SCR Catalyst Control via NOx-Ammonia Signal Separation
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Solution Overview
Problem
Existing SCR catalyst control systems face challenges in accurately managing ammonia slip and NOx conversion efficiency due to cross-sensitivity of NOx sensors to ammonia, leading to incorrect dosing adjustments during transient engine conditions.
Innovation Solution
A closed-loop SCR catalyst control method using a model that differentiates between real NOx and ammonia components based on measured SCR-out NOx values, considering drift in NOx conversion efficiency and ammonia emission, allowing for precise adjustment of reductant supply to optimize NOx conversion efficiency while minimizing ammonia slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a post-SCR NOx sensor is used for closed-loop control, then NOx emission monitoring is improved, but measurement precision deteriorates due to cross-sensitivity to ammonia
Solution Approach 1:
The patent segments the sensor signal into two distinct components: a fast-varying component representing real NOx emissions and a slow-varying component representing ammonia slip. This is achieved through signal processing that separates the measured sensor output into these two parts based on their different temporal characteristics, allowing independent analysis and control of each component.
Solution Approach 2:
The patent applies dynamic filtering techniques to separate the static or slowly-varying ammonia signal from the dynamic NOx signal. By using dynamic signal processing methods, the system adapts to changing operating conditions while maintaining the ability to distinguish between the two gas components based on their different response times.
2Productivity
If excess urea is injected to maintain NOx conversion efficiency, then NOx conversion is improved, but ammonia slip increases
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the separated NOx and ammonia signals and adjusts the urea injection rate accordingly. The controller uses the real-time ammonia slip signal to reduce urea injection when slip is detected, while maintaining adequate injection levels to ensure NOx conversion efficiency, creating a self-regulating system that balances these two competing requirements.
Solution Approach 2:
The patent dynamically changes the urea injection parameter based on the separated sensor signals. By adjusting the injection rate as a variable parameter rather than using fixed dosing schedules, the system can optimize the balance between NOx conversion and ammonia slip control under different operating conditions.
3Productivity
If conventional SCR control is applied to passenger cars with frequent transient conditions, then NOx reduction is improved, but control accuracy deteriorates
Solution Approach 1:
The patent employs dynamic signal processing that adapts to transient operating conditions by exploiting the different temporal response characteristics of NOx and ammonia. During transient conditions, the fast-response NOx signal can be clearly distinguished from the slow-response ammonia signal, allowing accurate separation and control even when operating conditions change rapidly.
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 method effectively separates real NOx and ammonia signals from sensor data, enabling accurate reductant supply adjustments to achieve maximum NOx conversion efficiency with minimal ammonia slip, even under transient conditions.
Implementation Method 1
SCR catalysts remove nitrogen oxides (NOx), often the most abundant and polluting component in exhaust gases, through a chemical reaction between the exhaust gases, a reducing agent, and a catalyst
Implementation Method 2
an injection system is used to supply it into the exhaust gas stream entering the SCR catalyst where it decomposes into gaseous ammonia (NH3)
Data Source
AI summary
A method for controlling a selective catalytic reduction catalyst in an exhaust line of an internal combustion engine is disclosed, wherein the supply of a quantity of a gaseous ammonia reductant to the SCR catalyst uses a closed-loop SCR catalyst model coupled to a SCR-out NOx sensor that measures a SCR-out NOx emission value. The closed-loop SCR catalyst model uses a relationship linking the measured SCR-out NOx value to the NOx conversion efficiency and the ammonia slip. The actual NH3 emission value and/or an actual SCR-out NOx indicative value are computed based upon differentiation of said relationship.