Passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles

Abstract

This invention discloses a passive adsorption-selective catalytic reduction (CCR) device for diesel vehicles, comprising an electronically controlled nozzle, a first mixing chamber, a pre-catalytic oxidation-reduction chamber, a second mixing chamber, and a post-catalytic oxidation-reduction chamber arranged sequentially. The first mixing chamber includes a first urea solution inlet, a V-shaped breaker wall, and a W-shaped bottom mixing chamber. The V-shaped breaker wall is fixed to the rear wall of the first urea solution inlet pipe. The W-shaped bottom mixing chamber includes an inner cavity and an outer cavity. The inner cavity wall has staggered array openings, and the inner and outer cavities are connected through these openings. A guide wall structure is connected to the outermost pipe at the end of the first mixing chamber. The CCR chamber is connected to the end of the guide wall, and a three-zone integrated catalyst is located inside the CCR chamber. This invention solves the problems of severe NOx escape during the cold start phase, system complexity, and low-temperature urea crystallization in existing selective catalytic reduction technologies.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas treatment technology, and more specifically to a passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles. Background Technology

[0002] Nitrogen oxides (NOx) emitted by diesel vehicles pose serious health and environmental hazards, causing respiratory and cardiovascular diseases, weakening the immune system, and contributing to photochemical smog, acid rain, eutrophication, and ecosystem damage. To address stringent emission regulations and the problem of NOx escape from diesel vehicles, numerous studies and practices have explored effective control measures. Currently, there are still challenges both domestically and internationally regarding the control of rare NOx emissions. X Technology, selective catalytic reduction technology, NO X The four technologies related to diesel vehicle exhaust treatment include adsorption technology, plasma technology, etc. Currently, the mainstream SCR technology uses selective catalytic reduction (SCR) combined with urea injection to reduce NOx to N2 and H2O, but it requires high temperature (>200℃) to activate the catalyst, and has the following main drawbacks: (1) Low cold start efficiency at low temperatures leads to NOx escape; (2) Excessive urea injection can easily cause ammonia escape and secondary pollution; (3) It requires two independent SCR catalysts, multiple sensors and a complex control system, which is costly and takes up a lot of space; (4) Urea is prone to crystallization at low temperatures, which can clog nozzles or catalyst channels.

[0003] Currently, the field of diesel vehicle exhaust treatment still lacks an exhaust treatment technology that is low in energy consumption, high in efficiency, simple in process, low in cost, and widely applicable. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a passive adsorption-selective catalytic reduction (CCR) device for diesel vehicles, which solves problems such as severe NOx escape during cold start, system complexity, and low-temperature urea crystallization in existing CCR technologies.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles includes an electronically controlled nozzle, a first mixing chamber, a pre-catalytic oxidation-reduction chamber, a second mixing chamber, and a post-catalytic oxidation-reduction chamber arranged sequentially in the direction of exhaust gas flow. The first mixing chamber includes a first inlet of urea solution, a V-shaped crushing wall, and a W-shaped bottom mixing chamber. The V-shaped crushing wall is fixed to the rear end wall of the first inlet pipe of urea solution. The W-shaped bottom mixing chamber includes an inner cavity and an outer cavity. The inner cavity wall is provided with staggered array openings. The inner cavity and the outer cavity are connected through the staggered array openings. The end of the first mixing chamber is connected to a guide wall structure, which is composed of multiple continuously arranged frustum channels. The pre-catalytic oxidation-reduction chamber is connected to the end of the guide wall. Inside the pre-catalytic oxidation-reduction chamber, a new tightly coupled SCR catalyst, an ASC catalyst, a DOC catalyst, and a DPF catalyst are arranged in sequence. The new tightly coupled SCR catalyst is used for passive adsorption and selective catalytic reduction of nitrogen oxides. The second mixing chamber is equipped with a perforated spiral plate, and the post-catalytic oxidation-reduction chamber is equipped with a post-SCR catalyst and a post-DOC catalyst.

[0007] Specifically, the included angle of the V-shaped crushing wall is an acute angle, and the plate surface material is 316L stainless steel or ceramic coating.

[0008] Specifically, the aperture of the staggered array opening is 1-3 mm, the spacing between the openings is 2-3 times the aperture, and the cavity material of the W-shaped bottom mixing cavity is a nickel-based alloy or a ceramic composite material.

[0009] Specifically, the guide wall divides the pipe into multiple frustum channels, each channel has a rectangular cross-section, the width to height ratio of the channel is 1:1, and the included angle of the outermost wall surface of the guide wall is 16°.

