Urea mixer and diesel engine tail gas aftertreatment system

Abstract

According to the urea mixer and the diesel engine tail gas aftertreatment system, on the premise that the performance requirements of emission and the like are met, the back pressure of the aftertreatment mixer can be greatly reduced, generation of urea crystals is reduced, meanwhile, few parts are used, the mold opening cost and the part cost of the mixer are reduced, the mixing pipe is installed on the end cover, and the mixing effect is good. A front baffle is arranged at the front end of the mixing pipe, a notch is reserved between the front baffle and the lower portion of the mixing pipe to form a first gas inlet, a notch is formed in the upper portion of the side wall of the mixing pipe to form a second gas inlet, and the mixing pipe penetrates through the end cover and is provided with a gas flow outlet in the rear end of the end cover. And an injection opening of the gas-assisted urea injector faces the second gas inlet, and the area of the second gas inlet is larger than the area of the contact position of the maximum injection cone angle of urea injected by the gas-assisted urea injector and the mixing pipe, so that all urea injected by the urea injector is injected into the second gas inlet in the mixing pipe.

Description

Technical Field

[0001] The invention relates to the technical field of exhaust gas post-treatment, and in particular to a urea mixer and a diesel engine exhaust gas post-treatment system. Background Art

[0002] In recent years, in response to the energy crisis and climate change, countries have introduced more stringent fuel consumption and emission regulations. Diesel engines, as a power source for vehicles, will continue to exist for a long time, and automakers need to continue to improve the fuel economy of the entire vehicle. Among the next stage of emission regulations, the Euro VII emission regulations have been released first, which puts forward more stringent requirements for pollutant limits and higher requirements for commercial vehicle aftertreatment.

[0003] At present, diesel engine exhaust aftertreatment requires the installation of a mixer to improve the urea decomposition efficiency and the uniformity of the reductant distribution. The current domestic diesel engine aftertreatment technology route is DOC+DPF+mixer+SCR. The entire aftertreatment back pressure is generally not less than 18kpa, of which the back pressure caused by the mixer accounts for more than 40% of the back pressure generated by the entire aftertreatment system. At present, light trucks are promoting the no EGR (exhaust gas recirculation) solution, which can effectively reduce parts, reduce costs and improve reliability, but no EGR will lead to worsening NOx emissions, and more urea needs to be injected for selective reduction, which will have higher requirements for the mixer and SCR.

[0004] In the existing commercial vehicle after-treatment systems, pure liquid urea injection systems are mostly used, and the mixer solutions are all adapted to them; however, the urea atomization effect of the pure liquid urea injection unit is general, and a mixer is required to fully mix it to improve the efficiency of urea thermal decomposition and hydrolysis and ensure the uniformity of SCR; therefore, the mixer needs to fully disturb and mix the airflow. At the same time, considering the compact vehicle layout, the overall length of the after-treatment should be as short as possible. The mechanical structure of the mixer is often relatively complex and the back pressure is high. The back pressure of the mixer matching the pure liquid injection system accounts for more than 40% of the after-treatment; under the new fuel consumption regulations and emission regulations, the existing mixer status is difficult to adapt. In addition, for products that are very sensitive to fuel economy, such as marine diesel engines and fixed-source diesel engines, the back pressure requirements are very high, and high back pressure mixers cannot be adapted.

[0005] When the exhaust temperature is low or the urea injection volume is too large, the urea aqueous solution forms a liquid film on the wall of the mixer and has no time to decompose. Urea crystals will gradually precipitate. After the urea crystals are generated, the speed of crystallization will become faster and faster. The generation of crystals leads to less decomposed NH3, which affects the conversion efficiency of SCR. In severe cases, the crystals will block the mixer, causing excessive back pressure or blockage of the mixer. Commercial vehicles regenerate DPF by post-injection of diesel to increase the exhaust temperature and burn off the crystals in the mixer, but frequent regeneration will affect fuel consumption and cause oil dilution. For non-road agricultural machinery, on-site regeneration is required, and frequent regeneration affects production efficiency. Marine diesel engine aftertreatment does not have DPF, and crystals cannot be removed after generation. The mixer needs to be disassembled for removal. Minimizing the generation of urea crystals and reducing the cost of operation and maintenance are key points in aftertreatment design. In addition, existing mixer solutions have complex structures, expensive mold opening fees, a large number of parts, and high costs. There are several typical existing mixer solutions, such as swirl tube mixers, which have complex parts structures, high manufacturing precision requirements, high processing costs, and low adaptability. Summary of the invention

