NOx Sensor NH3 Interference Correction
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Solution Overview
Problem
Existing NOx sensors face challenges in accurately measuring NOx concentrations in exhaust gas containing both NOx and NH3, as NH3 is oxidized to NO, leading to incorrect detection of combustion-derived NOx due to incomplete chemical conversion of NH3 to N2, resulting in inaccurate subtraction of derived NO concentrations.
Innovation Solution
A NOx concentration measurement system comprising a NOx sensor, a detection section, and a calculation section that estimates NH3 concentration outside the sensor and calculates derived NO concentrations based on air fuel ratio, O2, and H2O levels, allowing for accurate measurement of combustion-derived NOx by subtracting derived NO from the sum concentration measured by the NOx sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If NH3 concentration in outside exhaust gas is used to estimate derived NO concentration, then the measurement process is simplified, but measurement precision deteriorates because not all NH3 is converted to NO in the gas chamber
Solution Approach 1:
The invention changes the parameters used for estimation from simple NH3 concentration to a comprehensive model considering NH3 concentration, air fuel ratio, O2 concentration, and H2O concentration. This allows accurate calculation of derived NO concentration by accounting for chemical reaction conditions, resolving the contradiction between simplicity and precision.
Solution Approach 2:
The invention introduces feedback by using detected values (air fuel ratio, O2 concentration, H2O concentration) to continuously adjust and refine the estimation of derived NO concentration. This feedback mechanism ensures accurate measurement despite varying chemical reaction conditions in the gas chamber.
2Measurement precision
If additional sensors are added to measure NH3 concentration outside the NOx sensor, then measurement precision improves, but device complexity increases
Solution Approach 1:
The invention makes the existing NOx sensor multi-functional by enabling it to detect multiple parameters (NOx concentration, air fuel ratio, O2 concentration, H2O concentration) that are then used together to estimate derived NO concentration. This eliminates the need for separate NH3 sensors while maintaining high measurement precision.
Solution Approach 2:
The system uses the NOx sensor itself and existing detection capabilities to gather all necessary data for estimating derived NO concentration, rather than requiring external NH3 sensors. The system serves its own measurement needs using its existing components and detection abilities.
3Reliability
If heat energy is supplied to NH3 in the gas chamber, then NH3 is chemically converted to N2, but this causes loss of information because the NOx sensor cannot detect the converted N2
Solution Approach 1:
The invention performs preliminary estimation of derived NO concentration based on NH3 concentration and chemical reaction conditions (air fuel ratio, O2, H2O) before the NH3 is completely converted to N2. This allows the system to calculate how much NO should have been present based on reaction stoichiometry, preserving the information that would otherwise be lost.
Solution Approach 2:
The invention uses detected parameters (air fuel ratio, O2 concentration, H2O concentration) as intermediaries to infer the amount of derived NO. These intermediaries provide information about the chemical reaction state, allowing indirect measurement of derived NO concentration even though N2 itself cannot be detected by the NOx sensor.
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 high-accuracy measurement of NOx concentrations in exhaust gas containing NOx and NH3 by accounting for the chemical reactions involving O2 and H2O, thereby correcting for the underestimation of derived NO concentrations and providing precise feedback for urea injection and engine control.
Implementation Method 1
The sensor cell has a solid electrolyte body having oxygen ion conductivity
Implementation Method 2
NH3 is oxidized in the NOx sensor to produce NO
Implementation Method 3
heat energy is supplied to NH3 when it is introduced into the gas chamber, and a part of NH3 is chemically changed to N2
Data Source
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AI summary
A NOx concentration measurement system (1) capable of measuring a concentration of NOx contained in exhaust gas which contains NOx and NH3 is provided. The system comprises a NOx sensor (2), a detection section (3), a NH3 concentration detection section, and a calculation section (7). The NOx sensor (2) comprises: a gas chamber (20) into which exhaust gas is introduced; a sensor cell (26s) having a solid electrolyte body of oxygen ion conductivity having a plate shape, on the surfaces of which electrodes are formed; and a gas introduction section (29) through which the exhaust gas is introduced into the gas chamber (20).