A method and system for reducing n2o emissions from a diesel engine

Abstract

The present application relates to a kind of for reducing diesel engine N2O emission post-processing method and system.The present application includes the temperature of the SCR catalyst, nitrogen oxide concentration in diesel engine exhaust and exhaust mass flow;In response to the temperature of the SCR catalyst reaches 190 DEG C, control the urea nozzle starts to carry out first injection urea;Greater than 230 DEG C and less than or equal to 280 DEG C, control urea nozzle stop injection urea, control to open electric heater and exhaust heating;Greater than 280 DEG C and less than 320 DEG C, control urea nozzle carries out second injection urea and makes electric heater keep heating state;Greater than or equal to 320 DEG C, electric heater stops heating;When being in the condition that exhaust temperature changes from high to low, maintain the temperature of the SCR catalyst above 280 DEG C.By the urea injection amount of urea nozzle to the SCR catalyst temperature zoning control, and in combination with the heating dynamic regulation of electric heater, the pollutant emission of diesel engine is greatly reduced, and the N2O emission control of diesel engine is realized.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas treatment technology, and in particular to an after-treatment method and system for reducing N2O emissions from diesel engines. Background Technology

[0002] Nitrogen dioxide (N2O) is present in relatively small amounts in primary vehicle emissions, so previous emission regulations did not restrict it. However, with the application of various types and configurations of aftertreatment catalysts in diesel vehicles, N2O emissions from diesel vehicles have become a pressing issue. N2O primarily originates from side reactions during the NOx catalytic conversion process in diesel engine aftertreatment systems. Currently, in the China VI emission standard aftertreatment system's DOC-SCR-ASC process for reducing NOx, N2O mainly comes from the SCR system.

[0003] The main pollutants in diesel engine exhaust are NOx and PM. In the China VI emission standard diesel engine aftertreatment system, Selective Catalytic Reduction (SCR) is typically used to reduce NOx in diesel vehicle exhaust, while particulate matter is captured by a Diesel Particulate Filter (DPF). To meet the China VI emission regulations, a Diesel Oxidation Catalyst (DOC) is usually added upstream of the DPF+SCR system to reduce HC, CO emissions, and soluble organic compounds in PM, while also regulating the temperature and NO2 ratio at the DPF and SCR inlets. At the downstream end of the SCR system, an Ammonia Slip Catalyst (ASC) is used to prevent the escape of residual NH3 from the SCR reaction. Depending on whether Exhaust Gas Recirculation (EGR) technology is used to reduce NOx emissions from the engine and the complexity of SCR control in the aftertreatment system, the mainstream technical routes for meeting the current China VI emission standards for heavy-duty diesel vehicles include the traditional EGR route and the high-efficiency SCR route. The traditional EGR route uses EGR technology to reduce NOx emissions from diesel vehicles to a low level (below 5g / kWh). Therefore, the SCR aftertreatment technology in the EGR route is less complex; a NOx conversion efficiency of over 92% is sufficient to control NOx emissions and meet the China VI requirements. However, due to the trade-off effect between NOx and PM, the introduction of EGR technology leads to an increase in particulate matter emissions from diesel vehicles. In contrast, the high-efficiency SCR route eliminates EGR technology in the engine, resulting in high overall vehicle NOx emissions (above 8g / kWh). Therefore, its NOx conversion efficiency must reach over 97% to meet the China VI requirements. To meet the high NOx conversion rate of SCR, precise control of urea injection is required. This requires higher injection precision, greater robustness, and more difficult OBD control. However, diesel vehicles have better fuel economy and are easier to achieve passive regeneration of DPF.