[0006] In view of the above problems, the present invention provides a urea mixer and an exhaust gas after-treatment system, which can significantly reduce the back pressure of the after-treatment mixer and reduce the formation of urea crystals while meeting the performance requirements such as emissions. At the same time, fewer parts are used, thereby reducing the mold opening cost and parts cost of the mixer.

[0007] The technical solution is as follows: a urea mixer comprises a mixer cylinder, an end cover is arranged in the mixer cylinder, the end cover divides the mixer cylinder into two parts, front and rear, and is characterized in that a mixing tube is installed on the end cover, a front baffle is arranged at the front end of the mixing tube, a gap is left between the front baffle and the lower part of the mixing tube to form a first air inlet, a gap is arranged at the upper part of the side wall of the mixing tube to form a second air inlet, the mixing tube passes through the end cover and an air flow outlet is arranged at the rear end of the end cover, a gas-assisted urea injector is arranged on the mixer cylinder, the injection port of the gas-assisted urea injector is arranged toward the second air inlet, there is no obstruction between the injection port of the urea injector and the second air inlet of the mixing tube, and the area of ​​the second air inlet is larger than the area of ​​the maximum injection cone angle of the gas-assisted urea injector spraying urea and the contact position of the mixing tube, so that all the urea sprayed by the urea injector is sprayed into the second air inlet on the mixing tube.

[0008] Furthermore, at the lower end of the first air inlet, the side wall of the mixing tube is bent inwardly to form a guide plate, and the guide plate is arranged to be inclined downward.

[0009] Furthermore, the mixing tube and the mixer cylinder are eccentrically arranged.

[0010] Furthermore, the cross-sectional area of ​​the mixing tube is 15%-25% of the cross-sectional area of ​​the mixer cylinder where the end cover contacts the mixer cylinder, and the cross-sectional area of ​​the mixing tube is larger than the minimum flow area of ​​the catalyst.

[0011] Furthermore, a rear baffle is provided at the rear end of the mixer cylinder, and the rear baffle completely blocks the end face of the mixer cylinder. Several air flow outlets are provided along the side wall of the mixing tube, and air flow guide plates are also provided on the outermost air flow outlets, and the air flow guide plates are symmetrically arranged.

[0012] Furthermore, the sum of the areas of the first air inlet and the second air inlet is greater than the minimum flow area of ​​the catalyst, and the sum of the areas of the airflow outlets is greater than the minimum flow area of ​​the catalyst.

[0013] Furthermore, the atomization distance of the urea injected by the gas-assisted urea injector from the injection point to the collision with the wall of the mixing tube is greater than the characteristic penetration distance of urea injection.

[0014] Furthermore, the end cover comprises a flat plate portion arranged along the radial direction of the mixer cylinder, and a flange is provided on the edge of the flat plate portion to cooperate with the mixer cylinder.

[0015] Furthermore, the pipe length of the mixing pipe is less than 160 mm.

[0016] Furthermore, there is an inclination angle between the nozzle of the gas-assisted urea injector and the cross section of the mixer cylinder.

[0017] Furthermore, the front baffle extends to the front side directly below the nozzle of the gas-assisted urea injector, so that the urea liquid dripping from the nozzle can enter the mixing pipe from the second air inlet.

[0018] Furthermore, a baffle slot is correspondingly provided on the side wall of the mixing tube, a hanging ear is correspondingly provided on the front baffle, a slot is provided on the rear baffle, and a block is correspondingly provided on the side wall of the mixing tube.

[0019] A diesel engine exhaust aftertreatment system is characterized by comprising the above-mentioned urea mixer and an SCR unit located at the rear end of the urea mixer.

