Light diesel engine tail gas aftertreatment system and control method thereof

Abstract

The invention provides a light diesel engine tail gas after-treatment system and a control method thereof, which can solve the problems of high cold start emission, catalyst poisoning caused by HC, N2O generation and difficulty in reaching the standard of PN10 emission in the prior art, meet the requirements of a new generation of emission regulations, and improve the emission efficiency. Comprising a ccDOC unit, a first urea injection unit, a ccSCR unit, a DPF unit, a second urea injection unit, a second SCR unit and an ASC unit which are sequentially arranged in the tail gas direction of an engine. The controller is electrically connected with the first urea spraying unit and the second urea spraying unit; and the controller controls the first urea injection unit to inject a first urea amount U1 into the tail gas in front of the ccSCR unit and controls the second urea injection unit to inject a second urea amount U2 into the tail gas in front of the second SCR unit according to a preset control method.

Description

Technical Field

[0001] This invention relates to the field of diesel engine exhaust aftertreatment technology, and in particular to a light-duty diesel engine exhaust aftertreatment system and its control method. Background Technology

[0002] Diesel engines are widely used in the transportation sector due to their excellent fuel economy and power performance. However, the nitrogen oxides (NOx) and particulate matter (PM) emitted by diesel engines pose serious threats to the atmospheric environment and human health. With increasingly stringent emission regulations worldwide, diesel engine exhaust aftertreatment technology faces significant challenges.

[0003] Currently, the Euro 7 regulations were released in 2024, with light-duty and heavy-duty vehicles to be implemented in phases from 2026 to 2029. China is expected to follow suit approximately two years later. The new generation of China VII emission standards imposes more stringent requirements on pollutant emission limits, particularly regarding emission control under actual driving conditions such as cold starts and low loads. Existing technical solutions have revealed the following technical problems in response to these stringent requirements: 1. Emission regulations have imposed stricter requirements on the cold start phase of vehicles, aiming to significantly reduce pollutant emissions during actual use, especially when starting in low-temperature environments.

[0004] Existing technological approach: Configuring a front-mounted electrically heated catalytic converter (EHC) on the vehicle. Electrical heating allows the catalytic converter to reach operating temperature more quickly, effectively reducing pollutant emissions during cold starts. However, this approach has the following drawbacks: Adding an EHC increases the complexity and cost of the aftertreatment system. It also exacerbates the impact on the vehicle's low-voltage systems, such as the 12V system. The core function of the EHC is to rapidly heat the catalyst using electricity, making it essentially a high-power electrical device. When integrated into a 12V system originally designed for conventional vehicle electrical systems (such as lights and audio), manufacturers are required to specifically strengthen and optimize the existing electrical system to ensure it can withstand the increased electrical load and avoid affecting other vehicle functions and safety.

[0005] 2. Emission regulations have imposed stricter requirements on nitrogen oxides. Diesel engines will generally be equipped with tightly coupled selective catalytic reduction (ccSCR) systems, along with upgraded urea injection systems and high-precision nitrogen oxide sensors, to further reduce ammonia slip. This approach will have the following problems: A. HC will compete with urea (or ammonia) in the SCR system for active sites on the catalyst surface, thereby inhibiting the reduction reaction of nitrogen oxides and causing a decrease in overall conversion efficiency.

[0006] B. Some HC may undergo incomplete oxidation on the catalyst, leading to coking and carbon buildup on the catalyst surface, covering the active centers, causing reversible poisoning of the catalyst, and affecting its long-term stability.

[0007] C. In order to address the impact of HC on cCSCR, more complex control methods need to be developed to ensure the conversion efficiency of NOx in the presence of HC. At the same time, it may be necessary to develop more advanced catalyst material coating technology that is resistant to HC poisoning.

[0008] D. To achieve high NOx conversion efficiency at low temperatures, control systems typically employ an "NH3 excess" strategy, which involves injecting excess urea into the CCSCR to store a large amount of NH3. When vehicle operating conditions change (e.g., from high-speed driving to congested urban traffic), the exhaust gas temperature rises, and the excess NH3 stored in the CCSCR is released, resulting in "NH3 leakage." This leaked NH3 enters the downstream DOC with the airflow, where it is oxidized within the DOC's active temperature window, generating large amounts of N2O and causing N2O emissions to exceed standards.