[0004] Both EGR and high-efficiency SCR routes require the synergistic effect of multiple catalysts to reduce NOx and PM emissions from diesel engines. For PM control, the DPF (Distillation Processing Unit) is the primary site for particulate matter capture in the diesel engine aftertreatment system, but DOC (Distillation Catalyst) combined with hydrocarbon injection can achieve its active regeneration. For NOx emission control, SCR is the main catalytic conversion site, but DOC can achieve better catalytic conversion by changing the NO2 ratio at the SCR inlet. Simultaneously, NH3 and excess NOx at the SCR outlet are further converted in ASC (Acoustic Sterile Extraction Unit). Therefore, the catalytic conversion performance of the DOC-SCR-ASC catalyst in the diesel engine aftertreatment system is crucial to the system's ability to reduce NOx emissions, and developing high-performance catalysts is an important aspect of diesel engine NOx emission control. For DOC, honeycomb ceramics made of materials such as cordierite and silicon carbide are generally used as supports. A rough, porous coating material is coated on the support surface to increase the specific surface area of ​​the catalyst and uniformly disperse the active components; γ-Al2O3 is commonly used as the coating material. The active component of the DOC catalyst is crucial to the catalytic oxidation effect of DOC. Currently, platinum group metals such as platinum (Pt) and palladium (Pd) are widely used due to their excellent oxidation performance and heat resistance. Currently, SCR catalysts mainly employ metal-exchanged molecular sieve catalysts. Copper-based molecular sieve catalysts, especially those with chabazite (CHA) structures such as Cu-SSZ-13 and Cu-SAPO-34, exhibit good SCR activity and hydrothermal stability, a wider temperature window, and are less susceptible to degradation by unburned HC due to their small-pore structure.

[0005] Because Cu-SAPO-34 suffers from H2O poisoning at low temperatures, Cu-SSZ-13 molecular sieve catalysts have become the preferred SCR catalysts under the current China VI emission regulations. ASC catalysts need to completely oxidize excess NH3 to N2 and H2O at low temperatures without producing excess NOx. Currently, catalysts with a mixed bottom platinum group metal layer and a top SCR layer are generally used to achieve high NH3 conversion and high N2 selectivity. NO and NO2 generated in the bottom platinum group metal layer react with some of the NH3 in the top SCR layer to generate N2. Commercially, Pt / Al2O3 is generally used as the bottom layer, with Cu-SSZ-13 catalyst as the top layer. In the process of synergistic multi-catalytic control of NOx in diesel engine exhaust through DOC+SCR+ASC, it is necessary not only to improve the NOx conversion rate of the system but also to minimize the formation of byproducts. Summary of the Invention

[0006] Therefore, the present invention provides an aftertreatment method and system for reducing N2O emissions from diesel engines. By controlling the urea injection quantity of the urea nozzle through temperature zone control of the SCR catalyst and combining it with the dynamic heating regulation of the electric heater, the pollutant emissions of the diesel engine are significantly reduced, thereby achieving N2O emission control of the diesel engine.

[0007] To solve the above-mentioned technical problems, the present invention provides an aftertreatment method for reducing N2O emissions from diesel engines, which is applied to an aftertreatment system. The aftertreatment system includes an electric heater, a urea injector, and an SCR catalyst arranged sequentially from upstream to downstream along the exhaust passage of the diesel engine.

[0008] The method includes:

[0009] When the exhaust temperature changes from low to high:

[0010] The upstream and downstream exhaust temperatures of the SCR catalyst are obtained, and the temperature of the SCR catalyst is obtained based on the average value of the upstream and downstream exhaust temperatures.

[0011] To obtain the concentration of nitrogen oxides and the mass flow rate of the exhaust gas from the diesel engine;

[0012] In response to the SCR catalyst temperature reaching 190°C, the urea nozzle is controlled to begin the first urea injection; and when the SCR catalyst temperature is greater than or equal to 190°C and less than or equal to 230°C, the urea injection rate is based on the nitrogen oxide concentration, the exhaust gas mass flow rate, and the set NH3 and NO concentrations. X The molar mass ratio is calculated, wherein the molar mass ratio is set to 1.2;

[0013] In response to the temperature of the SCR catalyst being greater than 230°C and less than or equal to 280°C, the urea nozzle is controlled to stop injecting urea, and the electric heater is controlled to be turned on to heat the exhaust gas.

[0014] In response to the SCR catalyst being heated to a temperature greater than 280°C and less than 320°C, the urea nozzle is controlled to perform a second urea injection and the electric heater is kept in a heated state. At this time, the molar mass ratio is set to 1.

[0015] The electric heater stops heating in response to the SCR catalyst being heated to a temperature greater than or equal to 320°C.