[0010] Specifically, the electronically controlled nozzle is an inverted U-shaped urea pressure pipe structure, the ratio of the thickness of the spray plate to the diameter of the spray hole is h / d=0.5~2, and the valve core is provided with an internal non-sealed heat insulation sleeve.

[0011] Specifically, the new tightly coupled SCR catalyst is a Cu-S34@S34 molecular sieve catalyst, and the N2O generation concentration of the Cu-S34@S34 molecular sieve catalyst is less than 10 ppm.

[0012] Furthermore, the device also includes a control system, which triggers a regeneration mode based on signals from the temperature sensor before the first mixing chamber, the nitrogen oxide sensor, and the temperature sensors before and after the particle capture device; when the total carbon and nitrogen content is greater than a preset total, or the total sulfur content is greater than a preset poisoning level, or the actual conversion rate of nitrogen oxides in the pre-stage is less than a first preset conversion rate, or the actual conversion rate of nitrogen oxides in the post-stage is greater than a second preset conversion rate.

[0013] Specifically, a perforated spiral plate is provided at the entrance of the second mixing chamber. The perforated spiral plate is fixed by a mounting thread, and the spiral structure of the perforated spiral plate is used to extend the airflow path.

[0014] Specifically, the post-catalytic oxidation-reduction chamber is connected to the end of the pre-catalytic oxidation-reduction chamber via a pipeline, and a post-SCR catalyst and a post-DOC catalyst are sequentially arranged inside the post-catalytic oxidation-reduction chamber.

[0015] Based on the above technical solution, the present invention also provides a corresponding diesel vehicle exhaust treatment method, including the following steps: Step S1: The exhaust gas is sent into the first mixing chamber. The urea solution is crushed by the impact of the V-shaped crushing wall. Then, it undergoes multi-stage diffusion mixing between the inner and outer chambers of the W-shaped bottom mixing chamber through staggered array openings. After being rectified by the guide wall, it enters the pre-catalytic oxidation-reduction chamber. Step S2: The exhaust gas treated by the pre-catalytic oxidation-reduction chamber enters the second mixing chamber, where it is further mixed with the urea solution through a perforated spiral plate, and then enters the post-catalytic oxidation-reduction chamber for secondary catalytic purification. Step S3: During the cold start phase, when the exhaust gas temperature is below 210°C, the PNA component in the newly coupled SCR catalyst adsorbs NOx in the exhaust gas. Step S4: In the high-temperature stage, when the exhaust gas temperature is higher than 210℃, the NOx adsorbed by PNA is desorbed and selectively catalytically reduced together with the NOx in the exhaust gas at the SCR active sites.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. In the cold start stage (<210℃), the PNA component adsorbs NOx to prevent escape; in the high temperature stage (>210℃), the desorbed NOx is reduced by SCR together with the fresh NOx, which widens the active temperature window and improves the overall treatment efficiency.

[0017] 2. The V-shaped crushing wall, W-shaped bottom mixing chamber, and staggered array opening structure of the first mixing chamber of the present invention enhance the uniformity of urea atomization and waste gas mixing, and the ammonia uniformity index can reach 0.92, effectively avoiding crystallization blockage when large doses of urea are injected.

[0018] 3. This invention integrates the SCR and NOx adsorber into a dual-function catalyst, reducing the size and complexity of the device and lowering the cost.

[0019] 4. The dual-stage mixing chamber design of this invention enables the front chamber to meet the strong mixing requirements of high concentration NOx during cold starts, while the rear chamber meets the requirements of low concentration, low temperature and low pressure drop, resulting in higher overall energy efficiency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the overall structure of a passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to the present invention. Figure 2 This is a schematic diagram of the first mixing chamber structure of the present invention; Figure 3 This is a schematic diagram of the perforated spiral plate structure of the present invention.

[0022] In the diagram, 1. Electronically controlled nozzle; 2. First inlet of urea solution; 3. First mixing chamber; 4. Pre-catalytic oxidation-reduction chamber; 5. DOC catalyst; 6. W-shaped bottom mixing chamber; 7. Second inlet of urea solution; 8. Second mixing chamber; 9. Post-catalytic oxidation-reduction chamber; 10. Diesel engine exhaust outlet; 11. Post-DOC catalyst; 12. Post-SCR catalyst; 13. DPF catalyst; 14. ASC catalyst; 15. New tightly coupled SCR catalyst; 16. Guide wall; 17. V-shaped crushing wall; 18. Diesel engine exhaust inlet; 19. Inner cavity; 20. Outer cavity; 21. Staggered array of openings; 22. Perforated spiral plate; 23. Mounting thread. Detailed Implementation

