SCR Injector Diagnosis via Exhaust Gas Analysis
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Solution Overview
Problem
The existing SCR system injectors deteriorate over time, leading to inconsistent urea injection amounts, which can result in either insufficient or excessive urea injection, causing nitrogen oxide levels to exceed reference values, violating exhaust gas regulations and generating ammonia smells or contamination.
Innovation Solution
A method involving an NOx sensor at the exhaust pipe to detect nitrogen oxides and ammonia levels, diagnosing injector failure by comparing these levels to pre-defined reference values, and controlling the injector to inject urea at predetermined intervals, with electronic control units determining suitable diagnosis conditions such as engine RPM, vehicle speed, and temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the injector is used for repeated operations over time, then the injector performs injection function, but the injector deteriorates and injects urea amount smaller or excessively larger than reference value
Solution Approach 1:
The system performs preliminary diagnosis actions by detecting NOx and ammonia levels before significant injector failure occurs. The ECU continuously monitors exhaust gas composition and compares it against reference values to detect injector deterioration early, allowing for timely maintenance before the injector completely fails.
Solution Approach 2:
The system establishes a feedback loop where the ECU detects NOx and ammonia levels in the exhaust gas, compares these measurements against reference values, and uses this information to diagnose injector status. This feedback mechanism allows the system to monitor injector performance continuously and alert operators to deterioration.
2Device complexity
If the injector injects urea amount smaller than reference value, then the injection process is simpler, but exhaust gas rules cannot be satisfied
Solution Approach 1:
The ECU uses feedback from NOx and ammonia sensors to monitor whether the injector is delivering the correct urea amount. By comparing detected gas composition against reference values, the system can identify when the injector is under-dosing urea, which would lead to excessive NOx emissions, and trigger appropriate responses.
Solution Approach 2:
The system replaces complex mechanical injection control mechanisms with an electronic control and sensing system. The ECU electronically monitors injection effectiveness through chemical analysis of exhaust gas composition, substituting for purely mechanical injection timing and dosage control.
3Reliability
If the injector injects urea excessively larger than reference value, then the injection system is more robust, but ammonia smells and contaminations are generated
Solution Approach 1:
The ammonia sensor provides feedback to the ECU about the amount of ammonia in the exhaust gas. When the injector over-doses urea, excessive ammonia is produced that doesn't react with NOx. The sensor detects this excess ammonia, allowing the system to identify injector over-performance and prevent contamination issues.
Solution Approach 2:
The system uses electronic sensing and control to precisely monitor and regulate urea injection levels, replacing robust but imprecise mechanical injection systems. This allows the system to maintain reliable operation while preventing over-injection that would cause ammonia contamination.
4Measurement precision
If an NOx sensor is provided at rear end of exhaust pipe to detect NOx and ammonia levels, then the diagnosis accuracy is improved, but the device complexity increases
Solution Approach 1:
The NOx sensor system is designed to perform multiple functions: detecting both NOx levels and ammonia levels, providing data for injector diagnosis, and enabling emission monitoring. This multi-functionality justifies the added complexity by consolidating multiple measurement capabilities into a single sensor system.
Solution Approach 2:
The sensor system serves the dual purpose of both monitoring emissions for environmental compliance and diagnosing injector health. The same NOx and ammonia detections used for emission reporting also provide the diagnostic information needed to assess injector performance, making the system self-sufficient.
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 effectively detects injector failures, preventing exhaust gas rule violations and ammonia contamination by accurately determining urea injection amounts, ensuring proper chemical reactions and reducing environmental and health hazards.
Implementation Method 1
detecting an amount of NOx and an amount of ammonia through an NOx sensor provided at a rear end of the exhaust pipe
Implementation Method 2
urea is converted into ammonia (NH3) through hydrolysis
Implementation Method 3
The converted ammonia (NH3) and nitrogen oxides (NOx) chemically react with each other on a catalyst and are converted into water and nitrogen
Implementation Method 4
chemically react with each other on a catalyst
Data Source
AI summary
The present disclosure provides a method of diagnosing a failure of a Selective Catalytic Reduction (SCR) system, the method including: injecting urea into the interior of an exhaust pipe using an injector; after the injection step, detecting an amount of NOx and an amount of ammonia through an NOx sensor provided at a rear end of the exhaust pipe; and diagnosing a failure of the injector based on at least one of the amount of NOx and the amount of ammonia.