Aftertreatment system and midline injection system

Abstract

Post-treatment system, comprehensive: an aftertreatment component (170) designed to treat exhaust gas exiting from an engine (110); a reactor tube (140, 510) arranged upstream of the aftertreatment component, wherein the reactor tube is designed to receive the exhaust gas from the engine; a liquid-only metering unit (150) for injecting diesel exhaust fluid into the exhaust gas received by the engine, wherein the liquid-only metering unit injects the diesel exhaust fluid at a center line (610) of the reactor tube to provide a uniform dispersion of the diesel exhaust fluid over at least a part of the aftertreatment component; and a knife-edge fastening (220) designed for fastening the liquid-only dosing unit inside the reactor tube, the knife-edge fastening comprising: a leading edge comprising a knife-edge structure, wherein the leading edge points towards an incoming exhaust gas stream, and a trailing edge comprising a knife-edge structure, with the trailing edge pointing away from the exhaust flow.

Description

TECHNICAL AREA

[0001] The present disclosure relates in general to an aftertreatment system for treating exhaust gases from internal combustion engines and a midline injection system for injecting diesel exhaust fluid into exhaust gas exiting an engine. background

[0002] Aftertreatment systems are a significant technology for reducing harmful emissions from internal combustion engines. Aftertreatment systems generally comprise a storage source for reducing agent (especially diesel exhaust fluid) and a metering unit, which includes a pump unit for pressurizing the reducing agent. The aftertreatment systems may also include a metering unit for delivering a controlled amount or rate of reducing agent into an exhaust stream, as well as an injector that provides a reducing agent solution to a degradation section of an exhaust stream path located upstream of an aftertreatment component (e.g., a selective catalytic reduction catalyst).

[0003] Various aftertreatment systems employ liquid-only dosing units (i.e., without air assistance) to inject a reducing agent, such as diesel exhaust fluid, into an exhaust stream within an exhaust pipe. Such systems currently utilize tangential and / or wall injection methods, which require equipment elements that provide backflow zones and nucleation sites for urea deposit formation. For example, a nucleation inducer (i.e., a downstream mixing plate) is currently used to achieve uniformity of the diesel exhaust fluid in the exhaust stream before it reaches the aftertreatment component.

[0004] From US Patent 2012 / 0020854A1, a method, system, and apparatus for injecting a liquid reducing agent into an exhaust gas and for vaporizing and decomposing the liquid reducing agent at an elevated temperature are known. The method comprises providing an exhaust pipe with an inner surface and arranging the exhaust pipe in fluid communication upstream of a catalyst. The method also includes the steps of arranging an inner cone in the exhaust pipe parallel to the exhaust pipe, attaching an injection nozzle to the outside of the exhaust pipe in fluid communication with the inner cone, injecting the liquid reducing agent into the inner cone, and directing the exhaust gas into a passage between the inner surface of the exhaust pipe and the inner cone. The exhaust gas is also guided within the inner cone.

[0005] From DE 10 2008 042 678 A1, an exhaust gas purification device for cleaning the exhaust gas of an internal combustion engine is known. The exhaust gas purification device has an exhaust gas passage through which the exhaust gas flows, a reducing agent injector that injects a reducing agent into the exhaust gas passage, and a reduction catalyst that is provided in the exhaust gas passage downstream of the reducing agent injector to support at least one reduction reaction between a component of the exhaust gas and the reducing agent. The exhaust gas passage has a curved section formed by a bend. The reducing agent injector is provided on the outside of the bend to inject the reducing agent in a direction that deviates from a tangent line that is tangential to a central axis line of the curved section at its downstream end, towards the inside of the bend of the curved section.

