obtained by the gas concentration detection unit.

[0027] A control method for a composite dual-stage SCR system comprises the following steps:

[0028] Determine the urea injection control strategy of the first SCR located upstream and the second SCR located downstream and the working strategy of the electric heating device according to the nitrogen oxide concentration and nitrogen dioxide ratio detected by the gas concentration detection unit and the temperature obtained by the exhaust temperature unit, and control the first SCR, the second SCR and the electric heating device to work respectively according to the determined strategy;

[0029] When the temperature at the first SCR is less than the set value, the electric heating device is started until the exhaust temperature is greater than or equal to the set value. At the same time, the second SCR does not inject urea during this stage, and the first SCR adopts the first injection strategy;

[0030] When the temperature at the inlet of the first SCR is greater than the set value, the first SCR adopts the second injection strategy and determines the temperature at the inlet of the second SCR at the same time:

[0031] When the temperature at the second SCR is less than or equal to the set value, and the nitrogen dioxide ratio of the second SCR is less than the set threshold, the second SCR adopts the first injection strategy; when the nitrogen dioxide ratio is greater than or equal to the set threshold, the second SCR adopts the second injection strategy;

[0032] When the second SCR temperature is greater than a set value, the second SCR adopts a second injection strategy.

[0033] As a further step, the first injection strategy is to set the ammonia nitrogen ratio to 1;

[0034] The second injection strategy is: when the corresponding SCR inlet temperature is lower than a predetermined value, the ammonia nitrogen ratio is set to 1.1; when the corresponding SCR inlet temperature is greater than or equal to a predetermined value, the ammonia nitrogen ratio is set to 1.2, and the predetermined value is greater than the set value.

[0035] A post-treatment system comprises the above-mentioned composite dual-stage SCR system.

[0036] A vehicle comprises the composite dual-stage SCR system or the after-treatment system.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention adopts a two-stage SCR system which has the beneficial effect of significantly reducing nitrogen oxide emissions. Through the synergistic effect of the two-stage SCR, the emission concentration of nitrogen oxides can be effectively reduced. Among them, the upstream SCR is close to the turbine, and the exhaust temperature of the environment in which it is located is relatively high. This feature makes it play a key role in the cold start stage. During the cold start process, the exhaust temperature is low when the engine is initially running, and traditional single-stage SCR systems often find it difficult to effectively deal with nitrogen oxide emissions at this time. The upstream SCR in the present invention, by virtue of the advantage of high exhaust temperature, can quickly start the catalytic reaction, thereby significantly reducing nitrogen oxide emissions during cold start;

[0039] The downstream SCR, with its longer structure, provides sufficient reaction space and time for the full conversion of nitrogen oxides. After the exhaust gas is initially treated by the upstream SCR, it enters the downstream SCR. In its longer reaction channel, the remaining nitrogen oxides are further fully mixed with the urea solution and undergo catalytic reduction reactions, ensuring the adequacy and integrity of the reaction process, and being able to more comprehensively and deeply reduce the overall nitrogen oxide concentration.

[0040] The use of copper-iron-based composite SCR in the downstream of the two-stage SCR system in the present invention brings beneficial effects in reducing nitrous oxide emissions. During the SCR reaction process, although the copper-based SCR exhibits good catalytic reduction performance of nitrogen oxides under many working conditions, its reaction mechanism easily leads to the formation of nitrous oxide, a strong greenhouse gas, under low-temperature and ammonia-rich conditions. In contrast, the iron-based SCR has a better decomposition ability for nitrous oxide under the same conditions. Therefore, the present invention innovatively adopts a copper-iron-based composite SCR, making full use of the efficient conversion ability of the copper-based SCR for nitrogen oxides and the effective decomposition ability of the iron-based SCR for nitrous oxide. The emission of nitrous oxide is suppressed by the organic combination and synergistic effect of the two.

[0041] The electric heating thermal management measures adopted in the present invention show many beneficial effects in the operation of the entire SCR system, especially in the control of nitrogen oxide and nitrous oxide emissions during the cold start phase. During the cold start phase, the engine exhaust temperature is at a low level. This low temperature state seriously restricts the normal and efficient operation of the SCR system, making it difficult to effectively control nitrogen oxide emissions. The electric heating thermal management measures in the present invention can directly act on the exhaust temperature at the front end of the SCR system through the precise process of converting electrical energy into thermal energy, prompting the temperature of the reaction system to rise rapidly, effectively shortening the time required for the SCR catalyst to reach its active range.