[0016] When the exhaust temperature changes from high to low:

[0017] In response to the temperature of the SCR catalyst dropping from above 320°C, the electric heater is turned on to maintain the temperature of the SCR catalyst above 280°C.

[0018] In one embodiment of the present invention, based on the nitrogen oxide concentration, the exhaust gas mass flow rate, and the set values ​​of NH3 and NO... X The ratio of molar mass to urea mass is used to determine the urea injection rate of the urea nozzle, including determining the urea injection rate using the following formula:

[0019] ,

[0020] Where: Q1 is the urea injection rate, in g / h;

[0021] Q represents the exhaust gas mass flow rate, measured in kg / h.

[0022] A represents NO in the exhaust gas. X Emission concentration;

[0023] N represents NH3 and NO. X The ratio of their molar masses;

[0024] 1000 is the exhaust flow rate converted from kg / h to g / h;

[0025] 60 is the molar mass of urea;

[0026] 28.9 is the molar mass of the exhaust gas;

[0027] 2 mol of urea produces 2 mol of NH3;

[0028] 0.325 is the mass concentration of the urea aqueous solution.

[0029] The present invention also provides an aftertreatment system for reducing N2O emissions from diesel engines, comprising:

[0030] An electric heater installed in the exhaust passage of the diesel engine, an SCR catalyst installed downstream of the electric heater, a urea injector installed upstream of the SCR catalyst, a first exhaust temperature sensor for measuring the exhaust temperature upstream of the SCR catalyst, a second exhaust temperature sensor for measuring the exhaust temperature downstream of the SCR catalyst, an exhaust flow sensor for measuring the exhaust mass flow rate, a nitrogen oxide sensor for measuring the nitrogen oxide concentration in the exhaust, and a controller electrically connected to the above components; wherein:

[0031] The controller is configured to perform an aftertreatment method for reducing N2O emissions from a diesel engine.

[0032] In one embodiment of the present invention, the SCR catalyst is a vanadium-based SCR catalyst, a copper-based SCR catalyst, or an ASC catalyst.

[0033] In one embodiment of the present invention, the electric heater and the SCR catalyst are connected by a stainless steel exhaust pipe.

[0034] In one embodiment of the present invention, the electric heater is an EHC electric heater.

[0035] The technical solution of the present invention has the following advantages compared with the prior art:

[0036] The present invention discloses an aftertreatment method and system for reducing N2O emissions from diesel engines. By controlling the urea injection quantity of the urea nozzle through temperature zone control of the SCR catalyst and combining it with the dynamic heating regulation of the electric heater, the pollutant emissions of the diesel engine are significantly reduced, thereby achieving N2O emission control of the diesel engine. Attached Figure Description

[0037] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0038] Figure 1 This is a schematic diagram of the structure of an aftertreatment system for reducing N2O emissions from diesel engines according to an embodiment of the present invention.

[0039] Figure 2 This is a graph showing the N2O emission test results of the copper-based SCR catalyst in an embodiment of the present invention.

[0040] Explanation of reference numerals in the instruction manual:

[0041] 100. Electric heater;

[0042] 200. Urea nozzle;

[0043] 300, SCR catalyst;

[0044] 400. First exhaust temperature sensor;

[0045] 500. Second exhaust temperature sensor;

[0046] 600. Exhaust flow sensor;

[0047] 700. Nitrogen and oxygen sensor;

[0048] 800, Controller. Detailed Implementation

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0050] In this invention, when directions (up, down, left, right, front, and back) are described, it is only for the convenience of describing the technical solution of this invention, and does not indicate or imply that the technical features referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0051] In this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc., are understood to exclude the stated number; "above," "below," "within," etc., are understood to include the stated number. In the description of this invention, the terms "first" and "second" are used only to distinguish technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0052] In this invention, unless otherwise explicitly defined, the terms "setting," "installing," and "connecting" should be interpreted broadly. For example, they can refer to a direct connection or an indirect connection through an intermediate medium; a fixed connection, a detachable connection, or an integrally formed connection; a mechanical connection, an electrical connection, or a connection capable of mutual communication; or the internal connection of two components or the interaction between two components. Those skilled in the art can reasonably determine the specific meaning of the above terms in this invention based on the specific content of the technical solution.

