SCR Catalytic Converter Ammonia Dosing Control
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Solution Overview
Problem
Existing methods for operating exhaust gas cleaning systems with SCR catalytic converters face challenges in accurately determining the addition rate of ammonia, leading to potential overdosing and increased NH3 slip, which affects nitrogen oxide conversion efficiency.
Innovation Solution
A method that calculates the ammonia level in the SCR catalytic converter using a computational model to achieve a target efficiency through either model-based filling level control or efficiency control, switching between these controls based on predetermined values such as ammonia storage capacity, exhaust gas temperature, and NOx mass flow, ensuring optimal NOx conversion without NH3 slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If model-based filling level control is used to achieve high NOx conversion efficiency, then nitrogen oxide conversion is improved, but parameter changes cause errors to accumulate over time leading to incorrect dosing
Solution Approach 1:
The patent implements a feedback mechanism where the actual NH3 fill level is periodically measured and compared with the modeled fill level. When deviations exceed a threshold, the dosing rate is corrected accordingly. This closed-loop feedback prevents error accumulation and maintains dosing accuracy despite parameter changes over time.
Solution Approach 2:
The system dynamically adjusts the dosing rate based on detected deviations between modeled and actual fill levels. By changing the dosing parameter in response to measured conditions, the system compensates for accumulated errors and maintains optimal NOx conversion efficiency.
2Productivity
If reducing agent addition rate is increased to improve NOx conversion, then nitrogen oxide removal is enhanced, but ammonia slip increases causing harmful emissions
Solution Approach 1:
The system uses feedback control to continuously monitor the actual NH3 fill level and adjust the dosing rate accordingly. By comparing measured values with target values, the system maintains the reducing agent addition rate within optimal ranges that maximize NOx conversion while preventing excessive NH3 slip.
Solution Approach 2:
The patent employs a two-stage dosing approach: first establishing a base dosing rate for optimal conversion, then applying corrective adjustments only when deviations are detected. This partial correction strategy ensures sufficient NOx removal while avoiding excessive ammonia addition that would cause harmful 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 achieves high NOx conversion efficiency across a wide operating range while minimizing NH3 slip, ensuring low NOx emissions and maintaining control accuracy.
Implementation Method 1
In the hot exhaust gas, NH3 is released by thermolysis and/or hydrolysis as the actual selective reducing agent
Implementation Method 2
In the hot exhaust gas, NH3 is released by thermolysis and/or hydrolysis as the actual selective reducing agent
Implementation Method 3
for the catalytically assisted removal of nitrogen oxides (NOx) from internal combustion engine exhaust gases
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method for operating an exhaust gas treatment system, comprising an SCR catalytic converter (5) for cleaning an exhaust gas of a motor vehicle internal combustion engine (1), wherein a metering unit (27) controllable by a control unit adds an ammonia-containing reducing agent to the exhaust gas at an adjustable metering rate, and an exhaust enriched with ammonia according to the metered addition is fed to the SCR catalytic converter (5). A computer model calculates an ammonia filling level value (F) for a filling level of ammonia stored in the SCR catalytic converter (5) and a model metering rate (D) for the metered addition of the reducing agent into the exhaust gas, at which a target filling level of ammonia stored in the SCR catalytic converter (5) specified by the computer model and/or a target efficiency (?) specified by the computer model for a nitrogen oxide conversion (UNOx) with ammonia stored in the SCR catalytic converter (5) and/or fed to the SCR catalytic converter (5) must be at least approximately achieved. According to the invention, either a model-based filling level regulation for achieving the target filling level or a model-based efficiency control for achieving the target efficiency (?) is performed according to predetermined values for certain operating variables such as a temperature of the exhaust gas or of the SCR catalytic converter (5).