NOx Sensor Efficiency Determination in Diesel Exhaust
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Solution Overview
Problem
Existing methods for determining the efficiency of exhaust gas cleaning devices in diesel internal combustion engines, particularly for oxidation catalytic converters and particle filters, are complex and costly, requiring multiple NOx sensors and significant evaluation efforts.
Innovation Solution
A method using only two NOx sensors, one upstream and one downstream of a reduction catalytic converter, with NO2 cross-sensitivity, to determine the NO and NO2 concentrations and NO/NO2 ratio, allowing for efficient and reliable assessment of the oxidation catalytic converter and particle filter efficiency without additional structural complexity or sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple NOx sensors (three or more) are arranged upstream and downstream of catalytic converters to determine efficiency, then measurement precision and reliability improve, but device complexity and component cost increase
Solution Approach 1:
The second NOx sensor positioned downstream of the reduction catalytic converter is designed with NO2 cross-sensitivity, allowing it to perform dual functions: monitoring NOx concentrations for emission control and providing data for efficiency determination of upstream catalytic converters. This multi-functionality eliminates the need for separate dedicated sensors for each monitoring task.
Solution Approach 2:
The patent combines the functions of multiple sensors into a minimal two-sensor configuration. The first sensor upstream of the oxidation catalytic converter and the second sensor downstream of the reduction catalytic converter work together, with the second sensor's NO2 cross-sensitivity enabling it to contribute to efficiency monitoring of upstream components, thereby merging multiple monitoring functions into fewer components.
2Reliability
If three NOx sensors are used with different cross-sensitivity characteristics (NO2 cross-sensitivity for upstream sensors, NH3 cross-sensitivity for downstream sensor), then efficiency determination reliability improves, but manufacturing cost and system complexity increase
Solution Approach 1:
The second NOx sensor is specified with NO2 cross-sensitivity to perform multiple functions: it monitors NOx for emission control purposes and simultaneously provides measurement data for determining the efficiency of the oxidation catalytic converter and particle filter, eliminating the need for specialized sensors with different cross-sensitivity characteristics.
Solution Approach 2:
Both NOx sensors in the system are specified with similar NO2 cross-sensitivity characteristics, creating homogeneity in sensor specifications. This simplifies manufacturing and calibration processes compared to using sensors with different specialized characteristics, while still enabling reliable efficiency determination through the control unit's evaluation algorithm.
3Device complexity
If NO2 cross-sensitivity is utilized in the downstream NOx sensor for efficiency determination, then component complexity is reduced, but measurement precision for NH3 detection may be affected
Solution Approach 1:
The patent extracts and utilizes specifically the NO2 cross-sensitivity characteristic of the second NOx sensor for the purpose of efficiency determination, while the control unit's evaluation algorithm accounts for this cross-sensitivity to maintain accurate NH3 detection. The system separates the function of efficiency monitoring from dedicated NH3 sensing requirements.
Solution Approach 2:
The control unit adjusts its evaluation parameters and calculation methods to account for the NO2 cross-sensitivity of the second sensor. By changing the interpretation parameters in the control algorithm rather than the physical sensor characteristics, the system maintains measurement precision while utilizing the cross-sensitivity for efficiency determination.
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 approach simplifies the determination of exhaust gas cleaning device efficiency by utilizing existing sensors, reducing structural complexity and evaluation efforts, while providing reliable data for monitoring the performance of oxidation catalytic converters and particle filters, and detecting potential aging or sulphurization issues.
Implementation Method 1
two NOx sensors, one arranged upstream of an oxidation catalytic converter and/or a particle filter and one arranged downstream of a reduction catalytic converter, whose signal values are based on the NO, NO2 and NH3 concentrations in the exhaust gas
Data Source
Figure 1
AI summary
The invention relates to a method for determining the efficiency of an exhaust gas purification device (2) of an internal combustion engine, in particular a diesel internal combustion engine (1), especially for motor vehicles, with a first NOx sensor (7) upstream of an oxidation catalyst (3) and/or a particulate filter (4) and a second NOx sensor (8) arranged downstream of a reduction catalyst (5), as well as with a device (10) for metered supply of a reducing agent, wherein the signals of the two NOx sensors (7, 8) are supplied to a control unit (9) by means of which at least a supply quantity of the reducing agent is specified.According to the invention, to determine an efficiency, in particular an NO2 formation efficiency, of at least the oxidation catalyst (3) and/or the particulate filter (4), the control unit (9) determines the NO and NO2 concentration and/or the NO2/NO ratio of the exhaust gas flow at the measuring position of the second NOx sensor (7) and/or downstream of the reduction catalyst (5) solely on the basis of the signal values detected by the two NOx sensors (7, 8). Furthermore, a suitable device for carrying out such a method is proposed.