US-12618348-B2 - Exhaust aftertreatment unit

Abstract

An exhaust aftertreatment unit for cleaning exhaust gases, the exhaust aftertreatment unit including a fluid channel for providing a fluid pathway for the exhaust gases, the fluid channel having an outer casing; a catalyst casing housing a selective catalyst reduction (SCR) catalyst and an ammonia slip catalyst (ASC) arranged downstream of the SCR catalyst, the catalyst casing being arranged inside the outer casing forming an intermediate space between the inner and outer casings; and a detector configured to measure ammonia and/or NOx in the exhaust gases; wherein the catalyst casing includes one or more perforations upstream of the ASC to enable a by-pass flow of exhaust gases from inside the catalyst casing into the intermediate space, and wherein the detector is arranged in the fluid channel to measure the ammonia and/or NOx in the exhaust gases including the by-pass flow.

Inventors

• Gert-Ove Wahlström
• Martin Petersson

Assignees

• VOLVO TRUCK CORPORATION

Dates

Publication Date

20260505

Application Date

20250325

Priority Date

20240402

Claims (20)

1. 1 . An exhaust aftertreatment unit for cleaning exhaust gases, the exhaust aftertreatment unit comprising: a fluid channel for providing a fluid pathway for the exhaust gases, the fluid channel comprising an outer casing, a catalyst casing housing a selective catalyst reduction (SCR) catalyst and an ammonia slip catalyst (ASC) arranged downstream of the SCR catalyst, the catalyst casing being arranged inside the outer casing forming an intermediate space between the inner and outer casings, and a detector configured to measure ammonia and/or NOx in the exhaust gases, wherein the catalyst casing comprises one or more perforations upstream of the ASC to enable a by-pass flow of exhaust gases from inside the catalyst casing into the intermediate space, and wherein the detector is arranged in the fluid channel to measure the ammonia and/or NOx in the exhaust gases including the by-pass flow.
2. 2 . The exhaust aftertreatment unit of claim 1 , wherein the detector is arranged in fluid communication with the intermediate space.
3. 3 . The exhaust aftertreatment unit of claim 1 , wherein the detector is arranged in the fluid channel parallel to, or downstream of, the ASC.
4. 4 . The exhaust aftertreatment unit of claim 1 , wherein the fluid channel further comprises an inlet portion for receiving the exhaust gases to the catalyst casing, and an outlet portion for discharging exhaust gases from the catalyst casing and the intermediate space, wherein the detector is arranged in the intermediate space or in the outlet portion.
5. 5 . The exhaust aftertreatment unit of claim 4 , wherein the intermediate space is in direct fluid communication with the outlet portion.
6. 6 . The exhaust aftertreatment unit of claim 4 , further comprising a separation wall arranged in the fluid channel between the outer casing and the catalyst casing, the separation wall being arranged upstream of the one or more perforations for preventing direct fluid communication between the inlet portion and the intermediate space.
7. 7 . The exhaust aftertreatment unit of claim 1 , wherein the catalyst casing comprises a catalyst casing inlet and a catalyst casing outlet arranged downstream of the catalyst casing inlet, and wherein the SCR catalyst and the ASC are arranged in between the catalyst casing inlet and catalyst casing outlet.
8. 8 . The exhaust aftertreatment unit of claim 1 , wherein the one or more perforations of the catalyst casing is arranged in between the SCR catalyst and the ASC.
9. 9 . The exhaust aftertreatment unit of claim 1 , wherein the SCR catalyst is physically divided into a SCR upstream part and a SCR downstream part, and wherein the one or more perforations of the catalyst casing is arranged in between the SCR upstream part and the SCR downstream part.
10. 10 . The exhaust aftertreatment unit of claim 1 , wherein the one or more perforations are a plurality of perforations distributed evenly along a circumference of the catalyst casing.
11. 11 . The exhaust aftertreatment unit of claim 1 , wherein the SCR catalyst and the ASC are comprised in a common catalyst substrate.
12. 12 . The exhaust aftertreatment unit of claim 1 , further comprising a borehole in the SCR catalyst, wherein the one or more perforations are aligned with the borehole.
13. 13 . The exhaust aftertreatment unit of claim 1 , further comprising an injector configured to inject a reductant upstream of the SCR catalyst.
14. 14 . The exhaust aftertreatment unit of claim 13 , further comprising a control unit configured to adjust the reductant injection rate of the injector in response to the measured ammonia and/or NOx by the detector.
15. 15 . The exhaust aftertreatment unit of claim 14 , wherein the control unit is configured to adjust the reductant injection rate of the injector to reduce the amount of ammonia reaching the ASC.
16. 16 . The exhaust aftertreatment unit of claim 1 , wherein the one or more perforations are designed with a variable opening to control the flow rate of the by-pass flow.
17. 17 . The exhaust aftertreatment unit of claim 1 , further comprising a particulate filter arranged upstream of the SCR catalyst.
18. 18 . The exhaust aftertreatment unit of claim 17 , wherein the SCR catalyst is a downstream SCR catalyst, and the exhaust aftertreatment unit further comprising an upstream SCR catalyst arranged upstream of the particulate filter.
19. 19 . The exhaust aftertreatment unit of claim 1 , wherein the outer casing comprises an inner wall facing the fluid pathway and the catalyst casing comprises an outer wall facing the inner wall of the outer casing, and wherein the intermediate space is arranged between the inner wall of the outer casing and the outer wall of the catalyst casing.
20. 20 . A vehicle comprising the exhaust aftertreatment unit of claim 1 .

