SCR Ammonia Slip Detection via NOx Sensor Feedback Control
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Solution Overview
Problem
Existing methods for determining ammonia slippage in SCR systems for internal combustion engines are either slow to adapt or have low efficiency in achieving the stoichiometric addition of ammonia, leading to inefficiencies in nitrogen oxide reduction and ammonia usage.
Innovation Solution
A method involving an SCR catalyst, an ammonia addition point upstream of the catalytic converter, and nitrogen oxide sensors to regulate the amount of ammonia added, using an integrating control component to detect and correct deviations, with threshold values to prevent ammonia slip, and optionally utilizing a storage catalytic converter to optimize ammonia storage and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If more ammonia is added to achieve higher nitrogen oxide conversion rate, then the conversion efficiency is improved, but ammonia slip increases causing odor nuisance
Solution Approach 1:
The patent employs a feedback control mechanism using a nitrogen oxide sensor downstream of the SCR catalyst to monitor exhaust gas composition. The control unit continuously adjusts the ammonia injection amount based on the measured nitrogen oxide levels, ensuring optimal conversion while preventing excessive ammonia addition that would cause slip and odor nuisance.
Solution Approach 2:
The system dynamically changes the ammonia injection parameter based on operating conditions such as exhaust temperature, load, and measured nitrogen oxide levels. By adapting the injection amount to current parameters, the system achieves high conversion efficiency without excessive ammonia that would lead to slip.
2Reliability
If existing control methods are used to regulate ammonia addition, then the system operates continuously, but the adaptation speed is slow and efficiency is low
Solution Approach 1:
The control unit uses real-time feedback from the nitrogen oxide sensor to rapidly adjust ammonia injection. This closed-loop control enables fast adaptation to changing operating conditions while maintaining continuous stable operation, overcoming the slowness of existing control methods.
Solution Approach 2:
The patent replaces slow mechanical or predetermined control mechanisms with an electronic control system that processes sensor signals and adjusts injection based on real-time measurements, significantly increasing adaptation speed while maintaining operational reliability.
3Productivity
If ammonia injection amount is increased to compensate for conversion losses, then more nitrogen oxides are converted, but the amount of ammonia leaving the SCR catalyst increases
Solution Approach 1:
The nitrogen oxide sensor provides feedback on the actual conversion performance, allowing the control unit to precisely adjust ammonia injection to match the exact amount needed for conversion. This prevents both under-injection (reducing conversion) and over-injection (causing ammonia slip and loss).
Solution Approach 2:
The system uses its own output (nitrogen oxide measurements from the sensor) to self-regulate the ammonia injection amount, automatically optimizing the balance between conversion efficiency and ammonia utilization without external intervention.
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 quickly and reliably detects and prevents ammonia slip, optimizing ammonia usage and nitrogen oxide reduction, even under varying temperature conditions, and ensures efficient operation of the SCR system.
Implementation Method 1
the so-called SCR process (selective catalytic reduction) has become established. For this purpose, an SCR catalytic converter is used, which has a coating that enables the reaction at relatively low temperatures. In selective catalytic reduction, the nitrogen oxide compounds are reacted with ammonia to form nitrogen and water.
Implementation Method 2
The urea-water solution is converted into ammonia and water thermally in the exhaust gas (thermolysis) and/or hydrolytically in a hydrolysis catalytic converter.
Implementation Method 3
The urea-water solution is converted into ammonia and water thermally in the exhaust gas (thermolysis) and/or hydrolytically in a hydrolysis catalytic converter.
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for determining the reducing agent slip of an exhaust gas treatment device (23), said method having at least the following steps: determining a difference (5) of the sensor signals (3, 4) of a second nitrogen oxide sensor (29) and of a device (41) for determining a nitrogen oxide quantity in the exhaust gas flow direction (31) upstream of the SCR catalytic converter (25); determining a control deviation (7) from the difference (5) and a target value (6) of the control element (2); determining a gradient (21) of the integrating control component (20); and establishing reducing agent slip if the control deviation (7) exceeds a first threshold value (9) and the gradient (21) exceeds a second threshold value (10). The method according to the invention and a correspondingly designed and equipped device allow the reliable establishment of a reducing agent slip and the use of a very fast control element.