[0006] From US 2006 / 0 037 309 A1, an emission control system for an engine for reducing NOx emissions is known, wherein the system comprises an ammonia injector, a control unit for controlling the ammonia injector and a catalyst, wherein the control unit includes a transmitter for transmitting information regarding the amount of ammonia consumed and the amount of NOx reduced. Summary

[0007] Various embodiments provide an aftertreatment system comprising an aftertreatment component designed to treat exhaust gas exiting an engine, a reactor tube, a liquid-only metering unit, and a knife-edge attachment. The reactor tube is located upstream of the aftertreatment component and is designed to receive exhaust gas from the engine. The liquid-only metering unit is designed to inject diesel exhaust fluid into the exhaust gas received from the engine. The liquid-only metering unit injects the diesel exhaust fluid at the centerline of the reactor tube to provide a uniform dispersion of the diesel exhaust fluid over at least a portion of the aftertreatment component.The knife-edge mounting is designed for securing the liquid-only dosing unit within the reactor tube, wherein the knife-edge mounting has a leading edge pointing towards an incoming exhaust gas stream and a trailing edge pointing away from the exhaust gas stream. The leading edge and the trailing edge comprise a knife-edge structure.

[0008] Further embodiments provide a centerline injection system for injecting diesel exhaust fluid into exhaust gas exiting an engine. The centerline injection system comprises a reactor tube, a liquid-only metering unit, and a knife-edge mounting. The reactor tube is located upstream of an aftertreatment component designed to treat the exhaust gas and designed to receive the exhaust gas from the engine. The liquid-only metering unit is designed to inject diesel exhaust fluid into the exhaust gas. The liquid-only metering unit injects the diesel exhaust fluid along a centerline of the reactor tube to provide a uniform dispersion of the diesel exhaust fluid over at least a portion of the aftertreatment component. The knife-edge mounting is designed to secure the liquid-only metering unit's injection nozzle within the reactor tube.The knife-edge mounting features a trailing edge pointing away from an incoming exhaust stream and a leading edge pointing towards the exhaust stream, each with a knife-edge structure to minimize backflow zones and exhaust deflections. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The details of one or more implementations of the subject matter described in this specification are specified in the accompanying figures and the following description.

[0010] Other features and aspects of the object will become apparent from the description, figures, and claims presented herein. Fig. Figure 1 is a schematic view of a system with a liquid-only dosing unit according to an exemplary embodiment. Fig. Figure 2 is a top-view cross-sectional view of an embodiment of a decomposition reactor tube connected to an injection nozzle (INJ) of a liquid-only metering unit. Fig. Figure 3 is a front view of the decommissioning reactor tube of Fig. 2. Fig. Figure 4 is a side cross-sectional view of the decommissioning reactor tube of Fig. 2. Fig. Figure 5 is a cross-sectional view of a converging decomposition reactor tube with centerline injection of diesel exhaust fluid according to one embodiment. Fig. Figure 6 is a front view of the converging decomposition reactor tube of Fig. 5. Fig. Figure 7 is a side view of the converging decomposition reactor tube of Fig. 5. DETAILED DESCRIPTION

[0011] For the purpose of promoting an understanding of the principles of the disclosure, reference is now made to the embodiments illustrated in the drawings, and these are described using special language. It is understood, however, that no limitation of the scope of the disclosure is intended, and all modifications and alterations of the illustrated embodiments, as well as further applications of the principles of the disclosure as illustrated herein, which would normally occur to a person skilled in the art to whom the disclosure relates, are included herein.

[0012] The apparatus and systems described herein relate to a system with a liquid-only metering unit that injects diesel exhaust fluid along the centerline of a principal axis (i.e., along a primary flow direction) of a degradation reactor tube (also referred to as the "reactor tube") used in an aftertreatment system. The reactor tube may be used with an aftertreatment component such as a selective catalytic reduction catalyst. According to one embodiment, the reactor tube serves as a degradation chamber in which exhaust gas from an engine interacts with a reducing agent (e.g., diesel exhaust fluid). Further embodiments of the systems described herein also include a reducing agent injection nozzle assembly designed to minimize exhaust flow deflections and eliminate backflow zones (e.g., at the tip of an injection nozzle).The use of this fastening method can also eliminate the need for device elements that could facilitate deposit nucleation. According to several embodiments, the systems and devices described herein provide an injection point that maximizes the uniformity of the reducing agent (i.e., diesel exhaust fluid) within a degradation reactor tube. Further advantages realized by implementing the features described herein include minimized urea deposits along the inner surface of the degradation reactor tube.