[0020] The urea mixer of the present invention has the following advantages:

[0021] The mixing tube of the urea mixer of the present invention adopts a dual-channel air intake design. The design of the first air inlet realizes air intake at the bottom of the front section of the mixing tube. The mixing tube and the front baffle form a flow channel to purge the bottom urea liquid film to avoid bottom crystallization. The guide plate of the first air inlet is tilted downward to prevent the urea liquid from flowing back under the condition of rapid acceleration and deceleration. The second air inlet is set so that the urea sprayed by the gas-assisted urea injector is completely sprayed into the second air inlet on the mixing tube and mixed with the exhaust gas. The atomization stroke of the urea sprayed by the gas-assisted urea injector from the nozzle to the wall collision with the inner wall of the mixing tube is greater than the characteristic penetration distance of the urea injection, so as to avoid the wall collision before the urea is fully atomized. In addition, due to the gas-assisted injection of the gas-assisted urea injector, the size of the atomized particles is very small, which can ensure that the urea thermal decomposition and hydrolysis efficiency is higher, reduce the generation of liquid film and the formation of urea crystals after the wall collision, and the urea crystals are not easy to accumulate inside the mixer, thereby reducing the frequency and difficulty of maintenance.

[0022] In the whole mixer structure design, the atomized urea is only collided, swirled and atomized in the mixing tube, because the mixing tube does not contact the external low-temperature components and is always in the exhaust gas flow. Therefore, the inner wall temperature of the mixing tube is at a relatively high level, which can greatly reduce the risk of urea forming a liquid film here and reduce the risk of urea crystal formation. The setting of the airflow outlet is coordinated with the guide plate, so that the exhaust gas flow is circumferentially disturbed in the mixer tube and then discharged upward, which further promotes the uniform mixing of urea and exhaust gas, and improves the treatment efficiency and system stability.

[0023] The mixer of the present invention has a simple structure and adopts fewer parts. It can be assembled through simple welding and slot matching, which reduces the difficulty and complexity of assembly. By using fewer parts, the mold opening cost and parts cost of the mixer are reduced, and no complicated parts development is required. The circumferential arrangement space of the post-treatment urea nozzle is larger. The components in the mixer can be prepared as a whole first, and there is no need for secondary development of any components. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a perspective view of a urea mixer in one embodiment from a first viewing angle;

[0025] Figure 2 is a front view of a urea mixer in one embodiment;

[0026] Figure 3 for Figure 2 A schematic cross-sectional view along the AA direction;

[0027] Figure 4 for Figure 2 A cross-sectional schematic diagram along the BB direction;

[0028] Figure 5 is a perspective view of a urea mixer in one embodiment from a second viewing angle;

[0029] Figure 6 is a perspective view of a urea mixer in another embodiment from a first perspective;

[0030] Figure 7 is a front view of a urea mixer in another embodiment;

[0031] Figure 8 for Figure 7 A schematic cross-sectional view in the CB direction; DETAILED DESCRIPTION

[0032] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. In the description of this specification, the description of the reference term "embodiment" etc. means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0033] See Figures 1 to 8 A urea mixer comprises a mixer cylinder 1, an end cover 2 is arranged in the mixer cylinder 1, the end cover 2 divides the mixer cylinder 1 into two parts, a front part and a rear part, a slot 3 is arranged on the end cover 2, a mixing tube 4 is installed on the slot 3, a front baffle 5 is arranged at the front end of the mixing tube 4, a gap is left between the front baffle 5 and the lower part of the mixing tube 4 to form a first air inlet 6, a gap is arranged at the upper part of the side wall of the mixing tube to form a second air inlet 7, the mixing tube 4 passes through the end cover 2 and an air flow outlet 12 is arranged at the rear end of the end cover 2, a gas-assisted urea injector 8 is arranged on the mixer cylinder, and the accompanying drawings show that The gas-assisted urea injector is omitted, and only a simple outline of the gas-assisted urea injector 8 is given to schematically indicate the approximate arrangement position of the gas-assisted urea injector 8. The injection port of the gas-assisted urea injector 8 is arranged toward the second air inlet 7. There is no obstruction between the injection port of the urea injector 8 and the second air inlet 7 of the mixing tube. The area S1 of the second air inlet 7 is larger than the area S2 of the contact position of the maximum injection cone angle R1 of the gas-assisted urea injector and the mixing tube, so that all the urea sprayed by the urea injector 8 is sprayed into the second air inlet 7 on the mixing tube. Figure 3 The schematic diagram of the maximum injection cone angle R1 of the gas-assisted urea injector for urea injection is given in FIG. Figure 4 Schematic representation of the area S1 of the second air inlet 7 and a schematic representation of the area S2 of the contact position between the maximum injection cone angle R1 of the gas-assisted urea injector and the mixing tube are given in FIG.

