NOx Sensor with Dual Electrodes for Exhaust Gas Selectivity
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Solution Overview
Problem
Existing NOx sensors face calibration maintenance issues and selectivity problems due to interference from gases like CO, H2, HC, NH3, CO2, and H2O, making them ineffective for reliable NOx measurement in exhaust gas environments.
Innovation Solution
The development of NOx sensors comprising a planar sensor element with a NOx sensing cell, reference electrodes, and an electrolyte layer, operating at specific temperatures with dopant materials, and a heater to maintain calibration and reduce interference, allowing for accurate NOx measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance oxide method is used to measure NOx partial pressure, then NOx measurement capability is achieved, but selectivity deteriorates due to interference from CO, H2, HC, NH3, CO2, and H2O
Solution Approach 1:
The sensor is divided into multiple sensing cells (first NOx sensing cell, second NOx sensing cell, and air-fuel sensing cell) with different functionalities. Each cell targets specific gases or measurement aspects, allowing the system to differentiate NOx signals from interfering gases through comparative measurement and signal processing.
Solution Approach 2:
A catalyst is introduced as an intermediary component between the exhaust gas and the sensing cells. The catalyst selectively converts NH3 and other interfering substances before they reach the sensors, preventing false readings while allowing NOx to be measured accurately.
2Measurement precision
If semiconducting oxides are used for NOx sensing, then NOx detection is enabled, but calibration stability deteriorates
Solution Approach 1:
The sensor operates at elevated temperatures (maintained by an integrated heater) to optimize the electrochemical reactions in the sensing cells. This temperature control stabilizes the sensor response characteristics and reduces drift, improving calibration stability without sacrificing detection capability.
Solution Approach 2:
The sensor employs a composite structure combining multiple electrode materials, electrolyte layers, and catalyst materials. This composite approach leverages the complementary properties of each material to achieve both sensitive NOx detection and stable, drift-free operation over time.
3Object-affected harmful factors
If multiple sensing cells and catalysts are added to improve selectivity, then gas interference is reduced, but device complexity increases
Solution Approach 1:
Multiple sensing functions (NOx detection, air-fuel ratio sensing, catalytic conversion) are merged into a single integrated sensor device. The sensing cells and catalyst are combined in one compact structure, eliminating the need for separate sensors and reducing overall system complexity despite the enhanced functionality.
Solution Approach 2:
The sensor device performs multiple functions simultaneously: it detects NOx concentration, measures air-fuel ratio, and catalytically processes interfering gases. This multi-functionality is achieved within a single integrated platform, reducing the number of separate components needed in the exhaust monitoring system.
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 sensors provide reliable NOx measurement with improved selectivity and durability, enabling effective feedback control loops for pollution reduction systems, such as SCR catalysts in diesel vehicles.
Implementation Method 1
an electrolyte layer (16) between the first sensing electrode (12) and the first reference electrode (14), and between the second sensing electrode (18) and the second reference electrode (20)
Implementation Method 2
a heater to maintain calibration
Data Source
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AI summary
Disclosed herein are NOx sensors and method of using the same. In one embodiment, a method for sensing NOx comprises: contacting a first NOx electrode (12) with the gas, contacting a second NOx electrode (18) with the gas, determining a NO2 emf between the first NOx electrode and a first reference electrode (14), determining a NOx emf between the second NOx electrode and a second reference electrode (20), and determining a NO2 concentration and a NO concentration using the NO2 emf and the NOx emf. The first electrode (12) can be at a first temperature of greater than or equal to about 700° C, and the second electrode (18) can be at a second temperature of about 500°C to 650 C.