DOC NO2 Generation On-Board Diagnostics for SCR Efficiency
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Solution Overview
Problem
Diesel engine exhaust treatment systems face inefficiencies in NOx reduction due to suboptimal NO2:NOx ratios, especially at lower temperatures, which affects the performance of SCR catalysts, and there is a need for monitoring the exhaust system to prevent component failures and environmental contamination.
Innovation Solution
A diagnostic method that determines SCR efficiency by comparing NOx sensor readings before and after the DOC, triggering notifications based on threshold conditions including ammonia loading, temperature, and exhaust flow rate, and adjusting the Fe:Cu ratio in the SCR catalysts to optimize NOx conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the NO2:NOx ratio is increased to improve SCR efficiency at lower temperatures, then NOx conversion efficiency is improved, but the system becomes more sensitive to NO2 supply management and requires precise control
Solution Approach 1:
The patent employs feedback control by using NOx sensors positioned before and after the SCR catalyst to monitor NOx concentrations. The control module compares these readings to determine SCR efficiency and adjusts urea injection rates accordingly, creating a closed-loop system that automatically maintains optimal NO2:NOx ratios without requiring complex manual control.
Solution Approach 2:
The diagnostic system performs self-monitoring and self-diagnosis of the SCR system efficiency. By automatically detecting deviations from expected performance and triggering diagnostic routines, the system serves itself to maintain optimal operation without external intervention, reducing the burden on operators while maintaining high conversion efficiency.
2Productivity
If DOC oxidation efficiency is improved to increase NO2 production for SCR, then SCR performance is enhanced, but DOC degradation becomes harder to detect without specific diagnostic methods
Solution Approach 1:
The system uses feedback from NOx sensors to monitor DOC performance indirectly. By comparing expected versus actual SCR efficiency and analyzing the relationship between urea injection rates and NOx reduction, the system can detect DOC degradation trends and trigger diagnostic routines to assess DOC health.
Solution Approach 2:
The patent uses SCR efficiency as an intermediary indicator to assess DOC performance. Rather than directly measuring DOC oxidation efficiency, the system monitors the downstream effect on SCR performance and uses this indirect measurement to infer DOC health status, enabling reliable detection of DOC degradation.
3Productivity
If Fe-based SCR catalysts are used to improve NOx conversion, then conversion efficiency increases, but the system becomes more sensitive to NO2 in the feed requiring precise NO2 management
Solution Approach 1:
The control module continuously monitors NOx concentrations and SCR efficiency, using this feedback to adjust urea injection rates in real-time. This ensures that the Fe-based SCR catalyst receives the optimal NO2:NOx ratio for maximum conversion efficiency while compensating for variations in feed composition.
Solution Approach 2:
The system dynamically changes operational parameters, specifically the urea injection rate, based on real-time measurements of NOx concentrations and SCR efficiency. This parameter adjustment optimizes the NO2:NOx ratio entering the Fe-based SCR catalyst, maintaining high conversion efficiency despite variations in exhaust composition.
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 ensures the DOC operates within specifications, maintaining efficient NOx reduction and preventing system failures, thereby reducing environmental impact and regulatory noncompliance by accurately monitoring and adjusting the exhaust treatment system.
Implementation Method 1
a diesel oxidation catalyst (DOC), to convert HC and CO to CO2 and water
Implementation Method 2
The efficiency of this reduction reaction is significantly impacted by the ratio of NO2:NOx in the exhaust stream entering the SCR catalyst
Implementation Method 3
the use of a selective catalytic reduction ("SCR") catalyst for the reduction of NOx. This technology involves the catalytically-enhanced reduction of NO to nitrogen and water by ammonia
Data Source
AI summary
A method for exhaust aftertreatment includes determining a diagnostic condition with respect to a threshold diagnostic condition, determining an SCR efficiency as a ratio of a readout of a first NOx sensor at a first NOx sensing position with respect to a readout of a second NOx sensor at a second NOx sensing position, the first NOx sensing position located about an engine out area within an exhaust stream before a DOC and the second NOx sensing position located about an output of an SCR device within the exhaust stream; and comparing the SCR efficiency to a threshold SCR efficiency range. If the SCR efficiency is less than the threshold SCR efficiency range, then trigger DOC failure for NO oxidation, and if the SCR efficiency is greater than or equal to the threshold SCR efficiency range, then DOC is determined to be operating within specifications.