Segmented Pump Electrode Gas Sensor for NOx Accuracy
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Solution Overview
Problem
Existing gas sensors face challenges in accurately measuring nitrogen oxide (NOx) concentrations at high oxygen levels due to NOx resolution occurring before the measurement electrode, which degrades measurement accuracy.
Innovation Solution
A limiting current type gas sensor with a specific configuration, including a sensor element with an oxygen ion conductive solid electrolyte, a main pump cell, a measurement pump cell, and a porous protection film, is designed to maintain oxygen partial pressure and prevent NOx resolution, ensuring accurate NOx measurement even at high oxygen concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high pump voltage is applied to pump out oxygen from measurement gas with high oxygen concentration, then oxygen removal efficiency is improved, but NOx resolution occurs which degrades measurement accuracy
Solution Approach 1:
The pump electrode is divided into multiple segments along the gas flow direction, with each segment independently controllable. This allows selective application of pump voltage to different regions, enabling efficient oxygen removal from high-oxygen-concentration gas while preventing NOx resolution in downstream measurement regions.
Solution Approach 2:
Different pump voltages are applied to different segments of the pump electrode according to the local oxygen concentration distribution. Higher voltages are applied upstream where oxygen concentration is high, while lower or zero voltage is applied downstream where measurement occurs, creating locally optimized conditions for both oxygen removal and measurement accuracy.
2Productivity
If the inner space volume is increased to reduce diffusion resistance, then gas flow efficiency is improved, but oxygen concentration becomes non-uniform causing localized NOx resolution
Solution Approach 1:
The pump electrode is segmented to provide localized control over different regions of the inner space. This enables management of oxygen concentration distribution throughout the space, preventing localized accumulation that would cause NOx resolution while maintaining overall gas flow efficiency.
Solution Approach 2:
The pump voltage applied to different segments is dynamically adjusted based on local oxygen concentration conditions. This parameter control ensures uniform oxygen distribution throughout the inner space, preventing the non-uniformity that leads to localized NOx resolution.
3Productivity
If multiple pump cells are used to handle high oxygen concentration, then oxygen removal capability is improved, but device complexity increases
Solution Approach 1:
Instead of adding multiple separate pump cells, the pump electrode within a single pump cell is segmented into multiple independently controllable sections. This achieves the functionality of multiple pump cells (distributed oxygen removal capability) while maintaining a compact single-cell structure, thus improving oxygen removal capability without proportionally increasing device 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 sensor effectively suppresses NOx resolution and maintains accurate NOx measurement by controlling oxygen partial pressure, thereby ensuring reliable NOx concentration measurement across varying oxygen levels.
Implementation Method 1
a main pump cell which is an electrochemical pump cell constituted by an inner pump electrode including one or two unit electrode parts and provided to face the first inner space, an external pump electrode provided on a surface of the sensor element, and the solid electrolyte located between the inner pump electrode and the external pump electrode; the main pump cell pumps out oxygen in the measurement gas introduced into the first inner space through an application of a predetermined main pump voltage between the inner pump electrode and the external pump electrode
Implementation Method 2
a measurement pump cell which is an electrochemical pump cell constituted by the measurement electrode, the external pump electrode, and the solid electrolyte located between the measurement electrode and the external pump electrode; the measurement pump cell pumps out oxygen generated by a reduction of NOx in the measurement gas reaching near the measurement electrode in the measurement electrode, through an application of a predetermined pump voltage between the inner pump electrode and the external pump electrode
Implementation Method 3
a measurement electrode provided to face the second inner space and covered by a porous protection film providing a predetermined diffusion resistance, the measurement electrode functioning as a reduction catalyst for NOx
Implementation Method 4
a porous protection film providing a predetermined diffusion resistance
Implementation Method 5
an oxygen ion conductive solid electrolyte
Data Source
AI summary
A sensor element includes: a main pump cell constituted by an inner electrode provided to face a first inner space into which a measurement gas is introduced, an external electrode provided on an element surface, and a solid electrolyte therebetween; and a measurement pump cell constituted by a measurement electrode provided to face a second inner space communicated with the first inner space, an external electrode, and a solid electrolyte therebetween. A diffusion resistance from a gas inlet to the inner electrode is 200 to 1000 cm−1. For the first inner space and a unit electrode part of the inner electrode, a space length is 2.5 to 10 mm, a space thickness is 50 to 300 μm, an electrode length/the space length is 0.5 to 1.0, and an electrode width/the space width is 0.5 to 1.0.