SCR Catalyst NH3 Fill Level Model Correction
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Solution Overview
Problem
Current SCR systems face challenges in accurately determining the ammonia (NH3) fill level in the catalytic converter, leading to inefficient NOx conversion due to mechanical wear and imprecise urea dosing, resulting in ammonia slip and increased NOx emissions, especially at high temperatures.
Innovation Solution
Implementing a method to adjust the NH3 fill level model by briefly exceeding the slip limit of the SCR catalytic converter, using a second SCR or ASC catalytic converter to detect and absorb ammonia slip, and correcting the fill level model based on temperature and system aging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the SCR catalytic converter is dimensioned larger to improve NH3 storage capacity, then ammonia slip is reduced, but the exhaust system becomes more expensive and requires more installation space
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring ammonia slip concentrations and using this information to dynamically adjust the urea dosing rate. The control unit receives signals from sensors detecting ammonia slip and modifies the reducing agent injection quantity accordingly, creating a closed-loop control system that maintains optimal NH3 storage capacity without requiring oversized catalytic converters
Solution Approach 2:
The system dynamically changes the dosing parameter (urea injection rate) based on operating conditions, catalyst temperature, and detected ammonia slip levels. By adjusting the reducing agent quantity in real-time rather than using fixed dosing rates, the system optimizes NH3 storage capacity adaptively, eliminating the need for larger converter volume
2Object-affected harmful factors
If conservative NH3 target fill level values are used to prevent ammonia slip at high temperatures, then ammonia slip is reduced, but the NOx conversion efficiency drops when the calculated fill level is reduced
Solution Approach 1:
The control system uses feedback from ammonia slip sensors to dynamically adjust dosing strategies. When ammonia slip is detected, the system responds by modifying the reducing agent injection rate, allowing it to maintain high NOx conversion efficiency while preventing slip conditions, rather than operating conservatively at reduced efficiency
Solution Approach 2:
The system transitions from static, conservative target fill level values to dynamic adjustment of dosing parameters based on real-time operating conditions. The control unit adapts the reducing agent injection rate dynamically according to catalyst temperature, load conditions, and detected ammonia slip, optimizing both slip prevention and NOx conversion efficiency
3Productivity
If the dosing quantity of reducing agent is increased to maintain NH3 fill level, then NOx conversion is improved, but ammonia slip increases when the catalytic converter is overfilled
Solution Approach 1:
The system implements closed-loop feedback control where ammonia slip sensors continuously monitor exhaust gas composition and provide signals to the control unit. When ammonia slip is detected, the feedback mechanism automatically reduces the reducing agent dosing quantity, preventing overfilling while maintaining optimal NOx conversion efficiency
Solution Approach 2:
The system temporarily allows for partial over-dosing of reducing agent to maintain NH3 fill level during periods of high NOx emissions, but uses ammonia slip detection to trigger corrective reduction in dosing. This partial excessive action followed by correction optimizes NOx conversion while preventing sustained ammonia slip
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 optimal NOx conversion by preventing the fill level model from being outdated, allowing the SCR catalytic converter to operate at maximum efficiency, reducing ammonia slip, and minimizing NOx emissions, while also reducing the catalytic converter volume and exhaust gas backpressure.
Implementation Method 1
The chemical reaction at the SCR catalytic converter is selective, i. H. that preferred nitrogen oxides (NO, NO 2) are reduced, while undesirable side reactions with oxidation of sulfur dioxide to sulfur trioxide are largely suppressed. Ammonia (NH 3 ), which is added to the exhaust gas, is required for the selective catalytic reduction.
Implementation Method 2
A hydrolysis reaction produces ammonia and CO 2 from the urea water solution.
Implementation Method 3
In the event of an overdose of ammonia, this converts the NH 3 back into nitrogen and water.
Data Source
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AI summary
Method for operating an exhaust gas purification system (1) in an exhaust gas stream (2) for an internal combustion engine, wherein the exhaust gas purification system (1) comprises, in the flow direction of an exhaust gas from the internal combustion engine: a NOx sensor (3), an injection device (4) for introducing a reducing agent (e.g., a urea solution) into the exhaust gas stream (2), a temperature sensor (12), an SCR catalyst (5) (SCR = selective catalytic reduction), and an NH3 or NOx sensor (6), as well as a separate control unit (7) for evaluating and/or controlling at least one NOx sensor signal, a reducing agent sensor signal, and an exhaust gas temperature sensor signal, wherein the control unit (7) has an NH3 level model of the SCR catalyst (5) by measuring the exhaust gas temperature; - If a defined temperature, which is between 300°C and 400°C, preferably at 350°C, is exceeded: Increase the amount of reducing agent introduced until the NH3 orNOx sensor (6) detects NH3 slip; - Correction of the fill level model by overwriting the currently calculated NH3 fill level with the maximum fill level at the current temperature; - Reduction of the reducing agent injection quantity. The method according to the invention prevents unintentional emptying of reducing agent from the SCR catalyst. An NSC (9), DOC and/or DPF or CSF (10) can be arranged upstream of the SCR catalyst (5), and a second SCR catalyst (8) and/or an ASC can be arranged downstream of the SCR catalyst (5).