[0013] With reference to Fig. Figure 1 shows a schematic view of a system 100 with a degradation reactor tube 140 according to an exemplary embodiment. The system 100 comprises an engine 110, a diesel oxidation catalyst (DOC) 120, a diesel particulate filter (DPF) 130, a degradation reactor tube 140, a liquid-only metering unit 150, a diesel exhaust fluid (DEF) supply 160, and an aftertreatment component 170. The system 100 may also include a dispensing mechanism for delivering reducing agent (e.g., diesel exhaust fluid) from the diesel exhaust fluid supply 160 (e.g., a reservoir) to an exhaust system connected to the engine 110. In one embodiment, the system 100 is provided on a vehicle powered by the engine 110.In other embodiments, the system 100 can be provided on a motor 110 which is used in other applications, such as power generation, pumping systems or any other application, that receives or uses power from the motor 110.

[0014] The engine 110 can be a diesel engine or any suitable internal combustion engine equipped with exhaust gas treatment using a reducing agent. The engine 110 generates exhaust gas from combustion that occurs within the engine cylinders during operation. The engine 110 can comprise one or more engine cylinders that receive fuel and air through an intake system (not shown) to generate combustion. In some embodiments, the intake system can include a turbocharger that receives compressed air from the atmosphere and transfers the air to an intake manifold connected to the engine cylinders. The energy released by combustion within the engine cylinders is used to propel, for example, a vehicle in which the engine 110 is housed. The exhaust gas resulting from combustion can exit the engine through an exhaust manifold (not shown).

[0015] The exhaust gas can pass through several components before entering the atmosphere. Furthermore, with reference to… Fig. 1. The exhaust gas from the engine 110 exits and flows into the diesel oxidation catalyst 120. The diesel oxidation catalyst 120 is an exhaust gas aftertreatment system that oxidizes elements present in the exhaust gas. The diesel oxidation catalyst 120 can, for example, oxidize hydrocarbons and carbon monoxide into carbon dioxide and water. The exhaust gas can also pass through the diesel particulate filter 130, which filters out particles and soot from the exhaust gas. After exiting the diesel particulate filter 130, the exhaust gas can flow into a degradation reactor tube 140. The degradation reactor tube 140 is designed to receive the exhaust gas in a channel along with a reducing agent in such a way that the exhaust gas and the reducing agent can mix properly and be degraded.In a typical implementation, the reducing agent in the form of diesel exhaust fluid can comprise a urea-based solution that mixes with the exhaust gas to effect chemical degradation to ammonia. One example of diesel exhaust fluid comprises a solution of 32.5% high-purity urea and 67.5% deionized water. However, it is understood that other diesel exhaust fluid solutions and reducing agents can also be used. As described above, the degradation reactor tube 140 serves as a chamber for the diesel exhaust fluid to interact with elements in the exhaust gas and degrade to ammonia.

[0016] According to some embodiments, the liquid-only metering unit 150 is connected to the decomposition reactor tube 140 to transfer diesel exhaust fluid to the decomposition reactor tube 140. The liquid-only metering unit 150 may include an injection nozzle configured to inject the diesel exhaust fluid into the exhaust gas flowing through the decomposition reactor tube 140. The liquid-only metering unit 150 is positioned such that the injection nozzle for injecting diesel exhaust fluid is located on and / or in the immediate vicinity of a centerline of the decomposition reactor tube 140. The liquid-only metering unit 150 receives diesel exhaust fluid from the diesel exhaust fluid supply 160, which stores a supply of diesel exhaust fluid for use in the aftertreatment system.

[0017] The exhaust gas flows from the reactor tube 150 into the aftertreatment component 170, as shown in Fig. Figure 1 shows the post-treatment component 170, which can comprise a selective catalytic reduction catalyst. According to one embodiment, the post-treatment component 170 can be used to convert nitrogen oxides into less harmful substances, such as nitrogen and water. To enable this conversion, the post-treatment component 170 uses a reducing agent, such as urea, to convert the nitrogen oxides into, for example, diatomic nitrogen and water.