[0023] To facilitate understanding and implementation of the present invention by those skilled in the art, the various steps of the method proposed in this invention are described in detail below. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various modifications or alterations to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0024] Example 1 like Figure 1 As shown, this embodiment provides a passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles, including an electronically controlled nozzle 1, a first mixing chamber 3, a pre-catalytic oxidation-reduction chamber 4, a second mixing chamber 8, and a post-catalytic oxidation-reduction chamber 9 arranged sequentially according to the exhaust gas flow direction; The first mixing chamber 3 includes a urea solution first inlet 2, a V-shaped crushing wall 17, and a W-shaped bottom mixing cavity 6. The V-shaped crushing wall 17 is fixed to the rear wall of the urea solution first inlet 2 pipe. Figure 2As shown, the W-shaped bottom mixing chamber 6 includes an inner chamber 19 and an outer chamber 20. The inner chamber wall is provided with staggered array openings 21. The inner chamber 19 and the outer chamber 20 are connected through the staggered array openings 21. The end of the first mixing chamber 3 is connected to a guide wall 16 structure by an outward expansion pipe. The guide wall 16 is composed of multiple continuously arranged frustum channels. The guide wall 16 divides the pipeline space into several truncated pyramidal channels. Each channel has a rectangular cross-section and a width-to-height ratio of 1:1. The total channel is evenly divided into several sub-channels. In this embodiment, the outermost wall of the guide wall 16 has an included angle of 16°. The surface of the guide wall 16 is polished or coated to reduce frictional resistance and prevent particulate matter from adhering. This allows the gas to flow evenly from the outer cavity 20 of the W-shaped bottom mixing chamber into the pre-catalytic oxidation-reduction chamber 4, thereby improving the exhaust gas purification rate. The pre-catalytic oxidation-reduction chamber 4 is connected to the end of the guide wall 16. The pre-catalytic oxidation-reduction chamber 4 is provided with a new tightly coupled SCR catalyst 15, an ASC catalyst, a DOC catalyst 5 and a DPF catalyst 13 in sequence. The new tightly coupled SCR catalyst 15 is used for passive adsorption and selective catalytic reduction of nitrogen oxides. All the flue gas after emission reduction is discharged through the diesel engine exhaust outlet (10). In this embodiment, a novel tightly coupled Cu-S34@S34 molecular sieve catalyst 15 is embedded in the pre-catalytic oxidation-reduction chamber 4. This catalyst has a wider temperature window and good N2 selectivity, produces N2O concentration of less than 10 ppm, inhibits NH3 peroxidation, and has better low-temperature hydrothermal stability and sulfur poisoning resistance. The second mixing chamber 8 is provided with a perforated spiral plate 22, and the post-catalytic oxidation-reduction chamber 9 is provided with a post-SCR catalyst 12 and a post-DOC catalyst 11.

[0025] Specifically, the V-shaped cross-section of the V-shaped crushing wall 17 is formed by two symmetrically inclined metal plates fixedly connected. A W-shaped bottom mixing chamber 6 is connected to the end of the V-shaped crushing wall 17 pipe. The bottom of the W-shaped bottom mixing chamber 6 is in a continuous wave shape, and the plate surface is made of 316L stainless steel or ceramic coating, which is periodically arranged by symmetrical concave and convex units.

[0026] Specifically, the aperture of the staggered array opening 21 is 1~3mm, the spacing between the openings is 2~3 times the aperture, and the cavity material of the W-shaped bottom mixing cavity 6 is a nickel-based alloy or a ceramic composite material.

[0027] Specifically, the guide wall 16 divides the pipe into multiple frustum channels, each channel has a rectangular cross-section, the width to height ratio of the channel is 1:1, and the included angle of the outermost wall surface of the guide wall is 16°.

[0028] Specifically, the novel tightly coupled SCR catalyst 15 is a Cu-S34@S34 molecular sieve catalyst, and the N2O generation concentration of the Cu-S34@S34 molecular sieve catalyst is less than 10 ppm. Specifically, a perforated spiral plate 22 is provided at the entrance of the second mixing chamber 8, such as... Figure 3 As shown, the perforated spiral plate 22 is fixed by the mounting thread 23, and the spiral structure of the perforated spiral plate 22 is used to extend the airflow path.

[0029] Specifically, the post-catalytic oxidation-reduction chamber 9 is connected to the end of the pre-catalytic oxidation-reduction chamber 4 via a pipe, and the post-SCR catalyst 12 and the post-DOC catalyst 11 are sequentially arranged inside the post-catalytic oxidation-reduction chamber 9.

