Exhaust Gas Purification System with Urea Injector and Gas Sensors
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Solution Overview
Problem
Current exhaust gas purification systems face challenges in accurately measuring and distinguishing between NO, NO2, and NH3 concentrations in the presence of oxygen, leading to inefficiencies in NOx purification and difficulty in diagnosing catalyst deterioration, particularly in diesel engines with lean combustion, where increased urea injection results in unreacted ammonia discharge and incomplete NOx reduction.
Innovation Solution
An exhaust gas purification system incorporating a urea water injector and gas sensors with a solid electrolyte structure, capable of accurately measuring NO, NO2, and NH3 concentrations using a preliminary oxygen concentration control unit and target component acquisition unit, which adjusts the oxygen concentration and temperature to differentiate between these components, allowing for precise control of the urea injector and detection of catalyst deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the injected amount of urea is increased to improve NOx purification efficiency, then the NOx purification efficiency increases, but unreacted ammonia is discharged into the atmosphere
Solution Approach 1:
The patent employs feedback control by using gas sensors to continuously monitor the concentrations of NO, NO2, and NH3 in the exhaust gas. Based on these real-time measurements, the control unit adjusts the urea injection amount dynamically. When NH3 concentration reaches a threshold, the system reduces urea injection to prevent excessive ammonia discharge, while maintaining high NOx purification efficiency through optimal dosing.
Solution Approach 2:
The system changes the parameter of urea injection amount based on real-time exhaust gas composition. By monitoring NO, NO2, and NH3 concentrations and adjusting the injection rate accordingly, the system optimizes the chemical reaction conditions to maximize NOx conversion while minimizing unreacted ammonia emissions.
2Measurement precision
If conventional sensors are used to measure exhaust gas components, then the total amount of NOx can be measured, but it is not possible to distinguish between NO, NO2, and NH3 respectively
Solution Approach 1:
The patent segments the measurement function by using multiple specialized gas sensors, each designed to detect specific components (NO, NO2, NH3) separately. This segmentation allows the system to measure not only the total NOx amount but also the individual concentrations of each component, providing detailed compositional information for precise control.
Solution Approach 2:
The patent introduces an intermediary conversion process where NH3 is converted to NO2 through a catalytic converter before detection. This intermediary step enables the sensor system to distinguish between original NO2 and NH3-derived NO2, allowing separate quantification of each component through differential measurement approaches.
3Measurement precision
If oxide semiconductor electrodes are used for NO and NO2 measurement, then selectivity is excellent, but sensitivity output characteristics have opposite polarity making correct measurement impossible when both components coexist
Solution Approach 1:
The patent introduces an intermediary catalytic conversion step where NH3 is converted to NO2 before reaching the oxide semiconductor sensors. This allows the system to measure total NO2 (original + converted from NH3) and, by combining with direct NH3 measurement or differential calculations, distinguish and quantify each component separately despite the opposite polarity characteristics of the sensors.
4Reliability
If a sensor system is designed to distinguish between NO and NO2 for DOC catalyst diagnosis, then safer fault diagnosis is achieved, but the system complexity increases
Solution Approach 1:
The patent designs a universal gas sensor system that simultaneously performs multiple functions: monitoring NO, NO2, and NH3 concentrations for SCR control, diagnosing DOC catalyst performance, and detecting SCR catalyst efficiency. This multi-functional approach enables accurate fault diagnosis without requiring separate specialized sensor systems for each function, thereby limiting the increase in overall 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
The system enables accurate and prolonged measurement of exhaust gas components, optimizing NOx purification efficiency, reducing ammonia emissions, and effectively diagnosing catalyst deterioration, thereby improving fuel efficiency and compliance with emission regulations.
Implementation Method 1
a gas sensor capable of measuring respective concentrations of a plurality of target components in a gas to be measured
Implementation Method 2
gas sensors with a solid electrolyte structure
Data Source
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AI summary
The present invention relates to an exhaust gas purification system and an exhaust gas purification method. The exhaust gas purification system (200) is provided with: an injector (210) for injecting urea water, said injector being installed between a combustion device (202) and a selective catalytic reduction (SCR) catalyst (206); a first gas sensor (10A) which is installed downstream of the SCR catalyst (206), and which detects the NO concentration and the NH3 concentration in exhaust gas outputted from the SCR catalyst (206); and an opening amount control means (216) for controlling the opening amount of the injector (210) for injecting urea water.