[0034] In the embodiment, the front baffle 5 extends to the front side directly below the nozzle of the gas-assisted urea injector 8, so that the urea liquid dripping from the nozzle can enter the mixing tube 4 from the second air inlet 7. When the injection pressure is too low, the urea droplets can also enter the mixing tube 4. In the embodiment, at the lower end of the first air inlet 7, the side wall of the mixing tube is bent inward to form a guide plate 9. The guide plate 9 is inclined downward along the axial direction of the mixing tube to prevent the urea liquid from flowing back under sudden acceleration and deceleration.

[0035] In the embodiment, a rear baffle 10 is provided at the rear end of the mixer cylinder 1, and the rear baffle 10 completely blocks the end face of the mixer cylinder 1. A plurality of airflow outlets 12 are provided along the side wall of the mixing tube 4, and airflow guide plates 11 are also provided on the outermost airflow outlets 12, respectively. The airflow guide plates 11 are symmetrically arranged, and the arrangement of the airflow outlet cooperates with the guide plate to make the exhaust gas flow be circumferentially disturbed in the mixer tube and then discharged upward, thereby further promoting the uniform mixing of urea and exhaust gas, and improving the treatment efficiency and system stability.

[0036] In the embodiment, the mixing tube adopts a dual-channel air intake method. The second air intake pipe at the bottom of the front section of the mixing tube intakes air. The front half of the mixing tube is arranged at a bevel angle to form a flow channel with the front baffle to purge the bottom urea liquid film to avoid bottom crystallization. At the same time, the inclined angle is arranged to prevent the urea liquid from flowing back under sudden acceleration and deceleration; in the upper part of the mixing tube, the urea spray is mixed with the exhaust gas to enter the second air intake pipe; at the rear end of the mixing tube, through two symmetrically distributed guide plates, the exhaust gas flow is circumferentially disturbed in the mixer tube and then discharged upward.

[0037] In the urea mixer in the embodiment, the atomized urea collides, swirls, and atomizes only in the mixing tube. Since the mixing tube does not contact external low-temperature components and is always in the high-temperature exhaust gas flow, the inner wall temperature of the mixing standard tube is at a relatively high level, which can greatly reduce the risk of urea generating a liquid film here and reduce the risk of urea crystal formation.

[0038] In one embodiment, the mixing tube 4 and the mixer barrel 1 are eccentrically arranged, and the cross-sectional area of ​​the mixing tube 4 is 15%-25% of the cross-sectional area of ​​the barrel at the contact point between the end cover and the mixer barrel 1, and the cross-sectional area of ​​the mixing tube 4 is larger than the minimum flow area of ​​the catalyst. The larger the diameter, the slower the flow rate, which is not conducive to the mixed evaporation of urea. If the flow rate is too fast, the back pressure will increase, which may cause abnormal noise. By setting the diameter of the mixing tube appropriately, the effect of urea mixed evaporation is ensured while reducing the back pressure. In addition, the sum of the areas of the first air inlet 6 and the second air inlet 7 is greater than the minimum flow area of ​​the catalyst, the sum of the areas of the multiple air flow outlets 12 is greater than the minimum flow area of ​​the catalyst, and the pipe length of the mixing tube 4 is less than 160mm to ensure the passability of the airflow and reduce the back pressure of the mixer; by setting the size of the mixing tube, the airflow channel area is effectively increased, ensuring the efficient passage of the airflow, thereby significantly reducing the back pressure of the post-processing mixer, helping to improve the operating efficiency of the engine, reducing fuel consumption, and indirectly improving the overall economy.