[0018] The liquid-only metering unit 150 can include various structures to facilitate the transfer of diesel exhaust fluid from the diesel exhaust fluid supply 160 to the liquid-only metering unit 150 and the delivery of the diesel exhaust fluid to parts of an exhaust system (e.g., the decommissioning reactor tube 140). The liquid-only metering unit 150 can, for example, include a pump, a filter screen, and a check valve upstream of the pump to receive diesel exhaust fluid from the diesel exhaust fluid supply 160. In one configuration, the pump is a diaphragm pump, although it is understood that any other type of pump can be used. The pump delivers pressurized diesel exhaust fluid at a pre-set pressure, which can flow through a second check valve, a pulsation dampener and a second filter to provide pressurized reducing agent to a metering valve (i.e., the injector).

[0019] The diesel exhaust fluid supply 160 stores a reservoir of diesel exhaust fluid and can be vented so that, for example, reducing agent can be drawn from a port in the reservoir of the diesel exhaust fluid supply 160. A channel can extend from the port on the diesel exhaust fluid supply 160 to the liquid-only metering unit 150 to allow the liquid-only metering unit 150 to be in fluid communication with the fuel injector. The liquid-only metering unit 150 can also be in fluid communication with the fuel injector. When the liquid-only metering unit 150 is operating, it draws reducing agent from the diesel exhaust fluid supply 160 through the channel and transfers the reducing agent to the fuel injector. A return flow channel (not shown) can be provided for the return of excess reducing agent to the diesel exhaust liquid supply 160.According to some embodiments, the liquid-only dosing unit 150 is controlled by a controller.

[0020] With reference to Fig. Figure 2 shows a top-section cross-sectional view of an embodiment of a decommissioning reactor tube 140, which is connected to an injection nozzle 210 of a liquid-only metering unit 150. The injection nozzle 210 injects diesel exhaust liquid into the exhaust stream at the centerline of the decommissioning reactor tube 140. Fig. Figure 2 shows the injection nozzle 210 injected into the decomposition reactor tube 140 in the same direction as the exhaust gas flow through it. This centerline injection of the diesel exhaust gas provides greater uniformity across the selective catalytic reduction catalyst, for example, by requiring fewer additional components for mixing the reducing agent with the exhaust gas. Thus, fewer flow mixing components are needed to mix the diesel exhaust gas with the exhaust gas, as centerline injection allows mixing without the use of additional structures.

[0021] Fig. Figure 2 further describes a "knife-edge" diesel exhaust fluid injector mounting 220, designed for mounting the injector nozzle 210 of the liquid-only metering unit 150 in the center of the decommissioning reactor tube 140. It should be noted that the term "knife-edge," as used herein, should be interpreted broadly. For example, "knife-edge" may refer to an elongated, pointed structure similar to an edge on the sharp end of a knife. However, this term should be interpreted in a manner readily understood by someone skilled in the art. The knife-edge diesel exhaust fluid injector mounting 220 facilitates the alignment of the injector nozzle 210 to enable it to inject diesel exhaust fluid in close proximity to the centerline of the decommissioning reactor tube 140.The impact of the diesel exhaust fluid on the walls of the decommissioning reactor tube 140 is minimized by the torque of the exhaust gas traversing the decommissioning reactor tube 140. In some embodiments, the knife-edge diesel exhaust fluid injector assembly 220 is designed to fit into a standard exhaust pipe (e.g., 5 to 6 inches in diameter, cylindrical). The knife-edge diesel exhaust fluid injector assembly 220 is attached to an inner surface of the exhaust pipe (e.g., the decommissioning reactor tube 140) and is directly exposed to the exhaust gas flow passing through the exhaust pipe to which the knife-edge diesel exhaust fluid injector assembly 220 is attached.The arrangement of the knife-edge diesel exhaust fluid injector assembly 220 within the decommissioning reactor tube 140 also provides insulation for the injector 210 of the liquid-only metering unit 150, which is attached to the knife-edge diesel exhaust fluid injector assembly 220. The knife-edge diesel exhaust fluid injector assembly 220 is sealed to prevent the escape of exhaust gases. In some embodiments, one or more edges of the knife-edge diesel exhaust fluid injector assembly 220 are tapered into a structure similar to the tip of a knife (hereinafter referred to as the knife edge). For example, the leading edge of the knife-edge diesel exhaust fluid injector assembly 220, which is exposed to the exhaust gas flow, is a knife edge in some embodiments.The pointed knife edge(s) of the knife-edge diesel exhaust fluid injector mounting 220 minimize the deflection of exhaust flow lines and pressure drop in the decommissioning reactor tube 140. In other embodiments, a trailing edge of the knife-edge diesel exhaust fluid injector mounting 220 is also designed similarly to the tip of a knife (i.e., as a knife edge). The trailing edge of the knife-edge diesel exhaust fluid injector mounting 220 is designed to enable a uniform exhaust flow transition along the decommissioning reactor tube 140.