[0030] Working principle and process: The diesel engine exhaust gas inlet 18 is connected to the diesel vehicle exhaust pipe, and the exhaust gas enters the first mixing chamber 3; the urea solution first inlet 2 is connected to the vehicle urea supply system; in the first mixing chamber, the V-shaped crushing wall 17 atomizes and crushes the urea solution, and then the mixed gas flow enters the W-shaped bottom mixing chamber 6. The staggered array of openings 21 on the inner wall of the chamber allows the urea and exhaust gas to be fully mixed. After mixing, the gas enters the pre-catalytic oxidation-reduction chamber 4 evenly through the truncated pyramidal channel of the guide wall 16. During the cold start phase (<210℃), the gas enters the pre-catalytic oxidation-reduction chamber 4 at low temperatures. The SCR catalyst is not yet activated. The PNA catalyst captures NOx through physical adsorption and weak chemical bonding. The DOC catalyst 5 utilizes residual O2 in the exhaust gas to oxidize some HC and CO, releasing heat to assist in temperature rise. The DPF catalyst 13 captures PM to prevent particulate matter from escaping at low temperatures. During the high-temperature phase (>210℃), the NOx adsorbed by the PNA catalyst desorbs and enters the SCR catalyst layer together with NOx in the fresh exhaust gas. After the urea solution is atomized in the first mixing chamber 3, it is fully mixed with the exhaust gas. NH3 and NOx undergo selective reduction reactions on the surface of the SCR catalyst. The DOC catalyst 5 further oxidizes the remaining HC and CO. The DPF catalyst 13 promotes PM oxidation and regeneration through the catalytic coating. The post-catalytic oxidation-reduction chamber 9 is connected by a pipeline. Urea solution is replenished through the second inlet 7. The perforated spiral plate 22 further promotes gas-liquid mixing. The post-SCR catalyst 12 and the post-DOC catalyst 11 complete secondary purification.

[0031] In this embodiment, the inner cavity 19 and outer cavity 20 of the W-shaped bottom mixing chamber 6 are connected by an interlaced array of openings 21, where the urea solution is atomized and premixed with the exhaust gas; the spiral structure of the perforated spiral plate 22 is used to extend the airflow path, increase the contact time between the urea solution and the exhaust gas, and enhance the reduction efficiency.

[0032] It should be noted that in diesel engine SCR systems, the uniformity of urea solution spray is an important factor affecting NOx catalytic conversion performance. However, due to the large range of urea droplet diameters, it is difficult to directly evaluate the uniformity of urea solution spray based on droplet diameter. Usually, the uniformity of NH3 distribution at the front end of the SCR carrier is used to evaluate the NH3 mixing degree of the entire SCR system. The uniformity of NH3 distribution at the front end of the SCR carrier has a certain impact on NOx conversion efficiency and NH3 leakage control. The simulation objects are two different mixing chambers of the SCR system, with an exhaust gas inlet diameter of 30 mm.

[0033] Ammonia uniformity analysis: The uniformity of NH3 distribution is determined by the internal structure of the exhaust pipe. The higher the uniformity index of the NH3 cross-sectional distribution, the lower the NO content of the SCR system. X The higher the conversion efficiency, the better. Therefore, to achieve a high NOx conversion efficiency and prevent ammonia leakage, it is essential to ensure good mixing between NH3 and exhaust gas. Excessive airflow velocity in the exhaust pipe increases the resistance encountered by the urea solution during its movement, affecting its evaporation and pyrolysis rate, as well as the uniformity of NH3 distribution at the front cross-section of the SCR carrier. Uneven NH3 concentration distribution, such as high concentrations in certain areas, can lead to overly vigorous chemical reactions, with some NH3 not having enough time to react, increasing the NH3 leakage rate. Conversely, in areas with low NH3 concentrations, NOx conversion efficiency will be too low, affecting denitrification performance and leading to NO... X The emissions do not meet the China VII emission standard.

[0034] In this embodiment, the ammonia uniformity index is calculated according to the following formula: ; ; In the above formula, Number of units; For the first NH3 concentration in each unit; index The closer the value is to 1, the more uniform the distribution of NH3.

[0035] Calculations using the formula show that the uniformity index of the first mixing chamber of the device is 0.92, and the ammonia uniformity index of the second mixing chamber is 0.87; the pressure drop of the first mixing chamber is 6092 Pa, and the pressure drop of the second mixing chamber is 5582 Pa; the ammonia uniformity index and pressure drop of the mixing chambers both meet the requirements; this proves that the dual mixing chamber design of the device fits the actual needs of the device.

