Variable Cross-Section Switchback Mixer for SCR Systems
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Solution Overview
Problem
Conventional exhaust aftertreatment systems for IC engines face inefficiencies in mixing exhaust reductants with exhaust gases, leading to reduced catalytic conversion efficiency, increased backpressure, and deposits on system components, which affect fuel economy and operational costs.
Innovation Solution
The introduction of a body mixer with a housing featuring multiple passageways and partition walls that redirect the exhaust gas flow to increase residence time and facilitate efficient mixing of exhaust reductants with exhaust gases before they enter the selective catalytic reduction (SCR) system, reducing backpressure and deposits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional mixing arrangements are used, then device complexity is reduced, but mixing efficiency deteriorates leading to reduced catalytic conversion efficiency
Solution Approach 1:
The mixing body is segmented into multiple passageways (first, second, third passageways) with partition walls, creating a complex flow path that enhances mixing efficiency while maintaining manageable structural complexity through modular segmentation
Solution Approach 2:
The mixing body introduces a switchback arrangement that redirects exhaust gas flow in multiple directions (first direction toward second passageway, second direction opposite toward third passageway, third direction opposite toward SCR system), adding spatial dimensionality to the mixing process to improve contact between exhaust reductant and exhaust gas
2Loss of time
If exhaust gas flow is redirected through multiple passageways, then residence time increases improving mixing, but backpressure increases
Solution Approach 1:
The variable cross-sectional areas of the passageways dynamically adjust the flow characteristics, with larger cross-sections in later passageways compensating for pressure losses and maintaining adequate flow velocity throughout the extended residence time
Solution Approach 2:
The cross-sectional area parameter is varied along the flow path, with the third passageway having a larger cross-sectional area than the first passageway, which helps reduce backpressure while maintaining increased residence time for effective mixing
3Productivity
If exhaust reductant is injected into the system, then catalytic reduction of NOx and SOx is enabled, but deposits form on sidewalls and components
Solution Approach 1:
The mixing body performs preliminary mixing of exhaust reductant with exhaust gas before the mixture reaches the SCR catalyst, ensuring more complete reaction and reducing the formation of deposits on downstream components by pre-consumption of reactive species
Solution Approach 2:
The mixing body acts as an intermediary device between the exhaust reductant injection point and the SCR catalyst, facilitating controlled mixing and reaction that prevents direct contact of unreacted reductant with catalyst surfaces, thereby reducing deposit formation
4Use of energy by moving object
If mixing efficiency is improved through complex passageway arrangement, then fuel economy improves, but device complexity increases
Solution Approach 1:
The mixing body is divided into segmented passageways with partition walls that create efficient flow patterns, achieving improved fuel economy through better mixing while keeping the structural complexity manageable through systematic segmentation rather than monolithic complex design
Solution Approach 2:
The mixing body structure serves multiple functions simultaneously: it mixes exhaust reductant with exhaust gas, increases residence time, manages flow distribution, and reduces backpressure through its variable cross-section design, thereby achieving fuel economy improvements without proportionally increasing complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the mixing of exhaust reductants with exhaust gases, improving catalytic conversion efficiency, reducing backpressure, and minimizing deposits within the aftertreatment system, thereby improving fuel economy and reducing operational costs.
Implementation Method 1
The first passageway is structured to receive a flow of exhaust gas from the filter and direct the flow of the exhaust gas towards the second passageway. The second passageway is structured to redirect the flow in a second direction substantially opposite the first direction towards the third passageway.
Implementation Method 2
The body mixer is configured to mix the exhaust reductant with the exhaust gas as the exhaust gas flows through the first passageway, the second passageway, and the third passageway.
Data Source
AI summary
An aftertreatment system includes a filter configured to receive an exhaust gas and a selective catalytic reduction (SCR) system configured to treat the exhaust gas. A body mixer is disposed downstream of the filter and upstream of the SCR system. The body mixer includes a housing defining an internal volume and including at least a first passageway, a second passageway, and a third passageway. The first passageway receives a flow of the exhaust gas from the filter and directs the flow of the exhaust gas towards the second passageway. The second passageway redirects the flow in a second direction opposite the first direction towards the third passageway. The third passageway redirects the flow in a third direction opposite the second direction towards the SCR system. An injection port is disposed on a sidewall of the housing and configured to communicate an exhaust reductant into the internal volume.