Ammonia Slip Detection in Diesel SCR Systems
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Solution Overview
Problem
Ammonia slip in diesel engine exhaust gas treatment systems leads to inaccurate NOx readings, resulting in inefficient selective catalytic reduction (SCR) systems, as ammonia is detected as NOx, causing lower efficiency calculations.
Innovation Solution
A method that reduces exhaust gas recirculation (EGR) when a threshold increase in NOx is detected, allocating sensor output to either NOx or ammonia based on changes, and adjusts operating parameters such as EGR or urea injection to correct for ammonia slip, thereby improving SCR efficiency and reducing ammonia leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SCR system is loaded with urea to a point of saturation, then the NOx reduction efficiency is improved, but ammonia slip increases and is detected as NOx by the sensor
Solution Approach 1:
The system performs preliminary action by temporarily reducing EGR before taking measurement. This preparatory step creates a condition where NOx emissions increase if the SCR system is functioning properly, allowing the control system to distinguish between actual NOx leakage and ammonia slip that is being falsely detected as NOx by the sensor.
Solution Approach 2:
The system uses feedback by monitoring sensor output changes in response to EGR reduction. The control system adjusts EGR based on sensor feedback, and when ammonia slip is detected (indicated by lack of expected sensor response), it reduces urea injection to correct the condition, creating a closed-loop control system that maintains both efficiency and measurement accuracy.
2Loss of information
If ammonia slip is detected by the NOx sensor, then the sensor provides continuous monitoring, but the accuracy of NOx measurement deteriorates due to ammonia interference
Solution Approach 1:
The system performs a preliminary EGR reduction maneuver to test the SCR system's response. By temporarily reducing EGR and observing whether NOx emissions increase as expected, the system can determine if the sensor is detecting actual NOx or ammonia slip, thereby maintaining continuous monitoring while preserving measurement accuracy through intelligent interpretation of sensor data.
Solution Approach 2:
The system changes operating parameters by temporarily reducing EGR to create a test condition. This parameter change allows the system to observe sensor response and distinguish between NOx and ammonia detection, maintaining both continuous monitoring and measurement accuracy through dynamic parameter adjustment.
3Measurement precision
If EGR is reduced to test for ammonia slip, then the ability to detect ammonia slip is improved, but NOx emissions from the engine increase
Solution Approach 1:
The system uses periodic action by temporarily reducing EGR only for the duration needed to assess ammonia slip conditions, then restoring EGR to normal levels. This brief, periodic intervention allows accurate ammonia slip detection while minimizing the increase in NOx emissions, as the high-emission state is maintained only momentarily.
Solution Approach 2:
The system rushes through the EGR reduction phase quickly, minimizing the time spent in the high-emission state. By rapidly assessing sensor response during the brief EGR reduction window and immediately restoring normal EGR levels, the system achieves accurate ammonia slip detection while the harmful effect of increased NOx emissions is minimized through rapid transition.
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 reduces errors in SCR efficiency calculations and decreases ammonia slip, enhancing the overall efficiency of the exhaust gas treatment system by accurately distinguishing between NOx and ammonia contributions.
Implementation Method 1
a urea based selective catalytic reduction (SCR) system
Data Source
AI summary
Various systems and methods are described for detecting ammonia slip. In one example method, an amount of exhaust gas recirculation is reduced when output from an exhaust gas sensor indicates an increase in nitrogen oxide above a threshold amount. When the sensor output increases above a second threshold while the exhaust gas recirculation is reduced, the sensor output is allocated to nitrogen oxide; and when the sensor output does not increase above a second threshold while the exhaust gas recirculation is reduced, the sensor output is allocated to ammonia.