Description

CROSS REFERENCE TO RELATED APPLICATION This application claims priority to European Patent Application No. 24168046.1, filed on Apr. 2, 2024, the disclosure and content of which is incorporated by reference herein in its entirety. TECHNICAL FIELD The disclosure relates generally to aftertreatment systems of a vehicle. In particular aspects, the disclosure relates to an exhaust aftertreatment unit. The disclosure can be applied to heavy-duty vehicles, such as trucks, buses, and construction equipment, among other vehicle types including marine vessels. Although the disclosure may be described with respect to a particular vehicle, the disclosure is not restricted to any particular vehicle. BACKGROUND Exhaust gases emitted by internal combustion engines contain various pollutants, including nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM). These pollutants have significant environmental impacts, contributing to air pollution, acid rain, and health issues in humans. Consequently, stringent regulations have been implemented worldwide to reduce these emissions, prompting the development of exhaust aftertreatment technologies. Among these technologies, selective catalyst reduction (SCR) systems have been widely adopted for NOx reduction in e.g., diesel engines. These systems use a reductant, typically urea-based Diesel Exhaust Fluid (DEF) or AdBlue, which is converted into ammonia (NH3) to catalytically reduce NOx into nitrogen (N2) and water (H2O). However, the efficiency of SCR systems depends significantly on the accurate measurement of exhaust gas properties, including NOx and NH3 concentrations, to optimize the injection of the reductant and maximize NOx reduction while minimizing ammonia slip. Existing exhaust aftertreatment units often face challenges related to the accurate measurement of gas properties, especially under varying engine loads and exhaust flow conditions. These challenges include low pressure differences over sampling channels used to measure gas properties for specific portions of the system, particularly at low engine speeds and loads, resulting in inadequate flow through the sampling channels. This can lead to inaccurate gas property measurements, affecting the ability of the system to make proper responsive actions. Furthermore, the physical integration of sensors and measurement devices of detectors within the exhaust system poses significant challenges. The limited space between components, such as between different types of catalytic converters, restricts the positioning of the detectors. Given these challenges, there exists a need for an improved exhaust aftertreatment unit that addresses at least some of the limitations of current systems. SUMMARY According to a first aspect of the disclosure, an exhaust aftertreatment unit for cleaning exhaust gases is provided. The exhaust aftertreatment unit comprises: a fluid channel for providing a fluid pathway for the exhaust gases, the fluid channel comprising an outer casing; a catalyst casing housing a selective catalyst reduction, SCR, catalyst and an ammonia slip catalyst, ASC, arranged downstream of the SCR catalyst, the catalyst casing being arranged inside the outer casing forming an intermediate space between the inner and outer casings; and a detector configured to measure ammonia and/or NOx in the exhaust gases, wherein the catalyst casing comprises one or more perforations upstream of the ASC to enable a by-pass flow of exhaust gases from inside the catalyst casing into the intermediate space, and wherein the detector is arranged in the fluid channel to measure the ammonia and/or NOx in the exhaust gases including the by-pass flow. The first aspect of the disclosure may seek to overcome problems with measurement accuracy and/or unwanted emissions and/or exhaust aftertreatment adaptability. For example, owing to the by-pass flow originating from the one or more perforations upstream of the ASC, early detection of potential emission issues can be achieved by measuring ammonia and/or NOx in the by-pass flow (or in the exhaust gas including the by-pass flow). In other words, as the content of the exhaust gases in the by-pass flow is based on conditions upstream of the ASC, the measurement of ammonia and/or NOx by the detector will reflect, at least in part, the conditions upstream of the ASC. For example, an early detection of ammonia, or of an undesirable high amount of ammonia, entering the ASC can be provided by the first aspect. As ammonia may be converted into N2O in the ASC, and as N2O is not easily detected downstream of the ASC, this type of emission could otherwise pass unnoticed. N2O is a stable molecule and a strong greenhouse gas. Moreover, the positioning of the detector may be less fixed, as long as the detector is arranged to measure ammonia and/or NOx in an exhaust stream including the by-pass flow. Hereby, the adaptability of the exhaust aftertreatment unit may be improved, e