[0009] 3. Emission regulations have imposed stricter requirements on particulate matter. The Euro 7 standard has tightened the particle size threshold for particulate number (PN) detection from 23 nanometers (PN23) in Euro 6 to 10 nanometers (PN10). This means that more previously unmonitored and finer particulate matter has been brought under regulatory control.

[0010] The China VI emission standard technology route combines DOC (Diesel Oxide), DPF (Distilled Powder Fluid Extractor), mixer, and SCR (Self-Containing Filter). The high-efficiency DPF achieves over 99% filtration efficiency for solid particles (mainly soot), and PN23 filtration can reliably meet regulatory requirements. However, for China VII, stricter PN10 regulations may lead to urea or cyanuric acid particles generated by the SCR system. If these particles penetrate the DPF, PN10 levels will exceed the limit. The China VII aftertreatment technology route optimizes the DPF, developing higher porosity and more complex pore structures, with a smaller median pore size. This effectively increases the capture of particles between PN10 and PN23. However, the reduced median pore size further increases the back pressure of the DPF. Under the new fuel consumption regulations and requirements, balancing back pressure and DPF filtration performance has become a key focus in the development of China VII DPFs. Summary of the Invention

[0011] To address the aforementioned problems, this invention provides a light-duty diesel engine exhaust aftertreatment system and its control method, which can solve the problems of high cold start emissions, catalyst poisoning caused by HC, N2O generation, and difficulty in meeting PN10 emission standards in the prior art, and meet the requirements of the new generation of domestic emission regulations.

[0012] The technical solution is as follows: A light-duty diesel engine exhaust aftertreatment system, characterized in that it comprises components arranged sequentially along the direction of engine exhaust: ccDOC unit; First urea injection unit; ccSCR unit; DPF unit; Second urea injection unit; Second SCR unit; ASC unit; The controller is electrically connected to the first urea injection unit and the second urea injection unit; According to a preset control method, the controller controls the first urea injection unit to inject a first urea amount U1 into the exhaust gas in front of the ccSCR unit, and controls the second urea injection unit to inject a second urea amount U2 into the exhaust gas in front of the second SCR unit. A first nitrogen oxide sensor is disposed between the ccDOC unit and the ccSCR unit to detect the nitrogen oxide concentration Q1 at the ccSCR inlet; The second nitrogen oxide sensor is located downstream of the second SCR unit and is used to detect the nitrogen oxide concentration Q2 at the outlet of the diesel engine exhaust aftertreatment system. A first temperature sensor is installed at the inlet of the cCSCR unit to detect the inlet temperature T1 of the cCSCR unit. A second temperature sensor is installed at the inlet of the second SCR unit to detect the inlet temperature T2 of the second SCR unit. The controller is electrically connected to the first and second nitrogen oxide sensors and the first and second temperature sensors, and is used to receive the detection signals from each sensor.

[0013] The ccDOC unit uses a metal carrier.

[0014] A control method for the above-mentioned diesel engine exhaust aftertreatment system, characterized by comprising the following steps: Step 101: Obtain the nitrogen oxide concentration Q1 and temperature T1 at the inlet of the ccSCR unit, and the nitrogen oxide concentration Q2 and temperature T2 at the outlet of the diesel engine exhaust aftertreatment system. Step 102: Calculate the first urea amount U1 required to meet the target conversion efficiency based on the temperature T1 and the nitrogen oxide concentration Q1; Step 103: Calculate the second urea quantity U2 based on the temperature T2 and the nitrogen oxide concentration Q2; Step 104: Determine whether the calculated first urea amount U1 exceeds the preset maximum injection threshold Umax; if yes, control the actual injection amount of the first urea injection unit to the maximum injection threshold Umax, and control the actual injection amount of the second urea injection unit to U2+(U1-Umax); if no, control the first and second urea injection units to inject the calculated first urea amount U1 and second urea amount U2 respectively.

[0015] Furthermore, in step 102, the efficiency λ1 of the current operating condition of the ccSCR unit is obtained from the SCR efficiency model based on the inlet temperature T1 of the ccSCR unit, and the first urea amount U1 injected in front of the ccSCR unit is calculated in combination with the nitrogen oxide concentration Q1 in front of the ccSCR unit. In step 103, the efficiency λ2 of the second SCR unit under the current operating condition is calculated in the SCR efficiency model based on the temperature T2 at the inlet of the second SCR unit. Combined with the nitrogen oxide concentration Q2 after the ASC unit, the amount of second urea injected before the second SCR unit is calculated, U2.