[0036] Example 2 Based on Example 1, when the NOx concentration in the exhaust gas significantly increases under high load conditions, the main SCR catalyst 15 and the post-SCR catalyst 12 of the dual-stage SCR system work together. The first-stage SCR catalyst 15 treats most of the NOx, the ECU controls the electronically controlled nozzle 6 to pressurize the injection, and the perforated spiral plate 22 reduces the urea atomization particle size from 50μm to below 21μm. The post-SCR catalyst 12 suppresses the NOx peak value from >500ppm to <21ppm within 0.5 seconds. The remaining portion is further catalyzed and reduced by the post-SCR catalyst 12 after the urea solution is mixed a second time by the perforated spiral plate 22 in the post-catalytic oxidation-reduction chamber.

[0037] DOC catalyst 5 and post-DOC catalyst 11 simultaneously oxidize HC and CO, while DPF catalyst 13 captures particulate matter, achieving synergistic purification of all pollutants.

[0038] In this embodiment, by integrating the PNA adsorption function with SCR catalysis into the same catalytic oxidation-reduction chamber, the space of the traditional independent adsorber is eliminated, reducing the overall length of the device by about 30%. The design of the flow guide wall 16 and the truncated pyramid channel ensures uniform airflow distribution and improves purification efficiency at low temperatures. The compact design of the perforated spiral plate 22 and the W-shaped bottom mixing chamber 6 further reduces the complexity of the pipeline and facilitates installation in a limited space.

[0039] In this embodiment, when the main catalytic chamber fails, the post-catalytic chamber can independently undertake the purification task; when the post-catalytic chamber is blocked, the pre-catalytic chamber can still maintain a NOx conversion rate of >80%.

[0040] Example 3 Based on Embodiment 1, this embodiment also includes a control system and a first temperature sensor T1 located at the inlet of the first mixing chamber, a second temperature sensor T2 located between the first mixing chamber and the particulate capture device, a third temperature sensor T3 located at the outlet of the particulate capture device, a first nitrogen oxide sensor N1 located at the inlet, a second nitrogen oxide sensor N2 located at the outlet of the first mixing chamber, and a third nitrogen oxide sensor N3 located at the outlet of the second mixing chamber. T1 and N1 respectively detect the first temperature and the first nitrogen oxide concentration at the inlet of the first mixing chamber 3 of the exhaust gas, T2 and N2 respectively detect the second temperature and the second nitrogen oxide concentration at the outlet of the first mixing chamber 3 of the exhaust gas, T3 detects the third temperature of the exhaust gas at the outlet of the particulate capture device, and N3 detects the third nitrogen oxide concentration of the exhaust gas at the outlet of the second mixing chamber 8.

[0041] Based on the first temperature of the first mixing chamber pre-temperature sensor, the first nitrogen oxide concentration, the second temperature before the particle capture device and the third temperature after it, the first urea injection amount before the first mixing chamber and the second urea injection amount before the second nitrogen oxide are calculated and injected through the electronically controlled nozzle 1. In this embodiment, the electronically controlled nozzle 1 is optimized with an inverted U-shaped urea pressure tube and an optimized orifice ratio. Assuming the thickness of the nozzle plate is h and the diameter of the injection hole is d, then h / d = 0.5~2, which improves the atomization effect of the urea solution and avoids urea crystallization clogging the injection hole. An internal non-sealed heat insulation sleeve is designed outside the valve core, which has the effect of heat insulation and cooling, and can effectively reduce the temperature of the urea nozzle, making the nozzle less prone to crystallization and clogging.

[0042] The control system triggers the regeneration mode based on the signals from the temperature sensor before the first mixing chamber 3, the nitrogen oxide sensor, and the temperature sensors before and after the particle capture device. When the total carbon and nitrogen content is greater than the preset total, or the total sulfur content is greater than the preset poisoning amount, or the actual conversion rate of nitrogen oxides in the pre-stage is less than the first preset conversion rate, or the actual conversion rate of nitrogen oxides in the post-stage is greater than the second preset conversion rate, the control system triggers the regeneration mode.

[0043] When the regeneration function is triggered, the feedforward oil quantity of the first mixing chamber 3 device is calculated based on the first temperature before the first mixing chamber 3 device, the target temperature, the exhaust gas mass flow rate and the exhaust gas specific heat capacity, and the required fuel is injected into the first mixing chamber 3 device, and the control system enters the regeneration mode.