[0022] The knife-edge shapes of the leading and / or trailing edges, together with a converging geometry of the dismantling reactor tube 140, also prevent backflow zones within various areas of the dismantling reactor tube 140. For example, the knife edges prevent backflow zones near the tip of the injection nozzle 210, which is exposed within the dismantling reactor tube 140. The dismantling reactor tube 140 and the knife-edge diesel exhaust fluid injection nozzle mounting 220 are designed with connections for routing various lines, as required. For example, the dismantling reactor tube 140 and the knife-edge diesel exhaust fluid injection nozzle mounting 220 are designed to accommodate the diesel exhaust fluid line 240, which serves as a channel for transferring diesel exhaust fluid between the injection nozzle 210 and the diesel exhaust fluid supply 160.In embodiments where electrical lines 230 are used for communication with components such as a control unit, the decomposition reactor tube 140 and / or the knife-edge diesel exhaust fluid injection nozzle assembly 220 are designed to enable suitable communication via the electrical lines 230. Thus, in some embodiments, the decomposition reactor tube 140 and / or the knife-edge diesel exhaust fluid injection nozzle assembly 220 have connections that accommodate the electrical lines 230 to facilitate the aforementioned communication. In some embodiments, wireless communication methods can be used in the liquid-only metering unit 150 to inject diesel exhaust fluid into the exhaust stream.Additionally, the decommissioning reactor tube 140 and / or the knife-edge diesel exhaust fluid injector mounting 220 may include connections for one or more coolant lines for the system.

[0023] Fig. 3 and Fig. Figure 4 shows different views of the decommissioning reactor tube 140 from Fig. 2. In Fig. Figure 3 is a front view of the decommissioning reactor tube of Fig. Figure 2 shows the knife-edge diesel exhaust fluid injection nozzle assembly 220, which is located at the center of the decommissioning reactor tube 140 to facilitate centerline injection of diesel exhaust fluid into the decommissioning reactor tube 140 by means of an injection nozzle 210. The diesel exhaust fluid line 240 is shown between the decommissioning reactor tube 140 and the diesel exhaust fluid supply 160. An electrical line 230 is shown attached to the knife-edge diesel exhaust fluid injection nozzle assembly 220, although wireless communication technology can be used in the system. Fig. Figure 4 shows a side cross-sectional view of the decommissioning reactor tube 140. Fig. 2 and Fig. 3. The injector nozzle 210 is shown attached to the knife-edge diesel exhaust fluid injector assembly 220, which protrudes inside the cavity of the decommissioning reactor tube 140 to allow the injector nozzle 210 to inject diesel exhaust fluid near the centerline of the decommissioning reactor tube 140. The diesel exhaust fluid line 240 and the electrical lines 230 are also shown connected to the injector nozzle 210.

