SCR Ammonia Slip Control Using Single-Sensor Feedback
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Solution Overview
Problem
Existing SCR systems face challenges in accurately controlling ammonia levels to achieve maximum NOx conversion efficiency while minimizing ammonia slip, requiring complex sensor setups and significant processing power.
Innovation Solution
A method and system that utilize a single ammonia sensor to control urea dosing through a feedback loop with a transfer function model, estimating ammonia slip based on target values, actual measurements, and open loop control inputs, optimizing NOx conversion efficiency and reducing ammonia emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ammonia sensors are used to control urea dosing in SCR systems, then ammonia slip control is improved, but device complexity increases due to additional sensors and processing requirements
Solution Approach 1:
The patent implements a feedback control system where ammonia sensor measurements are continuously compared against target ammonia slip values, and the urea dosing rate is adjusted based on the deviation. This closed-loop feedback mechanism enables precise ammonia slip control while using a single ammonia sensor, resolving the contradiction by achieving high measurement precision without proportionally increasing device complexity.
Solution Approach 2:
The patent introduces a transfer function model as an intermediary that translates ammonia sensor readings into appropriate urea dosing commands. This mediator processes the sensor information and generates control signals, simplifying the overall system architecture while maintaining accurate ammonia slip control, thus resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If complex sensor setups and processing algorithms are used to control ammonia levels, then ammonia slip control accuracy is improved, but processing power requirements increase
Solution Approach 1:
The feedback control algorithm continuously adjusts urea dosing based on ammonia sensor readings, achieving accurate ammonia level control through iterative correction rather than complex open-loop calculations. This approach maintains high control accuracy while using computationally efficient algorithms, resolving the contradiction between measurement precision and processing power requirements.
Solution Approach 2:
The patent employs a transfer function model that dynamically adjusts control parameters based on operating conditions such as exhaust flow rate and catalyst temperature. By adapting parameters rather than using fixed complex algorithms, the system achieves accurate ammonia control with computationally efficient calculations, resolving the contradiction between control accuracy and processing power consumption.
3Measurement precision
If multiple sensors are used to fully characterize exhaust gas composition, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the single ammonia sensor perform multiple functions: measuring ammonia slip for control purposes, providing feedback for the transfer function model, and enabling adjustment of urea dosing. This multi-functional use of a single sensor achieves effective exhaust gas characterization without requiring multiple specialized sensors, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The transfer function model acts as an intermediary that infers complete exhaust gas composition information from the single ammonia sensor reading, combined with other available engine parameters. This mediator compensates for the limited sensor input by using mathematical relationships to derive comprehensive exhaust characterization, resolving the contradiction between measurement precision and sensor quantity.
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 maintains optimal ammonia levels in SCR catalysts, enhancing NOx conversion efficiency and minimizing ammonia slip with reduced sensor requirements and processing power, compatible with both steady-state and transient operations.
Implementation Method 1
Selective Catalytic Reduction (SCR) systems... SCR catalysts require closed loop control... NOx sensors are widely used to perform this closed loop control
Data Source
AI summary
A system of controlling ammonia levels in a catalytic exhaust system comprising:means to provide a target value for ammonia slip/ammonia output from said system or a catalytic unit of said system; first comparison means to compare said target value with a feedback value to provide a command value based on said comparison, and means to control the dosing of a reducing agent such as urea into said exhaust system based on said command value;means to input said command value to a transfer function or model to provide an estimated value of ammonia slip/ammonia output from said catalytic unit/system; means to measure actual ammonia slip/ammonia output from said unit/system; second comparison means to compare said actual value with said estimated value; means to provide said feedback value based on the output from said comparison means.