SCR Reducing Agent Metering Control via NOx Sensor Feedback
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Solution Overview
Problem
Existing methods for metering ammonia-releasing reducing agents in internal combustion engines struggle to accurately adjust quantities due to dynamic operating conditions and sensor inertia, leading to inefficiencies in NOx conversion and potential ammonia slip.
Innovation Solution
A method that uses a control unit to adjust the metered quantity of reducing agents based on a stored model, incorporating multiple operating parameters and real-time sensor feedback from NOx sensors downstream of the SCR catalyst, allowing for continuous correction to maintain optimal NOx and NH3 levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pure open-loop control method is used to meter the reducing agent, then the device complexity is reduced, but the measurement precision of NOx conversion cannot be compensated for errors and environmental influences
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual NOx concentration downstream of the SCR catalyst using a NOx sensor and comparing it with the nominal value. The control unit adjusts the reducing agent metering quantity based on the deviation between actual and nominal measurements, enabling compensation for errors and environmental influences while maintaining acceptable system complexity.
2Measurement precision
If a standard closed-loop control circuit with continuous adjustment is used, then the measurement precision is improved, but the device complexity increases and the system cannot respond to highly dynamic processes due to sensor inertia
Solution Approach 1:
The patent applies dynamics by adapting the control strategy to the operating conditions. During highly dynamic processes, the system uses pre-stored correction values associated with different operating parameter classes rather than continuous adjustment. This allows the system to respond appropriately to dynamic changes while avoiding the limitations imposed by sensor inertia and excessive system complexity.
Solution Approach 2:
The patent implements preliminary action by pre-determining and storing correction values for various operating parameter classes before actual operation. When the engine operates in a particular class, the corresponding pre-stored correction value is applied, enabling rapid response without waiting for continuous sensor feedback during dynamic transitions.
3Adaptability or versatility
If the metered quantity is adjusted continuously to compensate for changing operating conditions, then the adaptability is improved, but the loss of time increases due to sensor inertia and system response delays
Solution Approach 1:
The patent applies preliminary action by pre-determining correction values for different operating parameter classes and storing them in advance. When the engine operates in a particular class, the corresponding pre-stored correction value is applied immediately, eliminating the time delay associated with real-time calculation and continuous adjustment during dynamic operating conditions.
Solution Approach 2:
The patent implements periodic action by periodically updating correction values based on operating parameter classes rather than continuous adjustment. This allows the system to adapt to changing conditions through discrete updates triggered by transitions between operating classes, reducing the time loss associated with continuous sensor feedback and system response delays.
4Device complexity
If a single correction value is used for all operating conditions, then the device complexity is reduced, but the adaptability to different operating parameter classes deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the operating space into multiple parameter classes based on operating conditions. Different correction values are stored and applied for each class, allowing the system to adapt to different operating conditions while maintaining relatively simple control logic. The segmentation enables selective application of appropriate correction values without requiring complex real-time calculations.
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 enables precise adjustment of reducing agent quantities, optimizing NOx conversion while minimizing ammonia slip and accommodating changes in operating conditions, thereby improving the efficiency and reliability of NOx reduction in internal combustion engines.
Implementation Method 1
selective catalytic reduction
Implementation Method 2
4NO+4NH3+O2→4N2+6H2O
Implementation Method 3
Urea decomposes at high temperatures into isocyanic acid and ammonia: (NH2)2CONH3+HNCO
Implementation Method 4
The isocyanic acid is hydrolyzed by water in the exhaust gas to NH3 and CO2: HNCO+H2O→NH3+CO2
Implementation Method 5
compares the change in the measured value of at least one NOx sensor installed downstream of the SCR catalyst
Data Source
AI summary
A method for application in conjunction with an exhaust gas post-treatment system for metering an ammonia-releasing reducing agent into the exhaust gas stream of an internal combustion engine installed in a motor vehicle and operated with excess air. A control unit meters the quantity of reducing agent as a function of a stored model and during the operation of the internal combustion engine varies the metered quantity during certain operating phases and compares the change in the measured value of at least one NOx sensor installed downstream of the SCR catalyst with an expected value.