SCR Ammonia Slip Control via Virtual Sensor
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Solution Overview
Problem
SCR systems face challenges in controlling ammonia slip due to cross-sensitivity of NOx sensors and ammonia storage capacity, leading to inefficiencies and increased operating costs, especially in mobile applications with varying engine load and speed profiles.
Innovation Solution
A method is introduced to control the SCR aftertreatment system by adjusting the deNOx efficiency target in response to detected ammonia slip conditions, reducing the reductant supply and incrementally increasing the target until slip correction conditions are met, without relying on ammonia sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a NOx sensor is used to monitor exhaust gas composition for SCR control, then feedback control capability is provided, but the sensor cross-sensitivity to ammonia complicates accurate NOx measurement and ammonia slip detection
Solution Approach 1:
The patent introduces an intermediary computational model that processes the cross-sensitive NOx sensor signal along with engine operating parameters to indirectly infer ammonia slip conditions. Instead of directly measuring ammonia, the system uses the NOx sensor output combined with a chemical reaction model of the SCR catalyst to detect ammonia slip, thereby resolving the contradiction between using the sensor for feedback control and avoiding its cross-sensitivity interference.
2Object-generated harmful factors
If the deNOx efficiency target is increased to improve NOx reduction performance, then NOx emissions are reduced, but ammonia slip increases and reductant utilization efficiency decreases
Solution Approach 1:
The patent implements a feedback control mechanism where the measured NOx sensor output is continuously compared against expected values based on engine operating conditions and SCR catalyst state. When deviations indicate ammonia slip, the system adjusts the reductant injection rate and deNOx efficiency target dynamically, creating a closed-loop control that balances NOx reduction with ammonia slip prevention and optimizes reductant utilization.
3Reliability
If an NH3 sensor is added to the control system to improve ammonia slip detection, then control capabilities are enhanced, but system cost increases
Solution Approach 1:
The patent creates a virtual copy or model of the ammonia sensing function by using computational methods that process existing sensor data (NOx sensor, temperature sensors, engine parameters) to infer ammonia slip conditions. This virtual sensor approach provides ammonia slip detection capability without the cost and complexity of installing physical ammonia sensors, thereby resolving the contradiction between detection accuracy and system complexity.
4Productivity
If reductant injection rate is increased to maintain target deNOx efficiency, then NOx conversion is improved, but ammonia slip increases under certain operating conditions
Solution Approach 1:
The patent implements dynamic adjustment of the deNOx efficiency target and reductant injection rate based on real-time detection of ammonia slip conditions and engine operating parameters. Instead of maintaining a fixed target efficiency, the system adaptively modifies control parameters to optimize NOx conversion while preventing ammonia slip, allowing the operating point to move dynamically along the efficiency-ammonia slip trade-off curve.
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 effectively reduces ammonia slip, improves control accuracy, and minimizes false fault indications, leading to more efficient reductant utilization and reduced operating costs.
Implementation Method 1
a selective catalytic reduction (SCR) catalyst disposed in the exhaust gas flow
Implementation Method 2
injected particles of the reductant may need to evaporate into the exhaust stream
Implementation Method 3
hydrolyze from urea to ammonia
Implementation Method 4
the reductant catalyst may include some ammonia storage capacity... by adsorbing some of the injected ammonia
Data Source
AI summary
An exhaust aftertreatment system includes a selective catalytic reduction (SCR) catalyst is disposed in an exhaust gas system of an internal combustion engine. A reductant injector is coupled to the exhaust gas stream at a position upstream of the SCR catalyst. A controller is configured to determine an NH3 slip condition and control operation of the exhaust aftertreatment system in response to the NH3 slip condition to improve deNOx efficiency and reduce NH3 slip.