[0044] Comparative Example 1 To demonstrate the advantages of this invention in the synergistic optimization of catalyst function and hybrid structure, this comparative example simulates the monolithic SCR / ASC / PNA / DOC integrated catalyst disclosed in the closest prior art (CN111050908B), but placed in a simplified flow channel, including: I. System Composition; Catalyst: The PNA / SCR-ASC / DOC-DPF three-zone integrated catalyst described in Example 1 is used. This catalyst is mounted on an integrated cordierite honeycomb support, with PNA (passive NOx adsorption) zone, SCR-ASC (selective catalytic reduction-ammonia escape catalysis) blend zone and DOC (diesel oxidation catalysis) zone sequentially loaded along the axial direction.

[0045] Reactor and Mixing System: The catalyst is encapsulated in a cylindrical stainless steel shell with a matched inner diameter. A straight pipe, five times the diameter of the original pipe, is connected upstream of the catalyst as a mixing section, and a conventional Y-type static mixer is installed thereon. Urea solution is injected into the front end of the static mixer through a commercially available mass-produced urea nozzle (injection pressure 0.4 MPa).

[0046] Control strategy: The urea injection rate is controlled in a closed loop based on feedback from the downstream NOx sensor and the standard stoichiometric ratio.

[0047] II. Test conditions; The same high-load transient test cycle as in Example 2 of this invention was employed. The exhaust gas temperature was stepped up from 200°C to 450°C. At 300°C, NO was pulsedly injected into the exhaust gas, causing the inlet NOx concentration to rise from 100 ppm to 500 ppm within 0.5 seconds and maintain this level for 10 seconds. The space velocity was 40,000 h⁻¹.

[0048] III. Test Results; NOx instantaneous purification performance: When the inlet NOx concentration reaches a peak of 500 ppm, the system outlet NOx concentration reaches a maximum of 38 ppm, and only drops back to a steady-state level within 5 seconds after the peak.

[0049] Ammonia slip and byproducts: The average ammonia slip concentration was 9 ppm throughout the transient test. Meanwhile, the average N₂O (nitrous oxide) formation concentration was 11 ppm.

[0050] Performance stability: After five repeated transient tests, the relative standard deviation (RSD) of the NOx peak conversion rate was ±4.1%.

[0051] Test results show that even when using the same advanced multifunctional integrated catalyst as existing technologies, without targeted front-end mixing and flow field optimization design, the system still suffers from problems such as response lag, high purification peak, excessive byproduct formation, and insufficient stability when facing transient NOx shocks of high concentration. This invention combines a highly efficient multi-stage mixing chamber (W-shaped bottom mixing chamber, perforated spiral plate) with a flow guiding structure and a bifunctional catalyst system, achieving rapid, efficient, and stable purification of transient pollutants.

[0052] Comparative Example 2 To demonstrate the advantages of this invention in urea atomization, mixing uniformity, and anti-crystallization design, a comparative system was constructed based on the prior art (CN112459884B) of a guide vane and fan-shaped mixer system, including: I. System Composition; Catalyst structure: It is manufactured in accordance with the structure described in the instruction manual and the attached drawings, including an intake end cap with a side air inlet, a guide plate with built-in upper / lower baffles with guide holes, a DOC carrier, a urea mixer, an SCR carrier, and an outlet end cap in a straight package.

[0053] Urea mixer: The core is the fan-shaped airflow urea mixer described in Examples 1-3, which consists of an upper perforated plate, a lower perforated plate, and a middle arc-shaped plate forming a mixing chamber, creating a forced clockwise swirling flow path. The urea nozzle is mounted laterally on the mixer.

[0054] Catalyst coating: DOC support coated with Pt-Pd / Al2O3 catalyst (3 g / ft³ Pt, 1 g / ft³ Pd). SCR support coated with commercial Cu-SAPO-34 molecular sieve catalyst.

[0055] II. Test conditions; A 200-hour low-temperature cycling durability test was conducted. Each cycle consisted of 30 minutes of operation at 180°C (simulating low-speed driving) followed by 10 minutes of operation at 250°C (simulating light load). The NOx concentration in the exhaust gas was maintained at 200 ppm throughout the test, and urea was injected at a stoichiometric ratio (ANR=1.0).

[0056] III. Test Results; Atomization performance: Measured at the mixer outlet using a laser diffractometer, the Sauder mean diameter (SMD) of urea droplets was 58 μm, and the particle size distribution range [(Dv90 - Dv10) / Dv50] was relatively large at 1.8.