[0039] In the embodiment, the atomization stroke of urea injected by the gas-assisted urea injector from the injection point to the collision with the wall of the mixing tube is greater than the characteristic penetration distance of the urea injection. The overall structure ensures that the urea avoids collision with the wall before it is fully atomized, ensures that the urea thermal decomposition and hydrolysis efficiency is higher, reduces the generation of liquid film after collision with the wall, and forms urea crystals. This not only optimizes the NOx emission reduction effect, but also reduces the risk of urea crystallization, and extends the maintenance cycle of the post-treatment system.

[0040] In one embodiment, the end cover 2 includes a flat plate portion 201 arranged along the radial direction of the mixer barrel 1, and a flange 202 is provided on the edge of the flat plate portion to cooperate with the mixer barrel 1. A baffle slot 401 is correspondingly provided on the side wall of the mixing tube 4, and a hanging ear 501 is correspondingly provided on the front baffle 5, which can be fixed by welding. A slot is provided on the rear baffle, and a block is correspondingly provided on the side wall of the mixing tube. The rear baffle can also be fixed by welding, and the mixing tube can also be fixed to the end cover by welding.

[0041] In the embodiment, the mixer assembly in the mixer cylinder has only a few parts: end cap, mixing tube, front baffle, and rear baffle. The mixer assembly is welded to the mixer cylinder through the end cap; the front baffle is assembled to the mixing tube through the ear and the baffle slot on the inner cylinder, and the rear baffle is also welded to the mixer cylinder; through simple welding and slot assembly, the difficulty and complexity of assembly are reduced, and by using fewer parts, the mold opening cost and parts cost of the mixer are reduced, which is convenient for production and assembly, accelerates the time to market, and enhances market competitiveness. The mixer has a simple structure and does not require complex parts development. The circumferential arrangement space of the post-treatment urea nozzle is larger. The components in the mixer can be prepared as a whole first, and there is no need for secondary development of any components.

[0042] The mixer structure in implementation is simple, and does not require complex parts development. The post-treatment urea injector has a larger circumferential arrangement space, and the components in the mixer can be prepared as a whole, without the need for any secondary development of components. This solution has strong adaptability, and the urea nozzle of the gas-assisted urea injector can be arranged within 180° circumferentially. It has strong versatility and can be arranged according to the nozzle arrangement position. The mixer component can be rotated circumferentially as a whole, reducing the difficulty of the deformation machine platform development.

[0043] In practice, there is an inclination angle between the nozzle of the gas-assisted urea injector and the cross section of the mixer cylinder 1, so that the position and size of the inner cylinder and the opening thereon can be arranged more conveniently. Figure 6 , 7 8. In one embodiment, the nozzle of the gas-assisted urea injector is tiltedly arranged on the mixer cylinder having a conical surface; see Figure 1-5 In another embodiment, it is achieved by providing a nozzle 7 with a corresponding bending angle, so that it can be adapted to a straight mixer barrel, and the components in the mixer can be universal without developing new parts, so that the performance verification of the mixer and the mixer development are platform-based, reducing development costs.

[0044] In an embodiment of the present invention, an exhaust gas after-treatment system is also provided, including a urea mixer and an SCR unit located at the rear end of the urea mixer. The mixer structure is optimized to enable urea and exhaust gas to be more fully mixed, and finally a uniform mixed gas is formed to enter the SCR unit, thereby improving the exhaust gas after-treatment effect and helping to meet more stringent emission standards.

[0045] The urea mixer in the embodiment is applied to the diesel engine exhaust after-treatment system. Taking the 2.0L displacement diesel engine exhaust after-treatment as an example, the conventional after-treatment system generates an overall back pressure of 22kp, of which the back pressure of the mixer is 8.5kpa. According to the full-load minimum fuel consumption rate of 200g / kwh, the after-treatment back pressure can be reduced to 3kpa by using the mixer in the scheme of the present invention. For the EGR route, the fuel consumption is reduced by 8g / kwh (4%), and the fuel consumption is reduced by 3g / kwh (1.5%) for the non-EGR route, and the fuel saving effect is obvious. In addition, this mixer can be applied in batches to products with high fuel saving requirements such as marine after-treatment.

