SCR Catalyst Ammonia Storage Estimation for NOx Control
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Solution Overview
Problem
Current methods for controlling NOx and particulate emissions in combustion engines face challenges in accurately adjusting the quantity of reducing agents like ammonia, leading to difficulties in maintaining perfect emission control, especially under varying engine conditions and temperature fluctuations, which can result in malfunction detection issues.
Innovation Solution
A method for controlling the NOx reduction system by estimating the mass of reducing agent stored in the catalyst based on temperature, NO2/NO ratio, and injection rates, using maps and aging factors to optimize the conversion potential and ensure real-time detection of abnormal operations without false malfunctions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the quantity of reducing agent (ammonia) injected into the exhaust line is increased to improve NOx reduction efficiency, then the conversion of nitrogen oxides improves, but the risk of ammonia slip increases and the system may generate false malfunction alerts due to imperfect control
Solution Approach 1:
The system uses a NOx sensor disposed downstream of the NOx trap to provide feedback on the actual NOx conversion efficiency. This feedback signal is processed by a control unit that compares the actual efficiency with the estimated conversion potential, enabling real-time adjustment of the reducing agent injection quantity to maintain optimal operation and avoid ammonia slip while preventing false malfunction alerts.
Solution Approach 2:
The control system dynamically adjusts the injection quantity of the reducing agent based on changing operating parameters such as exhaust gas temperature, engine load, and NOx concentration. By continuously adapting the injection parameters to current operating conditions, the system optimizes the balance between NOx reduction efficiency and ammonia slip prevention.
2Productivity
If the exhaust gas temperature is increased to improve the kinetics of the SCR reaction, then the reduction reaction efficiency improves, but the ability of the catalyst to store ammonia decreases due to competing desorption reaction
Solution Approach 1:
The system dynamically adapts the reducing agent injection strategy to the current exhaust gas temperature. At lower temperatures where ammonia storage capacity is high, the system reduces injection to prevent ammonia slip. At higher temperatures where reaction kinetics are improved, the system increases injection to maximize conversion, while accounting for the reduced storage capacity. This dynamic adjustment optimizes both reaction efficiency and ammonia utilization across varying thermal conditions.
3Measurement precision
If the quantity of urea injected is precisely adjusted to match the quantity of nitrogen oxides to be treated, then emission control precision improves, but the system complexity increases due to the need for accurate estimation and control mechanisms
Solution Approach 1:
The control system uses readily available sensor data (NOx sensor, temperature sensors) and engine operating parameters to autonomously estimate the ammonia storage capacity and conversion potential of the SCR catalyst. The system self-adjusts the reducing agent injection quantity based on these estimations without requiring complex external control mechanisms, achieving precise emission control through intelligent use of existing system components.
4Reliability
If a NOx sensor is used for closed-loop control to improve emission accuracy, then the conversion efficiency control improves, but the system fails to account for transient operating conditions where the sensor may not provide reliable data
Solution Approach 1:
The control system performs preliminary estimation of the ammonia storage capacity and conversion potential using engine operating parameters and temperature data before relying on NOx sensor feedback. This preliminary action allows the system to anticipate the SCR catalyst's behavior under transient conditions and pre-adjust the reducing agent injection strategy, ensuring reliable emission control even when NOx sensor data may be unreliable or delayed during rapid transients.
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 allows for precise control of NOx emissions, reducing the risk of false malfunction alerts and ensuring compliance with emission standards by optimizing the ammonia storage and injection in the SCR system, even under transient engine conditions.
Implementation Method 1
The ammonia reacts with the NOx on a catalyst to form inert nitrogen N2 and water H2O
Implementation Method 2
The SCR catalyst then serves to promote the reduction of NOx by NH3
Implementation Method 3
The mass of reducing agent stored in the catalyst complies with a given storage setpoint
Implementation Method 4
ammonia being obtained by thermolysis/hydrolysis of urea in the exhaust line according to the following reactions: (NH2)2CO → HNCO + NH3: thermolysis at 120°C
Implementation Method 5
HNCO + H2O → CO2 + NH3: hydrolysis at 180°C
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to a method for controlling a system for treating NOx in an exhaust line of an internal combustion engine, said system comprising means for introducing a reducing agent into the exhaust line upstream of an NOx reduction catalyst. The invention is characterised in that it consists in estimating the efficiency of the treatment in relation to a maximum conversion potential obtained if the ratio between the quantity of injected reducer and the quantity of NOx in the gas complies with a given set value and if the mass of reducing agent stored in the catalyst complies with a given storage set value.