[0057] Low-temperature conversion efficiency degradation: Initially, the NOx conversion rate was 68% at 180℃. After 200 hours of testing, the NOx conversion rate at this temperature decreased to 52%.

[0058] Back pressure increase and crystallization: After the test, the system exhaust back pressure increased by 22% compared with the initial value; disassembly and inspection revealed that there was obvious urea derivative crystal accumulation on the inlet end face of the SCR carrier and in the adjacent channels.

[0059] Airflow uniformity: The velocity relative standard deviation was 25% when the flow velocity was scanned at the outlet section of the SCR carrier, indicating that there is a significant non-uniformity in the airflow distribution.

[0060] Test results confirm that while the guide plate and specific fan-shaped swirl mixer in CN112459884B can achieve airflow redirection and initial mixing, the urea atomization fineness is insufficient and the droplet distribution is uneven, leading to significant low-temperature activity decay and a high risk of crystallization during long-term operation. The present invention employs a combination of V-shaped broken-wall primary atomization, multi-stage diffusion in the inner / outer cavities of the W-shaped bottom mixing chamber combined with staggered openings, and a guide wall rectification scheme, providing superior atomization quality, mixing uniformity, and flow stability, thereby ensuring the long-term, efficient, and reliable operation of the system.

[0061] Comparative Example 3 To demonstrate the advantages of this invention in terms of simplified system architecture, cost control, and reliability, this comparative example simulates the complex exhaust aftertreatment system described in the prior art (CN111350574B) in a complex system with bypass and active temperature control, including: I. System Composition; Piping and components: including diversion valves, exhaust gas coolers, DOC catalysts, first bypass pipes and reversing valves for parallel DOC, DPF, SCR catalysts, ASC, second bypass pipes and reversing valves for parallel SCR / ASC, and spiral tube pyrolyzers.

[0062] Control system: integrates multiple sensors (temperature, differential pressure) and actuators (reversing valve, cooler fan, fuel injector). The control logic follows the complex strategy described in Example 2 to achieve active intervention and mode switching (SCR / SNCR) of DPF regeneration temperature and SCR inlet temperature.

[0063] Urea supply: The urea solution is first pumped into the spiral tube pyrolyzer, where it is pyrolyzed using the heat of the waste gas to generate NH3, and then injected into the exhaust pipe.

[0064] II. Test conditions; Execute the World Unified Transient Cycle (WHTC) and record the system's emissions, energy consumption, and control actions throughout the cycle.

[0065] III. Test Results; NOx Emissions and Compliance: The weighted average NOx emission value of the WHTC cycle test is 0.39 g / kWh, which meets the China VI b limit (0.4 g / kWh), but the margin is only 2.5%.

[0066] System complexity and cost: The existing system (CN111350574B) contains more than 15 main sensors and actuators, and has more than 5,000 lines of control code; preliminary estimates suggest that its material and manufacturing costs are about 2.3 times that of the system described in the embodiments of the present invention.

[0067] Control delay and ammonia slip: During rapid acceleration in the cycle, due to sudden changes in exhaust gas flow and temperature, the control system experiences an average response delay of 1.5 seconds, resulting in a mismatch in urea (ammonia) injection during this period, with the measured instantaneous peak value of ammonia slip reaching as high as 22 ppm.

[0068] Additional fuel consumption: To actively increase DPF or SCR temperature, the fuel injectors operated for a cumulative 85 seconds during the test cycle, resulting in an additional fuel consumption rate of approximately 0.8%.