[0016] A light-duty diesel engine exhaust aftertreatment system, characterized in that it comprises components arranged sequentially along the direction of engine exhaust: ccDOC unit; First urea injection unit; ccSCR unit; ASC unit; DPF unit; A first nitrogen oxide sensor is disposed between the ccDOC unit and the ccSCR unit for detecting the nitrogen oxide concentration Q1 at the inlet of the ccSCR unit; The second nitrogen oxide sensor is located downstream of the ASC unit and is used to detect the nitrogen oxide concentration Q2 at the outlet of the ASC unit. A first temperature sensor is installed at the inlet of the ccSCR unit to detect the inlet temperature T1 of the ccSCR unit. The controller is electrically connected to the first urea injection unit, the first nitrogen oxide sensor, the second nitrogen oxide sensor, and the first temperature sensor; The controller controls the first urea injection unit to inject a first urea amount U1 into the exhaust gas in front of the ccSCR unit according to a preset control method.

[0017] Furthermore, the ccDOC unit uses a metal carrier.

[0018] A control method for the above-mentioned diesel engine exhaust aftertreatment system, characterized by comprising the following steps: Step 201: Obtain the nitrogen oxide concentration Q1 and temperature T1 at the inlet of the ccSCR unit, and obtain the nitrogen oxide concentration Q2 at the outlet of the ASC unit; Step 202: Calculate the first urea quantity U1 based on the temperature T1, the current ammonia storage amount of the ccSCR unit, and the nitrogen oxide concentrations Q1 and Q2, and control the first urea injection unit to perform injection. Furthermore, control methods also include: Based on the inlet temperature T1 of the ccSCR unit and the current ammonia storage capacity of the ccSCR unit, the efficiency λ1 of the ccSCR unit under the current operating conditions is obtained in the SCR efficiency model. The actual nitrogen oxide conversion efficiency λ3 of the ccSCR unit was obtained by using the nitrogen oxide concentration Q1 before the ccSCR unit and the nitrogen oxide concentration Q2 after the ASC unit. The current ammonia storage capacity of the ccSCR unit is obtained by the actual nitrogen oxide conversion efficiency λ3 of the ccSCR unit and the amount of urea injected.

[0019] Furthermore, the actual nitrogen oxide conversion efficiency λ3 is calculated using the following formula: .

[0020] Furthermore, when the actual nitrogen oxide conversion efficiency λ3 of the ccSCR unit remains below a set limit within the high-efficiency temperature range, a high-temperature regeneration procedure is triggered for the ccSCR unit to remove accumulated hydrocarbons and sulfur.

[0021] Compared with the prior art, the present invention has the following advantages: This invention moves the DOC (Diesel Oxide) stage forward to form ccDOC (Chemical Dioxide Catalyst) before the ccSCR (Chemical Separator Catalyst), so that hydrocarbons (HC) emitted by the engine are oxidized into CO2 and H2O before entering the ccSCR. This eliminates the competitive inhibition of the ccSCR catalyst by hydrocarbons and the risk of carbon poisoning. At the same time, by eliminating the downstream DOC unit, the problem of NH3 leaked from the ccSCR being oxidized into N2O in the downstream DOC can be avoided, effectively reducing greenhouse gas emissions and improving the long-term stability of the system. In this invention, the ccDOC unit uses a metal carrier ccDOC, which can significantly improve cold start performance. The metal carrier has the characteristics of high thermal conductivity and small heat capacity, which can quickly transfer exhaust heat to the entire catalyst carrier, so that the ccDOC can start working earlier in the cold start stage, effectively reducing NOx peak emissions. Compared with traditional ceramic carriers, metal carriers can significantly reduce the dependence on high-power EHC, and may even eliminate the need for EHC, reducing the pressure on the vehicle's 12V low-voltage electrical system and reducing system complexity and cost. This invention employs a two-stage urea injection unit. The first urea injection unit is positioned before the cCSCR unit and plays a major role in NOx treatment throughout the entire operating cycle. The second urea injection unit is positioned after the DPF unit and only plays an auxiliary role in NOx treatment during high-load or full-load periods. Since the urea particles generated by the main injection can be efficiently filtered by the DPF unit, and the subsequent auxiliary injection is less or not at all, the impact of urea crystal particles on PN10 can be significantly reduced, enabling PN10 emissions to meet the requirements of the new generation of emission regulations. This invention also provides a single-injection exhaust aftertreatment system. When the engine exhaust is low and there is sufficient space for the ccSCR, the downstream SCR and the second urea injection unit can be eliminated, and only the ASC unit is arranged after the ccSCR, further reducing the system complexity and cost. The carrier volume of the ccSCR unit and the downstream SCR can be flexibly allocated according to the spatial layout and exhaust temperature distribution factors of different vehicle models, making full use of the engine exhaust temperature while meeting the requirements of the new generation of emission regulations. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the diesel engine exhaust aftertreatment system according to Embodiment 1 of the present invention; Figure 2 This is a flowchart of the control method of the diesel engine exhaust aftertreatment system according to Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the diesel engine exhaust aftertreatment system according to Embodiment 2 of the present invention; Figure 4 This is a flowchart of the control method of the diesel engine exhaust aftertreatment system according to Embodiment 2 of the present invention. Detailed Implementation

