Post-treatment system for heavy-duty diesel engine

Abstract

The utility model relates to the field of heavy-duty diesel engines, in particular to an after-treatment system for a heavy-duty diesel engine, which is sequentially provided with a tight coupling catalytic device cc-SCR, a diesel oxidation catalyst DOC, a diesel particulate filter DPF, a selective catalytic reduction device SCR and an ammonia escape catalyst ASC in a pipeline support combination mode. The tight coupling catalytic device cc-SCR and the diesel oxidation catalyst DOC are arranged on the upstream of the diesel particulate filter DPF, the selective catalytic reduction device SCR is arranged on the downstream of the diesel particulate filter DPF, and the ammonia escape catalyst ASC is located at the rear end of the selective catalytic reduction device SCR. Exhaust gas sequentially flows through a tight coupling catalytic device cc-SCR, a diesel oxidation catalyst DOC, a diesel particulate filter DPF, a selective catalytic reduction device SCR and an ammonia escape catalyst ASC, and the purpose of emission reduction is achieved.

Description

Technical Field

[0001] This utility model relates to the field of heavy-duty diesel engine, and more specifically to an after-treatment system for heavy-duty diesel engines. Background Technology

[0002] Global emission regulations for NOx emissions from vehicle exhaust are constantly being upgraded, and after-treatment technology is an important way to achieve energy conservation and emission reduction. In the field of heavy-duty diesel engines, diesel engines still have certain advantages in the future due to their power, reliability and fuel economy, but their emissions of nitrogen oxides and particulate matter are one of the main sources of air pollution.

[0003] At present, an after-treatment system for heavy-duty diesel engines is proposed to solve the problems mentioned in the background art. Utility Model Content

[0004] The purpose of this invention is to provide an aftertreatment system for heavy-duty diesel engines that is designed with two stages based on the SCR reaction mechanism under steady-state cycle WHSC and transient cycle WHTC conditions. By controlling different nitrogen-ammonia ratios and exhaust temperatures, the NOx conversion efficiency of the aftertreatment system is improved, thereby achieving the goal of energy saving and emission reduction.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0006] An aftertreatment system for a heavy-duty diesel engine comprises, in sequence via pipe supports, a tightly coupled catalytic converter (cc-SCR), a diesel engine oxidation catalyst (DOC), a diesel engine particulate filter (DPF), a selective catalytic reduction (SCR), and an ammonia slip catalyst (ASC). The tightly coupled catalytic converter (cc-SCR) and the diesel engine oxidation catalyst (DOC) are located upstream of the diesel engine particulate filter (DPF), the selective catalytic reduction (SCR) is located downstream of the diesel engine particulate filter (DPF), and the ammonia slip catalyst (ASC) is located downstream of the selective catalytic reduction (SCR). Exhaust gas flows sequentially through the tightly coupled catalytic converter (cc-SCR), the diesel engine oxidation catalyst (DOC), the diesel engine particulate filter (DPF), the selective catalytic reduction (SCR), and the ammonia slip catalyst (ASC).

[0007] Further specifying, temperature sensors are installed on both the front and rear ends of the tightly coupled catalytic converter (cc-SCR) and selective catalytic reduction (SCR) pipes, and a first urea nozzle and a second urea nozzle are also provided on the front end pipe. The first urea nozzle and the second urea nozzle are respectively located in front of the temperature sensors at the front ends of the tightly coupled catalytic converter (cc-SCR) and the selective catalytic reduction (SCR).

[0008] Further specifying, a first NOx sensor is installed on the pipeline between the tightly coupled catalytic converter cc-SCR and the turbocharger turbine. The first NOx sensor is located at the front end of the first urea nozzle. A second NOx sensor is installed at the rear end of the ammonia escape catalyst ASC. The first NOx sensor measures the engine's raw NOx emissions, and the second NOx sensor provides signals to the SCR system and the OBD system.

[0009] The advantages of this utility model over the current technology are as follows:

[0010] 1. Under steady-state and transient cycle conditions, a two-stage system (pre-stage and post-stage) was designed based on the selective catalytic reduction (SCR) reaction mechanism. By controlling different ammonia-nitrogen ratios and exhaust temperatures, the NOx conversion efficiency of the aftertreatment system was improved, achieving the goal of energy conservation and emission reduction.

[0011] 2. Closely coupled catalytic converters (cc-SCR) are beneficial for improving the NOx conversion efficiency of the aftertreatment system. However, the conversion efficiency of the subsequent SCR decreases as the conversion efficiency of the preceding cc-SCR increases. An excessively high ammonia-to-nitrogen ratio in the preceding cc-SCR is not conducive to the NOx emission control of the aftertreatment system and the full utilization of the performance of the subsequent SCR catalyst.

[0012] 3. Control the urea injection at the front end of the CC-SCR and SCR. The urea injection system can calculate the required urea injection amount based on information such as the temperature of the CC-SCR and SCR catalysts and the operating conditions of the diesel engine. The metering injection pump injects the vehicle urea solution into the exhaust pipe as needed to maximize the NOx conversion efficiency of the aftertreatment system. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the system of this utility model;

[0014] Figure 2 The curves showing the relationship between the conversion efficiency, ammonia leakage, and NSR of this invention are shown.