[0024] Fig. Figure 5 is a cross-sectional view of a converging decomposition reactor tube 510 with centerline injection of diesel exhaust fluid according to one embodiment. The converging decomposition reactor tube 510 comprises a geometric structure with converging sides of the tube, i.e., the decomposition reactor tube 510 has a converging geometry towards one end. Since the converging decomposition reactor tube 510 extends from the center of the tube towards both ends of the tube, the radial spacing around the tube converges from a larger to a smaller distance. The converging decomposition reactor tube 510 has an inlet 520 and an outlet 530. Exhaust gas from engine 110 enters the inlet 520 of the converging decomposition reactor tube 510 and traverses the entire length of the converging decomposition reactor tube 510. The exhaust gas exits the converging decomposition reactor tube 510 through the outlet 530.The converging decomposition reactor tube 510 converges towards the inlet 520 and outlet 530. The geometric structure of the converging decomposition reactor tube 510 allows for the centerline addition of diesel exhaust fluid into the converging decomposition reactor tube 510. The converging decomposition reactor tube 510 further enables the mixing of the diesel exhaust fluid with the exhaust gas due to the torque and movement of the exhaust gas through the converging decomposition reactor tube 510.

[0025] As in Fig. As shown in Figure 5, the geometric shape of the converging walls of the converging decomposition reactor tube 510 further facilitates the simplified routing of the diesel exhaust liquid line 240, electrical lines 230, coolant lines, etc. According to some embodiments, the converging decomposition reactor tube 510 utilizes the knife-edge diesel exhaust liquid injection nozzle attachment 220 described above to allow the liquid-only metering unit 150 to inject diesel exhaust liquid into a centerline of the exhaust stream within the converging decomposition reactor tube 510. Fig. Figure 5 shows the knife-edge diesel exhaust fluid injector mount 220 such that a trailing edge and a leading edge each have a knife-tip shape. The leading edge of the knife-edge diesel exhaust fluid injector mount 220 points in the direction of the incoming exhaust flow and minimizes backflow zones. The leading edge of the knife-edge diesel exhaust fluid injector mount 220 minimizes the deflection of exhaust flow lines and minimizes the pressure drop in exhaust pipes. The trailing edge points in the same direction as the incoming exhaust flow and is designed to allow a smooth exhaust flow transition anywhere in the converging decomposition reactor tube 510. The trailing edge further prevents backflow zones near the injector tip, minimizes the deflection of exhaust flows, and minimizes the pressure drop in the exhaust pipe (e.g., in the decomposition reactor tube 140 and in the converging decomposition reactor tube 510).The knife-edge diesel exhaust fluid injector mounting 220 from . Fig. 5 is completely sealed to prevent the escape of exhaust gases from the converging decomposition reactor tube 510.

[0026] In Fig. 6 and Fig. 7 are different views of the converging decomposition reactor tube 510 from Fig. 5 shown. Fig. Figure 6 is a front view of the converging decomposition reactor tube 510 of Fig. Figure 5 shows the injection nozzle 210 injecting diesel exhaust fluid at the center line 610 of the converging decomposition reactor tube 510. The diesel exhaust fluid line 240 is shown between the decomposition reactor tube 140 and the diesel exhaust fluid supply 160. An electrical line 230 is also shown connected to the knife-edge diesel exhaust fluid injection nozzle mounting 220. Fig. Figure 7 is a side view of the converging decomposition reactor tube 510 of Fig.Figure 5 shows the following. As described above, exhaust gas enters the converging decomposition reactor tube 510 through the inlet 520 and exits the converging decomposition reactor tube 510 through the outlet 530. The diesel exhaust liquid line 240 and the electrical line 230 are also shown as being communicatively coupled to the converging decomposition reactor tube 510.

[0027] The preceding description of the embodiments of the disclosure has been presented for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the invention to the form exactly disclosed, as modifications and variants are possible in light of the foregoing teachings or can be acquired through implementation of the invention. The embodiments have been chosen and described to explain the principles of the invention and its practical application, and to enable the person skilled in the art to use the disclosure in different embodiments and with different modifications as appropriate for the intended use. Further substitutions, modifications, changes, and omissions to the operating conditions of the disclosure and the arrangement of the various embodiments may be made without departing from the scope of the present invention.When reading the claims, the use of words such as "a," "at least a," or "at least a part" does not imply an intention to limit the claim to only one element, unless the claim specifically states otherwise. The use of the phrase "at least a part" and / or "a part" means that the element may comprise a part and / or the entire element, unless the claim specifically states otherwise.