[0023] Example 1: Reference Figure 1 This embodiment provides a light-duty diesel engine exhaust aftertreatment system. The exhaust gas emitted by the engine flows sequentially through the various components of the system in the direction shown by the arrows. The exhaust aftertreatment system in this embodiment includes: ccDOC unit 1 is a tightly coupled diesel oxidation catalyst located near the engine exhaust manifold. It is used to oxidize carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas from the engine into carbon dioxide (CO2) and water (H2O), and at the same time oxidize some nitric oxide (NO) into nitrogen dioxide (NO2) to facilitate the rapid reaction of downstream SCR. In this embodiment, the ccDOC unit uses a metal carrier. The metal carrier has the characteristics of low heat capacity and high thermal conductivity, which can quickly absorb the heat of the exhaust gas after the engine is cold-started and reach the operating temperature, thereby intervening in the catalytic reaction in advance at low temperature stage and effectively reducing pollutant emissions during cold start. The first urea injection unit 2 is located after the ccDOC unit 1 and before the ccSCR unit 3. The first urea injection unit 2 is used to inject urea aqueous solution into the exhaust gas as the main source of NOx reducing agent. In the embodiment, a gas-assisted injection unit can be used to atomize the urea solution with compressed air to make the droplets smaller, so that they can evaporate and decompose into ammonia (NH3) more quickly and fully before entering the ccSCR unit, thereby improving the urea utilization rate. The ccSCR unit 3 is a tightly coupled selective catalytic reduction unit located after the first urea injection unit. It is used to reduce NOx into harmless nitrogen and water by utilizing the ammonia produced by the decomposition of the urea injected in the previous stage under the action of a catalyst. DPF Unit 4 is a diesel particulate filter located downstream of CCSCR Unit 3. It is used to filter and capture particulate matter (PM) in exhaust gas, especially soot particles. At the same time, since DPF Unit 4 is located downstream of the first urea injection unit 2, it can also efficiently capture solid particles generated by incomplete decomposition of urea injection, which helps control PN10 emissions. The second urea injection unit 5 is located downstream of the DPF unit 4 and upstream of the second SCR unit 6. The second urea injection unit 5 serves as an auxiliary injection unit. The second SCR unit 6 employs a selective catalytic reduction device and is located in [location missing]. It is used to treat NOx that has penetrated the pre-stage unit. The second urea injection unit 5 upstream of the second SCR unit 6 provides urea. Since most of the NOx has already been treated in the ccSCR unit 3, the load on the second SCR unit 6 is relatively low. ASC Unit 7 employs an ammonia escape catalyst, located downstream of the second SCR Unit 6, to oxidize excess ammonia escaping from ccSCR Unit 3 and the second SCR Unit 6, preventing it from being directly released into the atmosphere and causing secondary pollution.

