Gas Sensor NOx Sensitivity via NO2 Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The sensitivity of existing NO2 detection in gas sensors is lower than that of NO, primarily due to the slow diffusion of NO2 through the diffusion resistor section, which limits the detection of NOX concentration.
Innovation Solution
A gas sensor design incorporating a reduction section upstream of the diffusion resistor section, where NO2 is reduced to NO, and a second oxygen pump cell downstream to enhance sensitivity, with optional heating and catalysts to facilitate the reduction reaction, and a porous structure with higher porosity than the diffusion resistor section to minimize flow resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffusion resistor section is used to control gas flow into the measurement chamber, then the measurement precision is improved, but the diffusion speed of NO2 is reduced, lowering the sensitivity
Solution Approach 1:
The reduction section is placed upstream of the diffusion resistor section to convert NO2 to NO before the gas enters the measurement chamber. This preliminary conversion action ensures that the gas species with faster diffusion characteristics (NO) passes through the diffusion resistor, thereby maintaining both measurement precision and detection sensitivity.
Solution Approach 2:
The invention changes the chemical parameter of the gas by converting NO2 to NO through the reduction section. This parameter change (chemical composition transformation) allows the gas to have different diffusion properties, resolving the contradiction between measurement precision and diffusion speed.
2Measurement precision
If the sensitivity to NO2 is improved by reducing it to NO before measurement, then the detection accuracy is improved, but the device complexity increases due to additional components
Solution Approach 1:
The reduction section is integrated with the existing sensor structure, combining the reduction function with the measurement chamber system. This merging approach improves NO2 detection sensitivity while minimizing the increase in device complexity by utilizing the existing structural framework.
Solution Approach 2:
The reduction section serves multiple functions: it converts NO2 to NO for improved detection, and also prepares the gas composition for accurate measurement by the subsequent oxygen pump cell. This multi-functionality justifies the additional component by providing multiple benefits within a single structural addition.
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 design enhances the sensitivity of the gas sensor for NOX detection by ensuring NO2 is converted to NO before passing through the diffusion resistor, thereby improving detection speed and accuracy without limiting the flow of NOX.
Implementation Method 1
a reduction section provided upstream of the diffusion resistor section and reducing NO2 contained in the object gas introduced into the first measurement chamber to NO
Implementation Method 2
a diffusion resistor section which limits flow of the object gas therethrough
Implementation Method 3
Oxygen contained in the exhaust gas introduced into the first measurement chamber is pumped out to the outside by the cell, whereby the concentration of oxygen remaining in the exhaust gas introduced into the second measurement chamber is adjusted
Implementation Method 4
NO is decomposed to nitrogen and oxygen by the catalytic action of an electrode formed of noble metal such as Pt or Rh
Implementation Method 5
a heater for heating the reduction section may be provided
Data Source
Figure 1
Figure 2
AI summary
[Objective] To provide a gas sensor which can improve the sensitivity to NO x . [Means for Solution] A reduction section 18 for reducing NO 2 contained in exhaust gas to NO is provided on the upstream side of a first diffusion resistor section 103 provided to limit the flow of the exhaust gas into a first measurement chamber 101. When NO x passes through the first diffusion resistor section 103, NO 2 which is greater in molecular weight than NO is lower in the degree of diffusion than NO. Since NO 2 is reduced to NO at the reduction section 18, the exhaust gas passing through the first diffusion resistor section 103 hardly contains NO 2 . Therefore, the speed of flow of NO x through the first diffusion resistor section 103 is not limited by NO 2 , whereby sensitivity for detection of NO x can be improved.