Claims

[1] Post-treatment system, comprising: an aftertreatment component (170) designed to treat exhaust gas exiting from an engine (110); a reactor tube (140, 510) arranged upstream of the aftertreatment component, wherein the reactor tube is designed to receive the exhaust gas from the engine; a liquid-only metering unit (150) for injecting diesel exhaust fluid into the exhaust gas received by the engine, wherein the liquid-only metering unit injects the diesel exhaust fluid at a center line (610) of the reactor tube to provide a uniform dispersion of the diesel exhaust fluid over at least a part of the aftertreatment component; and a knife-edge fastening (220) designed for fastening the liquid-only dosing unit inside the reactor tube, the knife-edge fastening comprising: a leading edge comprising a knife-edge structure, wherein the leading edge points towards an incoming exhaust gas stream, and a trailing edge comprising a knife-edge structure, with the trailing edge pointing away from the exhaust flow. [2] Post-treatment system according to claim 1, wherein: the reactor tube (140, 510) has a converging geometry towards at least one end of the reactor tube; and The knife-edge structure and the converging geometry of the reactor tube provide insulation from the exhaust gases to protect the liquid-only dosing unit (150). [3] Post-treatment system according to claim 1, wherein: the reactor tube (140, 510) has a converging geometry towards at least one end of the reactor tube; and The knife-edge structure and the converging geometry of the reactor tube serve to minimize pressure drop and backflow zones of the exhaust gas. [4] Post-treatment system according to any one of claims 1 to 3, wherein the reactor tube (140, 510) comprises a plurality of converging walls designed to converge towards at least one end of the reactor tube. [5] Post-treatment system according to one of claims 1 to 4, wherein the knife edge attachment (220) is completely sealed to prevent the escape of exhaust gases from the reactor tube (140, 510). [6] Post-treatment system according to any one of claims 1 to 5, wherein the reactor tube (140, 510) comprises one or more connections configured to accommodate one or more coolant lines, electrical lines (230) and reducing agent supply lines (240). [7] Aftertreatment system according to one of claims 1 to 6, wherein the torque of the exhaust gas through the reactor tube (140, 510) requires the mixing of the diesel exhaust liquid injected at the center line (610) of the reactor tube. [8] Centerline injection system for injecting diesel exhaust fluid into exhaust gas exiting an engine (110), the centerline injection system comprising: a reactor tube (140, 510) arranged upstream of an aftertreatment component (170) designed to treat the exhaust gas exiting the engine, wherein the reactor tube is designed to receive the exhaust gas from the engine; a liquid-only metering unit (150) designed to inject diesel exhaust fluid into the exhaust gas, wherein the liquid-only metering unit injects the diesel exhaust fluid at a centerline (610) of the reactor tube to provide a uniform dispersion of the diesel exhaust fluid over at least a portion of the aftertreatment component; and a knife-edge fastening (220) designed for fastening the liquid-only metering unit inside the reactor tube, wherein the knife-edge fastening has a trailing edge and a leading edge each with a knife-edge structure to minimize backflow zones and exhaust gas deflections, wherein the trailing edge points away from the exhaust gas stream and the leading edge points towards the incoming exhaust gas stream. [9] Centerline injection system according to claim 8, wherein the reactor tube (140, 510) comprises a plurality of converging walls designed to converge towards one or more ends of the reactor tube. [10] Centerline injection system according to claim 8 or 9, wherein the knife edge attachment (220) is completely sealed to prevent the exhaust gases from escaping from the reactor tube (140, 510). [11] Centerline injection system according to one of claims 8 to 10, wherein the reactor tube (140, 510) and the knife edge attachment (220) comprise one or more connections configured to accommodate one or more coolant lines, electrical lines (230) and reducing agent supply lines (240).

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