[0024] The controller is electrically connected to the first urea injection unit 2 and the second urea injection unit 5. The controller is shown in the figure. According to the preset control method, the controller controls the first urea injection unit 2 to inject the first urea amount U1 into the exhaust gas in front of the ccSCR unit 3, and controls the second urea injection unit 5 to inject the second urea amount U2 into the exhaust gas in front of the second SCR unit 6. The first nitrogen oxide sensor 9 is located between the ccDOC unit and the ccSCR unit and is used to detect the nitrogen oxide concentration Q1 at the ccSCR inlet. The second nitrogen oxide sensor 10 is located downstream of the second SCR unit and is used to detect the nitrogen oxide concentration Q2 at the outlet of the diesel engine exhaust aftertreatment system. The first temperature sensor 11 is located at the inlet of the cCSCR unit 3 and is used to detect the inlet temperature T1 of the cCSCR unit 3. The second temperature sensor 8 is located at the inlet of the second SCR unit 6 and is used to detect the inlet temperature T2 of the second SCR unit 6. The controller is electrically connected to the first nitrogen oxide sensor 9, the second nitrogen oxide sensor 10, the first temperature sensor 11, and the second temperature sensor 8, and is used to receive the detection signals from each sensor.

[0025] The exhaust gas from the engine first enters the cccDOC unit, where HC and CO are oxidized, and some NO is oxidized to NO2. Before the purified exhaust gas enters the cccSCR unit, the first urea injection unit injects a urea solution. Urea hydrolyzes and pyrolyzes in the high-temperature exhaust gas to produce NH3. In the cccSCR unit, NH3 reduces most of the NOx to N2 and H2O. The exhaust gas then enters the DPF unit, where solid particulate matter is captured. If the NO is not completely converted by the cccSCR unit under high load conditions, the second urea injection unit 5 starts injection to provide urea to the second SCR unit for further NOx treatment. The exhaust gas then passes through the ASC unit, where the escaped NH3 is oxidized, resulting in exhaust gas that meets emission standards.

[0026] In this embodiment, DOC is moved forward before ccSCR, so HC is oxidized before entering ccSCR, avoiding competition between HC and NH3 for active sites on the catalyst surface, protecting the activity of ccSCR catalyst, and avoiding problems such as NOx conversion efficiency decline and catalyst carbon poisoning. By moving DOC forward, the entire aftertreatment system is more adaptable to changes in fuel quality and engine operating conditions, and the system operates more stably. Under most operating conditions, only the first urea injection unit needs to operate. Since the DPF unit follows immediately after it, the generated urea particles are effectively filtered, ensuring that PN10 meets the standard. Under extreme operating conditions such as rapid acceleration or high load, which generate a large amount of NOx, the second urea injection unit starts auxiliary injection. Due to its small injection volume and low frequency, its impact on PN10 emissions is controllable. In addition, some of the ammonia generated after the first urea injection unit is adsorbed on the cC-SCR unit. Unreacted ammonia will be carried by the airflow through the DPF unit to the second SCR unit and be adsorbed. It can also participate in the subsequent reduction reaction, improving the overall utilization rate of ammonia.

[0027] Reference Figure 2 The flow chart of the control method corresponding to the diesel engine exhaust aftertreatment system in this embodiment includes the following steps: Step 101: Obtain the nitrogen oxide concentration Q1 and temperature T1 at the inlet of the ccSCR unit, the nitrogen oxide concentration Q2 at the outlet of the diesel engine exhaust aftertreatment system, and the temperature T2 at the inlet of the second SCR unit. Step 102: Calculate the first urea amount U1 required to meet the target conversion efficiency based on the temperature T1 and the nitrogen oxide concentration Q1; Step 103: Calculate the second urea quantity U2 based on the temperature T2 and the nitrogen oxide concentration Q2; Step 104: To prevent incomplete urea decomposition due to excessive injection, the system presets a maximum injection threshold Umax related to the current operating conditions. The maximum injection threshold Umax represents the maximum urea injection amount at this position. If the injection amount exceeds Umax, the urea cannot be completely decomposed, and urea crystal particles will be formed, which may increase PN10 emissions. It is determined whether the calculated first urea amount U1 exceeds the preset maximum injection threshold Umax. If so, the actual injection amount of the first urea injection unit is controlled to the maximum injection threshold Umax, and the actual injection amount of the second urea injection unit is controlled to U2 + (U1 - Umax). This ensures that the injection of the first and second urea injection units is reasonably distributed under the condition that the total NOx conversion demand remains unchanged, which can ensure the full decomposition of urea and avoid PN10 exceeding the standard. If not, the first and second urea injection units are controlled to inject the calculated first urea amount U1 and second urea amount U2, respectively.

