Heavy-Duty Engine NOx Sensor Diagnostics Across Dual SCR Systems
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Solution Overview
Problem
The performance of NOx sensors in exhaust after-treatment systems of heavy-duty engines varies due to production inconsistencies and degradation over time, making it difficult to perform accurate diagnostics without affecting system performance or increasing tailpipe emissions.
Innovation Solution
A method involving engine control units to perform intrusive diagnostics by varying DEF injection rates and engine parameters, using linear regression to correct sensor measurements, ensuring accurate NOx level monitoring and compliance with emissions standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intrusive diagnostics are performed by varying DEF injection rates and engine parameters to monitor NOx sensor performance, then measurement precision is improved, but tailpipe emissions increase and system efficiency deteriorates
Solution Approach 1:
The system performs sensor diagnostics during cold start conditions before the SCR system is actively reducing emissions. By conducting measurements during this preliminary phase when the SCR catalyst is not yet active, the system can characterize sensor performance without interfering with emission reduction operations, thus avoiding increased tailpipe emissions
Solution Approach 2:
The system uses feedback from multiple NOx sensors positioned at different locations (upstream and downstream of SCR) to monitor and characterize sensor drift over time. This feedback mechanism allows the control unit to detect measurement deviations and adjust or replace sensors accordingly, improving measurement precision while maintaining normal emission control during regular operation
2Measurement precision
If multiple NOx sensors are deployed upstream and downstream of SCR systems to monitor emissions, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system divides the monitoring function into multiple segments by placing NOx sensors at different locations (upstream of first SCR, downstream of first SCR, upstream of second SCR, downstream of second SCR). This segmentation allows the system to monitor NOx levels at critical points throughout the exhaust after-treatment system, improving overall measurement precision while distributing the complexity across multiple simple, standardized sensor units rather than one complex monitoring system
3Productivity
If DEF injection rate is increased to maintain efficient SCR operation under varying conditions, then productivity is improved, but loss of substance increases due to excess ammonia
Solution Approach 1:
The system dynamically adjusts DEF injection rates based on real-time feedback from upstream NOx sensors and operating conditions. By continuously monitoring actual NOx levels and adapting the DEF dosing rate accordingly, the system maintains optimal SCR performance and productivity while minimizing excess ammonia injection, thus reducing substance loss and preventing ammonia slip
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
Ensures precise NOx sensor performance monitoring without increasing tailpipe emissions, maintaining system efficiency, and adhering to regulatory standards.
Implementation Method 1
close-coupled selective catalytic reduction system
Implementation Method 2
DEF is an aqueous solution that evaporates and decomposes to chemically release ammonia
Implementation Method 3
underbody selective catalytic reduction system downstream of the close-coupled selective catalytic reduction system
Implementation Method 4
diesel oxidation catalyst (DOC) to oxidize unburned fuel and carbon monoxide
Implementation Method 5
diesel particulate filter (DPF) for control of particulate matter (PM)
Data Source
AI summary
A heavy-duty truck has a diesel engine, an exhaust after-treatment system, and an engine control unit. The exhaust after-treatment system includes a close-coupled selective catalytic reduction system and an underbody selective catalytic reduction system, a first NOx sensor upstream of the close-coupled selective catalytic reduction system, a second NOx sensor between the two selective catalytic reduction systems, and a third NOx sensor downstream of the underbody selective catalytic reduction system. The engine control unit may perform methods allowing intrusive diagnostics to be performed on exhaust gas NOx sensors using the selective catalytic reduction systems during normal operation of the heavy-duty truck.