Engine NOx Mass Flow Estimation for Sensor Diagnostics
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Solution Overview
Problem
Existing methods for estimating nitrogen oxides (NOx) mass flow rates in engine exhaust gases and diagnosing NOx sensors are inadequate, leading to potential inaccuracies in monitoring and maintenance alerts.
Innovation Solution
A method that calculates the NOx mass flow rate by multiplying the exhaust gas mass flow rate, NOx base concentration, and a NOx ratio specific to the engine's current operating state, using engine control unit calculations and stored tables to adjust for various operating parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a nitrogen oxides sensor is used to sense the level of nitrogen oxides in exhaust gas, then the level of nitrogen oxides can be monitored, but the accuracy of the measurement may be compromised if the sensor malfunctions or drifts over time
Solution Approach 1:
The system uses feedback by comparing the sensor's measured nitrogen oxides level against an independently calculated expected level (derived from engine operating parameters and a nitrogen oxides map). This feedback mechanism enables continuous validation of sensor accuracy and triggers diagnostic alerts when discrepancies indicate sensor malfunction or drift, thereby maintaining measurement precision and reliability over time.
Solution Approach 2:
The system performs self-diagnosis by automatically comparing sensor readings with expected values calculated from engine operating conditions. The control module monitors the sensor's own performance without requiring external calibration or manual intervention, enabling the system to self-verify sensor accuracy and generate maintenance alerts when the sensor deviates from expected performance.
2Measurement precision
If on-board diagnostics compare sensed nitrogen oxides level to an estimated value, then sensor operation can be determined, but the diagnostic accuracy depends on the accuracy of the estimated value
Solution Approach 1:
The system performs preliminary action by pre-calculating and storing nitrogen oxides expected levels in a map or lookup table across various engine operating conditions (speed, load, temperature, etc.). This pre-computed reference data is generated before actual operation, allowing the diagnostic system to quickly compare sensor readings against accurate expected values without requiring complex real-time calculations, thereby maintaining high diagnostic accuracy while minimizing information loss.
3Reliability
If the nitrogen oxides sensor is disposed downstream of the catalytic device, then the sensor can monitor treated exhaust gas, but the sensor is exposed to harsh chemical environments that may affect its longevity and accuracy
Solution Approach 1:
The system implements self-service through continuous self-diagnosis, where the control module automatically monitors sensor performance by comparing readings against expected values. This enables early detection of sensor degradation or malfunction caused by harsh chemical environments, allowing for timely maintenance or replacement before complete failure occurs, thereby extending effective service life while maintaining monitoring reliability.
Solution Approach 2:
The feedback mechanism continuously validates sensor readings against independently calculated expected nitrogen oxides levels. When the sensor begins to drift or fail due to exposure to harsh exhaust environments, the feedback system detects the discrepancy and triggers diagnostic alerts, enabling proactive maintenance and ensuring reliable monitoring throughout the sensor's service life.
Data Source
AI summary
A method of estimating a mass flow rate of nitrogen oxides in exhaust gas includes sensing a mass flow rate of a flow of exhaust gas from the engine. A nitrogen oxides base concentration for when the engine is operating at a reference state is defined, and a nitrogen oxides ratio for a current operating state of the internal combustion engine is calculated. The mass flow rate of the flow of exhaust gas, the nitrogen oxides base concentration, and the nitrogen oxides ratio for the current operating state of the engine are multiplied together to define an estimated value of the current mass flow rate of nitrogen oxides in the flow of exhaust gas from the engine. The estimated value of the mass flow rate of nitrogen oxides may be compared to the output from a nitrogen oxides sensor to determine proper functionality of the nitrogen oxides sensor.