[0028] In one embodiment, in step 102, the efficiency λ1 of the current operating condition of the ccSCR unit is obtained from the pre-set SCR efficiency model based on the inlet temperature T1 of the ccSCR unit. Combined with the nitrogen oxide concentration Q1 before the ccSCR unit, the first amount of urea U1 that the first urea injection unit needs to inject is calculated to achieve the target NOx conversion rate. The SCR efficiency model in this embodiment adopts the existing technology, specifically an SCR efficiency model based on the MAP diagram. The MAP diagram is calibrated, and the inlet temperature T of the ccSCR unit is used as input. The efficiency λ1 is obtained by the search method. In step 103, the efficiency λ2 of the second SCR unit under the current operating condition is calculated in the SCR efficiency model based on the temperature T2 at the inlet of the second SCR unit. Combined with the nitrogen oxide concentration Q2 after the ASC unit, the amount of second urea U2 that the second urea injection unit needs to inject to eliminate this part of NOx is calculated. Since there is no NOx sensor between the two SCRs, the efficiency monitoring mainly monitors the overall efficiency of the two SCRs, which can be used to control regeneration.

[0029] The first urea injection unit is located before the DPF unit and plays a major role in NOx treatment throughout the entire operating cycle. Even if a small amount of urea particles are generated, they will be filtered by the DPF unit and will not affect PN10 emissions. The second urea injection unit is located after the DPF unit and is only activated under high or full load conditions when the first-stage injection cannot meet the NOx conversion requirements. The injection volume is small, which can reduce the risk of urea particles being generated after the DPF unit and ensure that PN10 emissions meet the standards. When the injection volume of the first-stage urea injection unit exceeds the threshold, the excess is allocated to the second-stage urea injection unit through an overflow compensation strategy. This can ensure that the urea in the first stage is fully decomposed and achieve reasonable allocation and efficient utilization of ammonia resources. Under the condition of ensuring full decomposition of urea, the urea injected by the first-stage urea injection unit decomposes into NH3. The NH3 that has not reacted in the cCSCR can penetrate the DPF unit to reach the second SCR unit and be adsorbed, participating in the subsequent SCR reaction, further improving the utilization efficiency of ammonia.

[0030] Example 2: For applications where the engine's original NOx emissions are low, or where the chassis has sufficient space to accommodate a large-volume CCSCR, the following can be adopted: Figure 3 The system shown in Embodiment 2 is an adjustment based on Embodiment 1, and its structure along the exhaust direction is as follows: ccDOC Unit 1; First urea injection unit 2; ccSCR Unit 3; ASC Unit 7; DPF Unit 4; The first nitrogen oxide sensor 9 is located between the ccDOC unit 1 and the ccSCR unit 3 and is used to detect the nitrogen oxide concentration Q1 at the inlet of the ccSCR unit. The second nitrogen oxide sensor 10 is located downstream of the ASC unit 7 and is used to detect the nitrogen oxide concentration Q2 at the outlet of the ASC unit. The first temperature sensor 11 is located at the inlet of the cCSCR unit 3 and is used to detect the inlet temperature T1 of the cCSCR unit 3. The controller is electrically connected to the first urea injection unit 2, the first nitrogen oxide sensor 9, the second nitrogen oxide sensor 10, and the first temperature sensor 11. According to the preset control method, the controller controls the first urea injection unit 2 to inject the first urea amount U1 into the exhaust gas in front of the ccSCR unit 3.

[0031] Compared with Example 1, Example 2 omits the second urea injection unit and the second SCR unit. The system in Example 2 also preferably uses a metal carrier ccDOC to ensure excellent cold start performance.

[0032] The exhaust gas from the engine passes through the ccDOC unit, ccSCR unit, ASC unit and DPF unit in sequence. The exhaust gas that finally meets the emission standards only has one urea injection unit and one SCR, making the system structure simpler and the cost lower.

[0033] like Figure 4 As shown, the control method for a single-injection exhaust aftertreatment system provided in this embodiment includes the following steps: Step 201: Obtain the nitrogen oxide concentration Q1 and temperature T1 at the inlet of the ccSCR unit, and obtain the nitrogen oxide concentration Q2 at the outlet of the ASC unit; Step 202: Calculate the first urea quantity U1 based on the temperature T1, the current ammonia storage quantity of the ccSCR unit, and the nitrogen oxide concentrations Q1 and Q2, and control the first urea injection unit to perform injection. Unlike Example 1, in Example 2, the controller not only calculates the efficiency λ1 of the cSCR unit under the current operating conditions based on the inlet temperature T1 of the cSCR unit, but also considers the current ammonia storage capacity of the catalyst. The ammonia storage capacity refers to the amount of NH3 adsorbed inside the catalyst. The cSCR catalyst has a certain ammonia storage capacity, and the stored NH3 can play a buffering role when the operating conditions change rapidly, thereby improving the dynamic response performance of the system.