[0069] Test results show that while a complex solution involving adding exhaust gas cooling / heating, multiple bypass switching, and independent pyrolysis units to address all operating conditions can meet the edge requirements of emission regulations, it results in a series of drawbacks, including extreme system complexity, high cost, slow control response, ammonia slip peaks, and additional energy consumption. This invention abandons this additive approach to complexity. Through an intelligent integrated design of a "passive adsorption-catalysis" dual-function catalyst and highly efficient mixed pretreatment, it achieves superior emission control and operational economy with a simpler, more passive, and more reliable architecture, demonstrating outstanding simplification, innovation, and technological advancement.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles, characterized in that, It includes an electronically controlled nozzle (1), a first mixing chamber (3), a pre-catalytic oxidation-reduction chamber (4), a second mixing chamber (8), and a post-catalytic oxidation-reduction chamber (9) arranged sequentially according to the direction of exhaust gas flow. The first mixing chamber (3) includes a first inlet (2) of urea solution, a V-shaped crushing wall (17) and a W-shaped bottom mixing chamber (6). The V-shaped crushing wall (17) is fixed on the pipe wall at the rear end of the pipe of the first inlet (2) of urea solution. The W-shaped bottom mixing chamber (6) includes an inner cavity (19) and an outer cavity (20). The inner cavity pipe wall is provided with staggered array openings (21). The inner cavity (19) and the outer cavity (20) are connected through the staggered array openings (21). The end of the first mixing chamber (3) is connected to a guide wall (16) structure. The guide wall (16) is composed of multiple continuously arranged truncated pyramidal channels. The pre-catalytic oxidation-reduction chamber (4) is connected to the end of the guide wall (16). The pre-catalytic oxidation-reduction chamber (4) is provided with a new tightly coupled SCR catalyst (15), an ASC catalyst (14), a DOC catalyst (5), and a DPF catalyst (13) in sequence. The new tightly coupled SCR catalyst (15) is used for passive adsorption and selective catalytic reduction of nitrogen oxides. The second mixing chamber (8) is provided with a perforated spiral plate (22), and the post-catalytic oxidation-reduction chamber (9) is provided with a post-SCR catalyst (12) and a post-DOC catalyst (11).

2. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The included angle of the V-shaped crushing wall (17) is an acute angle, and the plate material is 316L stainless steel or ceramic coating.

3. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The aperture of the staggered array opening (21) is 1~3mm, the spacing between the openings is 2~3 times the aperture, and the cavity material of the W-shaped bottom mixing cavity (6) is a nickel-based alloy or a ceramic composite material.

4. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The guide wall (16) divides the pipeline into multiple frustum channels. Each channel has a rectangular cross-section with a width-to-height ratio of 1:

1. The outermost wall of the guide wall has an included angle of 16°.

5. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The electronically controlled nozzle (1) has an inverted U-shaped urea pressure pipe structure, and the ratio of the thickness of the nozzle plate to the diameter of the nozzle is h / d=0.5~2. The valve core is provided with an internal non-sealed heat insulation sleeve.

6. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The new tightly coupled SCR catalyst (15) is a Cu-S34@S34 molecular sieve catalyst, and the N2O generation concentration of the Cu-S34@S34 molecular sieve catalyst is less than 10 ppm.

7. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, It also includes a control system, which triggers a regeneration mode based on the signals from the temperature sensor before the first mixing chamber (3), the nitrogen oxide sensor, and the temperature sensors before and after the particle capture device; when the total carbon and nitrogen content is greater than the preset total, or the total sulfur content is greater than the preset poisoning amount, or the actual conversion rate of the nitrogen oxides in the pre-stage is less than the first preset conversion rate, or the actual conversion rate of the nitrogen oxides in the post-stage is greater than the second preset conversion rate.

8. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The second mixing chamber (8) is provided with a perforated spiral plate (22) at the entrance. The perforated spiral plate (22) is fixed by a mounting thread (23). The spiral structure of the perforated spiral plate (22) is used to extend the airflow path.

9. The passive adsorption-selective catalytic reduction device for nitrogen oxides in diesel vehicles according to claim 1, characterized in that, The post-catalytic oxidation-reduction chamber (9) is connected to the end of the pre-catalytic oxidation-reduction chamber (4) through a pipe. The post-catalytic oxidation-reduction chamber (9) is provided with a post-SCR catalyst (12) and a post-DOC catalyst (11) in sequence.

10. A method for treating diesel vehicle exhaust gases, employing the apparatus as described in any one of claims 1 to 9, characterized in that, include: Step S1: The exhaust gas is sent into the first mixing chamber (3). The urea solution is crushed by impact of the V-shaped crushing wall (17). Then, it is mixed in a multi-stage diffusion process between the inner cavity (19) and the outer cavity (20) of the W-shaped bottom mixing chamber (6) through the staggered array openings (21). After being rectified by the guide wall (16), it enters the pre-catalytic oxidation-reduction chamber (4). Step S2: The exhaust gas treated by the pre-catalytic oxidation-reduction chamber (4) enters the second mixing chamber (8), and is further mixed with urea solution through the perforated spiral plate (22), and then enters the post-catalytic oxidation-reduction chamber (9) for secondary catalytic purification; Step S3: During the cold start phase, when the exhaust gas temperature is below 210°C, the PNA component in the newly coupled SCR catalyst (15) adsorbs NOx in the exhaust gas. Step S4: In the high-temperature stage, when the exhaust gas temperature is higher than 210℃, the NOx adsorbed by PNA is desorbed and selectively catalytically reduced together with the NOx in the exhaust gas at the SCR active sites.

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