SCR Catalyst Capacitance Detection for Ammonia Adsorption
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Solution Overview
Problem
Existing exhaust purification systems using SCR catalysts face challenges in accurately determining the adsorbed amount of ammonia (NH3) due to uneven distribution, leading to suboptimal correction of aqueous urea solution injection and potential NH3 slip.
Innovation Solution
The system employs capacitance detecting units at the inlet and outlet of the SCR catalyst to calculate the adsorbed amount of NH3 based on capacitance measurements, allowing precise detection and correction of the aqueous urea solution injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an NH3 sensor is used to estimate the adsorbed amount of NH3 in the SCR catalyst, then the injection amount of aqueous urea solution can be corrected, but the measurement precision is insufficient due to uneven NH3 distribution and sensor placement limitations
Solution Approach 1:
The SCR catalyst is divided into multiple sections along the exhaust gas flow direction, with separate capacitance detecting units installed in each section. This segmentation allows independent measurement of NH3 adsorption in each region, capturing the uneven distribution pattern and providing precise data for injection amount correction without requiring complex sensor arrays.
Solution Approach 2:
The patent replaces the conventional NH3 sensor-based detection system with a capacitance detection system. The capacitance detecting units measure changes in electrical capacitance caused by NH3 adsorption on the catalyst, substituting mechanical/chemical sensing with an electrical field-based method that provides higher precision and enables sectioned measurement of adsorption distribution.
2Reliability
If aqueous urea solution injection is corrected based on estimated NH3 adsorption, then NH3 slip can be reduced, but the correction accuracy is insufficient leading to suboptimal purification efficiency
Solution Approach 1:
The patent implements a feedback control system where capacitance detecting units continuously monitor NH3 adsorption levels in different sections of the SCR catalyst. The microcontroller processes these measurements and adjusts the aqueous urea solution injection amount in real-time, creating a closed-loop system that maintains optimal purification efficiency and prevents NH3 slip by continuously adapting injection rates to actual adsorption conditions.
Solution Approach 2:
The capacitance detecting units are positioned to detect NH3 adsorption before the exhaust gas exits the SCR catalyst, allowing the system to predict upcoming adsorption saturation and adjust injection rates in advance. This preliminary detection enables proactive correction of injection amounts, preventing NH3 slip before it occurs and maintaining optimal purification efficiency throughout the catalytic process.
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 approach enables precise detection of NH3 adsorption across the SCR catalyst, ensuring accurate control of urea solution injection, reducing NH3 slip, and enhancing NOx reduction and purification efficiency.
Implementation Method 1
a first capacitance detecting unit for detecting (measuring) capacitance of the selective reduction catalyst
Implementation Method 2
capacitance of the selective reduction catalyst
Data Source
AI summary
An exhaust purification system includes a selective catalytic reduction (SCR) catalyst disposed at an exhaust system of an engine for using ammonia that is generated from urea water as a reducing agent to reduce NOx contained in exhaust gas, a device that injects urea water to the SCR catalyst, an inlet-side electrode that detects capacitance within the SCR catalyst at least from a vicinity of an inlet of the SCR catalyst to a vicinity of an intermediate section in an exhaust gas flowing direction, an outlet-side electrode that detects the capacitance within the SCR catalyst at least from the vicinity of the intermediate section to an outlet of the SCR catalyst in the exhaust gas flowing direction, and a calculation unit that calculates an ammonia adsorption amount within the SCR catalyst on a basis of the capacitances detected from the inlet-side and the outlet-side electrodes.