[0034] In step 202 of the embodiment, the following specific steps are performed: Based on the inlet temperature T1 of the cCSCR unit and the current ammonia storage capacity of the cCSCR unit, the efficiency λ1 of the cCSCR unit under the current operating condition is obtained in the SCR efficiency model. The SCR efficiency model in this embodiment adopts existing technology, specifically an SCR efficiency model based on a MAP diagram. The MAP diagram is calibrated, and the inlet temperature T of the cCSCR unit and the current ammonia storage capacity are used as inputs. The efficiency λ1 is obtained by a search method. With nitrogen oxide sensors before and after the cCSCR unit, the model efficiency can be calculated more accurately by using the nitrogen oxide sensors before and after the SCR unit and combining them with the current ammonia storage capacity. The actual nitrogen oxide conversion efficiency λ3 of the ccSCR unit is obtained by using the nitrogen oxide concentration Q1 before the ccSCR unit and the nitrogen oxide concentration Q2 after the ASC unit. The actual nitrogen oxide conversion efficiency λ3 is calculated by the following formula: ; The current ammonia storage capacity of the ccSCR unit is obtained by the actual nitrogen oxide conversion efficiency λ3 of the ccSCR unit and the amount of urea injected.

[0035] In the embodiment, step 203 may also be included: when the actual nitrogen oxide conversion efficiency of the ccSCR unit... When the temperature remains below the set limit within the high-efficiency temperature range, a high-temperature regeneration program is triggered for the cCSCR unit to remove accumulated hydrocarbons and sulfur. High-temperature regeneration can ablate carbon deposits and sulfides on the catalyst surface, restore catalyst activity, and ensure long-term stable operation of the system.

[0036] In Example 2, the second urea injection unit and the second SCR are eliminated, reducing system complexity and cost. Since the only first urea injection unit is located before the DPF, urea particles are efficiently filtered by the DPF unit, eliminating the risk of PN10 exceeding the standard caused by urea injection after the DPF unit. For models with low NOx emissions from the original engine or with sufficient space in the chassis to install a large-volume ccSCR, the exhaust aftertreatment system solution in Example 2 can be selected. Since there is only one SCR, the SCR carrier volume can be flexibly designed according to the vehicle space, without being limited by the front and rear stage allocation.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A light-duty diesel engine exhaust aftertreatment system, characterized in that, Including those arranged sequentially along the direction of engine exhaust: ccDOC unit; First urea injection unit; ccSCR unit; DPF unit; Second urea injection unit; Second SCR unit; ASC unit; Also includes: A first nitrogen oxide sensor is disposed between the ccDOC unit and the ccSCR unit to detect the nitrogen oxide concentration Q1 at the ccSCR inlet; The second nitrogen oxide sensor is located downstream of the second SCR unit and is used to detect the nitrogen oxide concentration Q2 at the outlet of the diesel engine exhaust aftertreatment system. A first temperature sensor is installed at the inlet of the cCSCR unit to detect the inlet temperature T1 of the cCSCR unit. A second temperature sensor is installed at the inlet of the second SCR unit to detect the inlet temperature T2 of the second SCR unit. The controller is electrically connected to the first urea injection unit and the second urea injection unit. The controller is also electrically connected to the first and second nitrogen oxide sensors and the first and second temperature sensors to receive the detection signals from each sensor. Based on the received detection signals from each sensor, the controller controls the first urea injection unit to inject a first amount of urea U1 into the exhaust gas before the CCSCR unit, and controls the second urea injection unit to inject a second amount of urea U2 into the exhaust gas before the second CCSCR unit.

2. The light-duty diesel engine exhaust aftertreatment system according to claim 1, characterized in that, The ccDOC unit uses a metal carrier.