[0015] The labels in the diagram correspond to: 1- Closely coupled catalytic converter (cc-SCR), 2- Diesel engine oxidation catalyst (DOC), 3- Selective catalytic reduction (SCR), 4- Ammonia escape catalyst (ASC), 5- Diesel engine particulate filter (DPF), 6- Urea injection device, 7- First NOx sensor, and 8- Second NOx sensor. Detailed Implementation

[0016] To enable those skilled in the art to better understand the technical solution of this utility model, the technical solution of this utility model will be further described below in conjunction with the accompanying drawings and embodiments. Example

[0017] like Figure 1 and Figure 2 As shown, an aftertreatment system for heavy-duty diesel engines includes a cc-SCR, DOC, DPF, SCR, and ASC system connected via pipe supports. The cc-SCR is a tightly coupled copper-based + copper-based system, which can improve NOx emissions by 16%–22%. This tightly coupled approach effectively reduces NOx emissions in the aftertreatment system. The conversion efficiency is as follows: DOC (Diesel Oxidation Catalyst) is an exhaust aftertreatment device installed in the diesel engine exhaust system to reduce carbon monoxide, hydrocarbons, and / or catalytically convert nitric oxide into nitrogen dioxide. DPF (Diesel Particulate Filter) is an exhaust aftertreatment device installed in the diesel engine exhaust system, through which all exhaust flows via a carrier for filtration to reduce particulate matter. When the inlet surface of the DPF carrier is coated with an oxidizing catalyst, it is called a catalytic particulate filter. SCR (Selective Catalytic Reduction) is an exhaust aftertreatment device installed in the engine exhaust system to selectively catalytically reduce nitrogen oxides (NOx) in the exhaust to reduce NOx emissions. ASC (Ammonia Slip Catalyst) is used to treat unreacted excess ammonia, oxidizing it into nitrogen and water to avoid ammonia emissions pollution. The cc-SCR and DOC are located upstream of the DPF, the SCR downstream of the DPF, and the ASC downstream of the SCR. The exhaust flows sequentially through the cc-SCR, DOC, DPF, SCR, and ASC. The ASC (Automatic Supercharger) has temperature sensors installed on both the front and rear pipes of the cc-SCR and SCR. A urea injection device, comprising a first urea nozzle and a second urea nozzle, is also installed on the front pipes of the cc-SCR and SCR. These nozzles are located in front of the temperature sensors at the front of the cc-SCR and SCR, respectively. The urea injection system injects urea upstream of the cc-SCR and SCR as needed through the first and second nozzles. The ASC oxidizes leaked ammonia into nitrogen and water. A differential pressure sensor is installed on the DPF (Diverterless Power Filter) to measure the airflow resistance and monitor its condition. A first NOx sensor is installed on the pipe between the cc-SCR and the turbocharger turbine, located in front of the first urea nozzle. A second NOx sensor is located at the rear of the ASC. The first NOx sensor measures the engine's raw NOx emissions, while the second NOx sensor provides a closed-loop signal to both the SCR system and the OBD (On-Board Diagnostics) system.

[0018] The working principle of the post-processing system is as follows:

[0019] During diesel engine operation, exhaust flows sequentially through the cc-SCR, DOC, DPF, SCR, and ASC catalytic converter. As the exhaust flows through the DOC, hydrocarbons (HC) and carbon monoxide (CO) are oxidized into carbon dioxide and water by the oxidation catalyst, achieving CO and HC purification. Nitric oxide is oxidized into nitrogen dioxide by the oxidation catalyst. The exhaust then flows through the DPF, where particulate matter is captured and intercepted by the wall-flow DPF, achieving particulate purification. As particulate matter increases in the DPF channel, the exhaust resistance of the DPF increases, affecting engine fuel consumption and even normal operation. To avoid this, the DPF system must burn off the carbon soot from the intercepted particles, i.e., regeneration. The nitrogen dioxide generated by oxidation in the DOC can react with the carbon particles intercepted by the DPF at temperatures above 250°C, burning off the carbon soot and achieving continuous (passive) regeneration of the DPF. If a vehicle is driven at low speed and light load for a long time, the exhaust temperature is low, and continuous regeneration fails. When the DPF resistance increases to a set value, the engine automatically performs in-cylinder post-injection of diesel (or uses an HC injector to inject diesel into the exhaust pipe) to increase the DPF temperature and perform active regeneration. The urea injection system can calculate the required urea injection amount based on information such as the temperature of the cc-SCR and SCR catalysts and the diesel engine operating conditions. The metering injection pump injects automotive urea solution into the exhaust pipe as needed. The urea solution decomposes into NH3, which enters the cc-SCR and SCR catalysts and reacts with NOx inside the catalysts to generate nitrogen and water, thus purifying NOx. The ASC oxidizes the excess ammonia that has not reacted after SCR into nitrogen and water. A differential pressure sensor is installed on the DPF to measure the airflow resistance of the DPF, thereby monitoring the state of the DPF.

