Dual SCR Region Emission Control for NOx Conversion and Slip Reduction
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Solution Overview
Problem
Selective catalytic reduction (SCR) systems face a trade-off between NOx conversion efficiency and reductant slip, where high NOx conversion efficiency can lead to reductant storage on the catalyst, increasing the risk of reductant slipping through the exhaust tailpipe, while lower reductant injection decreases NOx conversion efficiency and allows NOx emissions.
Innovation Solution
Implementing multiple SCR regions in series, with reductant delivery adjusted based on the conditions of each region to optimize NOx conversion efficiency and reduce reductant slip, including monitoring storage capacity and temperature to select appropriate operating modes and using an oxidation catalyst to capture and convert slipped reductant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large amount of reductant is injected, then NOx conversion efficiency is improved, but reductant slip increases
Solution Approach 1:
The SCR catalyst is divided into multiple regions (first SCR region and second SCR region) with different functions. The first region operates at higher temperature for rapid NOx conversion, while the second region operates at lower temperature for reductant storage and conversion of slipped reductant. This segmentation allows the system to achieve high NOx conversion efficiency while minimizing reductant slip by distributing the conversion function across multiple specialized zones.
2Object-generated harmful factors
If a lesser amount of reductant is injected, then reductant slip is reduced, but NOx conversion efficiency decreases
Solution Approach 1:
The system performs preliminary action by injecting reductant upstream of the first SCR region where it can be rapidly converted to ammonia at high temperature. This preliminary conversion prevents reductant from reaching the tailpipe while the converted ammonia then flows to the second SCR region for further NOx conversion. This two-stage approach ensures complete NOx conversion while minimizing reductant slip.
3Manufacturing precision
If multiple SCR regions are used with independent control, then performance is improved, but device complexity increases
Solution Approach 1:
The control functions for multiple SCR regions are merged into a single unified control system. Instead of independently controlling reductant delivery to each SCR region, the system uses one reductant injector upstream of the first SCR region and a single controller that manages both regions based on their respective conditions (temperature, storage capacity). This merging approach maintains the performance benefits of multiple regions while significantly reducing control system 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 approach maintains high NOx conversion efficiency while minimizing reductant slip across a wider range of operating conditions without requiring independent control of reductant delivery to each SCR region, effectively balancing storage and conversion efficiency.
Implementation Method 1
Selective catalytic reduction (SCR) systems may be used in a vehicle to facilitate reduction of engine output NOx by a reductant, such as urea or ammonia
Implementation Method 2
using an oxidation catalyst to capture and convert slipped reductant
Implementation Method 3
a great amount of reductant may be stored on an SCR catalyst
Data Source
AI summary
Methods and systems for controlling an emission control system of a vehicle having a first SCR region upstream of a second SCR region are provided herein. One exemplary method includes, in a first mode: adjusting an amount of reductant injected upstream of a first SCR region based on a condition of the first SCR region. The method may also include, in a second mode: adjusting the amount of reductant injected upstream of the first SCR region based on a condition of the second SCR region.