3. A control method for a diesel engine exhaust aftertreatment system as described in claim 1 or 2, characterized in that, Includes the following steps: Step 101: Obtain the nitrogen oxide concentration Q1 and temperature T1 at the inlet of the ccSCR unit, and the nitrogen oxide concentration Q2 and temperature T2 at the outlet of the diesel engine exhaust aftertreatment system. Step 102: Calculate the first urea amount U1 required to meet the target conversion efficiency based on the temperature T1 and the nitrogen oxide concentration Q1; Step 103: Calculate the second urea quantity U2 based on the temperature T2 and the nitrogen oxide concentration Q2; Step 104: Determine whether the calculated first urea amount U1 exceeds the preset maximum injection threshold Umax; If yes, then the actual injection amount of the first urea injection unit is controlled to be the maximum injection threshold Umax, and the actual injection amount of the second urea injection unit is controlled to be U2+(U1-Umax); if no, then the first and second urea injection units are respectively controlled to inject the calculated first urea amount U1 and second urea amount U2.

4. The control method for the diesel engine exhaust aftertreatment system according to claim 3, characterized in that: In step 102, the efficiency λ1 of the current operating condition of the ccSCR unit is obtained from the SCR efficiency model based on the inlet temperature T1 of the ccSCR unit, and the first urea amount U1 injected in front of the ccSCR unit is calculated in combination with the nitrogen oxide concentration Q1 in front of the ccSCR unit.

5. The control method for the diesel engine exhaust aftertreatment system according to claim 3, characterized in that: In step 103, the efficiency λ2 of the second SCR unit under the current operating condition is calculated in the SCR efficiency model based on the temperature T2 at the inlet of the second SCR unit. Combined with the nitrogen oxide concentration Q2 after the ASC unit, the amount of second urea injected before the second SCR unit is calculated, U2.

6. A light-duty diesel engine exhaust aftertreatment system, characterized in that, Including those arranged sequentially along the direction of engine exhaust: ccDOC unit; First urea injection unit; ccSCR unit; ASC unit; DPF unit; Also includes: A first nitrogen oxide sensor is disposed between the ccDOC unit and the ccSCR unit for detecting the nitrogen oxide concentration Q1 at the inlet of the ccSCR unit; The second nitrogen oxide sensor is located downstream of the ASC unit and is used to detect the nitrogen oxide concentration Q2 at the outlet of the ASC unit. A first temperature sensor is installed at the inlet of the ccSCR unit to detect the inlet temperature T1 of the ccSCR unit. The controller is electrically connected to the first urea injection unit, the first nitrogen oxide sensor, the second nitrogen oxide sensor, and the first temperature sensor; The controller controls the first urea injection unit to inject a first amount of urea U1 into the exhaust gas in front of the ccSCR unit according to the detection signals received from each sensor.

7. The light-duty diesel engine exhaust aftertreatment system according to claim 6, characterized in that, The ccDOC unit uses a metal carrier.

8. A control method for a light-duty diesel engine exhaust aftertreatment system as described in claim 6 or 7, characterized in that, Includes the following steps: Step 201: Obtain the nitrogen oxide concentration Q1 and temperature T1 at the inlet of the ccSCR unit, and obtain the nitrogen oxide concentration Q2 at the outlet of the ASC unit; Step 202: Calculate the first urea amount U1 based on the temperature T1, the current ammonia storage amount of the ccSCR unit, and the nitrogen oxide concentrations Q1 and Q2, and control the first urea injection unit to inject the first urea amount U1.

9. The control method for the exhaust aftertreatment system of a light-duty diesel engine according to claim 8, characterized in that, Step 202 is executed as follows: Based on the inlet temperature T1 of the ccSCR unit and the current ammonia storage capacity of the ccSCR unit, the efficiency λ1 of the ccSCR unit under the current operating conditions is obtained in the SCR efficiency model. The actual nitrogen oxide conversion efficiency λ3 of the ccSCR unit was obtained by using the nitrogen oxide concentration Q1 before the ccSCR unit and the nitrogen oxide concentration Q2 after the ASC unit. The current ammonia storage capacity of the cCSCR unit is obtained by considering the actual nitrogen oxide conversion efficiency λ3 of the cCSCR unit and the amount of urea injected. The actual nitrogen oxide conversion efficiency λ3 is calculated using the following formula: .

10. The control method for the exhaust aftertreatment system of a light-duty diesel engine according to claim 9, characterized in that: When the actual nitrogen oxide conversion efficiency of the ccSCR unit When the temperature remains below the set limit within the high-efficiency temperature range, a high-temperature regeneration process is triggered for the ccSCR unit to remove accumulated hydrocarbons and sulfur.

Images