[0020] Under steady-state cycle (WHSC) and transient cycle (WHTC) conditions, a two-stage system was designed based on the selective catalytic reduction (SCR) mechanism, namely cc-SCR and SCR in the WHTC cycle. Since the melting point of urea at room temperature is 165 ℃, urea does not participate in the reaction across the entire temperature range for SCR in the aftertreatment system. The commonly used operating temperature range for SCR in the system is 300-450 ℃. Within this temperature range, SCR can achieve the maximum conversion efficiency. Tight coupling of cc-SCR is beneficial to improving the NOx conversion efficiency of the aftertreatment system. However, the conversion efficiency of the subsequent SCR decreases as the conversion efficiency of the preceding cc-SCR increases. An excessively high ammonia-to-nitrogen ratio in the preceding cc-SCR is not conducive to NOx emission control in the aftertreatment system and the full utilization of the performance of the subsequent SCR catalyst.

[0021] Therefore, the urea injection before the cc-SCR and SCR is generally controlled. The urea injection system can calculate the required urea injection amount based on information such as the temperature of the cc-SCR and SCR catalysts and the operating conditions of the diesel engine (cc-SCR:SCR is generally 0.5:1). The metering injection pump injects the automotive urea solution into the exhaust pipe through the nozzle as needed, so as to maximize the NOx conversion efficiency of the aftertreatment system.

[0022] In cases where SCR catalyst performance is compromised, an indirect method can be used to test the uniformity of the flow field in the aftertreatment encapsulation. This test method is based on ensuring uniform mixing of the urea solution and exhaust gas. The test conditions are: exhaust temperature 350–450℃, space velocity (20000±300) h⁻¹, (40000±300) h⁻¹, and (60000±300) h⁻¹, with NH₃ / NO₃ gradually increasing from 0.2 to 1.2 at 0.2 intervals. The stable conversion efficiency and ammonia leakage are tested at each injection rate. The relationship curves between conversion efficiency, ammonia leakage, and NSR are plotted. If the conversion efficiency of the aftertreatment sample below different equivalence injection rates is close to the theoretical value, it indicates that the internal flow field distribution of the aftertreatment is uniform and the overall operation is normal. Conversely, if the efficiency is not high, it indicates a problem with the uniformity of the flow field.

[0023] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the actual arrangement on the pipeline support in the process. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the equipment or components referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0024] The above provides a detailed description of an after-treatment system for heavy-duty diesel engines provided by this utility model. The specific embodiments are only used to help understand the method and core ideas of this utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made to this utility model without departing from the scope of this utility model, and these improvements and modifications also fall within the protection scope of the claims of this utility model.

Claims

1. An aftertreatment system for a heavy-duty diesel engine, characterized in that: The system is constructed by connecting pipe supports and sequentially assembling a tightly coupled catalytic converter (cc-SCR) (1), a diesel engine oxidation catalyst (DOC) (2), a diesel engine particulate filter (DPF) (5), a selective catalytic reduction (SCR) (3), and an ammonia escape catalyst (ASC) (4). The tightly coupled catalytic converter (cc-SCR) (1) and the diesel engine oxidation catalyst (DOC) (2) are located upstream of the diesel engine particulate filter (DPF) (5), the selective catalytic reduction (SCR) (3) is located downstream of the diesel engine particulate filter (DPF) (5), and the ammonia escape catalyst (ASC) (4) is located at the rear end of the selective catalytic reduction (SCR) (3). The exhaust gas flows sequentially through the tightly coupled catalytic converter (cc-SCR) (1), the diesel engine oxidation catalyst (DOC) (2), the diesel engine particulate filter (DPF) (5), the selective catalytic reduction (SCR) (3), and the ammonia escape catalyst (ASC) (4).

2. The aftertreatment system for a heavy-duty diesel engine according to claim 1, characterized in that: Temperature sensors are installed on both ends of the pipelines of the tightly coupled catalytic catalytic device cc-SCR (1) and the selective catalytic reduction device SCR (3), and a urea injection device (6) is also provided on the front end pipeline. The urea injection device (6) includes a first urea nozzle and a second urea nozzle. The first urea nozzle and the second urea nozzle are respectively located in front of the temperature sensors at the front end of the tightly coupled catalytic catalytic device cc-SCR (1) and the selective catalytic reduction device SCR (3).

3. The aftertreatment system for a heavy-duty diesel engine according to claim 1, characterized in that: A first NOx sensor (7) is installed on the pipeline between the tightly coupled catalytic converter cc-SCR (1) and the turbocharger turbine. The first NOx sensor (7) is located at the front end of the first urea nozzle. A second NOx sensor (8) is set at the rear end of the ammonia escape catalyst ASC (4). The first NOx sensor (7) measures the engine's raw NOx emissions, and the second NOx sensor (8) provides signals for the SCR system and the OBD system.

4. The aftertreatment system for a heavy-duty diesel engine according to claim 1, characterized in that: A differential pressure sensor is installed on the diesel particulate filter (DPF) (5).

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