[0042] The ammonia nitrogen ratio and NO2 proportion control measures implemented by the present invention have a beneficial effect in suppressing the generation of nitrous oxide. In the copper-based SCR nitrous oxide generation pathway, the ammonia nitrogen ratio and NO2 proportion are important parameters that affect the generation of nitrous oxide. Excessive concentrations of the two in a specific temperature range will affect the selective catalytic reduction reaction in the copper-based SCR, and promote the generation of nitrous oxide. The control measures for the two can effectively maintain the concentrations of ammonia and NO2 within a reasonable range, avoiding excessive concentrations in the sensitive temperature range, thereby macroscopically suppressing the generation conditions of nitrous oxide.

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. 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.

[0045] Figure 1 A schematic diagram of the structure of a composite dual-stage SCR system according to an embodiment;

[0046] Figure 2 The figure is a flow chart of a urea injection strategy based on thermal management measures according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0048] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0049] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0050] In the absence of conflict, the embodiments in this application and the features in the embodiments may be combined with each other.

[0051] Embodiment 1

[0052] A composite two-stage SCR system, this embodiment is applied to diesel vehicle post-treatment, such as Figure 1 As shown, the system includes a copper-based LO-SCR located upstream, namely the first SCR or called the upstream SCR), a first ASC, a DOC, a DPF, a copper-iron composite-based SCR located downstream (namely the second SCR or called the downstream SCR), a second ASC, a calculation control unit (an ECU calculation control unit may be used), an electric heating device, a gas concentration detection unit, and an exhaust temperature unit;

[0053] The gas concentration detection unit includes: a first NOx concentration sensor, a first NO concentration sensor, a second NOx concentration sensor, and a second NO concentration sensor; the exhaust temperature unit includes: a post-turbine exhaust temperature sensor, a first SCR temperature sensor, and a second SCR temperature sensor.

[0054] like Figure 1 As shown, the first SCR, the first ASC, the DOC, the DPF, the second SCR, and the second ASC are arranged in a straight line, wherein the first SCR is closely attached to the rear of the turbine.

[0055] In this embodiment, the second SCR is a copper-iron composite-based SCR. In the set length, the first three quarters use copper-based SCR to ensure the NOx conversion efficiency of the system under low temperature conditions; the last quarter uses iron-based SCR, which uses the advantage of iron-based SCR in catalytic decomposition of N2O gas to suppress N2O emissions.

[0056] The electric heating device is placed before the first SCR. Preferably, a 3.9 kW or 7.2 kW power heater is selected according to the exhaust flow rate of the diesel engine. It is used for exhaust heat management to quickly increase the temperature in the first SCR;

[0057] The exhaust temperature unit is used to determine in which preset temperature range the upstream and downstream SCR temperatures are located; and feed the temperature back to the calculation control unit to determine the urea injection strategy.

[0058] The gas concentration detection unit is used to detect the nitrogen oxide concentration and nitrogen dioxide NO2 ratio at the upstream and downstream SCR inlet ends, and feed back to the calculation control unit to determine the urea injection strategy and calculate the ammonia nitrogen ratio and urea injection amount.

[0059] Embodiment 2:

[0060] This embodiment provides a urea injection control method based on thermal management measures for the system of embodiment 1, such as Figure 2 As shown:

[0061] The first injection strategy and the second injection strategy are set for both upstream and downstream SCRs;

[0062] Specifically, the two injection strategies are distinguished by the ammonia-nitrogen ratio calculated based on the nitrogen oxide concentration measured by each nitrogen oxide sensor;

[0063] The calculation process of urea injection amount based on ammonia nitrogen ratio is as follows:

[0064] ;

[0065] ;

[0066] ;

[0067] ;

[0068] ;

[0069] in, is the molar flow rate of nitrogen oxides; is the exhaust flow rate; is the molar concentration of nitrogen oxides; is the molar flow rate of ammonia; is the ammonia nitrogen ratio; is the urea injection amount; is the molar flow rate of urea; is the molar concentration of urea solution; is the molar mass of urea.

