SCR NOx Conversion Diagnostics for Diesel Exhaust Fluid Quality
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Solution Overview
Problem
Diesel engines face challenges in managing NOx emissions due to factors such as catalyst aging, out-of-specification diesel exhaust fluid (DEF), DEF injector failures, and DEF line blockages, which affect the efficiency of selective catalytic reduction (SCR) systems.
Innovation Solution
A method to evaluate the quality of DEF by measuring the NOx conversion efficiency of close-coupled and downstream SCR units at various temperatures and ammonia-to-NOx ratios, identifying any deviations from target efficiencies to diagnose potential issues with DEF quality or delivery components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If close-coupled SCR and DEF dosing system are added near the engine, then NOx emissions reduction efficiency is improved, but system complexity and susceptibility to DEF quality issues increase
Solution Approach 1:
The SCR system is divided into two separate units: a close-coupled SCR unit positioned near the engine and a downstream SCR unit positioned further downstream. This segmentation allows the close-coupled unit to benefit from high thermal energy for efficient NOx reduction while the downstream unit provides additional reduction capacity and compensates for any efficiency losses, thereby maintaining high overall productivity without requiring a single overly complex system
Solution Approach 2:
DEF quality evaluation acts as an intermediary diagnostic mechanism that monitors and assesses the quality of diesel exhaust fluid before it can cause problems in the SCR system. By continuously evaluating DEF quality through measurements of NOx conversion efficiency and comparing against expected performance, the system can detect issues early and prevent catastrophic failures, thereby managing the complexity of the DEF dosing system
2Use of energy by moving object
If close-coupled SCR unit is positioned near the engine, then thermal energy utilization is improved, but sensitivity to DEF quality variations and catalyst aging increases
Solution Approach 1:
The SCR system is divided into two separate units: a close-coupled SCR unit positioned near the engine and a downstream SCR unit positioned further downstream. This segmentation allows the close-coupled unit to benefit from high thermal energy for efficient NOx reduction while the downstream unit provides additional reduction capacity and compensates for any efficiency losses, thereby maintaining high overall productivity without requiring a single overly complex system
Solution Approach 2:
The system implements continuous feedback monitoring by measuring NOx conversion efficiency at multiple locations and comparing actual performance against expected performance based on DEF quality evaluations. This feedback mechanism allows the system to detect deviations caused by catalyst aging or DEF quality issues and adjust operations accordingly, thereby maintaining reliability despite the close-coupled unit's sensitivity to these factors
3Measurement precision
If DEF quality evaluation through NOx conversion efficiency measurement is implemented, then diagnostic accuracy is improved, but measurement and operational complexity increases
Solution Approach 1:
The SCR system performs self-diagnosis by using its own operational data (NOx conversion efficiency measurements) to evaluate DEF quality. The system compares actual conversion efficiency against expected efficiency based on measured DEF properties and operating conditions, allowing the system to self-assess its performance and diagnose issues without requiring external diagnostic equipment or complex additional instrumentation
Solution Approach 2:
The NOx conversion efficiency measurement serves multiple functions simultaneously: it monitors SCR catalyst performance, evaluates DEF quality, detects injector or pump failures, and identifies line blockages. This multi-functionality allows a single measurement parameter to provide comprehensive system diagnostics, thereby improving measurement precision without proportionally increasing system complexity
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 provides a robust diagnostic for DEF quality and operation, allowing for timely corrective actions to maintain optimal NOx conversion efficiency and compliance with emissions regulations.
Implementation Method 1
selective catalytic reduction (SCR) systems
Implementation Method 2
converts nitrogen oxides (NOx) into nitrogen and water through a chemical reduction reaction
Data Source
Figure 1A~1C
Figure 2
Figure 3A~3B
AI summary
The present disclosure describes methods for evaluating quality of DEF dosed to an EAS including a close coupled SCR unit a downstream SCR unit. A NOx conversion efficiency of the close coupled SCR unit and a NOx conversion efficiency of the downstream SCR unit are used to evaluate quality of DEF. In some embodiments, the NOx conversion efficiency of close coupled SCR unit is used to evaluate quality of DEF. Operation of an EAS using the results of the evaluation of quality of DEF are described.