Gas Sensor Inner Pump Electrode Geometry for NOx Accuracy
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Solution Overview
Problem
Existing gas sensors face challenges in accurately measuring nitrogen oxide (NOx) concentrations when the oxygen concentration in the measurement gas is high, as it can lead to premature NOx resolution, affecting detection 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 measurement electrode with a porous protection film, where the inner pump electrode has a planar shape with a larger front end and smaller rear end, and a planar area that covers at least 60% of the first inner space, to effectively pump out oxygen and suppress NOx resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional inner pump electrode configuration is used to pump out oxygen in high oxygen concentration regions, then oxygen pumping efficiency is improved, but NOx resolution occurs prematurely affecting measurement accuracy
Solution Approach 1:
The inner pump electrode is designed with a specific planar shape where the front end has a larger area and the rear end has a smaller area. This non-uniform geometry creates local quality variations that optimize oxygen pumping at the upstream high oxygen concentration region while preventing NOx resolution. The front end's larger area provides sufficient pumping capacity where oxygen concentration is highest, while the gradual transition to a smaller rear end area prevents excessive voltage application that would cause NOx resolution.
Solution Approach 2:
The invention changes the geometric parameters of the inner pump electrode, specifically setting the planar area of the front end to be larger than the rear end, with the front end length occupying 15-75% of the total electrode length. This parameter optimization ensures that the electrode area distribution matches the oxygen concentration gradient in the measurement gas, enabling effective oxygen removal without causing harmful NOx resolution reactions.
2Productivity
If high pump voltage is applied to pump out oxygen from high oxygen concentration measurement gas, then oxygen removal efficiency is improved, but NOx resolution occurs in the upstream portion
Solution Approach 1:
The non-uniform area distribution of the inner pump electrode creates local quality differences that match the spatial distribution of oxygen concentration. The larger front end area is positioned where oxygen concentration is highest, providing localized pumping capacity without requiring excessively high voltage. This prevents the generation of harmful NOx resolution while maintaining effective oxygen removal efficiency.
Solution Approach 2:
The invention converts the potential harm of high voltage application into a benefit by using the voltage necessary for oxygen pumping to drive oxygen ions through the solid electrolyte membrane. The controlled voltage application, optimized by the electrode geometry, ensures that oxygen is removed efficiently while the conditions for harmful NOx resolution are avoided through proper area distribution.
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 configuration allows for accurate NOx concentration measurement even at high oxygen levels by preventing NOx resolution in the first inner space, ensuring reliable detection of NOx concentrations.
Implementation Method 1
a sensor element formed of an oxygen ion conductive solid electrolyte
Implementation Method 2
a main pump cell which is an electrochemical pump cell constituted by an inner pump electrode 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
Implementation Method 3
said measurement electrode functioning as a reduction catalyst for NOx
Data Source
AI summary
A sensor element includes: a main pump cell constituted by an inner pump electrode facing a first inner space into which a measurement gas is introduced, an external pump electrode provided on an element surface, and a solid electrolyte located therebetween; and a measurement pump cell constituted by the measurement electrode facing a second inner space which is communicated with the first inner space and functioning as a reduction catalyst for NOx, and a solid electrolyte located therebetween. The inner pump electrode has a planar shape in which two parts of a front end part relatively having a large area and a rear end part relatively having a small area are sequentially connected in this order from an upstream side in a longitudinal direction of the sensor element while satisfying requirements of a predetermined size and area.