Gas Sensor Segmenting NOx and NH3 Detection
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Solution Overview
Problem
Existing NOx sensors face challenges in accurately measuring NOx and NH3 concentrations in exhaust gases due to interference from ammonia, especially at low temperatures, where the zirconia electrolyte's high resistance limits oxygen pumping and NOx reduction, making real-time measurements difficult.
Innovation Solution
A gas sensor with a laminated oxygen-ion conductive solid electrolyte structure, including a NOx sensor part and an NH3 sensor part, utilizing a heater to maintain an element control temperature between 400°C and 600°C, allowing simultaneous or selective determination of NOx and NH3 concentrations using a mixed potential cell and electrochemical pump cells, respectively, without changing the temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the control temperature for the NOx sensor is lowered to reduce interference, then the resistance of zirconia electrolyte increases and oxygen pumping and NOx reduction become insufficient
Solution Approach 1:
The sensor element is divided into two independent sensor parts: a NOx sensor part with a measurement pump cell and an NH3 sensor part with a mixed potential cell. Each part operates independently with its own measurement mechanism, allowing the NOx measurement to maintain sufficient temperature for reliable oxygen pumping while the NH3 measurement handles ammonia interference separately.
Solution Approach 2:
The sensor element integrates multiple functions into a single device: it can measure both NOx concentration and NH3 concentration simultaneously using different measurement principles (electrochemical pump cell for NOx, mixed potential cell for NH3), eliminating the need for separate sensors and temperature control systems.
2Adaptability or versatility
If the control temperature is switched to measure different gases, then measurement flexibility improves, but temperature stabilization time increases and real-time measurement becomes difficult
Solution Approach 1:
The sensor element maintains a constant control temperature (400-600°C) and uses different measurement cells (measurement pump cell for NOx, mixed potential cell for NH3) to detect different gases simultaneously or selectively, eliminating temperature switching and stabilization delays.
Solution Approach 2:
The system dynamically selects which measurement cell to use based on measurement needs, allowing flexible switching between NOx and NH3 measurement modes without physical or thermal changes, enabling real-time responsive measurement.
3Device complexity
If a single sensor measures both NOx and NH3 by changing temperature, then device complexity reduces, but measurement precision and response time deteriorate
Solution Approach 1:
The sensor element is segmented into two independent measurement systems within a single device: a measurement pump cell for NOx and a mixed potential cell for NH3. Each cell is optimized for its specific measurement task, ensuring high precision while maintaining a unified sensor structure.
4Measurement precision
If the diffusion resistance is increased to improve O2 pumping at lower temperatures, then NH3 measurement accuracy improves, but NOx reduction efficiency decreases
Solution Approach 1:
The sensor element separates the measurement functions into independent cells: the measurement pump cell handles NOx reduction and O2 pumping, while the mixed potential cell handles NH3 measurement. This segmentation allows each cell to be optimized for its specific function without compromising the other.
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
Enables precise and simultaneous measurement of NOx and NH3 concentrations at one control temperature, improving measurement precision and allowing for rapid switching between measurements, thus overcoming the limitations of conventional NOx sensors.
Implementation Method 1
a heater (72) located inside the sensor element (101) to heat the sensor element (101)
Implementation Method 2
a sensor element including a lamination of a plurality of oxygen-ion conductive solid electrolyte layers
Implementation Method 3
a measurement pump cell that is an electrochemical pump cell constituted by the NOx measurement electrode, the outer pump electrode, and a solid electrolyte between the NOx measurement electrode and the outer pump electrode
Implementation Method 4
The NH3 sensor part has a mixed potential cell constituted by the outer pump electrode, the reference electrode, and a solid electrolyte between the outer pump electrode and the reference electrode
Implementation Method 5
a front-end diffusion resistance providing part located between the external space and the at least one internal space to provide a diffusion resistance of 0.90 (1/mm) or higher and 6.00 (1/mm) or lower to the measurement gas
Implementation Method 6
the outer pump electrode having catalytic activity inactivated for NH3
Data Source
AI summary
Provided is a gas sensor having simpler configuration than a conventional multi-gas sensor, and being capable of measuring NOx and NH3 simultaneously. In the gas sensor determining a NOx concentration in a measurement gas based on a pump current flowing between a NOx measurement electrode and an outer pump electrode, the outer pump electrode has catalytic activity inactivated for NH3 so that a sensor element further includes a NH3 sensor part having a mixed potential cell constituted by the outer pump electrode, a reference electrode, and a solid electrolyte between these electrodes, and determination of a NH3 concentration based on a potential difference occurring between the outer pump electrode and the reference electrode and determination of a NOx concentration based on the pump current and the NH3 concentration can be performed simultaneously or selectively when the sensor element is heated to 400° C. or higher and 600° C. or lower.