Gas Sensor Segmented Pump Cell for NOx Measurement 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 NOx can be prematurely reduced before reaching the measurement electrode, leading to inaccurate readings.
Innovation Solution
A limiting current type gas sensor with a sensor element made of oxygen ion conductive solid electrolyte, featuring a main pump cell and a measurement pump cell, both with specific configurations and materials, including a cermet inner pump electrode of Au—Pt alloy and ZrO2, to control oxygen partial pressure and suppress NOx reduction, ensuring accurate NOx concentration measurement.
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 is prematurely reduced leading to measurement inaccuracy
Solution Approach 1:
The pump cell is divided into two distinct cells: a main pump cell for removing oxygen from the measurement gas, and a measurement pump cell for measuring NOx concentration. This segmentation allows each cell to operate under optimized conditions without interfering with the other, preventing premature NOx reduction while maintaining oxygen removal efficiency
Solution Approach 2:
A diffusion resistance member is introduced as an intermediary component between the main pump cell and the measurement pump cell. This member controls the diffusion of oxygen and NOx, allowing oxygen to be removed by the main pump cell while preventing excessive oxygen removal that would cause premature NOx reduction in the measurement cell
2Adaptability or versatility
If the oxygen concentration in the measurement gas is high, then the sensor can handle high oxygen environments, but NOx reduction occurs before reaching the measurement electrode
Solution Approach 1:
The sensor is segmented into a main pump cell for oxygen removal and a measurement pump cell for NOx measurement. This allows the sensor to maintain adaptability to high oxygen environments while ensuring that NOx measurement occurs under controlled oxygen partial pressure conditions in the measurement cell
Solution Approach 2:
The oxygen partial pressure is changed and controlled in different regions: high oxygen concentration is tolerated in the measurement gas input, but the oxygen partial pressure is lowered in the measurement pump cell through controlled diffusion and pumping, preventing premature NOx reduction while maintaining high oxygen environment compatibility
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 solution effectively suppresses NOx reduction even at high oxygen concentrations, allowing for precise NOx concentration measurement by maintaining controlled oxygen partial pressures and using a cermet electrode with optimized dimensions and materials to prevent premature NOx resolution.
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
Implementation Method 3
said measurement electrode functioning as a reduction catalyst for NOx
Implementation Method 4
covered with a porous protection film providing a predetermined diffusion resistance
Data Source
AI summary
A sensor element includes: a main pump cell constituted by an inner pump electrode facing the 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; a measurement electrode facing a second inner space communicating with the first inner space and functioning as a reduction catalyst for NOx; and a measurement pump cell constituted by the measurement electrode, the external pump electrode, and a solid electrolyte located therebetween. A diffusion resistance from the gas inlet to the inner pump electrode ranges from 200-1000 cm−1, a resistance of the main pump cell is equal to or smaller than 150Ω, a distance between the electrodes ranges from 0.1-0.6 mm, and the inner pump electrode which is a cermet made of an Au—Pt alloy and ZrO2 has an area ranging from 5-20 mm2.