[0046] The urea mixer in the solution of the present invention has a small number of parts, low raw material cost, and a material weight reduced by more than 50% compared with the existing solution. The subsequent processing technology is simple, and the one-time investment in the catalyst does not exceed 5,000 yuan, which makes the solution have high practical value and market potential in the field of engine exhaust aftertreatment.

[0047] In addition, it should be understood that although this specification is described according to implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A urea mixer, comprising a mixer cylinder, wherein an end cover is arranged in the mixer cylinder, and the end cover separates the mixer cylinder into two parts, front and rear, characterized in that: A mixing tube is installed on the end cover, and a front baffle is provided at the front end of the mixing tube. A gap is left between the front baffle and the lower part of the mixing tube to form a first air inlet. A gap is provided at the upper part of the side wall of the mixing tube to form a second air inlet. The mixing tube passes through the end cover and an air flow outlet is provided at the rear end of the end cover. A gas-assisted urea injector is provided on the mixer cylinder, and the injection port of the gas-assisted urea injector is arranged toward the second air inlet. There is no obstruction between the injection port of the urea injector and the second air inlet of the mixing tube. The area of ​​the second air inlet is larger than the area of ​​the maximum injection cone angle of the gas-assisted urea injector for injecting urea and the contact position of the mixing tube, so that all the urea sprayed by the urea injector is sprayed into the second air inlet on the mixing tube.

2. A urea mixer according to claim 1, characterized in that: At the lower end of the first air inlet, the side wall of the mixing tube is bent inward to form a guide plate, and the guide plate is arranged to be inclined downward.

3. A urea mixer according to claim 1, characterized in that: The mixing tube and the mixer cylinder are eccentrically arranged, the cross-sectional area of ​​the mixing tube is 15%-25% of the cross-sectional area of ​​the cylinder where the end cover contacts the mixer cylinder, and the cross-sectional area of ​​the mixing tube is larger than the minimum flow area of ​​the catalyst.

4. A urea mixer according to claim 1, characterized in that: A rear baffle is provided at the rear end of the mixer cylinder, and the rear baffle completely blocks the end face of the mixer cylinder. Several air flow outlets are provided along the side wall of the mixing tube, and air flow guide plates are also provided on the outermost air flow outlets, and the air flow guide plates are symmetrically arranged.

5. A urea mixer according to claim 1, characterized in that: The sum of the areas of the first air inlet and the second air inlet is greater than the minimum flow area of ​​the catalyst, the sum of the areas of the airflow outlets is greater than the minimum flow area of ​​the catalyst, and the pipe length of the mixing tube is less than 160 mm.

6. A urea mixer according to claim 1, characterized in that: The atomization stroke of urea injected by the gas-assisted urea injector from the injection point to the collision with the wall of the mixing tube is greater than the urea injection characteristic penetration distance.

7. A urea mixer according to claim 4, characterized in that: The end cover is provided with a slot, on which a mixing tube is installed. The end cover includes a flat plate portion arranged along the radial direction of the mixer cylinder, and a flange is provided on the edge of the flat plate portion to cooperate with the mixer cylinder. The side wall of the mixing tube is correspondingly provided with a baffle slot, the front baffle is correspondingly provided with a hanging ear, the rear baffle is provided with a slot, and the side wall of the mixing tube is correspondingly provided with a block.

8. A urea mixer according to claim 1, characterized in that: A nozzle of the gas-assisted urea injector has an inclination angle with a cross section of the mixer cylinder.

9. A urea mixer according to claim 1, characterized in that: The front baffle extends to the front side directly below the nozzle of the gas-assisted urea injector, so that the urea liquid dripping from the nozzle can enter the mixing pipe from the second air inlet.

10. A diesel engine exhaust aftertreatment system, characterized in that: It comprises the urea mixer as claimed in any one of claims 1 to 9 and an SCR unit located at the rear end of the urea mixer.

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