[0053] Example 1

[0054] Reference Figure 1 As shown, this embodiment provides an aftertreatment method for reducing N2O emissions from diesel engines. The method is characterized by its application in an aftertreatment system, which includes an electric heater 100, a urea injector 200, and an SCR catalyst 300 arranged sequentially from upstream to downstream along the diesel engine's exhaust passage. After being discharged from the diesel engine, the exhaust gas first enters the electric heater 100, then passes through the SCR catalyst 300, and then... Figure 1 Flowing in the direction shown;

[0055] The method includes:

[0056] When the exhaust temperature changes from low to high, the following control strategy is implemented:

[0057] The upstream exhaust temperature t1 and the downstream exhaust temperature t2 of the SCR catalyst 300 are obtained. Based on the average value of the upstream exhaust temperature t1 and the downstream exhaust temperature t2, the temperature of the SCR catalyst 300 is obtained as t = 1 / 2 * (t1 + t2).

[0058] Obtain the nitrogen oxide concentration A and exhaust mass flow rate Q in the diesel engine exhaust;

[0059] In response to the SCR catalyst 300 temperature t reaching 190°C, the urea nozzle is controlled to begin the first urea injection. When the SCR catalyst 300 temperature t is greater than or equal to 190°C and less than or equal to 230°C (190°C ≤ t ≤ 230°C), the urea injection quantity is based on the nitrogen oxide concentration A, the exhaust gas mass flow rate Q, and the set NH3 and NO concentrations. X The molar mass ratio N is calculated, wherein the molar mass ratio N is set to N=1.2. At this time, the SCR catalyst 300 has a high ammonia storage capacity, and the NH3 generated by the decomposition of the extra injected urea can be stored in the SCR catalyst 300.

[0060] In response to the SCR catalyst 300 temperature t being greater than 230°C and less than or equal to 280°C (230°C < t ≤ 280°C), the urea nozzle 200 is controlled to stop injecting urea, and the electric heater 100 is controlled to be turned on to heat the exhaust gas; at this time, it is necessary to raise the SCR catalyst 300 temperature t to greater than 280°C as soon as possible.

[0061] In response to the SCR catalyst 300 being heated to a temperature greater than 280°C and less than 320°C (280°C < t < 320°C), the urea nozzle 200 is controlled to perform a second urea injection, and the electric heater 100 is kept in a heated state. At this time, the molar mass ratio N is set to N=1. A higher NO content can be achieved under the condition of N=1.0. X Conversion efficiency;

[0062] In response to the SCR catalyst 300 being heated to a temperature t greater than or equal to 320°C (t≥320°C), the electric heater 100 stops heating.

[0063] When the exhaust temperature changes from high to low, the following control measurements are performed:

[0064] In response to the temperature t of the SCR catalyst 300 decreasing from above 320°C, the electric heater 100 is turned on to maintain the temperature of the SCR catalyst 300 above 280°C.

[0065] Specifically, based on the nitrogen oxide concentration, the exhaust gas mass flow rate, and the set NH3 and NO concentrations...X The molar mass ratio is used to determine the urea injection rate of the urea nozzle 200, including determining the urea injection rate using the following formula:

[0066] ,

[0067] Where: Q1 is the urea injection rate, in g / h;

[0068] Q represents the exhaust gas mass flow rate, measured in kg / h.

[0069] A represents NO in the exhaust gas. X Emission concentration;

[0070] N represents NH3 and NO. X The molar mass ratio; calibrated in controller 800 according to emission requirements;

[0071] 1000 is the exhaust flow rate converted from kg / h to g / h;

[0072] 60 is the molar mass of urea;

[0073] 28.9 is the molar mass of the exhaust gas;

[0074] 2 mol of urea produces 2 mol of NH3;

[0075] 0.325 is the mass concentration of the urea aqueous solution.

