SCR Catalyst Reagent Quality Estimation via NOx Conversion Monitoring
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Solution Overview
Problem
Existing methods for monitoring the quality of urea-based reagents in SCR catalysts for diesel engines are inadequate, as they fail to detect dilution when the engine is running and can be misled by changes unrelated to reagent quality, leading to increased maintenance costs and potential NOx emission issues.
Innovation Solution
A method that sets a lower demanded NOx conversion rate than the maximum achievable by the SCR catalyst, allowing for the estimation of urea concentration by comparing actual and demanded NOx conversion rates, thereby eliminating the need for additional sensors and accounting for catalyst degradation and ammonia storage effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reagent quality sensor using ultrasonic density measurements or electrical characterization is used, then reagent quality can be detected, but the sensor is expensive and results in increased maintenance costs
Solution Approach 1:
The SCR catalyst system performs self-diagnosis by monitoring its own NOx conversion efficiency. The control unit compares the actual NOx conversion rate with the demanded conversion rate, allowing the system to detect reagent quality issues without external sensors. This eliminates the need for expensive dedicated quality sensors while maintaining detection capability.
Solution Approach 2:
The existing NOx sensors and control unit, originally designed for emission control, are repurposed to also perform reagent quality monitoring. The same hardware infrastructure serves dual functions: controlling NOx reduction and detecting reagent dilution, thereby eliminating the need for additional specialized sensors.
2Measurement precision
If NOx conversion rate comparison before and after engine stop is used to detect dilution, then reagent quality can be monitored, but dilution occurring with the engine running is not detected and other changes may result in erroneous conclusions
Solution Approach 1:
The control unit periodically compares the actual NOx conversion rate with the demanded conversion rate during engine operation. This continuous periodic monitoring allows detection of reagent dilution at any time during operation, not just during engine stops, and provides multiple data points for reliable quality assessment.
Solution Approach 2:
The system uses feedback from the NOx sensors to continuously monitor conversion efficiency. The control unit receives real-time feedback on actual versus demanded conversion rates, allowing it to detect deviations caused by reagent dilution and adjust or alert operators accordingly, ensuring continuous reliable monitoring.
3Productivity
If the demanded NOx conversion rate is set at maximum capacity, then NOx emission control is optimized, but catalyst degradation and ammonia storage effects reduce measurement accuracy for reagent quality
Solution Approach 1:
The control unit intentionally operates the SCR catalyst at a lower demanded conversion rate than its maximum capacity during reagent quality monitoring. This partial action creates a buffer that accounts for catalyst degradation and ammonia storage effects, allowing more accurate detection of reagent quality changes without requiring the catalyst to operate at full capacity.
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 accurately estimates reagent quality, reduces system complexity, and prevents ammonia slip, enhancing NOx emission control while minimizing the impact of catalyst degradation and maintenance costs.
Implementation Method 1
an injection system is used to supply it into the exhaust gas stream entering the SCR catalyst where it decomposes into hydro cyanic acid (NHCO) and gaseous ammonia (NH3), which then reacts with the SCR catalyst, converting NOx in the exhaust stream into harmless nitrogen and water
Implementation Method 2
an injection system is used to supply it into the exhaust gas stream entering the SCR catalyst where it decomposes into hydro cyanic acid (NHCO) and gaseous ammonia (NH3)
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention concerns a method for estimating the quality of an urea based reagent in terms of urea concentration, said reagent being injected upstream of a SCR catalyst (5) in an exhaust aftertreatment system (1), comprising setting a demanded NOx conversion rate substantially lower than a currently estimated maximum NOx conversion rate of said SCR catalyst (5), monitoring an actual NOx conversion rate for a certain time period, and estimating the urea concentration of said reagent based on comparing the monitored actual NOx conversion and the demanded NOx conversion during said time period. The invention further concerns a corresponding system.