[0070] The first injection strategy sets the ammonia-nitrogen ratio to 1.

[0071] The second injection strategy sets the ammonia nitrogen ratio to be greater than or equal to 1.1. Specifically, when the corresponding SCR inlet temperature is lower than 550 degrees Celsius, the ammonia nitrogen ratio is set to 1.1; when the corresponding SCR inlet temperature is higher than 550 degrees Celsius, the ammonia nitrogen ratio is set to 1.2.

[0072] Further, a complete urea injection control strategy in coordination with thermal management measures, such as Figure 2 As shown:

[0073] When the inlet temperature of the upstream copper-based SCR is below 250 degrees Celsius, the electric heating device is started to quickly raise the exhaust temperature to 250 degrees Celsius and maintain it above this temperature. When the exhaust temperature after the turbine reaches above 250 degrees Celsius, the electric heating device stops heating. At the same time, the downstream SCR does not inject urea at this stage, and the upstream SCR adopts the first injection strategy.

[0074] When the upstream SCR temperature reaches above 250°C, the upstream SCR adopts the second injection strategy and determines the downstream SCR inlet temperature at the same time.

[0075] When the downstream SCR inlet temperature is below 250°C, the NOx sensor is used to determine the NO2 ratio in the exhaust gas at the downstream SCR inlet. The NO2 ratio calculation process is as follows:

[0076] ;

[0077] in, is the proportion of NO2, is the concentration of nitrogen oxides in the exhaust gas; is the concentration of nitrogen monoxide in the exhaust gas; when the NO2 proportion is lower than the set threshold (preferably 0.2), the downstream adopts the first injection strategy; when the NO2 proportion rises above the threshold, the downstream SCR adopts the second injection strategy.

[0078] When the downstream temperature reaches above 250°C, the downstream SCR adopts the second injection strategy.

[0079] Embodiment 3

[0080] A post-treatment system includes the composite two-stage SCR system provided in the first embodiment.

[0081] Embodiment 4

[0082] A vehicle includes the composite dual-stage SCR system provided in the first embodiment or the post-treatment system provided in the third embodiment.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention without creative labor shall be included in the protection scope of the present invention.

Claims

1. A composite two-stage SCR system, characterized in that: It includes a first SCR, a first ASC, a DOC, a DPF, a second SCR, a second ASC, a calculation control unit, an electric heating device, a gas concentration detection unit and an exhaust temperature unit, wherein: The first SCR is arranged upstream, and an electric heating device is arranged at the front end thereof; the second SCR is arranged downstream, and a first ASC, a DOC and a DPF are arranged in sequence between the first SCR and the second SCR; A second ASC is disposed at the rear end of the second SCR; The gas concentration detection unit is used to detect the nitrogen oxide concentration and nitrogen dioxide ratio at the first SCR and the second SCR, and feed back to the calculation control unit; The exhaust temperature unit is used to obtain the exhaust temperature after the turbine, the temperature at the first SCR and the second SCR, and feed them back to the calculation control unit; The calculation control unit is used to determine the urea injection control strategy of the first SCR and the second SCR and the working strategy of the electric heating device according to the nitrogen oxide concentration and the nitrogen dioxide ratio detected by the gas concentration detection unit and the temperature obtained by the exhaust temperature unit, and control the first SCR, the second SCR and the electric heating device to work respectively according to the determined strategy; The computing control unit is configured as follows: When the temperature at the first SCR is less than the set value, the electric heating device is started until the exhaust temperature is greater than or equal to the set value. At the same time, the second SCR does not inject urea during this stage, and the first SCR adopts the first injection strategy; When the temperature at the inlet of the first SCR is greater than the set value, the first SCR adopts the second injection strategy and determines the temperature at the inlet of the second SCR at the same time: When the temperature at the second SCR is less than or equal to the set value, and the nitrogen dioxide ratio of the second SCR is less than the set threshold, the second SCR adopts the first injection strategy; when the nitrogen dioxide ratio is greater than or equal to the set threshold, the second SCR adopts the second injection strategy; When the second SCR temperature is greater than the set value, the second SCR adopts the second injection strategy; The first injection strategy is to set the ammonia nitrogen ratio to 1; The second injection strategy is: when the corresponding SCR inlet temperature is lower than a predetermined value, the ammonia nitrogen ratio is set to 1.1; when the corresponding SCR inlet temperature is greater than or equal to a predetermined value, the ammonia nitrogen ratio is set to 1.2, and the predetermined value is greater than the set value.