[0076] It should be noted that current diesel engine China VI after-treatment systems typically use SCR technology to reduce NOx emissions. X Regarding emissions, the commonly used SCR catalysts on the market are copper-based molecular sieve SCR catalysts. The N2O emissions in diesel engine exhaust are very low, with N2O formation mainly originating from the SCR reaction. This invention conducts N2O emission tests using copper-based SCR catalysts, and the results are as follows... Figure 2 As shown, the initial injection temperature of the SCR urea injection system is typically set at 190℃. It can be observed that between 190℃ and 250℃, N2O emissions gradually increase with the increase of the SCR catalyst temperature. At 250℃, N2O emissions show a significant peak, indicating that the SCR catalyst generates the most N2O at 250℃. When the temperature continues to rise to 300℃–350℃, N2O emissions rapidly decrease and reach their lowest point at 350℃. When the temperature continues to rise to 400℃–450℃, N2O emissions gradually increase again. In other words, the SCR catalyst generates more N2O near 250℃, while the 300℃–350℃ range is more conducive to N2O decomposition or reduces its formation.

[0077] The above method is based on this characteristic to design control strategies:

[0078] The first injection is carried out in the low temperature range of 190℃ to 230℃, and the ammonia storage capacity of the catalyst is used to pre-store NH3, so as to avoid pushing the reaction point to the peak region of 250℃.

[0079] Stop spraying in the 230℃~280℃ range and turn on the electric heater 100 to make the catalyst temperature quickly cross the 250℃ range where N2O is generated.

[0080] When the temperature rises to 280℃~320℃, it is sprayed again, and the molar ratio is set to 1.0, which corresponds to the low N2O emission zone. This ensures efficient NOx conversion while avoiding an increase in N2O.

[0081] If the temperature tends to drop below 320°C when the exhaust temperature decreases, the heater is used to maintain the temperature above 280°C to prevent frequent returns to the 250°C region and the generation of excessive N2O.

[0082] By rationally controlling injection and heating in different zones and avoiding the high emission temperature zone of N2O, the SCR system can not only efficiently remove NOx, but also significantly reduce N2O emissions.

[0083] Example 2

[0084] Based on the same inventive concept, this embodiment provides an aftertreatment system for reducing N2O emissions from diesel engines. The principle of solving the problem is similar to that of the aftertreatment method for reducing N2O emissions from diesel engines, and the repetitions will not be repeated.

[0085] This embodiment provides an aftertreatment system for reducing N2O emissions from diesel engines, comprising:

[0086] An electric heater 100 is installed in the exhaust passage of the diesel engine; an SCR catalyst 300 is installed downstream of the electric heater 100; a urea nozzle 200 is installed upstream of the SCR catalyst 300; a first exhaust temperature sensor 400 is used to measure the exhaust temperature upstream of the SCR catalyst 300; a second exhaust temperature sensor 500 is used to measure the exhaust temperature downstream of the SCR catalyst 300; an exhaust flow sensor 600 is used to measure the exhaust mass flow rate; a nitrogen oxide sensor 700 (NOx sensor) is used to measure the nitrogen oxide concentration in the exhaust; and a controller 800 is electrically connected to the above components; wherein:

[0087] The controller 800 is configured to perform the aforementioned aftertreatment method for reducing N2O emissions from diesel engines.

[0088] Furthermore, the SCR catalyst 300 is a vanadium-based SCR catalyst, a copper-based SCR catalyst, or an ASC catalyst.

[0089] Vanadium-based SCR catalysts: Vanadium-based SCR catalysts are one of the most commonly used catalysts in SCR systems. They are mainly composed of vanadium oxide (V2O5) and some auxiliary oxides. Vanadium-based catalysts have high catalytic activity and good thermal stability, and can effectively reduce emissions over a wide temperature range. In addition, vanadium-based SCR catalysts also have low sulfide sensitivity, which can reduce the poisoning effect of sulfides on the catalyst.

[0090] Copper-based SCR catalysts: Copper-based SCR catalysts are commonly used in SCR systems. They primarily consist of copper oxide (CuO) as the main active component. Copper-based SCR catalysts exhibit good catalytic activity and high selectivity, enabling efficient NO removal over a wide temperature range. X In addition to the reaction, copper-based SCR catalysts also have high high-temperature resistance, enabling them to maintain catalytic activity under high-temperature conditions.

[0091] ASC catalyst: ASC is an abbreviation for Ammonia Slip Catalyst, which is mainly used to eliminate excess or escaped NH3 in the engine exhaust system and oxidize NH3 to N2.

