SCR Reducing Agent Control via Cross-Sensitive NOx Sensor
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Solution Overview
Problem
Existing SCR systems face challenges in accurately dosing reducing agents due to ammonia slip, where increased ammonia can lead to increased NOx emissions downstream, making it difficult to determine whether to increase or decrease the reducing agent injection rate based on NOx measurements alone.
Innovation Solution
A method and system that utilize a NOx sensor cross-sensitive to NH3 to measure the combined concentration of NOx and NH3 downstream from the SCR elements, allowing for comparison with predetermined limit values to adjust reducing agent feeding, thereby detecting and addressing overdosing effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reducing agent injection rate is increased to reduce NOx emissions, then NOx reduction effectiveness improves, but ammonia slip increases leading to higher NOx concentration downstream
Solution Approach 1:
The system uses a NOx sensor cross-sensitive to NH3 positioned downstream from the SCR element to provide feedback on both NOx reduction effectiveness and ammonia slip. The control unit adjusts the reducing agent injection rate based on this combined signal, creating a closed-loop control system that balances NOx reduction with ammonia slip prevention.
Solution Approach 2:
The patent employs a NOx sensor that is cross-sensitive to NH3 as an intermediary measurement device. This sensor acts as a mediator that provides information about both NOx concentration and ammonia slip simultaneously, eliminating the need for separate sensors and enabling the control system to distinguish between actual NOx emissions and ammonia conversion effects.
2Ease of operation
If a simple NOx measurement is used to control reducing agent dosing, then the system is simple to operate, but it becomes difficult to determine whether to increase or decrease injection rate due to ammonia conversion
Solution Approach 1:
The system changes the measurement parameter by using a NOx sensor that is cross-sensitive to NH3 instead of a standard NOx sensor. This parameter change allows the sensor to detect both NOx and ammonia signals, providing the control system with additional information needed to make accurate dosing decisions without increasing system complexity.
3Productivity
If ammonia slip is allowed to increase, then reducing agent can be used more efficiently for NOx reduction, but excessive ammonia flows through the catalytic converter without reacting
Solution Approach 1:
The downstream NOx sensor provides continuous feedback on ammonia slip levels. When the sensor detects excessive ammonia in the exhaust stream, the control unit reduces the reducing agent injection rate to prevent further ammonia accumulation, thereby maintaining optimal reducing agent efficiency while preventing waste.
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 enables reliable and quick detection of overdosing, reducing the complexity of NOx measurement and ammonia slip issues, allowing for precise control of reducing agent injection to optimize NOx reduction without excessive ammonia conversion.
Implementation Method 1
one or more SCR elements for selective catalytic reduction
Implementation Method 2
an oxidation catalyst, which converts carbon monoxide (CO) and hydrocarbons to carbon dioxide and water
Implementation Method 3
a NOx sensor that is cross-sensitive to NH3 for determining the combined concentration of NH3 and NOx
Data Source
Figure 1~4
Figure 5
AI summary
The method of controlling reducing agent feeding into an exhaust system of an internal combustion engine (1) comprises the steps of determining a first concentration (NOx) on the downstream side of SCR elements (11) (101), determining a second concentration (NH3 or NH3+NOx) in the same location (102), comparing the first concentration to a first predetermined limit value (103), comparing the second concentration to a second predetermined limit value (104), and decreasing the reducing agent feeding in case the first concentration is below the first predetermined limit value and the second concentration is above the second predetermined limit value (105).