SCR Mid-Bed Sensor Feedback Control for Ammonia Slip
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Solution Overview
Problem
Existing engine aftertreatment control systems, particularly selective catalytic reduction (SCR) systems, face limitations in controlling the ammonia to nitrogen oxides (NH3 to NOx) ratio and NOx amount between SCR catalyst portions, lacking the ability to set these parameters to a selectable level.
Innovation Solution
A method and system for controlling reductant injection in SCR catalyst engine aftertreatment systems using mid-bed NOx and ammonia (NH3) feedback, which includes a controller that determines a feedforward mid-bed NOx target and ammonia to NOx ratio (ANR) constraint, adjusting reductant injection based on real-time sensor data and system conditions to maintain optimal emissions control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional SCR control systems minimize NOx value between catalyst portions and control NH3 to a selected concentration, then emissions compliance is achieved, but the ability to control NH3 to NOx ratio and NOx amount to selectable levels is lost
Solution Approach 1:
The patent implements a feedback control system that uses mid-bed NH3 and NOx sensors to monitor catalyst performance in real-time. The controller adjusts reductant injection rates based on feedback from these sensors, enabling precise control of NH3 to NOx ratio and NOx amount at selectable levels while maintaining emissions compliance.
Solution Approach 2:
The SCR catalyst is divided into multiple portions with mid-bed sensing capabilities. This segmentation allows independent monitoring and control of different catalyst zones, providing versatility in controlling NH3 to NOx ratio and NOx amount at different locations within the catalyst bed.
2Adaptability or versatility
If mid-bed NH3 and NOx sensing is implemented for feedback control, then control precision and adaptability improve, but system complexity and cost increase
Solution Approach 1:
The mid-bed sensing system serves multiple functions: monitoring NH3 concentration, measuring NOx levels, detecting catalyst degradation, and providing feedback for control adjustments. This multi-functionality reduces the need for separate specialized systems, thereby limiting the increase in overall system complexity.
Solution Approach 2:
The system uses the existing exhaust stream and catalyst structure to provide mid-bed sensing opportunities. The control system leverages naturally occurring mid-bed conditions and existing sensor technologies, reducing the need for additional complex infrastructure or invasive modifications.
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 the NH3 to NOx ratio and NOx amount, reducing emissions and improving the robustness and responsiveness of the SCR system, while minimizing ammonia slip and NOx emissions.
Implementation Method 1
selective catalytic reduction (SCR) systems that divide the SCR catalyst portions into more than one catalyst element
Data Source
AI summary
A method includes determining a current mid-bed NH3 amount by operating an NH3 sensor positioned at a mid-bed location for an engine aftertreatment system having two SCR catalyst beds. The method further includes operating a NOx sensor positioned at the mid-bed location, and interpreting a current mid-bed ammonia to NOx ratio (ANR) and a current mid-bed NOx in response to the mid-bed NH3 amount and the operating the NOx sensor. The method further includes correcting an output value of the NOx sensor for cross-sensitivity to NH3. The method includes determining a mid-bed ANR constraint, determining a feedforward mid-bed NOx target, and providing a reductant injector command in response to the current mid-bed ANR, the current mid-bed NOx, the ANR constraint, and the feedforward mid-bed NOx target.