[0092] Furthermore, the electric heater 100 is an EHC electric heater (electric heating cylinder), and the electric heater 100 and the SCR catalyst 300 are connected by a stainless steel exhaust pipe.

[0093] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0094] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0095] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0096] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0097] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An aftertreatment method for reducing N2O emissions from diesel engines, characterized in that, It is applied to an aftertreatment system, which includes an electric heater, a urea injector, and an SCR catalyst arranged sequentially from upstream to downstream along the exhaust passage of a diesel engine; The method includes: When the exhaust temperature changes from low to high: The upstream and downstream exhaust temperatures of the SCR catalyst are obtained, and the temperature of the SCR catalyst is obtained based on the average value of the upstream and downstream exhaust temperatures. To obtain the concentration of nitrogen oxides and the mass flow rate of the exhaust gas from the diesel engine; In response to the SCR catalyst temperature reaching 190°C, the urea nozzle is controlled to begin the first urea injection; and when the SCR catalyst temperature is greater than or equal to 190°C and less than or equal to 230°C, the urea injection rate is based on the nitrogen oxide concentration, the exhaust gas mass flow rate, and the set NH3 and NO concentrations. X The molar mass ratio is calculated, wherein the molar mass ratio is set to 1.2; In response to the temperature of the SCR catalyst being greater than 230°C and less than or equal to 280°C, the urea nozzle is controlled to stop injecting urea, and the electric heater is controlled to be turned on to heat the exhaust gas. In response to the SCR catalyst being heated to a temperature greater than 280°C and less than 320°C, the urea nozzle is controlled to perform a second urea injection and the electric heater is kept in a heated state. At this time, the molar mass ratio is set to 1. The electric heater stops heating in response to the SCR catalyst being heated to a temperature greater than or equal to 320°C. When the exhaust temperature changes from high to low: In response to the temperature of the SCR catalyst dropping from above 320°C, the electric heater is turned on to maintain the temperature of the SCR catalyst above 280°C.

2. The aftertreatment method for reducing N2O emissions from diesel engines according to claim 1, characterized in that, Based on the nitrogen oxide concentration, the exhaust gas mass flow rate, and the set values ​​for NH3 and NO... X The ratio of molar mass to urea mass is used to determine the urea injection rate of the urea nozzle, including determining the urea injection rate using the following formula: ， Where: Q1 is the urea injection rate, in g / h; Q represents the exhaust gas mass flow rate, measured in kg / h. A represents NO in the exhaust gas. X Emission concentration; N represents NH3 and NO. X The ratio of their molar masses; 1000 is the exhaust flow rate converted from kg / h to g / h; 60 is the molar mass of urea; 28.9 is the molar mass of the exhaust gas; 2 mol of urea produces 2 mol of NH3; 0.325 is the mass concentration of the urea aqueous solution.

3. An aftertreatment system for reducing N2O emissions from diesel engines, characterized in that, include: An electric heater installed in the exhaust passage of the diesel engine, an SCR catalyst installed downstream of the electric heater, a urea injector installed upstream of the SCR catalyst, a first exhaust temperature sensor for measuring the exhaust temperature upstream of the SCR catalyst, a second exhaust temperature sensor for measuring the exhaust temperature downstream of the SCR catalyst, an exhaust flow sensor for measuring the exhaust mass flow rate, a nitrogen oxide sensor for measuring the nitrogen oxide concentration in the exhaust, and a controller electrically connected to the above components; wherein: The controller is configured to perform an aftertreatment method for reducing N2O emissions from a diesel engine as described in any one of claims 1-2.

4. An aftertreatment system for reducing N2O emissions from diesel engines according to claim 3, characterized in that, The SCR catalyst is a vanadium-based SCR catalyst, a copper-based SCR catalyst, or an ASC catalyst.

5. An aftertreatment system for reducing N2O emissions from diesel engines according to claim 3, characterized in that, The electric heater is an EHC electric heater.

6. An aftertreatment system for reducing N2O emissions from diesel engines according to claim 3, characterized in that, The electric heater and the SCR catalyst are connected by a stainless steel exhaust pipe.

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