SCR Catalyst Virtual Brick Segmentation for Ammonia Slip Control
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Solution Overview
Problem
SCR catalysts in internal combustion engines face efficiency drops due to ammonia slip during transient operating conditions, particularly at high temperatures, which is not effectively managed by existing systems, risking non-compliance with Onboard Diagnostic guidelines.
Innovation Solution
The SCR catalyst is virtually subdivided into multiple bricks, with control strategies adjusting ammonia dosing based on target and actual fill levels, using temperature and enthalpy changes to manage ammonia distribution and minimize slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the SCR catalyst is installed close to the engine to convert nitrogen oxides early, then the NOx conversion efficiency is improved, but the catalyst is subjected to dynamic temperature gradients that increase ammonia desorption and ammonia slip
Solution Approach 1:
The SCR catalyst is virtually subdivided into multiple bricks (first brick, second brick, etc.) along the flow direction. This segmentation allows different control strategies to be applied to different regions of the catalyst, enabling the front region to receive targeted ammonia dosing while the rear region handles ammonia slip, thus resolving the contradiction between early NOx conversion and ammonia slip reduction
Solution Approach 2:
Different fill level control strategies are applied to different bricks of the SCR catalyst. The first brick operates with a target fill level optimized for NOx conversion under transient conditions, while subsequent bricks are controlled to manage ammonia slip. This local differentiation allows each region to perform its specific function optimally, addressing both the need for early conversion and the problem of ammonia slip
2Speed
If the temperature of the SCR catalyst increases due to engine load jump, then the reaction rate increases, but the ammonia storage capacity of the catalyst decreases leading to ammonia slip
Solution Approach 1:
The control system detects transient operating states (such as rapid load changes) and preemptively adjusts the ammonia dosing strategy before the temperature rise fully impacts ammonia storage capacity. By switching to a control strategy based on the first brick's target fill level during transients, the system prepares the catalyst to maintain optimal ammonia distribution, preventing ammonia slip before it occurs
Solution Approach 2:
The control strategy dynamically switches between different modes: under transient conditions, the system uses a control based on the first brick's target NH3 fill level to optimize ammonia distribution during rapid changes; under steady-state conditions, it transitions to a different control mode. This dynamic adaptation allows the system to maintain both high reaction rates and adequate ammonia storage capacity across varying operating conditions
3Object-generated harmful factors
If a second SCR catalyst is added downstream to adsorb ammonia slip, then ammonia slip is reduced, but the device complexity and monitoring requirements increase
Solution Approach 1:
Rather than adding a physically separate second catalyst, the system segments the single catalyst into multiple virtual bricks with different control strategies. The downstream region (second brick and beyond) is controlled to function similarly to a second catalyst by managing ammonia slip, thereby achieving the same effect without the complexity of an additional physical component
Solution Approach 2:
The single SCR catalyst is made multi-functional through virtual segmentation. The first brick primarily handles NOx conversion with optimized ammonia dosing, while the second brick and subsequent bricks handle both NOx conversion and ammonia slip management. This universal approach allows one physical catalyst to perform the functions of multiple catalysts, reducing 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 ensures high NOx conversion efficiency and reduces ammonia slip, maintaining compliance with diagnostic standards even under rapid load changes.
Implementation Method 1
The degree of coverage of the catalyst with adsorbed NH3 determines its efficiency
Implementation Method 2
Selective catalytic reduction (SCR) using ammonia (NH3) or ammonia-releasing reagents is a promising method for mitigating nitrogen oxides
Implementation Method 3
As the temperature of the filled SCR catalyst increases due to a load jump of the internal combustion engine, its ammonia storage capacity of the SCR catalyst decreases
Data Source
AI summary
A method for exhaust gas after-treatment of an internal combustion engine (10) having at least one SCR catalyst (22),wherein the at least one SCR catalyst (22) is subdivided into at least two virtual bricks,wherein, by means of a first control, a control of the at least one SCR catalyst (22) according to an overall NH3 target fill level (NH3ges) is carried out, wherein a switching from the first control into a second control for the at least one SCR catalyst (22) is carried out, wherein the second control of a NH3 fill level control is carried out based on a target NH3 fill level (mNH3CatSoll,SCR1B) of the first virtual brick of the at least one SCR catalyst (22).