2. A composite dual-stage SCR system as claimed in claim 1, characterized in that: The first SCR is a copper-based low-load-cold start selective catalytic converter, and the distance between the first SCR and the turbine is less than a set value.

3. A composite dual-stage SCR system as claimed in claim 1, characterized in that: The second SCR is a copper-iron composite-based SCR. In setting the SCR length, the first part adopts a copper-based SCR and the second part adopts an iron-based SCR. And the length of the first part is greater than the length of the second part.

4. A composite dual-stage SCR system as claimed in claim 1, characterized in that: The exhaust temperature unit includes a post-turbine exhaust temperature sensor, a first SCR temperature sensor, and a second SCR temperature sensor. The post-turbine exhaust temperature sensor is arranged at the rear end of the turbine and located at the front end of the electric heating device; the first SCR temperature sensor is arranged at the inlet end of the first SCR, and the second SCR temperature sensor is arranged at the inlet end of the second SCR.

5. A composite dual-stage SCR system as claimed in claim 1, characterized in that: The gas concentration detection unit includes a first nitrogen oxide concentration sensor, a first nitrogen monoxide concentration sensor, a second nitrogen oxide concentration sensor and a second nitrogen monoxide concentration sensor, wherein the first nitrogen oxide concentration sensor and the first nitrogen monoxide concentration sensor are arranged at the inlet end of the first SCR, and the second nitrogen oxide concentration sensor and the second nitrogen monoxide concentration sensor are arranged at the inlet end of the second SCR.

6. A composite dual-stage SCR system as claimed in claim 1, characterized in that: The nitrogen dioxide ratio is calculated based on the corresponding nitrogen oxide concentration and nitrogen monoxide concentration obtained by the gas concentration detection unit.

7. A control method for a composite dual-stage SCR system, comprising the composite dual-stage SCR system according to any one of claims 1 to 6, characterized in that: The following steps are involved: Determine the urea injection control strategy of the first SCR located upstream and the second SCR located downstream and the working strategy of the electric heating device according to the nitrogen oxide concentration and nitrogen dioxide ratio detected by the gas concentration detection unit and the temperature obtained by the exhaust temperature unit, and control the first SCR, the second SCR and the electric heating device to work respectively according to the determined strategy; When the temperature at the first SCR is less than the set value, the electric heating device is started until the exhaust temperature is greater than or equal to the set value. At the same time, the second SCR does not inject urea during this stage, and the first SCR adopts the first injection strategy; When the temperature at the inlet of the first SCR is greater than the set value, the first SCR adopts the second injection strategy and determines the temperature at the inlet of the second SCR at the same time: When the temperature at the second SCR is less than or equal to the set value, and the nitrogen dioxide ratio of the second SCR is less than the set threshold, the second SCR adopts the first injection strategy; when the nitrogen dioxide ratio is greater than or equal to the set threshold, the second SCR adopts the second injection strategy; When the second SCR temperature is greater than a set value, the second SCR adopts a second injection strategy.

8. A control method for a composite dual-stage SCR system as claimed in claim 7, characterized in that: The first injection strategy is to set the ammonia nitrogen ratio to 1; The second injection strategy is: when the corresponding SCR inlet temperature is lower than a predetermined value, the ammonia nitrogen ratio is set to 1.1; when the corresponding SCR inlet temperature is greater than or equal to a predetermined value, the ammonia nitrogen ratio is set to 1.2, and the predetermined value is greater than the set value.

9. A post-processing system, characterized in that: A composite dual-stage SCR system comprising any one of claims 1-6.

10. A vehicle, characterized in that: The invention comprises the composite dual-stage SCR system according to any one of claims 1 to 6 or the after-treatment system according to claim 9.

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