SCR Aftertreatment Extremum Seeking Control for Ammonia Slip
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Solution Overview
Problem
SCR aftertreatment systems face challenges in controlling ammonia levels due to storage capacity and transient engine conditions, leading to inefficiencies and increased operating costs, particularly in mobile applications where ammonia sensors are unreliable and ammonia is undesirably emitted.
Innovation Solution
Implementing an extremum seeking algorithm with a reductant injector and NOx sensors positioned strategically across SCR catalysts to determine optimal reagent injection amounts, minimizing NOx emissions by operating at an offset ammonia-to-NOx ratio, and using an ammonia oxidation catalyst to manage ammonia slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If ammonia is injected into the exhaust stream to reduce NOx emissions, then NOx reduction efficiency is improved, but ammonia storage capacity and unexpected release complicate the control process
Solution Approach 1:
The patent implements a feedback control system that continuously monitors ammonia-to-NOx ratio (ANR) and adjusts reductant injection accordingly. The controller receives ANR information and modifies injection commands to maintain optimal operation, thereby managing the complexity introduced by ammonia storage capacity while preserving NOx reduction efficiency
Solution Approach 2:
The system dynamically changes operational parameters including ANR targets and reductant injection rates based on real-time conditions. By adjusting these parameters in response to storage capacity changes and operating conditions, the system resolves the contradiction between maintaining efficient NOx reduction and managing control complexity
2Measurement precision
If ammonia sensors are used to monitor ammonia levels, then ammonia concentration measurement is improved, but cross-sensitivity with NOx and unreliable detection increase measurement errors
Solution Approach 1:
The patent uses ammonia-to-NOx ratio (ANR) as an intermediary parameter instead of direct ammonia concentration measurement. By calculating ANR from NOx sensor data and injection rates, the system avoids the reliability issues of ammonia sensors while still achieving effective monitoring and control of ammonia levels
Solution Approach 2:
The system replaces physical ammonia sensing with a computational approach using NOx sensor data and injection rate information to determine ANR. This substitution eliminates cross-sensitivity problems and improves both measurement precision and reliability
3Loss of energy
If reductant injection rate is increased to ensure sufficient ammonia availability, then NOx reduction is improved, but ammonia slip and operating costs increase
Solution Approach 1:
The patent implements dynamic adjustment of reductant injection rate based on real-time ANR feedback and predicted future ANR values. Rather than using fixed injection rates, the system continuously adapts injection timing and quantity to match actual demand, improving NOx reduction while minimizing ammonia slip and associated costs
Solution Approach 2:
The system performs preliminary calculations of future ANR values based on current operating conditions and predicted engine behavior. By anticipating future ammonia needs, the controller can optimize injection timing and quantity in advance, ensuring sufficient ammonia availability for NOx reduction while avoiding excessive injection that would lead to ammonia slip
4Quantity of substance
If SCR catalyst ammonia storage capacity is utilized, then ammonia availability is improved, but unexpected ammonia release and early catalyst adsorption reduce control accuracy
Solution Approach 1:
The patent incorporates feedback from ANR measurements to detect and respond to unexpected ammonia release from catalyst storage. When ANR deviates from expected values, the controller adjusts injection commands to compensate, thereby maintaining control accuracy despite the presence of ammonia storage capacity
Solution Approach 2:
The system dynamically changes ANR targets and injection parameters in response to catalyst storage state and operating conditions. By adapting these parameters to account for ammonia storage and release behavior, the system maintains both ammonia availability and control accuracy
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 ammonia levels at the SCR catalyst outlet, minimizing reductant inefficiency, and maintaining low or zero ammonia concentration, thereby optimizing SCR system performance and reducing operating costs.
Implementation Method 1
injected particles of the reducing agent may need to evaporate into the exhaust stream, hydrolyze from urea to ammonia
Implementation Method 2
SCR systems include a reduction catalyst and a reducing agent
Implementation Method 3
using an ammonia oxidation catalyst to manage ammonia slip
Implementation Method 4
An injector provides the reducing agent to the exhaust stream
Data Source
AI summary
A method includes providing: a selective catalytic reduction (SCR) catalyst disposed in an exhaust gas stream of an internal combustion engine, a reagent injector operationally coupled to the exhaust gas stream at a position upstream of the SCR catalyst, and a NOx sensor coupled to the exhaust gas stream at a position downstream of at least a first portion of the SCR catalyst. The method includes operating an extremum seeking controller to determine a first reagent injection amount corresponding to a predetermined slope of δNOx/δANR, the δNOx/δANR determined according to the NOx sensor, providing a reagent injection command in response to the first reagent injection amount, and injecting an amount of the reagent in response to the reagent injection command.